Poaceae — Grass Systematics

Last updated: September 20, 2026

1. Grasses as the Foundation of Food Security

We begin the study of one of the most significant families of flowering plants — Poaceae, or Gramineae, the grass family. This is not merely another taxonomic group in a systematics course. This is the family that, throughout the history of human civilization, has determined the possibilities of our survival and development. Today we will examine why grasses occupy a unique position in the structure of world agriculture and food security, become acquainted with the main cereal crops, and assess the scale of diversity of this remarkable family.

1.1. Global Importance of Grasses in Human Nutrition

Grasses form the basis of nutrition for the Earth’s population. According to the Food and Agriculture Organization of the United Nations (FAOSTAT), cereal crops occupy about 70% of the world’s cultivated area, and more than 50% of the calories in the human diet are provided by grasses (Connor et al., 2011). This figure becomes especially impressive when one considers that the planet’s population has exceeded 8 billion people.

Four species from the grass family — wheat, rice, maize, and barley — provide more than half of world grain production (Connor et al., 2011). Every year humanity produces about 2.2 billion tonnes of grain from these crops, which forms the basis both for direct human nutrition and for the feed base of livestock production. It is important to understand that a significant part of grain is fed to livestock and poultry, returning to us in the form of meat, milk, and eggs. Thus grasses indirectly provide about another 16% of energy and 34% of protein in our diet (Connor et al., 2011).

Why have grasses occupied such a dominant position? The answer lies in a unique combination of biological and economic properties. Grass grain has high energy density, stores well, is easily transported and processed. Grasses are, as a rule, annual plants, which allows a rapid harvest and adaptation of production to changing conditions. They are relatively resistant to diseases and pests, plastic with respect to environmental conditions, and their cultivation is amenable to mechanization (Connor et al., 2011).

1.2. Main Cereal Crops: Characteristics and Uses

Let us consider in more detail the main cereal crops that determined the development of agriculture.

Wheat (Triticum spp.)

Wheat is the most important food crop of the temperate zone and one of the oldest cultivated grasses. Global wheat production exceeds 770 million tonnes per year (FAOSTAT, 2020). Wheat ranks first among all agricultural crops by cultivated area and is the main source of plant protein in the diet of many countries.

Wheat grain contains 8–14% protein and 60–80% carbohydrates, making it a highly nutritious product (Connor et al., 2011). The unique property of wheat flour — the ability to form gluten — allows the production of a wide range of products: bread, pasta, confectionery, and groats. According to Hasanuzzaman (2019), wheat flour is used for bread, biscuits, muffins, noodles, cakes, sauces, pasta, and many other food products.

From a systematic point of view, wheat belongs to the genus Triticum, which includes both cultivated and wild species. We will examine the systematics of this genus in detail in subsequent lectures, but even now we should note that modern bread wheat varieties (Triticum aestivum) are hexaploid forms with the genomic formula AABBDD, which arose as a result of natural hybridization (Judd et al., 2018).

Rice (Oryza sativa)

Rice is the main food crop of the tropical and subtropical zones, the staple food of more than half of the world’s population. Global rice production is about 500 million tonnes (FAOSTAT, 2020). Unlike wheat, rice is cultivated mainly under irrigated agriculture, which determines its distribution in regions with sufficient water.

Rice is considered a “complete” food product due to its optimal nutrient ratio and low fat content (Hasanuzzaman, 2019). Rice is used to produce groats, flour, and starch; rice bran serves as a source of oil used in food and industry. Rice straw finds use in the production of paper, wickerwork, and building materials.

From a systematic point of view, rice belongs to the genus Oryza, which includes about 25 species distributed in the tropics and subtropics of both hemispheres. Cultivated rice (Oryza sativa) is a diploid with 24 chromosomes (2n = 24). Its wild relatives, in particular Oryza rufipogon and Oryza nivara, grow in Southeast Asia and represent enormous value as sources of genes for resistance to diseases and pests (Soreng et al., 2017).

Maize (Zea mays)

Maize, or corn, is the most important cereal crop of the Americas, which currently occupies a leading position in world production. More than 1.1 billion tonnes of maize grain are produced annually (FAOSTAT, 2020). Maize is exceptionally versatile in use: it is a food, feed, and industrial crop.

According to Hasanuzzaman (2019), maize is used for the production of corn flakes and porridges, serves as feed for livestock and poultry, and is a raw material for starch, high-fructose syrup, glucose, maltodextrin, fiber, and gluten. These products find application in the textile, paper, chemical, and pharmaceutical industries.

From the point of view of systematics, maize belongs to the genus Zea, which includes five species distributed in Mexico and Central America. Cultivated maize (Zea mays subsp. mays) originated from the wild subspecies Zea mays subsp. parviglumis, known as Balsas teosinte (Doebley, 2004). This discovery, made on the basis of molecular genetic studies, became one of the most important achievements of 20th-century systematics.

Barley (Hordeum vulgare)

Barley is the fourth most important cereal crop in the world, cultivated mainly in temperate latitudes. Global barley production is about 150 million tonnes (FAOSTAT, 2020). Barley is distinguished by high ecological plasticity: it matures under a short growing season and is resistant to drought and soil salinity, which makes it indispensable in regions with harsh climates.

Barley grain is used for the production of groats (pearl barley, barley groats), flour, and also as a raw material for brewing and the production of spirits (Hasanuzzaman, 2019). In a number of regions of the world, especially in mountainous and arid areas, barley replaces wheat as the main bread cereal. The feed value of barley is also great — it is widely used in livestock production.

From a systematic point of view, barley belongs to the genus Hordeum, which includes about 40 species. Cultivated barley (Hordeum vulgare) is a diploid with 14 chromosomes. Its wild relatives, in particular Hordeum spontaneum, grow in the Middle East and Central Asia, where the domestication of this crop occurred about 10,000 years ago (Judd et al., 2018).

Sorghum (Sorghum bicolor)

Sorghum is the most important grain and forage crop of the arid regions of Africa and Asia. Global sorghum production is about 60 million tonnes (FAOSTAT, 2020). Sorghum is distinguished by exceptional drought and heat resistance, which makes it indispensable in arid climates. This crop is capable of yielding where wheat and maize perish.

Sorghum grain is used as food in the form of groats and flour, and also for the production of starch and alcohol. Stems and leaves serve as feed for livestock and as raw material for the production of syrups and biofuel (Hasanuzzaman, 2019). In Africa, sorghum is one of the main food crops, providing nutrition for millions of people.

From a systematic point of view, sorghum belongs to the genus Sorghum, which includes about 25 species. Cultivated sorghum (Sorghum bicolor) is a diploid with 20 chromosomes. Wild relatives of sorghum grow in Africa and are valuable as sources of genes for drought and disease resistance (Soreng et al., 2017).

Millet (Panicum miliaceum, Pennisetum glaucum, etc.)

Millet is a group of small-seeded cereal crops cultivated mainly in the arid regions of Asia and Africa. This group includes common millet (Panicum miliaceum), pearl millet (Pennisetum glaucum), foxtail millet (Setaria italica), finger millet (Eleusine coracana), and other species. Global millet production is about 30 million tonnes (FAOSTAT, 2020).

Millet is distinguished by high drought resistance, early maturity, and undemandingness to soils. These qualities make it an important crop for regions with unfavorable farming conditions. Millet grain is used for the production of groats (millet), flour, and also as feed for poultry (Hasanuzzaman, 2019).

From a systematic point of view, millet crops belong to different genera of the subfamily Panicoideae. This is an example of convergent similarity of economically valuable traits in unrelated taxa.

1.3. Diversity of Grasses: From Bamboo to Feather Grass

The family Poaceae is one of the largest families of flowering plants. According to modern estimates, it includes about 12,000 species united in 768 genera (Soreng et al., 2017). It is the second family by number of species after Orchidaceae, but the first in economic importance and area occupied.

The diversity of grasses is impressive. Among them are found:

Giants of the plant world — bamboos (Bambusa, Phyllostachys, Dendrocalamus), reaching a height of 30–40 m. Bamboos form forests in tropical and subtropical Asia, and their woody stems (culms) are used as building material and raw material for the production of paper, furniture, and musical instruments. Young bamboo shoots are eaten (Judd et al., 2018).

Ephemeral grasses — plants of deserts and semi-deserts that complete their life cycle in a few weeks. An example is feather grass (Stipa), which forms vast steppes of Eurasia. The caryopses of feather grass are equipped with long awns that promote seed dispersal.

Hydrophytic grasses — plants of water bodies and swamps, such as rice (Oryza), reed (Phragmites), and wild rice (Zizania). These plants form unique ecosystems and have important economic significance.

Forage grasses — numerous species used to create pastures and hayfields. These are fescue (Festuca), ryegrass (Lolium), cocksfoot (Dactylis), timothy (Phleum), brome (Bromus), and many others. Forage grasses form the basis of the feed base of livestock production throughout the world.

Turf grasses — species used to create ornamental and sports lawns. These are bluegrass (Poa), fescue (Festuca), ryegrass (Lolium), and bentgrass (Agrostis). These plants are distinguished by their ability to regrow rapidly after mowing and to form a dense sward (Connor et al., 2011).

Weedy grasses — species that infest crops of cultivated plants and cause damage to agriculture. These are wild oat (Avena fatua), darnel (Lolium temulentum), foxtail (Setaria), barnyardgrass (Echinochloa), and couch grass (Elymus repens). Control of weedy grasses is an important task of plant protection.

Ornamental grasses — species grown to decorate gardens and parks. These are feather grass (Stipa), miscanthus (Miscanthus), fountain grass (Pennisetum), and reed grass (Calamagrostis). Ornamental grasses are valued for their elegant inflorescences and ability to create picturesque clumps.

From a systematic point of view, all this diversity fits into a coherent phylogenetic scheme, which we will examine in the next lecture. It is important to understand that behind external diversity lies a unity of body plan, conditioned by common origin.

1.4. Grasses and Food Security: A Systemic View

Food security is a state in which all people have physical and economic access to sufficient safe and nutritious food. Grasses play a central role in ensuring food security for several reasons.

First, grasses provide the main volume of calories and protein in the diet of the majority of the planet’s population. Without stable grain production it is impossible to feed humanity.

Second, grasses are distinguished by high yield and efficiency of land resource use. Modern varieties of wheat, rice, and maize are capable of yielding 5–10 tonnes per hectare, which allows providing food for a growing population with limited areas of agricultural land (Cassman et al., 2003, cited in Connor et al., 2011).

Third, grasses have good storability and transportability, which allows the creation of food reserves and their redistribution between regions. Grain can be stored for years without significant loss of nutritional qualities, which is critically important for ensuring stability of food supplies.

Fourth, grasses serve as the basis of the feed base of livestock production. The production of meat, milk, and eggs is impossible without the use of grain as feed. Thus grasses provide not only direct but also indirect nutrition for humanity.

However, dependence on grasses also creates certain risks. The concentration of production on a limited number of species makes the food system vulnerable to diseases, pests, and climate change. That is precisely why the study of the systematics and genetic diversity of grasses has not only academic but also enormous practical significance.

1.5. Grass Systematics as a Basis for Breeding and Plant Protection

Why do future specialists in agronomy, breeding, and plant protection need a deep knowledge of grass systematics?

First, accurate identification of species and varieties is a necessary condition for breeding work. Without knowledge of the taxonomic affiliation of the source material, it is impossible to plan crosses and predict the results of hybridization.

Second, understanding phylogenetic relationships allows targeted search for wild relatives of cultivated plants — sources of valuable genes. As we will see in the following lectures, many modern wheat varieties owe their disease resistance to genes transferred from wild species Aegilops and Triticum (Judd et al., 2018).

Third, knowledge of systematics is necessary for quarantine services. Many grasses are quarantine objects — species that pose a danger to agriculture and are subject to strict control during the import of plant products. Accurate identification of such species is a task of systematics.

Fourth, systematics helps in the control of weedy grasses. Many weeds are close relatives of cultivated plants, which complicates their selective destruction. Understanding relationships allows the development of effective herbicides and crop rotation systems.

Finally, grass systematics is important for the identification of forage and turf grasses. The correct selection of species for pastures, hayfields, and lawns requires knowledge of their biological characteristics and ecological requirements.

2. Phylogeny of Poaceae

In the previous chapter we became convinced that grasses play an exceptional role in ensuring the food security of humanity. Now our task is to understand how this enormous diversity — from bamboo to feather grass, from wheat to maize — is connected by common origin. Phylogeny, that is, the history of evolutionary development, gives us the key to understanding not only relationships but also the patterns of distribution of economically valuable traits. Knowledge of the phylogenetic structure of the family allows targeted search for sources of resistance to diseases, pests, and abiotic stresses among wild relatives of cultivated plants (Soreng et al., 2017; Judd et al., 2018).

The family Poaceae is a monophyletic group, that is, it originates from a single ancestor and includes all its descendants (Soreng et al., 2017; Judd et al., 2018). The monophyly of grasses is confirmed both by morphological characters (structure of the spikelet inflorescence, presence of lodicules, caryopsis as the fruit type, characteristic embryo) and by numerous molecular genetic data. In the system of the order Poales, which unites about 15 families, including Cyperaceae, Juncaceae, Typhaceae, and others, grasses occupy the position of one of the most advanced and at the same time largest branches (Soreng et al., 2017). The closest relatives of Poaceae are considered to be the small families Ecdeiocoleaceae and Joinvilleaceae, distributed in Australia and South America (Soreng et al., 2017).

The modern phylogenetic classification of grasses, based on analysis of DNA sequences (primarily plastid genes matK and ndhF, as well as nuclear genes), distinguishes within the family 12 subfamilies, 52 tribes, and 90 subtribes (Soreng et al., 2017). These subfamilies form several successively diverging lines, which are convenient to consider in order of their divergence: early branches (Anomochlooideae, Pharoideae, Puelioideae), the BEP clade (Bambusoideae, Ehrhartoideae, Pooideae), and the PACMAD clade (Panicoideae, Arundinoideae, Chloridoideae, Micrairoideae, Aristidoideae, Danthonioideae). Such a structure reflects the main stages of grass evolution and allows us to understand when and in which groups key economically valuable traits arose.

2.1. Early Divergent Lineages: Anomochlooideae, Pharoideae, Puelioideae

The first to separate from the common grass stem were three small subfamilies, which retained a number of archaic features and have limited distribution in tropical forests.

Anomochlooideae — the earliest branch, including only 4 species in two genera: Anomochloa and Streptochaeta (Soreng et al., 2017). These plants grow in the tropical forests of South America (Brazil) and Central America. They are characterized by a unique inflorescence structure that does not form typical spikelets but is represented by peculiar complex structures. Anatomically they retain a number of primitive features, for example, spirally arranged leaves (Soreng et al., 2017). They have no economic importance.

Pharoideae — the second branch, numbering 12 species in three genera: Pharus, Leptaspis, and Scrotochloa (Soreng et al., 2017). These grasses are distributed in tropical forests of both hemispheres. They have broad lanceolate leaves with a pronounced false petiole, which is uncharacteristic of most grasses. Their spikelets are one-flowered, and the inflorescences are panicles. Pharoideae also have no economic importance.

Puelioideae — the third branch, including 11 species in two genera: Puelia and Guaduella (Soreng et al., 2017). These plants are found in the tropical forests of Africa. They have relatively large spikelets with several flowers and a characteristic embryo structure. They have no economic importance.

All three subfamilies are C3 plants and retain a number of plesiomorphic (ancestral) features, which makes them important for understanding the evolution of the family (Soreng et al., 2017). However, their role in agricultural production is negligible.

2.2. The BEP Clade: Bambusoideae, Ehrhartoideae, Pooideae

The BEP clade (after the first letters of the subfamily names) unites three large subfamilies, which are predominantly C3 plants and include the most important cereal crops of the temperate zone, as well as bamboos. The name “BEP” was proposed in the literature to designate this group (Soreng et al., 2017; Judd et al., 2018). In some works the abbreviation BOP is used (Bambusoideae, Oryzoideae, Pooideae), where Oryzoideae corresponds to Ehrhartoideae. We will adhere to the name BEP, following Soreng et al. (2017).

Bambusoideae — Bamboos

The subfamily Bambusoideae is a unique group of grasses including both herbaceous and woody forms. This is the only large grass clade whose diversification occurred predominantly in forest ecosystems (Soreng et al., 2017; Judd et al., 2018). The total number of species is about 1670, united in 125 genera and 3 tribes (Soreng et al., 2017).

Tribe Arundinarieae — temperate woody bamboos. Distributed in East Asia and North America. Characterized by long rhizomes (leptomorph or pachymorph), a high degree of lignification of stems, and a complex branching system. Typical genera: Arundinaria, Sasa, Phyllostachys, Fargesia. Many species flower once in several decades, often dying after flowering (Soreng et al., 2017).

Tribe Bambuseae — tropical woody bamboos. Distributed in the tropics of both hemispheres. They differ from temperate bamboos by acropetal or bidirectional development of branches and predominantly pachymorph rhizomes. Typical genera: Bambusa, Dendrocalamus, Chusquea, Guadua. Many species have enormous economic importance as a source of building material, raw material for paper, furniture, musical instruments, and also as food plants (young shoots) (Judd et al., 2018).

Tribe Olyreae — herbaceous bamboos. Distributed in tropical forests of America and Africa. These are small forest herbs with relatively weakly lignified stems, unisexual spikelets, and seasonal flowering. Typical genera: Olyra, Pariana, Lithachne. They have almost no economic importance but play an important role in forest ecosystems (Soreng et al., 2017).

Bamboos are of enormous importance in the countries of Asia and Latin America. They are used for construction, furniture, paper, fabrics, and musical instruments. Young bamboo shoots are eaten. In addition, bamboos are an important source of wood fiber and biofuel (Judd et al., 2018).

Ehrhartoideae (Oryzoideae) — Rice and Its Relatives

The subfamily Ehrhartoideae, often called Oryzoideae, includes about 115 species in 19 genera and 4 tribes (Soreng et al., 2017). These are predominantly tropical and subtropical plants, among which the most important is rice.

Tribe Oryzeae — rice proper and its closest relatives. Includes the genera Oryza (rice), Zizania (wild rice), Leersia, Potamophila, and others. Cultivated rice (Oryza sativa) is one of the most important food grasses in the world, providing nutrition for more than half of the planet’s population (Hasanuzzaman, 2019). Wild species of Oryza (for example, O. rufipogon, O. nivara) are valuable sources of genes for resistance to diseases and pests (Soreng et al., 2017).

Tribe Ehrharteae — includes the genera Ehrharta, Microlaena, Tetrarrhena, Zotovia. Distributed in the Southern Hemisphere (Africa, Australasia). Some species are used as forage grasses.

Tribe Phyllorachideae — a small group including the genera Phyllorachis and Humbertochloa, distributed in tropical Africa and Madagascar. They have no economic importance.

Tribe Streptogyneae — a monotypic tribe with the genus Streptogyna, distributed in the tropics. It has an unclear systematic position and is sometimes considered incertae sedis within the subfamily (Soreng et al., 2017).

Rice is the only crop of this subfamily with global food significance. However, wild relatives of rice play an important role in breeding, since they carry genes for resistance to diseases, pests, and abiotic stresses (Judd et al., 2018).

Pooideae — Bluegrasses, the Most Important Temperate Cereals

The subfamily Pooideae is the largest in the grass family: about 3968 species in 202 genera, 15 tribes, and 30 subtribes (Soreng et al., 2017). These are predominantly plants of temperate and cold climates, although some species occur in tropical mountains. Pooideae include the most important cereal crops — wheat, barley, rye, and oats — as well as numerous forage and turf grasses. All representatives of the subfamily are C3 plants.

Tribe Triticeae — the most important economically. Includes the genera Triticum (wheat), Hordeum (barley), Secale (rye), Aegilops (goatgrass), Elymus (wheatgrass), Agropyron (crested wheatgrass), and others. Wheat, barley, and rye are the main bread cereals of the temperate zone. Many species of the tribe are used as forage grasses. The tribe is characterized by large spikelets with several flowers, often with awns. The genetic resources of wild species of Triticeae are of enormous importance for breeding (Soreng et al., 2017; Judd et al., 2018).

Tribe Poeae — the largest tribe of the subfamily, including about 121 genera and 2562 species (Soreng et al., 2017). It includes the genera Poa (bluegrass), Festuca (fescue), Lolium (ryegrass), Dactylis (cocksfoot), Phleum (timothy), Agrostis (bentgrass), Avena (oat), and many others. Oat (Avena sativa) is an important grain and forage crop. Bluegrass, fescue, and ryegrass are the main turf and pasture grasses of the temperate zone. The tribe Poeae is characterized by small spikelets with 1–5 flowers, often without awns.

Tribe Aveneae — sometimes considered a subtribe within Poeae, but in the classification of Soreng et al. (2017) it is separated as a distinct tribe. It includes the genera Avena, Helictotrichon, Trisetum, and others. Oat is the main crop of this group.

Tribe Meliceae — includes the genera Melica, Glyceria, Lycaeum, Schizachne, Streblochaete, Triniochloa. Distributed in temperate and cold regions. Some species are used as forage grasses.

Tribe Stipeae — feather grasses and their relatives. Includes the genera Stipa, Piptatherum, Nassella, Achnatherum, and others. Characterized by large awns on the lemmas. Distributed in steppes and semi-deserts. They have important ecological significance but limited economic importance.

Tribe Brachypodieae — a monotypic tribe with the genus Brachypodium. Includes several species distributed in temperate regions. Brachypodium distachyon is a model object in grass genetics.

Tribe Bromeae — includes the genus Bromus (brome) and close genera. Distributed in temperate regions. Many species are forage grasses, some are weeds.

Tribe Diarrheneae — a small tribe with the genera Diarrhena and Neomolinia. Distributed in East Asia and North America.

Tribe Duthieeae — includes the genera Duthiea, Pappagrostis, Pseudodanthonia, Sinochasea, Stephanachne. Distributed in Central Asia. They have no economic importance.

Tribe Lygeeae — a monotypic tribe with the genus Lygeum, distributed in the Mediterranean.

Tribe Nardeae — a monotypic tribe with the genus Nardus stricta (matgrass), distributed in Europe and Asia. It grows on poor acidic soils and is an indicator of pasture degradation.

Tribe Phaenospermateae — a monotypic tribe with the genus Phaenosperma, distributed in East Asia.

Thus the subfamily Pooideae includes the overwhelming majority of cereal crops of the temperate zone and the most important forage and turf grasses. Phylogenetic studies of this group are of paramount importance for breeding and plant introduction (Soreng et al., 2017).

2.3. The PACMAD Clade: Panicoideae, Arundinoideae, Chloridoideae, Micrairoideae, Aristidoideae, Danthonioideae

The PACMAD clade (after the first letters of the subfamily names) unites six subfamilies, most of which are characterized by C4 photosynthesis. These are predominantly plants of the tropical and subtropical zones, including the most important cereal crops — maize, sorghum, millet — as well as sugarcane. The name “PACMAD” was proposed in the literature to designate this group (Soreng et al., 2017; Judd et al., 2018). In some works the abbreviation PACCMAD is used, also including the subfamily Centothecoideae, which is currently considered part of Panicoideae.

Panicoideae — Panic Grasses, the Most Important Tropical Cereals

The subfamily Panicoideae is the second largest in the grass family: about 3241 species in 247 genera and 13 tribes (Soreng et al., 2017). These are predominantly tropical and subtropical plants, among which the most important cereal crops are maize, sorghum, millet, and also sugarcane. Most representatives are C4 plants, although some basal groups retain C3 photosynthesis.

Tribe Andropogoneae — the economically most important tribe of the subfamily. Includes the genera Zea (maize), Sorghum (sorghum), Saccharum (sugarcane), Andropogon (beardgrass), Bothriochloa, Dichanthium, Eulalia, Miscanthus (miscanthus), Imperata (cogongrass), Vetiveria (vetiver), and others. Maize (Zea mays) is one of the most important cereal crops in the world, used as a food, feed, and industrial crop (Hasanuzzaman, 2019). Sorghum (Sorghum bicolor) is the most important grain and forage crop of arid regions. Sugarcane (Saccharum officinarum) is the main source of sugar in the world. Many species are used as forage grasses (Soreng et al., 2017).

Tribe Paniceae — the second largest tribe of the subfamily. Includes the genera Panicum (panic), Setaria (foxtail, foxtail millet), Pennisetum (pearl millet), Cenchrus (sandbur), Digitaria (crabgrass), Echinochloa (barnyardgrass), Paspalum (paspalum), Axonopus (carpetgrass), and others. Common millet (Panicum miliaceum), foxtail millet (Setaria italica), and pearl millet (Pennisetum glaucum) are important cereal crops of the arid regions of Asia and Africa. Many species are forage grasses. Some are noxious weeds (Soreng et al., 2017).

Tribe Paspaleae — includes the genera Paspalum, Axonopus, Anthae-nantiopsis, Arthropogon, Otachyrium, and others. Distributed in the tropics and subtropics, especially in America. Some species are forage grasses (Soreng et al., 2017).

Tribe Arundinelleae — includes the genera Arundinella, Garnotia, Jansenella, and others. Distributed in the tropics of the Old World. They have almost no economic importance.

Tribe Centotheceae — includes the genera Centotheca, Megastachya, Chasmanthium, and others. A small group of tropical forest grasses. They have no economic importance.

Tribe Chasmanthieae — includes the genera Chasmanthium and Bromuniola. Distributed in America and Africa.

Tribe Cyperochloeae — a monotypic tribe with the genus Cyperochloa, distributed in Australia.

Tribe Gynerieae — a monotypic tribe with the genus Gynerium, distributed in tropical America.

Tribe Hubbardieae — a monotypic tribe with the genus Hubbardia, distributed in India.

Tribe Isachneae — includes the genera Isachne, Coelachne, Heteranthoecia, Limnopoa, Sphaerocaryum. Distributed in the tropics. Some species are forage grasses.

Tribe Lecomtelleae — a monotypic tribe with the genus Lecomtella, distributed in Madagascar.

Tribe Steyermarkochloeae — includes the genera Steyermarkochloa and Arundoclaytonia. Distributed in South America.

Tribe Tristachyideae — includes the genera Tristachya, Danthoniopsis, Dilophotriche, Gilgiochloa, Loudetia, Loudetiopsis, Tricopteryx, Zonotrichia. Distributed in the tropics, especially in Africa. Some species are forage grasses.

Tribe Zeugiteae — includes the genera Zeugites, Chevalierella, Lophatherum, Orthoclada. Distributed in the tropics of America, Asia, and Africa.

Panicoideae is the most important subfamily of grasses in the tropical and subtropical zones. Maize, sorghum, millet, and sugarcane have global food and industrial significance (Soreng et al., 2017; Hasanuzzaman, 2019).

Arundinoideae — Reeds

The subfamily Arundinoideae is a small group including about 40 species in 14 genera and 2 tribes (Soreng et al., 2017). These are predominantly C3 plants distributed in temperate and tropical regions, often in wetland habitats.

Tribe Arundineae — includes the genera Arundo (giant reed), Phragmites (reed), Molinia (purple moor grass), Moliniopsis, Hakonechloa, and others. Phragmites australis (common reed) is a cosmopolitan species playing an important role in wetland ecosystems. Arundo donax (giant reed) is used for making musical instruments, weaving, and paper production (Soreng et al., 2017).

Tribe Molinieae — includes the genera Molinia, Moliniopsis, Hakonechloa, Phragmites, Crinipes, Elytrophorus, Stypneiochloa, Pratochloa, and others. Distributed in temperate and tropical regions. Some species are forage grasses.

The economic importance of Arundinoideae is limited. Reed is used for weaving, paper production, and fuel. Some species are ornamental plants.

Chloridoideae — Chloridoid Grasses, C4 Grasses of Arid Regions

The subfamily Chloridoideae is a large group of C4 grasses including about 1602 species in 124 genera and 5 tribes (Soreng et al., 2017). These are predominantly plants of arid and semi-arid regions of the tropics and subtropics. They are characterized by C4 photosynthesis and resistance to drought and salinity.

Tribe Cynodonteae — the largest tribe of the subfamily, including about 850 species in 94 genera and 21 subtribes (Soreng et al., 2017). Includes the genera Cynodon (bermudagrass), Chloris (windmill grass), Eragrostis (lovegrass), Sporobolus (dropseed), Bouteloua (grama), Buchloe (buffalograss), Muhlenbergia (muhly), Distichlis (saltgrass), Leptochloa (sprangletop), Eleusine (goosegrass, finger millet), Dactyloctenium (crowfoot grass), Tragus (bur grass), Pappophorum, and others. Cynodon dactylon (bermudagrass) is an important turf and pasture grass, but also a noxious weed. Eragrostis tef (teff) is an important grain crop of Ethiopia. Eleusine coracana (finger millet) is a grain crop of Africa and India. Many species are forage grasses of arid regions (Soreng et al., 2017).

Tribe Eragrostideae — includes about 489 species in 14 genera. Includes the genera Eragrostis, Cladoraphis, Entoplocamia, Fingerhuthia, Richardsiella, Steirachne, Stiburus, Tetrachne, Uniola, and others. Eragrostis is the largest genus, including many forage and ornamental species.

Tribe Zoysieae — includes about 233 species in 4 genera. Includes the genera Zoysia (zoysia), Urochondra, Sporobolus, Psilolemma. Zoysia is an important turf grass resistant to trampling and drought.

Tribe Triraphideae — includes about 15 species in 3 genera: Triraphis, Habrochloa, Neyraudia. Distributed in the tropics of Africa and Asia.

Tribe Centropodieae — includes 6 species in 2 genera: Centropodia, Ellisochloa. Distributed in arid regions of Africa and Asia.

Chloridoideae are of enormous importance for pasture farming in arid regions. Teff and finger millet are important food crops in Africa and India. Many species are used for soil stabilization and erosion control (Soreng et al., 2017).

Micrairoideae — Micraira Grasses

The subfamily Micrairoideae is a small group of C4 grasses including about 184 species in 8 genera and 3 tribes (Soreng et al., 2017). Distributed in the tropics, predominantly in Australia and Southeast Asia.

Tribe Micraireae — a monotypic tribe with the genus Micraira, distributed in Australia. These are small cushion-like plants growing on rocks.

Tribe Eriachneae — includes the genera Eriachne and Pheidochloa. Distributed in Australia and Southeast Asia. Some species are forage grasses.

Tribe Isachneae — includes the genera Isachne, Coelachne, Heteranthoecia, Hubbardia, Limnopoa, Sphaerocaryum. Distributed in the tropics. Some species are forage grasses.

The economic importance of Micrairoideae is limited. Some species are used as forage grasses on poor soils.

Aristidoideae — Aristidoid Grasses

The subfamily Aristidoideae is a small group of C4 grasses including about 367 species in 3 genera: Aristida, Stipagrostis, Sartidia (Soreng et al., 2017). Distributed in arid and semi-arid regions of both hemispheres.

Tribe Aristideae — the only tribe of the subfamily. Aristida is the largest genus, including about 300 species. Characterized by three-awned lemmas. Distributed in steppes, semi-deserts, and deserts. Some species are forage grasses (when young), but most have low forage value. Stipagrostis is a characteristic genus of the deserts of Africa and Asia. Sartidia is a small genus distributed in Africa and Madagascar (Soreng et al., 2017).

The economic importance of Aristidoideae is limited. Some species are used as pasture plants in arid regions, but their forage value is low.

Danthonioideae — Danthonioid Grasses

The subfamily Danthonioideae is a small group of C3 grasses including about 292 species in 19 genera and 1 tribe (Soreng et al., 2017). Distributed predominantly in the Southern Hemisphere, especially in Australia, New Zealand, South Africa, and South America. Some species occur in mountainous regions of the tropics.

Tribe Danthonieae — the only tribe of the subfamily. Includes the genera Danthonia (danthonia), Cortaderia (pampas grass), Chionochloa (snow tussock), Rytidosperma (wallaby grass), Pentameris, Schismus (schismus), Tribolium, Merxmuellera, Pseudopentameris, Chaetobromus, Chimaerochloa, Geochloa, Notochloa, Phaenanthoecium, Plinthanthesis, Austroderia, Capeochloa, Tenaxia, and others. Cortaderia selloana (pampas grass) is a popular ornamental plant. Danthonia are forage grasses of temperate pastures. Schismus is a weed in arid regions (Soreng et al., 2017).

The economic importance of Danthonioideae is limited. Some species are used as forage grasses, ornamental plants, and for soil stabilization.

2.4. Phylogenetic Relationships and the Evolution of C4 Photosynthesis

The modern phylogenetic scheme of Poaceae is as follows: early branches (Anomochlooideae, Pharoideae, Puelioideae) successively diverge from the common stem, then follows the BEP clade (Bambusoideae, Ehrhartoideae, Pooideae), and then the PACMAD clade (Panicoideae, Arundinoideae, Chloridoideae, Micrairoideae, Aristidoideae, Danthonioideae) (Soreng et al., 2017; Judd et al., 2018). Such a topology is confirmed by analysis of both plastid and nuclear genes.

One of the most significant evolutionary events in the history of grasses is the origin of C4 photosynthesis. C4 photosynthesis is a mechanism that allows plants to use water and carbon more efficiently under conditions of high temperature and intense light. It arose independently in several lineages of flowering plants, including within the PACMAD clade. According to modern estimates, C4 photosynthesis evolved in the PACMAD clade no less than 22–24 times (Soreng et al., 2017). C4 photosynthesis is most widely represented in the subfamilies Chloridoideae and Panicoideae, where most species belong to it. In the subfamilies Aristidoideae, Micrairoideae, and some groups of Panicoideae, C4 photosynthesis is also dominant. At the same time, the subfamilies Arundinoideae and Danthonioideae remain predominantly C3 plants, and among Panicoideae there are basal groups with C3 photosynthesis (Soreng et al., 2017).

Understanding the evolution of C4 photosynthesis is of enormous practical importance. C4 plants (maize, sorghum, millet, sugarcane) are distinguished by high productivity and drought resistance, which makes them the most important crops under changing climate conditions. Studying the genetic mechanisms of C4 photosynthesis opens prospects for improving C3 crops such as wheat and rice (Judd et al., 2018).

2.5. Main Tribes and Their Economic Importance

Summarizing the review of Poaceae phylogeny, we can identify the main tribes of greatest economic importance:

Pooideae:

Triticeae — wheat, barley, rye, Aegilops, Elymus, Agropyron. The most important grain and forage crops of the temperate zone.
Poeae — bluegrass, fescue, ryegrass, cocksfoot, timothy, oat. The most important forage and turf grasses.
Aveneae — oats and their relatives. Grain and forage crops.
Stipeae — feather grasses. Ecological significance, limited economic importance.

Panicoideae:

Andropogoneae — maize, sorghum, sugarcane, miscanthus, vetiver. The most important grain, industrial, and forage crops of the tropics and subtropics.
Paniceae — panic, foxtail millet, pearl millet, crabgrass, barnyardgrass. Grain and forage crops, weeds.
Paspaleae — paspalum, carpetgrass. Forage grasses.

Chloridoideae:

Cynodonteae — bermudagrass, windmill grass, lovegrass, dropseed, grama, finger millet, teff. Forage, turf, and grain crops of arid regions.
Eragrostideae — lovegrass, uniola. Forage grasses.
Zoysieae — zoysia, dropseed. Turf and forage grasses.

Bambusoideae:

Bambuseae — tropical bamboos. Building material, paper, food.
Arundinarieae — temperate bamboos. Building material, ornamental plants.
Olyreae — herbaceous bamboos. Ecological significance.

Ehrhartoideae:

Oryzeae — rice, wild rice. The most important food crop.

Arundinoideae:

Arundineae — reed, giant reed. Weaving, paper, fuel.

Danthonioideae:

Danthonieae — danthonia, pampas grass. Forage and ornamental plants.

3. Key genera and their systematic position

In previous chapters, we established that the family Poaceae is a monophyletic group, within which three successively branching lineages are distinguished: early diverging lineages, the BEP clade, and the PACMAD clade. We also confirmed that the most important cereal crops are distributed among different subfamilies. Now our task is to examine in detail the key genera of grasses, their systematic position, morphological characteristics, distribution, and economic importance. Knowledge of the exact taxonomic affiliation of each genus is necessary for breeding work, quarantine control, variety identification, and the development of agronomic practices (Soreng et al., 2017; Judd et al., 2018).

In this lecture, we will successively examine the genera of greatest agricultural importance: Oryza (rice), Triticum (wheat), Hordeum (barley), Secale (rye), Avena (oats), Zea (maize), Sorghum (sorghum), Panicum (millet), Saccharum (sugarcane), Bambusa and Phyllostachys (bamboos). For each genus, we will indicate its systematic position, a brief morphological characterization, distribution, and economic importance.

3.1. Genus Oryza L. — rice

Systematic position

The genus Oryza belongs to the subfamily Ehrhartoideae (in some classifications, Oryzoideae), tribe Oryzeae, subtribe Oryzinae (Soreng et al., 2017). The subfamily Ehrhartoideae occupies a position in the BEP clade, being the sister group to the clade uniting Bambusoideae and Pooideae (Soreng et al., 2017; Judd et al., 2018).

Morphological characterization

Oryza — annual or perennial grasses, usually growing under conditions of excessive moisture. Stems erect or ascending, 0.5 to 2 m tall (in some varieties up to 3 m). Leaves linear-lanceolate, with well-developed sheaths. Inflorescence — a panicle with one-flowered spikelets. Spikelets bisexual, with two sterile lemmas reduced to small scales. Flowers have 6 stamens and one ovary. Fruit — a caryopsis covered by flowering scales (Hasanuzzaman, 2019). A characteristic feature of rice is the presence of air cavities (aerenchyma) in stems and leaves, which allows it to grow in flooded conditions.

Distribution

The genus includes about 25 species distributed in tropical and subtropical regions of Asia, Africa, America, and Australia. The center of origin and greatest diversity is Southeast Asia (Soreng et al., 2017). Cultivated rice (Oryza sativa L.) is a diploid with 24 chromosomes (2n = 24). Its wild relatives — O. rufipogon Griff. and O. nivara Sharma & Shastry — grow in Southeast Asia and are the most important sources of genes for resistance to diseases and pests (Judd et al., 2018).

Economic importance

Rice is the most important food crop in the world, providing food for more than half of the planet's population. World rice production exceeds 500 million t per year (FAOSTAT, 2020). The major producers are China, India, Indonesia, Bangladesh, and Vietnam. Rice is used as food in the form of grain, flour, and starch; rice bran serves as a source of oil. Rice straw is used for the production of paper, woven products, and building materials (Hasanuzzaman, 2019). In rice breeding, a huge role is played by wild species of Oryza, which carry genes for resistance to rice blast, bacterial blight, drought, and salinity (Soreng et al., 2017).

3.2. Genus Triticum L. — wheat

Systematic position

The genus Triticum belongs to the subfamily Pooideae, tribe Triticeae (Soreng et al., 2017). The tribe Triticeae is one of the most economically important, also including the genera Hordeum, Secale, Aegilops, Elymus, and others. The subfamily Pooideae occupies a position in the BEP clade and unites the most important cereal crops of the temperate zone (Soreng et al., 2017; Judd et al., 2018).

Morphological characterization

Wheat — annual grasses 0.4 to 1.5 m tall. Leaves linear, with sheaths. Inflorescence — a compound spike consisting of simple spikelets arranged on the ledges of the rachis. Spikelets two- or many-flowered, bisexual. Each spikelet has two glumes and 3–5 lemmas. Flowers with 3 stamens and one ovary. Fruit — a caryopsis covered by flowering scales (Hasanuzzaman, 2019). Wheat is characterized by a high ability to form gluten, which determines its baking qualities.

Distribution and genomic composition

The genus Triticum includes several species differing in chromosome number and genomic composition:

Diploid species (2n = 14): T. monococcum L. (einkorn), T. urartu Tumanian ex Gandilyan. Genomic formula AA.
Tetraploid species (2n = 28): T. turgidum L. (durum wheat, emmer), T. dicoccoides (Körn. ex Asch. & Graebn.) Schweinf. Genomic formula AABB.
Hexaploid species (2n = 42): T. aestivum L. (bread wheat), T. spelta L. (spelt). Genomic formula AABBDD.

The genus Bambusa includes about 120 species distributed in tropical and subtropical regions of Asia, Africa, America, and Australia. The genus Phyllostachys includes about 50 species distributed in temperate and subtropical regions of East Asia (China, Japan). The center of bamboo diversity is Southeast Asia (Judd et al., 2018).

Economic importance

Bamboos are of enormous economic importance in the countries of Asia and Latin America. Stems are used as building material, raw material for the production of furniture, paper, fabrics, and musical instruments. Young shoots are eaten. Bamboos are also used to create decorative compositions, hedges, for soil stabilization, and erosion control (Judd et al., 2018). In recent years, bamboo has been considered a promising source of biofuel and wood fiber.

4. Triticale and other interspecific hybrids

In previous chapters, we examined the phylogenetic structure of the family Poaceae and the systematic position of key genera. We confirmed that the most important cereal crops are distributed among different subfamilies and tribes. Now our task is to understand how systematics and phylogeny are related to practical breeding. One of the most powerful tools of breeding is hybridization — the crossing of organisms belonging to different species, genera, and even higher taxa. Hybridization allows combining in one organism valuable traits of parental forms that do not occur together in nature (Connor et al., 2011; Judd et al., 2018).

In this lecture, we will examine interspecific and intergeneric hybrids of grasses. We will pay special attention to triticale — a hybrid of wheat and rye, which has become an important cereal crop. We will also discuss other intergeneric hybrids, such as festulolium (a hybrid of fescue and ryegrass), and the problems arising during their creation: sterility, genomic instability, and the need for amphiploidy.

4.1. The concept of hybridization and its role in the evolution and breeding of grasses

Hybridization is the crossing of individuals belonging to different taxa. Depending on the taxonomic level, intraspecific, interspecific, and intergeneric hybridization are distinguished. Hybridization plays an enormous role in the evolution of plants: it leads to the emergence of new combinations of genes, and in the case of polyploidy — to the formation of new species (Judd et al., 2018). Among grasses, hybridization and polyploidy are especially widespread, which is associated with their biological characteristics: cross-pollination, the ability to reproduce vegetatively, and high tolerance to gene duplication.

In breeding, hybridization is used for:

Transferring genes for resistance to diseases and pests from wild species to cultivated ones.
Increasing yield and product quality.
Expanding the cultivation area of a crop by increasing winter hardiness, drought resistance, and salt tolerance.
Creating fundamentally new crops that did not exist in nature (for example, triticale).

According to Connor et al. (2011), hybridization and subsequent selection are the basis of modern breeding. Heterosis (hybrid vigor) makes it possible to obtain yields significantly exceeding those of parental forms. Polyploidy, often accompanying hybridization, increases the size of plants, cells, and organs, which can also be used in breeding.

4.2. Interspecific hybridization within genera

Wheat (Triticum)

The genus Triticum demonstrates a classic example of natural interspecific hybridization and polyploidy. As we have already noted, the evolution of wheat proceeded through successive acts of hybridization and chromosome doubling (Judd et al., 2018). Diploid species (2n = 14, genome AA) — T. monococcum, T. urartu — crossed with wild species of Aegilops (BB), which led to the emergence of tetraploid wheat T. turgidum (2n = 28, AABB). Then hybridization of T. turgidum with Aegilops tauschii (DD) gave rise to hexaploid bread wheat T. aestivum (2n = 42, AABBDD). These processes occurred in nature, but they can be reproduced artificially.

In wheat breeding, interspecific crosses are widely used to transfer genes for resistance to rust, powdery mildew, and Fusarium from wild species (T. dicoccoides, T. urartu, Aegilops spp.) to cultivated varieties. For example, genes for resistance to stem rust (Sr genes) are often transferred from Aegilops tauschii (Judd et al., 2018).

Rice (Oryza)

Cultivated rice (Oryza sativa) is crossed with wild species O. rufipogon, O. nivara, O. glaberrima, and others. The goal is to transfer genes for resistance to rice blast, bacterial blight, viral diseases, as well as genes that increase yield and grain quality (Soreng et al., 2017). Interspecific rice hybrids are often used in programs to create new varieties resistant to abiotic stresses.

Maize (Zea)

Maize (Zea mays subsp. mays) is crossed with teosinte (Zea mays subsp. parviglumis, Z. diploperennis, Z. luxurians) and with species of the genus Tripsacum. These crosses are used to transfer genes for resistance to diseases and pests, as well as to increase protein content in grain (Doebley, 2004). Hybridization of maize with teosinte played a key role in understanding the evolution of maize. As shown by Doebley (2004), Balsas teosinte (Z. mays subsp. parviglumis) is the direct ancestor of maize, and their crossing produces fertile offspring.

Other crops

Interspecific hybridization is also used in breeding barley (Hordeum vulgare × H. spontaneum), oats (Avena sativa × A. sterilis), sorghum (Sorghum bicolor × S. verticilliflorum), and sugarcane (Saccharum officinarum × S. spontaneum). In each case, the goal is to transfer valuable genes from wild relatives to cultivated forms (Connor et al., 2011).

4.3. Intergeneric hybridization

Triticale (×Triticosecale Wittm. ex A.Camus)

Triticale is a hybrid of wheat (Triticum spp.) and rye (Secale cereale). The name comes from combining the generic names: Triticum + Secale = Triticale (in Russian-language literature — triticale). It is the first successful artificial intergeneric hybrid that has become an independent cereal crop (Connor et al., 2011; Judd et al., 2018).

The history of triticale creation spans more than a century. The first attempts to cross wheat and rye were made in the late 19th century, but the resulting hybrids were sterile. Only in the 1930s, after the development of methods for doubling chromosome number using colchicine, was it possible to obtain fertile amphiploids. Modern triticales are amphiploids combining the genomes of wheat and rye. The most widespread are hexaploid triticales (2n = 42, AABBRR) and octoploid ones (2n = 56, AABBDDRR) (Judd et al., 2018).

Triticale combines the high yield and grain quality of wheat with the winter hardiness, drought resistance, and disease resistance of rye. Triticale grain is used for the production of bread, groats, and feed. However, the baking qualities of triticale are lower than those of wheat due to the characteristics of gluten. Triticale is cultivated in Russia, Poland, Germany, France, Canada, the USA, and Australia (Connor et al., 2011).

From a systematic point of view, triticale is not an independent genus, but a hybridogenous taxon designated as ×Triticosecale. According to the International Code of Nomenclature for algae, fungi, and plants, the sign “×” is used before the generic name for hybrids. Triticale does not have the status of a natural genus, but is considered a cultivated hybrid (Judd et al., 2018).

Festulolium (×Festulolium Asch. & Graebn.)

Festulolium is a hybrid of fescue (Festuca spp.) and ryegrass (Lolium spp.). Both genera belong to the subfamily Pooideae, tribe Poeae (Soreng et al., 2017). Festulolium combines the high forage productivity and quality of ryegrass with the resistance to adverse conditions and longevity of fescue. Hybrids are used in forage production to create highly productive pastures and hayfields (Soreng et al., 2017).

Festulolium is an amphiploid or allopolyploid obtained by crossing various species of Festuca and Lolium. The most widespread are hybrids F. pratensis × L. perenne (2n = 28) and F. arundinacea × L. multiflorum (2n = 42). Like triticale, festulolium is designated as ×Festulolium (Judd et al., 2018).

Other intergeneric hybrids

Besides triticale and festulolium, other intergeneric hybrids are used in grass breeding:

Wheat × goatgrass hybrids (Triticum × Aegilops). Used to transfer genes for resistance to diseases and pests. Some such hybrids have received the status of independent genera, for example, ×Aegilotriticum.
Wheat × wheatgrass hybrids (Triticum × Elymus). Used to transfer genes for resistance to drought and salinity.
Fescue × ryegrass hybrids (×Festulolium), described above.
Sorghum × sugarcane hybrids (Sorghum × Saccharum). Used to create highly productive forage crops.
Maize × Tripsacum hybrids (Zea × Tripsacum). Used to transfer genes for resistance to pests and diseases (Doebley, 2004).

4.4. Problems of intergeneric hybridization

The creation of intergeneric hybrids is associated with serious difficulties that breeders must overcome.

Sterility of F₁ hybrids

The first generation of hybrids (F₁) between species of different genera often turns out to be sterile. This is due to the mismatch of parental chromosomes: during meiosis, chromosomes cannot normally conjugate, which leads to the formation of unbalanced gametes. For example, wheat × rye hybrids (F₁) are sterile because wheat chromosomes (A, B, D) and rye chromosomes (R) are not homologous (Judd et al., 2018).

Genomic instability

Even if F₁ hybrids are capable of reproduction, their progeny may be genomically unstable. This manifests itself in variability of chromosome number, loss or rearrangement of chromosomes, which reduces fertility and productivity. Genomic instability is especially characteristic of distant hybrids (Connor et al., 2011).

Amphiploidy as a way to restore fertility

To restore the fertility of distant hybrids, amphiploidy is used — doubling the chromosome number of the F₁ hybrid. This leads to each chromosome receiving a homologous partner, and meiosis proceeds normally. Amphiploids are fertile and can reproduce by seeds. This is how triticale and festulolium were obtained (Judd et al., 2018). To induce amphiploidy, colchicine is used — an alkaloid that destroys the spindle apparatus and prevents chromosome segregation.

The role of polyploidy in the evolution of grasses

Polyploidy is the most important factor in the evolution of grasses. Many cultivated grasses are polyploids: wheat (hexaploid), oats (hexaploid), sugarcane (highly polyploid), triticale (hexa- or octoploid). Polyploidy increases the size of cells and organs, increases resistance to adverse conditions, and promotes speciation (Judd et al., 2018). In breeding, polyploidy is used to create new forms with improved economic traits.

4.5. Importance of hybridization for breeding

Hybridization, especially intergeneric, opens wide opportunities for breeders:

1. Transfer of genes for resistance to diseases and pests. Wild relatives of cultivated grasses carry genes for resistance to rust, smut, powdery mildew, viruses, and nematodes. Transferring these genes into cultivated varieties reduces yield losses and decreases pesticide use (Connor et al., 2011).

2. Increasing winter hardiness and drought resistance. Genes from rye, goatgrass, and wheatgrass can increase the adaptability of wheat to adverse conditions. This is how triticale was created — a crop combining the winter hardiness of rye with the yield of wheat.

3. Creation of new crops. Triticale is an example of a fundamentally new crop that did not exist in nature. Similarly, festulolium is a new forage crop combining the advantages of fescue and ryegrass.

4. Improving product quality. Interspecific hybridization is used to increase the content of protein, lysine, and oil in grain and to improve baking qualities.

5. Overcoming genetic erosion. The use of wild relatives in hybridization expands the genetic base of cultivated varieties and reduces their vulnerability to new diseases and pests (Soreng et al., 2017).

4.6. Examples of successful intergeneric hybrids in agriculture

Triticale is an important cereal crop. World production of triticale is about 15 million t per year. The major producers are Poland, Germany, France, Russia, and China. Triticale is used for the production of bread, groats, and feed (Connor et al., 2011).

Festulolium is a valuable forage crop. It is cultivated in Europe, North America, and Australia. It is used to create highly productive pastures and hayfields. It combines the high nutritional value of ryegrass with the resistance of fescue to diseases and adverse conditions (Soreng et al., 2017).

Sugarcane × sorghum hybrids are used to create highly productive forage crops resistant to drought and diseases.

5. Wild relatives of wheat and maize: genetic reserve

In previous lectures, we examined the phylogeny of grasses, their key genera, and interspecific hybridization. We confirmed that breeding of cultivated plants is impossible without genetic diversity. However, during domestication and subsequent breeding, cultivated varieties lose a significant part of their original genetic diversity. A paradox arises: the more perfect a variety is, the narrower its genetic base and the higher its vulnerability to new diseases, pests, and climate change. The solution to this problem lies in the use of wild relatives of cultivated plants — a natural reservoir of genes that were lost during breeding (Connor et al., 2011).

In this lecture, we will examine the wild relatives of two of the most important cereal crops — wheat and maize. We will discuss their systematic position, gene pools (GP1–GP3), importance for breeding for resistance to diseases, pests, and abiotic stresses, as well as measures for conserving the genetic reserve.

5.1. The concept of genetic reserve and gene pools

Genetic reserve (genetic resources) is the totality of genes and genotypes present in populations of cultivated plants, their wild relatives, and related species. Connor et al. (2011) emphasize that genetic resources include both modern varieties and lines, as well as old landraces, and wild species growing in the centers of origin of crops. Wild relatives are especially important because they carry genes for resistance to diseases, pests, drought, salinity, and other stresses that were lost during domestication.

In breeding, it is customary to distinguish three gene pools proposed by Harlan and de Wet (1971). This concept is widely used in modern breeding and systematics:

GP1 (primary gene pool) — includes cultivated forms and their closest wild relatives, which cross freely, produce fertile offspring, and have the same genome. Genes are transferred without special methods.
GP2 (secondary gene pool) — includes species with which crossing is possible but difficult. F₁ hybrids are often sterile or have reduced fertility. To obtain fertile offspring, chromosome doubling (amphiploidy) or special methods are required.
GP3 (tertiary gene pool) — includes species with which crossing requires special methods: embryo rescue, bridge crosses, and cytogenetic manipulations. Hybrids are usually sterile but can be used to transfer individual genes.

Knowledge of gene pools allows the breeder to purposefully select sources of genes and predict difficulties in crossing. For wheat and maize, these pools are well studied.

5.2. Wild relatives of wheat

Origin and genomic composition of wheat

As we have already noted, cultivated wheat arose as a result of natural hybridization and polyploidization. Diploid species Triticum urartu (genome AA) and Triticum monococcum (AA) crossed with wild species of Aegilops (BB), which led to the emergence of tetraploid wheat Triticum turgidum (AABB). Then hybridization of T. turgidum with Aegilops tauschii (DD) gave rise to hexaploid bread wheat Triticum aestivum (AABBDD) (Judd et al., 2018). Thus, the wild relatives of wheat include species of the genera Triticum and Aegilops, as well as more distant genera of the tribe Triticeae.

Gene pools of wheat

GP1 (primary gene pool) includes cultivated and wild species of Triticum with the same genomic composition: T. aestivum (AABBDD), T. turgidum (AABB), T. monococcum (AA), T. timopheevii (AAGG), as well as wild species T. boeoticum (AA), T. dicoccoides (AABB), T. araraticum (AAGG). Crosses within GP1 are easy, and the progeny are fertile. These species are sources of genes for resistance to rust, powdery mildew, and Fusarium, as well as genes that increase protein content and improve baking qualities (Judd et al., 2018).

GP2 (secondary gene pool) includes species of Aegilops that carry genomes homologous to wheat genomes: Ae. speltoides (BB), Ae. tauschii (DD), Ae. sharonensis, Ae. longissima, Ae. searsii, and others. Crossing wheat with these species is possible, but F₁ hybrids are often sterile. To restore fertility, chromosome doubling is used. Aegilops tauschii is the donor of the D genome of bread wheat; Ae. speltoides is the probable donor of the B genome. These species carry genes for resistance to stem and leaf rust, powdery mildew, viruses, and nematodes, as well as genes for drought and salt tolerance (Soreng et al., 2017; Judd et al., 2018).

GP3 (tertiary gene pool) includes more distant genera of the tribe Triticeae: Secale (rye), Hordeum (barley), Elymus (wheatgrass), Thinopyrum (wheatgrass), Agropyron (crested wheatgrass), Dasypyrum, Amblyopyrum, and others. Crossing wheat with these genera requires special methods: embryo rescue, bridge crosses, and cytogenetic manipulations. Hybrids are usually sterile but can be used to transfer individual genes. For example, Secale cereale is a source of genes for winter hardiness, disease resistance, and genes that increase lysine content in protein. Thinopyrum is a source of genes for salt tolerance and disease resistance. Elymus is a source of genes for perenniality and drought resistance (Connor et al., 2011; Soreng et al., 2017).

Importance of wild relatives of wheat for breeding

Wild relatives of wheat played an enormous role in 20th-century breeding. Examples:

Resistance to stem rust. Sr genes were transferred from Aegilops tauschii, Ae. speltoides, Triticum dicoccoides into cultivated varieties. This made it possible to prevent epiphytotics that had previously destroyed wheat yields.
Resistance to powdery mildew. Pm genes were transferred from Aegilops spp., T. dicoccoides, Secale cereale.
Resistance to Fusarium. Genes from T. dicoccoides, Aegilops spp.
Winter hardiness. Genes from Secale cereale (rye) are used to increase the winter hardiness of wheat.
Drought and salt tolerance. Genes from Aegilops spp., Thinopyrum spp., Elymus spp.
Grain quality. Genes from T. dicoccoides increase protein content and improve amino acid composition.

According to Connor et al. (2011), the conservation and use of wild relatives is the key to future food security. Without them, wheat breeding may face insurmountable difficulties with the emergence of new pathogen races.

5.3. Wild relatives of maize

Origin and systematic position

Maize (Zea mays subsp. mays) originates from the wild subspecies Balsas teosinte (Zea mays subsp. parviglumis Iltis & Doebley), growing in the Balsas River valley in Mexico (Doebley, 2004). The domestication of maize occurred about 9 thousand years ago. The genus Zea includes five species: Z. mays, Z. diploperennis, Z. perennis, Z. luxurians, Z. nicaraguensis. All of them are distributed in Mexico and Central America. The closest relative of maize is Balsas teosinte (Z. mays subsp. parviglumis), which crosses freely with maize and produces fertile offspring (Doebley, 2004).

Gene pools of maize

GP1 (primary gene pool) includes cultivated maize (Zea mays subsp. mays) and all subspecies of teosinte: Z. mays subsp. parviglumis, Z. mays subsp. mexicana, Z. mays subsp. huehuetenangensis, as well as other species of the genus Zea (Z. diploperennis, Z. perennis, Z. luxurians, Z. nicaraguensis). Crosses within GP1 are easy, and the progeny are fertile. Teosinte carries genes for resistance to diseases, pests, and drought, as well as genes that increase yield and protein content. Z. diploperennis is a perennial species, a source of genes for perenniality and disease resistance. Z. luxurians is a source of genes for resistance to the corn borer and other pests (Doebley, 2004).

GP2 (secondary gene pool) includes species of the genus Tripsacum (tripsacum). These are perennial grasses distributed in Mexico, Central and South America. Crossing maize with tripsacum is possible but requires special methods: embryo rescue and bridge crosses. F₁ hybrids are often sterile but can be used to transfer genes for resistance to pests (corn borer, armyworm) and diseases, as well as genes for perenniality and apomixis (Doebley, 2004). Tripsacum is also used to study the evolution of maize: intergenomic mapping involving Tripsacum helped reveal the structure of the maize genome (Doebley, 2004).

GP3 (tertiary gene pool) includes more distant genera of the subfamily Panicoideae: Sorghum, Saccharum, Miscanthus, Pennisetum, and others. Crossing maize with these genera is extremely difficult and requires complex biotechnological methods. These crosses are not yet of economic importance for maize breeding, but they are of interest for fundamental science.

Importance of wild relatives of maize for breeding

Wild relatives of maize are an invaluable source of genes for modern breeding:

Resistance to pests. Genes from Z. diploperennis, Z. luxurians, Tripsacum spp. are used to create varieties resistant to the corn borer, armyworm, and nematodes.
Resistance to diseases. Genes from teosinte (Z. mays subsp. mexicana, Z. diploperennis) increase resistance to common smut, Fusarium, and viral diseases.
Drought resistance. Genes from Z. mays subsp. parviglumis, Z. diploperennis are used to increase drought resistance of maize.
Perenniality. Z. diploperennis and Z. perennis are perennial species that can be used to create perennial maize.
Grain quality. Genes from teosinte increase protein and lysine content in grain.
Apomixis. Tripsacum has the ability for apomixis (seed reproduction without fertilization), which can be used to fix heterosis.

According to Doebley (2004), Balsas teosinte (Z. mays subsp. parviglumis) is the direct ancestor of maize, and its genome contains many alleles lost in cultivated varieties. The use of these alleles in breeding is the most important reserve for increasing yield and adaptability of maize.

5.4. Conservation of the genetic reserve

Conservation of the genetic reserve is a task of global scale. Connor et al. (2011) distinguish several forms of conservation:

1. Ex situ (outside natural habitats) — creation of genetic banks (germplasm banks) in which seeds, tubers, cuttings, and tissue cultures are stored. The largest genetic banks of cereal crops are located in the USA (National Center for Genetic Resources Preservation), China, India, Russia (VIR), Mexico (CIMMYT), and the Philippines (IRRI). These banks store thousands of accessions of cultivated varieties, landraces, and wild relatives.

2. In situ (in natural habitats) — creation of protected natural areas (reserves, national parks) where populations of wild relatives are conserved in their natural environment. This is especially important for preserving the evolutionary potential of species.

3. On-farm — conservation of landraces and old varieties by farmers who continue to cultivate them. This approach allows preserving genetic diversity under conditions of constant selection and adaptation to local conditions.

4. International agreements — the International Treaty on Plant Genetic Resources for Food and Agriculture, adopted under the auspices of FAO, ensures open access to genetic resources for breeders and researchers (Connor et al., 2011).

Connor et al. (2011) note that modern breeding increasingly depends on genetic banks, since wild populations are disappearing under the pressure of anthropogenic factors. Therefore, conservation of the genetic reserve is not only a scientific, but also an ethical and political task.

5.5. Practical importance of the genetic reserve for breeding

The use of wild relatives in breeding gives concrete practical results:

Reduction of yield losses from diseases and pests. Without resistance genes transferred from wild relatives, modern wheat and maize varieties would be extremely vulnerable to epiphytotics. For example, stem rust resistance genes transferred from Aegilops tauschii saved millions of hectares of wheat.
Expansion of the cultivation area. Winter hardiness genes from rye and drought resistance genes from Aegilops and teosinte make it possible to advance wheat and maize into new regions.
Improvement of product quality. Genes from T. dicoccoides and teosinte increase protein content and improve the amino acid composition of grain.
Creation of new crops. Triticale is an example of using wild relatives (rye) to create a fundamentally new crop.

6. Practical importance of grass systematics

In previous chapters, we examined the phylogeny of grasses, their key genera, interspecific and intergeneric hybridization, and the genetic reserve of wild relatives. Now our task is to show how systematic knowledge is applied in practice. Grass systematics is not only an academic discipline, but also a working tool for the agronomist, breeder, quarantine inspector, plant protection specialist, and forage production specialist (Connor et al., 2011; Judd et al., 2018).

In this chapter, we will examine five key areas of practical application of systematics: identification of species and varieties, quarantine control, breeding and hybridization, forage and turf grasses, and control of weedy grasses.

6.1. Identification of species and varieties

Accurate identification is the basis of any agronomic work. Without knowing what species or variety we are dealing with, it is impossible to correctly select agronomic practices, plan crop rotation, predict yield, or choose plant protection products. Systematics provides tools for such identification.

Morphological methods

Traditional identification of grasses is based on morphological characters: structure of the inflorescence (panicle, spike, raceme), spikelets, lemmas, awns, leaf blades and sheaths, as well as vegetative organs. For example, wheat (Triticum aestivum) is easily distinguished from rye (Secale cereale) by spike structure: in wheat the spike is dense, spikelets are arranged one per ledge of the rachis; in rye the spike is looser, spikelets are two-flowered. Barley (Hordeum vulgare) has three-spikelet groups on the ledge of the rachis. Maize (Zea mays) is distinguished by monoecious inflorescences: male tassels at the top, female ears in leaf axils (Zomlefer, 1994; Hasanuzzaman, 2019).

For identification of varieties within a species, finer characters are used: color and shape of grain, presence or absence of awns, stem height, disease resistance. However, morphological characters are not always reliable due to phenotypic plasticity and environmental influence. Therefore, molecular methods are increasingly used in modern systematics.

Molecular methods

Molecular genetic markers make it possible to identify species and varieties at the DNA level, which is especially important for distinguishing closely related taxa and hybrids. The following approaches are used:

DNA barcoding — sequencing of standard genome regions (for example, plastid genes rbcL, matK, ndhF) for species identification (Soreng et al., 2017). This method allows accurate species determination even from a fragment of a leaf or grain.
Microsatellite markers (SSR) — short repetitive sequences, highly polymorphic and convenient for genotyping varieties. They are used for variety passportization, assessment of genetic diversity, and seed purity control.
SNP markers (single nucleotide polymorphisms) — single nucleotide substitutions that allow distinguishing even closely related lines. In recent years, SNP markers have become the basis for creating high-density genetic maps and marker-assisted selection (MAS).

According to Judd et al. (2018), molecular methods have revolutionized systematics, making it possible to clarify phylogenetic relationships and identify cryptic species. In practical terms, this means that identification has become more accurate and objective.

Importance for seed production and variety control

Variety control and seed production are impossible without accurate identification. In the production of certified seeds, it is necessary to ensure that they belong to the declared variety. Molecular markers make it possible to detect admixtures of other varieties, as well as hybrids. For wheat, rice, and maize, standard sets of SSR markers recommended by international organizations (for example, UPOV) have been developed for variety identification (Connor et al., 2011).

6.2. Quarantine objects among grasses

Plant quarantine is a system of measures aimed at preventing the introduction and spread of dangerous pests, diseases, and weeds. Among grasses there are many quarantine objects, and their accurate identification is critically important.

Quarantine weedy grasses

Many grasses are noxious weeds that can cause enormous damage to agriculture. International and national quarantine lists include:

Cenchrus longispinus (long-spine sandbur) — a quarantine weed clogging pastures and crops. Its spiny spikelets injure animals and complicate harvesting.
Sorghum halepense (Johnson grass) — a dangerous quarantine weed distributed in warm regions. It forms powerful rhizomes, is difficult to eradicate, and reduces the yield of row crops.
Elymus repens (couch grass) — although not always included in quarantine lists, it is one of the most difficult weeds to eradicate, especially in the temperate zone.
Avena fatua (wild oat) — a specialized weed of oat and other cereal crops, a close relative of cultivated oats, which complicates its control.

Identification of these species requires knowledge of systematics: they can easily be confused with cultivated or less harmful species. For example, Sorghum halepense can be confused with cultivated sorghum (S. bicolor), and Avena fatua with cultivated oats (A. sativa). Accurate species determination is necessary for applying quarantine measures (Soreng et al., 2017; Zomlefer, 1994).

Quarantine diseases and pests of grasses

Systematics is also important for identifying pathogens and pests. For example:

Tilletia indica — the causal agent of Karnal bunt of wheat, a quarantine disease. Identification is based on spore morphology and molecular markers.
Mayetiola destructor (Hessian fly) — a dangerous pest of wheat, a quarantine object.
Diabrotica virgifera (western corn rootworm) — a quarantine pest of maize.

Although the systematics of pathogens and pests goes beyond plant systematics, knowledge of the systematics of host plants helps predict the spread and harmfulness of these organisms.

6.3. Breeding and hybridization

Systematics and phylogeny are the basis of modern breeding. As we noted in lecture 4, interspecific and intergeneric hybridization make it possible to transfer valuable genes from wild relatives to cultivated varieties. But for successful hybridization, it is necessary to know accurately the systematic position of the parental forms, their genomic composition, and phylogenetic relationships.

Choice of parents for crosses

When planning crosses, the breeder relies on data on gene pools (GP1–GP3). For example, to transfer stem rust resistance genes into wheat, Aegilops tauschii (GP2) is used. To increase winter hardiness — Secale cereale (GP3). For maize — teosinte (Zea mays subsp. parviglumis, Z. diploperennis) and Tripsacum (Doebley, 2004; Judd et al., 2018).

Creation of amphiploids

As we saw in the example of triticale, amphiploidy is used to restore the fertility of distant hybrids. Systematics helps determine which genomes can be combined and which cannot. For example, triticale (AABBRR or AABBDDRR) is the result of combining the genomes of wheat (A, B, D) and rye (R). Festulolium is the result of combining the genomes of fescue and ryegrass (Soreng et al., 2017).

Marker-assisted selection (MAS)

Modern breeding increasingly uses molecular markers to select desired genotypes. Systematics and phylogeny help identify genes controlling economically valuable traits and develop markers for tracking them. For example, for wheat, markers have been developed for genes for resistance to rust (Sr), powdery mildew (Pm), and Fusarium (Fhb). For maize — markers for genes for resistance to the corn borer, drought, as well as genes that increase lysine content (Doebley, 2004; Connor et al., 2011).

6.4. Forage and turf grasses

Grasses are the basis of forage production and turf management. Correct identification of species and varieties of forage and turf grasses is necessary for creating highly productive pastures, hayfields, and lawns.

Forage grasses

The main forage grasses of the temperate zone belong to the subfamily Pooideae, tribe Poeae: Lolium perenne (perennial ryegrass), Lolium multiflorum (Italian ryegrass), Festuca pratensis (meadow fescue), Festuca arundinacea (tall fescue), Dactylis glomerata (orchardgrass), Phleum pratense (timothy), Poa pratensis (Kentucky bluegrass). In the tropics and subtropics, C4 grasses are used: Panicum maximum (Guinea grass), Pennisetum purpureum (Napier grass), Sorghum sudanense (Sudan grass), Cynodon dactylon (Bermuda grass), and others (Soreng et al., 2017; Hasanuzzaman, 2019).

Systematics helps distinguish closely related species, for example, Lolium perenne and Lolium multiflorum, which differ in life span and type of tillering. Errors in identification can lead to incorrect selection of a grass mixture and reduced pasture productivity.

Turf grasses

Turf grasses are species capable of forming a dense stand resistant to mowing and trampling. The main turf grasses are: Poa pratensis (Kentucky bluegrass), Festuca rubra (red fescue), Lolium perenne (perennial ryegrass), Agrostis stolonifera (creeping bentgrass), Zoysia japonica (Japanese lawn grass). For each type of lawn (decorative, sports, parterre), certain species and varieties are selected. Systematics makes it possible to accurately determine the species affiliation of turf grass seeds, which is important when purchasing seeds and controlling quality (Connor et al., 2011).

6.5. Weedy grasses and their control

Weedy grasses are one of the most serious problems in agriculture. They compete with cultivated plants for light, water, and nutrients, reducing yield and product quality. Weed control requires accurate species identification, since different species require different control methods.

Main weedy grasses

The most harmful weedy grasses:

Avena fatua (wild oat) — a specialized weed of oats and other cereals. Close relationship with cultivated oats complicates selective control.
Lolium temulentum (darnel) — a poisonous weed clogging wheat and barley crops.
Setaria spp. (foxtail) — widespread weeds of row crops.
Echinochloa crus-galli (barnyardgrass) — one of the most harmful weeds of rice.
Sorghum halepense (Johnson grass) — a quarantine weed, difficult to eradicate due to powerful rhizomes.
Elymus repens (couch grass) — a perennial rhizomatous weed, especially harmful in the temperate zone.

Systematics helps distinguish these species from cultivated plants at early stages of growth, when morphological differences are minimal. For example, seedlings of Avena fatua and A. sativa are practically indistinguishable, which requires the use of molecular markers for identification (Soreng et al., 2017; Zomlefer, 1994).

Strategies for controlling weedy grasses

Knowledge of the systematics and biological characteristics of weeds makes it possible to develop effective control strategies:

Crop rotation — alternating crops with different life cycles and agronomic practices reduces weed infestation. For example, alternating winter and spring cereals, row crops, and perennial grasses.
Herbicides — selective herbicides act on certain groups of plants. Knowledge of the systematic affiliation of a weed makes it possible to choose the correct preparation. However, the close relationship between weed and crop (for example, Avena fatua and A. sativa) limits the use of herbicides.
Agronomic measures — tillage, sowing dates, seeding rates, and harvesting. For example, provoking weed seeds before sowing the crop.
Biological control — the use of natural enemies of weeds. For example, some insect species are used to control Sorghum halepense.

Connor et al. (2011) emphasize that an integrated plant protection system combining agronomic, chemical, and biological methods is the most effective and sustainable. Systematics is the basis for developing such systems.

7. Conclusion

The family Poaceae is one of the largest and, undoubtedly, the most economically important family of flowering plants. According to modern estimates, it includes about 11,500 species united in 768 genera, 12 subfamilies, 52 tribes, and 90 subtribes (Soreng et al., 2017). Grasses occupy about 70% of the world's sown areas, and more than 50% of the calories in the human diet are provided by them (Connor et al., 2011). The four main cereal crops — wheat, rice, maize, and barley — form the basis of the planet's food security. That is why grass systematics has not only academic but also paramount practical importance.

7.1. Phylogenetic structure of Poaceae: main results

The modern phylogenetic classification of grasses, based on molecular genetic data, distinguishes three successively branching lineages: early diverging lineages (Anomochlooideae, Pharoideae, Puelioideae), the BEP clade (Bambusoideae, Ehrhartoideae, Pooideae), and the PACMAD clade (Panicoideae, Arundinoideae, Chloridoideae, Micrairoideae, Aristidoideae, Danthonioideae) (Soreng et al., 2017; Judd et al., 2018). This structure reflects the main stages of the family's evolution and makes it possible to understand the patterns of distribution of economically valuable traits.

The early diverging lineages retain a number of archaic features and have limited distribution in tropical forests. They have no economic importance but are important for understanding the evolution of the family. The BEP clade unites bamboos, rice, and the most important cereal crops of the temperate zone — wheat, barley, rye, and oats. All members of this clade are C3 plants. The PACMAD clade includes maize, sorghum, millet, sugarcane, as well as many forage grasses of the tropics and subtropics. Most members of this clade possess C4 photosynthesis, which arose within it independently at least 22–24 times (Soreng et al., 2017).

The key conclusion: the phylogeny of Poaceae is well substantiated and serves as a reliable basis for classification, breeding, and prediction of plant properties. Understanding phylogenetic relationships makes it possible to purposefully search for wild relatives of cultivated plants — sources of valuable genes.

7.2. Economic importance of key genera

We examined in detail the systematic position of the most important genera of grasses. We confirmed that they are distributed among different subfamilies:

Ehrhartoideae: Oryza (rice) — the most important food crop of the tropics and subtropics.
Pooideae: Triticum (wheat), Hordeum (barley), Secale (rye), Avena (oats) — the most important cereal crops of the temperate zone, as well as numerous forage and turf grasses.
Panicoideae: Zea (maize), Sorghum (sorghum), Panicum (millet), Saccharum (sugarcane) — the most important cereal, forage, and industrial crops of the tropics and subtropics.
Bambusoideae: Bambusa, Phyllostachys (bamboos) — building material, paper, food, and ornamental plants.

Each genus is characterized by a certain set of morphological characters, genomic composition, and economic importance. Knowledge of the systematic position of key genera is necessary for correct identification, breeding, and agronomic practices (Hasanuzzaman, 2019; Judd et al., 2018).

7.3. Hybridization and genetic reserve

We examined interspecific and intergeneric hybridization as a powerful tool of breeding. Triticale (×Triticosecale) — a hybrid of wheat and rye — has become an important cereal crop combining the yield of wheat with the winter hardiness of rye. Festulolium (×Festulolium) — a hybrid of fescue and ryegrass — is a valuable forage crop. The creation of these hybrids became possible thanks to amphiploidy — chromosome doubling that restores fertility (Connor et al., 2011; Judd et al., 2018).

Wild relatives of wheat and maize are an invaluable genetic reserve for breeding. Genes for resistance to diseases, pests, drought, and salinity transferred from Aegilops, Triticum, Secale, teosinte, and Tripsacum have saved millions of hectares of crops and made it possible to expand the cultivation areas of crops (Doebley, 2004; Connor et al., 2011). Conservation of the genetic reserve is a necessary condition for the food security of humanity.

7.4. Practical importance of grass systematics

Grass systematics is not an abstract science, but a working tool for the agronomist, breeder, quarantine inspector, and plant protection specialist. We have shown that systematic knowledge is necessary for:

1. Identification of species and varieties — using morphological and molecular methods. This is the basis of seed production, variety control, and seed certification (Judd et al., 2018).

2. Quarantine control — accurate determination of quarantine objects (weeds, diseases, pests) prevents their introduction and spread (Soreng et al., 2017).

3. Breeding and hybridization — knowledge of phylogeny and gene pools makes it possible to purposefully transfer valuable genes from wild relatives to cultivated varieties (Connor et al., 2011).

4. Forage production and turf management — correct selection of species and varieties of forage and turf grasses ensures high productivity and quality (Hasanuzzaman, 2019).

5. Control of weedy grasses — accurate identification of weeds and knowledge of their biology make it possible to develop effective control strategies (Zomlefer, 1994).

7.5. Prospects and challenges

Despite the enormous successes of grass systematics, much remains to be done. Phylogenetic relationships of some groups remain unclear, especially within large genera such as Panicum, Eragrostis, and Festuca. Work continues on clarifying the boundaries of species and genera using whole-genome data. The development of genome editing methods opens new possibilities for targeted modification of economically valuable traits, but at the same time poses new questions for systematics and taxonomy (Soreng et al., 2017; Judd et al., 2018).

Global challenges — climate change, population growth, and reduction of arable land — require new approaches to breeding. Wild relatives of cultivated grasses are becoming an increasingly valuable resource, and their conservation is a task of paramount importance. Systematics plays a key role in the inventory, conservation, and use of this resource (Connor et al., 2011).

7.6. Final provisions

Summarizing, several main theses can be formulated:

1. Poaceae is a huge family with a clear phylogenetic structure. Modern classification distinguishes 12 subfamilies, 52 tribes, and 90 subtribes. The phylogeny of grasses is well substantiated by molecular data and reflects the main stages of the family's evolution (Soreng et al., 2017; Judd et al., 2018).

2. Grasses are the basis of humanity's food security. The four main cereal crops — wheat, rice, maize, and barley — provide more than half of world grain production and form the basis of the planet's population's nutrition (Connor et al., 2011).

3. Understanding systematics is necessary for breeding, plant protection, and quarantine. Accurate identification of species and varieties, knowledge of phylogenetic relationships and gene pools are necessary conditions for successful breeding, quarantine control, and weed control (Judd et al., 2018; Soreng et al., 2017).

4. Wild relatives are the key to the future of food security. Genes for resistance to diseases, pests, and abiotic stresses lost during domestication are preserved in populations of wild relatives. Their use in breeding is the most important reserve for increasing yield and adaptability of crops (Doebley, 2004; Connor et al., 2011).

5. Grass systematics is a dynamically developing field of knowledge. New molecular methods, whole-genome studies, and bioinformatics open new horizons for understanding the evolution and classification of grasses. Future specialists in agronomy, breeding, and plant protection must be prepared for constant updating of knowledge and the use of new methods (Soreng et al., 2017; Judd et al., 2018).

References

(2016). ‘An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV’, Botanical Journal of the Linnean Society, 181(1), 1-20. doi: 10.1111/boj.12385
Connor, D.J., Loomis, R.S., Cassman, K.G. (2011). ‘Genetic resources’, in Crop Ecology. Productivity and Management in Agricultural Systems. Cambridge, UK: Cambridge University Press, pp. 71-95.
Doebley, J. (2004). ‘The Genetics of Maize Evolution’, Annual Review of Genetics, 38(1), 37-59. doi: 10.1146/annurev.genet.38.072902.092425 (PubMed)
Ijaz, M., Nawaz, A., Ul-Allah, S., Rizwan, M.Shahid, Ullah, A., Hussain, M., Sher, A., Ahmad, S. (2019). ‘Crop Diversification and Food Security’, in Agronomic Crops. Singapore: Springer Singapore, 607-621. doi: 10.1007/978-981-32-9151-5_26
Judd, W.S., Campbell, C.S., Kellogg, E.A., Stevens, P.F., Donoghue, M.J. (2018). ‘Phylogenetic Relationships of Angiosperms’, in Plant Systematics. A Phylogenetic Approach. Sunderland, MA: Oxford University Press, pp. 237-588.
Judd, W.S., Campbell, C.S., Kellogg, E.A., Stevens, P.F., Donoghue, M.J. (2018). ‘The Science of Plant Systematics’, in Plant Systematics. A Phylogenetic Approach. Sunderland, MA: Oxford University Press, pp. 1-12.
Linder, H.P., Briggs, B.G., Johnson, L.A.S. (1998). ‘Ecdeiocoleaceae’, in Flowering Plants · Monocotyledons. Berlin, Heidelberg: Springer Berlin Heidelberg, 195-197. doi: 10.1007/978-3-662-03531-3_17
Naz, S., Fatima, Z., Iqbal, P., Khan, A., Zakir, I., Noreen, S., Younis, H., Abbas, G., Ahmad, S. (2019). ‘Agronomic Crops: Types and Uses’, in Agronomic Crops. Singapore: Springer Singapore, 1-18. doi: 10.1007/978-981-32-9151-5_1
Sharma, O.P. (2009). ‘Selected Families of Monocotyledons’, in Plant Taxonomy. New Delhi: Tata McGraw-Hill Education Private Limited, pp. 469-525.
Singh, G. (2019). ‘Major Families of Angiosperms’, in Plant Systematics. An Integrated Approach. Boca Raton, FL: CRC Press, pp. 307-493.
Soreng, R.J., Peterson, P.M., Romaschenko, K., Davidse, G., Teisher, J.K., Clark, L.G., Barberá, P., Gillespie, L.J., Zuloaga, F.O. (2017). ‘A worldwide phylogenetic classification of the Poaceae (Gramineae) II: An update and a comparison of two 2015 classifications’, Journal of Systematics and Evolution, 55(4), 259-290. doi: 10.1111/jse.12262
Stace, C.A., Bailey, J.P. (1999). ‘The value of genomic in situ hybridization (GISH) in plant taxonomic and evolutionary studies’, in Hollingsworth, P.M., Bateman, R.M., Gornall, R.J. (ed.) Molecular Systematics and Plant Evolution. London, UK: Taylor & Francis Limited, pp. 199-210.
Tanveer, A., Ikram, R.Muhammad, Ali, H.Haider (2019). ‘Crop Rotation: Principles and Practices’, in Agronomic Crops. Singapore: Springer Singapore, 1-12. doi: 10.1007/978-981-32-9783-8_1
Zomlefer, W.B. (1994). ‘Haemodoraceae, Typhaceae, Zingiberaceae, Costaceae, Cannaceae, Marantaceae, Xyridaceae, Commelinaceae, Eriocaulaceae, Juncaceae, Cyperaceae, Poaceae or Gramineae’, in Guide To Flowering Plant Families. USA: The University of North Carolina Press, pp. 315-356.
Коровин, О.А. (2023). ‘Систематика отдела Магнолиевые, или Покрытосеменные, — Magnoliophyta, или Angiospermae [Systematics of the division Magnoliophyta (or Angiospermae) — the Magnoliophytes, or Angiosperms]’, in Ботаника [Botany]. Москва: Кнорус, pp. 299-357.
Найда, Н.М. (2021). ‘Систематика растений [Plant Systematics]’, in Ботаника. Систематика растений [Botany. Plant Systematics]. Санкт-Петербург: Санкт-Петербургский государственный аграрный университет, pp. 7-106.
Яковлев, Г. П., Челомбитько, В. А., Дорофеев, В. И. (2008). ‘Отдель Цветковые, или Покрытосененные - Magnoliophyta, или Angiospermae [Division of Angiosperms - Magnoliophyta, or Angiospermae]’, in Ботаника [Botany]. Санкт-Петербург: СпецЛит, pp. 384-547.