Cultivated Plants, Their Wild Relatives, and Genetic Diversity

1.1. Genetic Diversity as a Strategic Resource

Food security relies not only on sufficient crop areas, fertilizers, and machinery. Its deep foundation is genetic diversity of cultivated plants and their wild relatives. Genetic diversity is understood as the diversity of alleles, genotypes, populations, and species that provides the adaptive potential of plants to changing environmental conditions. In the agrosphere, this diversity is represented by cultivars, lines, landraces, old local forms, wild relatives, and weedy relatives of cultivated species (Maxted et al., 2008; Welbaum, 2015).

The broader the genetic base of a crop, the higher the probability that among its forms there will be sources of resistance to disease, pests, drought, salinity, or cold. Conversely, a narrow genetic base means that all cultivated cultivars carry a similar set of alleles and may be simultaneously affected by the same pathogen or die from the same stress. That is why genetic diversity is regarded as a strategic resource of humanity, comparable in importance to soil, water, and energy (Maxted et al., 2008; Sadras and Calderini, 2015).

1.2. Domestication as a “Bottleneck”

The history of cultivated plants is a history of repeated reduction of diversity. During domestication, humans selected only a small part of individuals from a wild population that possessed desired traits: large fruits, non-dehiscing fruits, absence of bitterness, early ripening, uniform maturation. As a result, a so-called “bottleneck” arose — a sharp reduction in the number of genotypes that became the founders of cultivated cultivars (Rubatzky and Yamaguchi, 1997; Welbaum, 2015).

Domestication was accompanied by the fixation of traits useful to humans but often harmful for survival in nature: loss of natural seed dispersal, reduced seed dormancy, decreased bitterness and toxicity, reduced seed number, and loss of defense mechanisms against herbivores. In vegetatively propagated crops, for example garlic, banana, potato, yam, this led to an even more pronounced narrowing of diversity, because the progeny represents a clone of the original genotype (Rabinowitch and Currah, 2002; Rubatzky and Yamaguchi, 1997).

For garlic, it has been shown that long-term vegetative propagation fixed sterility in many cultivars; only in Central Asia, in the “garlic crescent” region, have fertile forms capable of sexual reproduction been preserved. This means that a significant part of the modern garlic assortment has limited potential for recombination and breeding improvement (Rabinowitch and Currah, 2002). Similar processes are known for potato, where domestication and subsequent spread led to the loss of a number of late blight resistance genes that have been preserved in wild species (Caliskan et al., 2023).

1.3. Narrowness of the Genetic Base of Modern Cultivars

Modern industrial crop production is characterized by a high degree of genetic unification. In the 20th–21st centuries, breeding was aimed at maximum productivity, technological suitability, and resistance to specific conditions, but was often accompanied by the displacement of local cultivars and landraces. As a result, the elite gene pool of many crops has become noticeably narrower than the gene pool of the species as a whole (Sadras and Calderini, 2015).

For example, in wheat, a significant part of modern cultivars derives from a limited number of parental lines; in rice, molecular studies reveal lower diversity in the cultivated gene pool compared with wild relatives; in maize, a decrease in diversity at average loci compared with wild ancestors has also been noted (Sadras and Calderini, 2015). For tomato, many disease resistance genes have been introgressed from wild species, but breeding for high productivity and transportability has narrowed the diversity of cultivated forms (Mattoo, 2017). In vegetable crops, including cucurbits, genetic erosion has been noted, associated with the displacement of local forms by exotic and improved cultivars (Pessarakli, 2016).

Potato is one of the most illustrative examples. Modern cultivars of tetraploid Solanum tuberosum possess high heterozygosity and complex tetrasomic inheritance; their genetic base is narrow, and inbreeding depression complicates the creation of pure lines. At the same time, wild potato relatives are distributed from the southwestern United States to central Argentina and Chile and carry enormous diversity for resistance to late blight, nematodes, viruses, cold, and drought (Campos and Ortiz, 2020; Caliskan et al., 2023; Vreugdenhil, 2007).

1.4. Vulnerability to Biotic and Abiotic Stresses

A narrow genetic base makes agrocenoses vulnerable to biotic stresses: diseases, pests, nematodes, and weeds. If all cultivars carry the same resistance gene, the appearance of a virulent pathogen strain can lead to mass crop damage. This is exactly what happened with potato late blight in Ireland in the 19th century, where genetically uniform plantings became the basis of a catastrophic famine. Modern examples include the emergence of new races of Phytophthora infestans that overcome previously effective resistance genes, and the spread of new species of Xanthomonas in tomato (Mattoo, 2017; Caliskan et al., 2023).

Abiotic stresses — drought, salinity, extreme temperatures, waterlogging — also require genetic diversity. It has been shown that modern potato cultivars suffer more from drought than landraces: in experiments, yield reduction in improved cultivars reached 48%, whereas in landraces it was 38% (Caliskan et al., 2023). Wild relatives and local cultivars often possess adaptations to marginal conditions: they grow from sea level to altitudes above 4500 m, under drought, frost, salinity, and poor soils (Maxted et al., 2008; Caliskan et al., 2023). This makes them an indispensable source of alleles for climate-oriented breeding.

1.5. Why Diversity Must Be Preserved and Used

The preservation of genetic diversity is necessary for three interrelated reasons. First, it provides insurance against catastrophic yield losses. Second, it serves as a source of alleles for breeding for resistance, quality, and adaptability. Third, it supports the evolutionary potential of cultivated species and their wild relatives in a changing environment (Maxted et al., 2008; Sadras and Calderini, 2015).

Conservation can be ex situ — in gene banks, seed collections, field collections, cryobanks, tissue cultures — and in situ — in natural habitats, protected areas, agroecosystems, and on farms. The largest repositories, such as VIR in St. Petersburg, the Svalbard Global Seed Vault, CGIAR collections, and national gene banks, provide long-term conservation of seeds and clones (Maxted et al., 2008; Welbaum, 2015; Pandey and Kasana, 2021). Botanical gardens also play an important role in conserving rare and endangered species, including wild relatives of cultivated plants (Pandey and Kasana, 2021).

However, conservation without use does not solve the problem. Diversity must be included in breeding programs: pre-breeding must be carried out, introgression lines must be created, and marker-assisted selection and genomic approaches must be used. Wild relatives and landraces carry useful alleles that can increase the yield, resistance, and quality of modern cultivars (Sadras and Calderini, 2015; Mattoo, 2017).

1.6. Conclusions

Genetic diversity is not an abstract category but a concrete resource on which the resilience of the food system depends. Domestication, breeding, and the spread of a limited number of cultivars have led to a narrowing of the genetic base of many crops. This makes crops vulnerable to diseases, pests, and climatic stresses. Wild relatives, landraces, old cultivars, and even weedy forms of cultivated species form a single evolutionary network in which alleles necessary for future breeding are stored. Systematics and taxonomy make it possible to identify these forms, understand their relationships, and purposefully search for donors of useful traits. Therefore, the next task of the module is to consider centers of origin, gene pools, mechanisms of hybridization and polyploidy, as well as strategies for conservation and use of diversity.

2.1. Historical Context and the Contribution of N. I. Vavilov

By the beginning of the 20th century, science already possessed a significant body of information about the geography of cultivated plants, but there was no unified theory explaining the patterns of their origin and distribution. Individual researchers — A. de Candolle, C. Darwin, C. Linnaeus — expressed assumptions about regions of domestication, but these ideas were fragmentary and were not supported by mass experimental material (Rubatzky and Yamaguchi, 1997; Westwood, 1993).

Nikolai Ivanovich Vavilov (1887–1943) — a Russian geneticist, breeder, geographer, and organizer of science — created a holistic doctrine of the centers of origin of cultivated plants. During numerous expeditions (Afghanistan, Iran, the Mediterranean, Ethiopia, China, Japan, North and South America, Central Asia), he collected tens of thousands of seed and tuber samples. Based on analysis of their morphological, biochemical, and genetic diversity, Vavilov established that the main diversity of cultivated plants is concentrated not in the places of their modern mass cultivation, but in certain relatively small regions, which he called centers of origin (Rubatzky and Yamaguchi, 1997; Welbaum, 2015; Korovkin, 2023).

Vavilov formulated the key principle: the center of origin of a species is the geographical area where the greatest genetic diversity of its forms is concentrated, including wild relatives and cultivated relatives. It is there that source material for breeding should be sought. This principle still remains the methodological basis for the purposeful search for donors of economically valuable traits (Maxted et al., 2008; Sadras and Calderini, 2015).

2.2. Main Centers of Origin of Cultivated Plants

Vavilov identified eight main centers of origin of cultivated plants (Rubatzky and Yamaguchi, 1997; Welbaum, 2015; Nayda, 2021; Meshkov, 2017). Let us consider each of them, indicating the most important cultivated species.

2.3. The Law of Homologous Series in Hereditary Variation

Vavilov did not limit himself to describing centers of origin. He formulated the law of homologous series in hereditary variation (1920), according to which genetically close species and genera possess similar series of hereditary variation. In other words, if a trait is found in one species — for example, a certain flower color, fruit shape, or disease resistance — then with high probability an analogous trait can be found in related species (Rubatzky and Yamaguchi, 1997; Sadras and Calderini, 2015; Korovkin, 2023).

This law has enormous practical significance for breeding. It makes it possible to predict where to look for the needed trait: if a form with rust resistance is found in one cereal species, it should be sought among related cereals. It was precisely on the basis of this principle that many donors of resistance to diseases, pests, and abiotic stresses were found (Maxted et al., 2008; Sadras and Calderini, 2015).

The law of homologous series also explains why centers of origin are characterized not only by species but also by intraspecific diversity: within one species in its center of origin, the maximum number of variants of traits can be found, while in other species they are represented only partially (Korovkin, 2023).

2.4. From Centers of Origin to Centers of Diversity: Modern Views

Modern science has refined and developed Vavilov’s doctrine. It has been established that the center of origin and the center of diversity do not always coincide. A species may originate from one region, but the maximum diversity of its forms may be concentrated in another — for example, as a result of secondary domestication, introgression, or natural hybridization (Maxted et al., 2008; Sadras and Calderini, 2015).

In addition, many crops are characterized by polyphyletic origin: they arose as a result of several independent events of domestication or hybridization. For example, the domesticated apple (Malus domestica) has a complex hybridogenic origin involving several wild species; cultivated forms of currant, raspberry, and strawberry also descend from several wild ancestors (Trunov, 2012). Wheat, oat, cotton, sugarcane, and banana arose as a result of allopolyploidy — the combination of genomes of different species (Taiz et al., 2023).

Modern views of centers of origin also include the concept of centers of diversity of cultivated plants, which may be primary (coinciding with centers of origin) and secondary (arising as a result of dispersal and subsequent diversification). Thus, for many vegetable crops the Mediterranean is the primary center, while secondary centers of diversity form in other regions — for example, in East Asia for crucifers (Gómez-Campo, 1999).

For potato, two centers are distinguished: the primary one — the Andes (Peru, Bolivia), where most wild species and landraces are concentrated, and the secondary one — Chile, where long-day forms formed that became the basis of modern commercial cultivars (Caliskan et al., 2023; Campos and Ortiz, 2020). For maize, the center of origin is Mexico, but secondary centers of diversity arose in the Andes and other regions (Welbaum, 2015).

Modern methodology for searching genetic resources relies not only on centers of origin but also on phytogeographic analysis, molecular phylogeny, and ecological modeling. This makes it possible to determine more precisely the regions where donors of specific traits — resistance to drought, cold, diseases — are most likely to be found (Maxted et al., 2008; Sadras and Calderini, 2015).

2.5. Significance of Vavilov’s Doctrine for Systematics and Breeding

Vavilov’s doctrine of centers of origin is of fundamental importance for the systematics and taxonomy of the agrosphere. It makes it possible to:

1. Identify relationships between cultivated plants and their wild relatives, which is necessary for constructing a natural classification.

2. Purposefully search for donors of economically valuable traits in natural populations and gene bank collections.

3. Predict the presence of traits in related species on the basis of the law of homologous series.

4. Plan expeditions and collections of genetic resources in regions with maximum diversity.

5. Assess the vulnerability of crops depending on the breadth of their genetic base and domestication history.

For the agrosphere, centers of origin are not only historical areas but also active reservoirs of genetic diversity that must be preserved and studied. That is why modern strategies for conserving CWR (crop wild relatives) and landraces rely on mapping centers of diversity and identifying priority territories for in situ protection (Maxted et al., 2008; Castañeda-Álvarez et al., 2015, cited in Maxted et al., 2008).

2.6. Conclusions

N. I. Vavilov’s doctrine of centers of origin of cultivated plants became a turning point in understanding the geography and evolution of the cultivated flora. The eight main centers — Chinese, Indian, Central Asian, Near Eastern, Mediterranean, Ethiopian, South American, and Central American — cover the vast majority of the most important food, industrial, medicinal, and ornamental crops. The law of homologous series in hereditary variation makes it possible to predict the presence of useful traits in related species. Modern science has supplemented Vavilov’s doctrine with ideas about the non-coincidence of centers of origin and diversity, the polyphyletic origin of many crops, and the role of hybridization and polyploidy. For the systematics of the agrosphere, this knowledge serves as the basis for the purposeful search, conservation, and use of genetic resources. The next topic — gene pools and categories of wild relatives of cultivated plants — logically develops these ideas.

3.1. Definition and Significance of CWR

Crop wild relatives (CWR) are understood as wild species that are closely related to cultivated plants and belong to the same or closely related gene pools. CWR may be direct ancestors of cultivated species or their close relatives with which crossing and gene transfer are possible (Maxted et al., 2008). It is CWR that serve as a natural reservoir of alleles lost during domestication and breeding, and they are regarded as a key resource for increasing the resistance, productivity, and adaptability of modern cultivars (Maxted et al., 2008; Sadras and Calderini, 2015).

Unlike cultivated cultivars, CWR grow in natural habitats and are subject to natural selection. They are adapted to a wide range of conditions — from arid steppes and semi-deserts to high mountains, from saline soils to waterlogged habitats. Many CWR carry genes for resistance to diseases and pests that were lost during domestication. For example, wild potato species growing in the Andes possess resistance to late blight, nematodes, viruses, cold, and drought (Caliskan et al., 2023; Vreugdenhil, 2007). Wild tomatoes carry genes for resistance to bacterial, fungal, and viral diseases, as well as to nematodes (Mattoo, 2017).

The conservation of CWR is not only a conservation task but also a strategic necessity for food security. According to estimates, less than 1% of the available genetic diversity of wild species has been used in breeding; the rest remains to be studied and involved in breeding programs (Caliskan et al., 2023). That is why international organizations, including FAO, CGIAR, and Bioversity International, give priority attention to the conservation of CWR in situ and ex situ (Maxted et al., 2008; Pandey and Kasana, 2021).

3.2. Gene Pools According to Harlan and de Wet

The concept of a gene pool was introduced by J. Harlan and J. de Wet (1971) to describe the degree of genetic closeness between a cultivated species and its wild relatives. The gene pool reflects the possibility of crossing and gene transfer between species. Three main pools are distinguished: GP1, GP2, and GP3 (Maxted et al., 2008; Sadras and Calderini, 2015).

3.3. Examples of Gene Pools for Major Crops

3.4. Use of CWR in Breeding

The use of CWR in breeding includes several stages: identification of a donor, introgression of genes, selection, and stabilization of the trait. Depending on the gene pool, different methods are used.

Introgression from GP1 is usually carried out through direct crosses and backcrossing. Hybrids are fertile, recombination is possible, although linkage drag of undesirable traits may be observed. To overcome linkage drag, multiple backcrosses, marker-assisted selection, and genomic selection methods are used (Sadras and Calderini, 2015).

Introgression from GP2 requires overcoming barriers of sterility and incompatibility. Embryo culture, chromosome doubling (colchicine), bridge crosses, and the use of 2n gametes are employed. For example, for potato the bridge species is S. verrucosum (2EBN), allowing genes to be transferred from 1EBN species (Campos and Ortiz, 2020). For tomato, bridge crosses with S. peruvianum and embryo culture are used (Mattoo, 2017).

Introgression from GP3 is possible only with the use of biotechnological methods: somatic hybridization (protoplast fusion), genetic transformation, and creation of synthetic amphiploids. An example is the transfer of the RB gene from S. bulbocastanum into potato, as well as the creation of synthetic hexaploid wheats involving Ae. tauschii (Campos and Ortiz, 2020; Taiz et al., 2023).

3.5. Examples of Successful Use of CWR

The history of breeding knows many examples of successful use of CWR. Let us give some of them.

Wheat resistance to rust. Genes for resistance to stem, leaf, and stripe rust have been introgressed into cultivated wheat from wild species of Triticum and Aegilops. The 1BL/1RS translocation from rye (Secale cereale) carries genes for resistance to rust and powdery mildew and increases yield; it is widely used in modern wheat cultivars (Sadras and Calderini, 2015; Taiz et al., 2023).

Tomato resistance to diseases. Genes for resistance to fusarium wilt (I, I-2, I-3), verticillium (Ve), bacterial wilt (Bwr-6, Bwr-12), nematodes (Mi-1), and viruses (TYLCV, TSWV, ToMV) have been introgressed from wild species S. pimpinellifolium, S. peruvianum, S. habrochaites, S. chilense. For example, the Mi-1 gene from S. peruvianum confers resistance to root-knot nematodes and has been used in commercial cultivars since the 1940s (Mattoo, 2017).

Potato resistance to nematodes. Genes for resistance to the golden potato cyst nematode (Globodera rostochiensis) — H1 from S. tuberosum Group Andigena, H2 from S. multidissectum, Fa and Fb from S. spegazzinii, Gpa2 from S. tuberosum — have been introgressed into cultivated cultivars. The Hero gene from S. pimpinellifolium confers a broad spectrum of resistance to G. rostochiensis and partial resistance to G. pallida (Campos and Ortiz, 2020; Caliskan et al., 2023).

Soybean resistance to nematodes. The Rhg1 gene from wild soybean Glycine soja confers resistance to the cyst nematode (Heterodera glycines). The copy number of the Rhg1 gene correlates with the level of resistance: more copies — higher resistance (Sadras and Calderini, 2015).

Rice resistance to drought. The QTL qtl12.1 from wild rice Oryza rufipogon increases yield under rainfed agriculture. Introgression of this QTL into cultivated cultivars made it possible to increase drought resistance without loss of productivity (Sadras and Calderini, 2015).

3.6. Problems and Limitations of Using CWR

Despite obvious advantages, the use of CWR is associated with a number of difficulties.

First, linkage drag — linked inheritance of undesirable alleles with the target gene. Wild relatives often carry alleles that reduce yield, fruit quality, and lodging resistance. To overcome linkage drag, multiple backcrosses and marker-assisted selection are required (Sadras and Calderini, 2015).

Second, genetic barriers — hybrid sterility, incompatibility, different levels of ploidy and EBN. Overcoming these barriers requires special methods: embryo culture, chromosome doubling, bridge crosses, somatic hybridization (Campos and Ortiz, 2020; Mattoo, 2017).

Third, limited availability of CWR. Many species grow in hard-to-reach regions, are endangered, and are not represented in gene banks. Conservation of CWR in situ and ex situ requires significant resources (Maxted et al., 2008).

Fourth, lack of knowledge about the genetic potential of many CWR. Many species are not characterized phenotypically or genotypically, and their useful alleles remain unknown. Their identification requires comprehensive studies — from field evaluation to whole-genome sequencing (Maxted et al., 2008; Sadras and Calderini, 2015).

3.7. Strategies for Searching Donors Based on Phylogeny

The modern strategy for searching for resistance donors relies on phylogenetic analysis. Phylogeny makes it possible to:

1. Determine relationships between the cultivated species and its wild relatives, which is necessary for choosing the correct gene pool.

2. Predict the presence of traits in related species on the basis of Vavilov’s law of homologous series.

3. Choose optimal introgression methods depending on the gene pool.

4. Identify priority species for conservation and study.

For example, to search for donors of potato late blight resistance, phylogenetic analysis points to species of section Petota growing in Mexico and South America as the most likely sources of genes. To search for donors of tomato TYLCV resistance, phylogeny points to species S. chilense and S. peruvianum (Mattoo, 2017; Campos and Ortiz, 2020).

3.8. Conclusions

CWR and gene pools GP1–GP3 represent a conceptual framework for understanding the degree of genetic closeness between cultivated plants and their wild relatives. GP1 includes forms with which crossing is possible without barriers; GP2 — species with which crossing is difficult but possible using special methods; GP3 — species whose genes can be transferred only with the help of biotechnologies. The use of CWR in breeding has made it possible to create cultivars resistant to diseases, pests, and abiotic stresses and to improve product quality. However, the use of CWR is associated with problems of linkage drag, genetic barriers, limited availability, and lack of knowledge. Modern strategies for searching donors rely on phylogeny, genomics, and phenotyping. The next topic — hybridization, polyploidy, and introgression — logically develops the understanding of the mechanisms underlying the use of CWR.

4.1. Hybridization as a Driving Force of Evolution of Cultivated Plants

Hybridization — crossing of genetically distinct forms — is one of the key mechanisms determining the origin and evolution of cultivated plants. In nature, hybridization occurs spontaneously when the ranges of closely related species overlap; in cultivation, humans deliberately use it to combine economically valuable traits of different forms. A distinction is made between intraspecific hybridization (crossing cultivars, lines, and landraces of one species), interspecific (crossing different species), and intergeneric (crossing representatives of different genera) (Rubatzky and Yamaguchi, 1997; Welbaum, 2015).

The role of hybridization in the evolution of cultivated plants is difficult to overestimate. Many important cultivated species arose precisely as a result of natural hybridization and subsequent polyploidization. Wheat, oat, cotton, sugarcane, banana, tobacco, potato, plum, cherry, currant, raspberry, strawberry — all these crops have a hybridogenic origin (Taiz et al., 2023; Welbaum, 2015; Trunov, 2012). For example, the domesticated apple (Malus domestica) arose as a result of complex hybridization involving several wild species — M. sieversii, M. sylvestris, M. baccata, and others (Trunov, 2012). Cultivated plum (Prunus domestica) has a polyphyletic origin: it arose from crossing blackthorn (P. spinosa) with cherry plum (P. cerasifera) and subsequent polyploidization (Westwood, 1993).

Hybridization not only creates new forms but also enriches the gene pool of cultivated plants with alleles from wild relatives. This process, called introgression, underlies modern breeding for resistance to diseases, pests, and abiotic stresses (Sadras and Calderini, 2015; Maxted et al., 2008).

4.2. Introgression of Genes from Wild Species

Introgression is the transfer of one or several alleles from a wild species into the genome of a cultivated plant. Unlike simple crossing, introgression presupposes not only obtaining a hybrid but also fixing the alien allele in the cultivated gene pool through multiple backcrosses with the recurrent parent (Sadras and Calderini, 2015).

The process of introgression includes several stages:

1. Identification of the donor — search for a wild species carrying the target allele.

2. Overcoming crossing barriers — incompatibility, hybrid sterility, differences in ploidy and EBN.

3. Obtaining F₁ hybrids — crossing the cultivated plant with the wild donor.

4. Backcrossing — multiple crossing of hybrids with the cultivated parent to restore economically valuable traits.

5. Selection — marker-assisted selection of the target allele and elimination of undesirable alleles from the wild donor.

6. Stabilization — obtaining a line or cultivar with the target trait in a cultivated genetic background (Sadras and Calderini, 2015).

Introgression can be carried out both through direct crosses (for GP1 and GP2 species) and through biotechnological methods — somatic hybridization, embryo culture, genetic transformation (for GP3 species) (Maxted et al., 2008; Campos and Ortiz, 2020).

A classic example of successful introgression is the transfer of the RB gene from the wild Mexican species Solanum bulbocastanum (1EBN) into cultivated potato. Because direct crossing is impossible due to differences in EBN, somatic hybridization of protoplasts was used, followed by multiple backcrosses with cultivated cultivars. As a result, cultivars possessing broad resistance to late blight were obtained (Campos and Ortiz, 2020; Caliskan et al., 2023).

Another example is the introgression of the Mi-1 gene from Solanum peruvianum into cultivated tomato. The gene confers resistance to root-knot nematodes (Meloidogyne spp.) and has been widely used in commercial cultivars since the 1940s (Mattoo, 2017). Genes for resistance to viruses (TYLCV, TSWV, ToMV), fungal and bacterial diseases have also been introgressed into tomato from wild species S. pimpinellifolium, S. habrochaites, S. chilense (Mattoo, 2017).

4.3. Polyploidy: Autopolyploidy and Allopolyploidy

Polyploidy — an increase in the number of chromosome sets in a cell — is widespread among cultivated plants. Polyploids contain more than two complete genomes; they arise as a result of meiotic errors (formation of 2n gametes), somatic chromosome doubling, or interspecific hybridization followed by polyploidization (Taiz et al., 2023; Welbaum, 2015).

Two main types of polyploidy are distinguished:

Autopolyploidy — an increase in the number of chromosome sets of the same species. Autopolyploids arise from the fusion of 2n gametes of one species or from somatic chromosome doubling. Examples: autotetraploid potato (Solanum tuberosum, 2n = 4x = 48), autotriploid banana (Musa spp.), autotetraploid alfalfa (Medicago sativa), autotetraploid cotton Gossypium hirsutum (Welbaum, 2015; Taiz et al., 2023). Autopolyploids are characterized by tetrasomic inheritance, which complicates breeding but simultaneously increases heterozygosity and heterosis (Campos and Ortiz, 2020).

Allopolyploidy — the combination of chromosome sets of different species in one organism. Allopolyploids arise from hybridization of two species followed by chromosome doubling. Examples: bread wheat (Triticum aestivum, 2n = 6x = 42, AABBDD), cotton Gossypium barbadense (2n = 4x = 52, AADD), tobacco (Nicotiana tabacum, 2n = 4x = 48), rapeseed (Brassica napus, 2n = 4x = 38, AACC), mustard Brassica juncea (2n = 4x = 36, AABB), Brassica carinata (2n = 4x = 34, BBCC) (Taiz et al., 2023; Gómez-Campo, 1999; Welbaum, 2015). Allopolyploids often demonstrate disomic inheritance, which simplifies breeding, and possess heterosis arising from the combination of different genomes (Taiz et al., 2023).

4.4. The Role of Polyploidy in the Origin of Cultivated Plants

Polyploidy played a key role in the evolution of many cultivated plants. According to estimates, all angiosperms have experienced at least one round of whole-genome duplication in their evolutionary history; many cultivated species are polyploids or paleopolyploids (Taiz et al., 2023).

Wheat is a classic example of allopolyploidy. Diploid species Triticum monococcum (AA) and Aegilops speltoides (BB) hybridized, giving rise to tetraploid Triticum turgidum (AABB, 2n = 4x = 28). Then tetraploid wheat hybridized with diploid Ae. tauschii (DD), which led to the emergence of hexaploid bread wheat T. aestivum (AABBDD, 2n = 6x = 42) (Taiz et al., 2023; Sadras and Calderini, 2015). Oat (Avena sativa, 2n = 6x = 42), cotton Gossypium hirsutum (2n = 4x = 52), and G. barbadense (2n = 4x = 52) arose in a similar way (Welbaum, 2015).

Sugarcane (Saccharum officinarum) is a complex polyploid complex with chromosome numbers from 80 to 120 and more. Modern sugarcane cultivars are hybrids of S. officinarum and S. spontaneum with different levels of ploidy; their genomes include sets from different species (Welbaum, 2015). Banana (Musa spp.) is also a polyploid complex: cultivated forms are represented by diploids (AA, BB), triploids (AAA, AAB, ABB), and tetraploids (AAAA). Triploid forms are sterile and reproduce vegetatively, which ensures their genetic uniformity and makes them vulnerable to diseases (Welbaum, 2015).

Potato is an example of a polyploid complex involving autopolyploidy and segmental allopolyploidy. Cultivated potato S. tuberosum (2n = 4x = 48) is an autotetraploid with tetrasomic inheritance, but with signs of segmental allopolyploidy. Wild potato species are represented by diploids (2n = 24), triploids (2n = 36), tetraploids (2n = 48), pentaploids (2n = 60), and hexaploids (2n = 72) (Campos and Ortiz, 2020; Caliskan et al., 2023; Vreugdenhil, 2007).

4.5. Examples of Polyploid Complexes in Cultivated Plants

4.6. Synthetic Amphiploids and Triticale

Synthetic amphiploids are forms created by humans through hybridization of two species followed by chromosome doubling. A classic example is triticale (×Triticosecale) — a hybrid of wheat (Triticum spp.) and rye (Secale cereale). Triticale combines the high yield and grain quality of wheat with the resistance of rye to diseases, cold, and poor soils. Depending on the initial parental forms, triticale can be hexaploid (2n = 42, AABBRR) or octoploid (2n = 56, AABBDDRR) (Taiz et al., 2023; Welbaum, 2015).

The creation of triticale became possible thanks to overcoming barriers between genera using embryo culture and chromosome doubling with colchicine. Triticale is grown in Russia, Poland, Germany, France, Australia, Brazil, and other countries; it is used as a grain, forage, and industrial crop (Welbaum, 2015).

Other examples of synthetic amphiploids: Triticale, ×Triticosecale, ×Festulolium (hybrid of fescue and ryegrass), ×Brassicoraphanus (hybrid of cabbage and radish), synthetic hexaploid wheats (T. turgidum × Ae. tauschii) (Taiz et al., 2023; Sadras and Calderini, 2015).

4.7. 2n Gametes and Sexual Polyploidization

2n gametes (unreduced gametes) are gametes with the somatic chromosome number, formed as a result of meiotic disturbances. They play a key role in natural polyploidization and in breeding. Several mechanisms of 2n gamete formation are distinguished: premature chromosome doubling, first division restitution (FDR), second division restitution (SDR), and post-meiotic doubling (Campos and Ortiz, 2020; Vreugdenhil, 2007).

FDR and SDR gametes are most common in potato. FDR gametes transmit about 80% of the parent’s heterozygosity to the progeny, SDR — about 40%. The use of 2n gametes makes it possible to overcome barriers between species with different levels of ploidy and EBN, and also to transmit economically valuable alleles from diploid species into tetraploid cultivated potato (Campos and Ortiz, 2020; Caliskan et al., 2023).

The formation of 2n gametes is controlled by recessive mutations: ps — for 2n pollen, os — for 2n eggs. These mutations are widespread among species of Solanum and are used in breeding programs (Campos and Ortiz, 2020). Similar mechanisms are known in alfalfa, clover, sweet potato, sugarcane, and other crops (Welbaum, 2015).

4.8. Endosperm Balance Number (EBN) and Its Role in Hybridization

Endosperm Balance Number (EBN) is a hypothesis proposed by Johnston and Hanneman (1980) explaining the success or failure of interspecific and interploid crosses in potato and other Solanaceae. According to this hypothesis, normal endosperm development requires a ratio of 2 maternal : 1 paternal EBN. Each species has a certain EBN value, which does not always coincide with the level of ploidy (Campos and Ortiz, 2020; Vreugdenhil, 2007).

For example, diploid species may have EBN = 1 or EBN = 2; tetraploid — EBN = 2 or EBN = 4; hexaploid — EBN = 4. Crossing is possible only when EBN coincides or when special methods are used (2n gametes, bridge crosses, somatic hybridization) (Campos and Ortiz, 2020; Caliskan et al., 2023).

The EBN hypothesis is of great practical importance: it makes it possible to predict the success of crosses and plan breeding programs. For example, to transfer genes from 1EBN species (S. bulbocastanum, S. pinnatisectum) into cultivated potato (4EBN), it is necessary to use bridge species with intermediate EBN (2EBN) or somatic hybridization methods (Campos and Ortiz, 2020; Caliskan et al., 2023).

4.9. Bridge Species and Overcoming Crossing Barriers

Bridge species are species used to overcome crossing barriers between two other species. A bridge species crosses with both parents, ensuring gene transfer between them. For example, Solanum verrucosum (2EBN) is used as a bridge species for transferring genes from 1EBN species into cultivated potato (4EBN). Crossing S. verrucosum with 1EBN species produces hybrids, which are then crossed with cultivated potato (Campos and Ortiz, 2020; Vreugdenhil, 2007).

Other methods of overcoming crossing barriers include:

• Embryo culture — extraction and cultivation of embryos on artificial media.
• Chromosome doubling — treatment with colchicine to obtain fertile amphiploids.
• Somatic hybridization — fusion of protoplasts of different species.
• In vitro fertilization — fertilization of egg cells in culture.
• Use of “mentor pollen” — pollination with a mixture of compatible and incompatible pollen (Campos and Ortiz, 2020; Mattoo, 2017).

These methods make it possible to involve GP2 and GP3 species in breeding, which cannot be used through direct crosses.

4.10. Conclusions

Hybridization, introgression, and polyploidy are interrelated mechanisms determining the evolution of cultivated plants and their genetic diversity. Hybridization creates new combinations of alleles; introgression transfers useful alleles from wild relatives into cultivated cultivars; polyploidy increases the number of genomes and creates new adaptive possibilities. Autopolyploids (potato, alfalfa, banana) and allopolyploids (wheat, cotton, rapeseed, tobacco) are widely represented among cultivated plants. Synthetic amphiploids, such as triticale, demonstrate the possibilities of purposeful creation of new cultivated forms. 2n gametes and EBN determine the success of interspecific crosses and are used to overcome barriers between species. Bridge species, embryo culture, somatic hybridization, and other methods make it possible to involve GP2 and GP3 species in breeding. The next topic — ex situ and in situ conservation — logically completes the review of genetic resources, their origin, and use.

5.1. Two Approaches to Conserving Genetic Resources

The conservation of plant genetic resources is carried out in two fundamentally different ways: ex situ (outside the natural environment) and in situ (in the natural environment). These approaches do not exclude but complement each other; their combination provides the most reliable insurance against loss of diversity (Maxted et al., 2008; Caliskan et al., 2023).

In situ (Latin “in place”) — conservation of species and populations in their natural habitats, in the ecosystems where they evolved and continue to evolve. This approach is applicable both to wild relatives of cultivated plants (CWR) and to landraces and old cultivars preserved in traditional agroecosystems (Maxted et al., 2008; Caliskan et al., 2023).

Ex situ (Latin “out of place”) — conservation of genetic material outside the natural environment: in gene banks, seed collections, field collections, cryobanks, and tissue cultures. This approach makes it possible to preserve a huge number of samples in a limited area and ensures their availability to breeders and researchers (Maxted et al., 2008; Welbaum, 2015; Caliskan et al., 2023).

Each approach has its advantages and limitations. In situ preserves the evolutionary potential of populations and their interaction with the environment but is subject to risks of natural disasters, climate change, and anthropogenic impact. Ex situ ensures reliable long-term storage but fixes only part of genetic diversity and does not allow populations to continue evolving (Maxted et al., 2008; Caliskan et al., 2023).

5.2. Ex Situ: Gene Banks, Seed Collections, Field Collections, Cryobanks, Tissue Cultures

5.3. In Situ: Protected Natural Areas, Agroecosystems, Farmer Cultivars

In situ — conservation of species and populations in their natural habitats. This approach is especially important for wild relatives of cultivated plants, which continue to evolve in nature under natural selection (Maxted et al., 2008; Caliskan et al., 2023).

Forms of in situ conservation:

• Protected natural areas — national parks, nature reserves, biosphere reserves, wildlife sanctuaries. They ensure protection of entire ecosystems, including CWR populations.
• Agroecosystems — traditional farming systems where local cultivars (landraces) have been grown for centuries and continue to adapt to local conditions.
• Farmer cultivars — cultivars maintained by farmers within traditional agriculture. They possess high adaptability and often carry alleles for resistance to diseases and abiotic stresses.

Unlike ex situ, in situ preserves not only genotypes but also ecological interactions, evolutionary processes, and cultural practices. However, in situ is subject to risks: climate change, anthropogenic impact, and natural disasters can lead to loss of populations (Maxted et al., 2008; Caliskan et al., 2023).

5.4. On-Farm: Conservation of Local Cultivars and Breeds

On-farm conservation is a form of in situ in which local cultivars and breeds are preserved directly on farms, under conditions of their traditional cultivation. This approach ensures the preservation not only of genetic diversity but also of related cultural practices, knowledge, and traditions (Maxted et al., 2008).

On-farm conservation is especially important for landraces, which often surpass modern cultivars in adaptability to marginal conditions. For example, more than 3,000 potato landraces are preserved in the Andes, grown by local farmers (Caliskan et al., 2023). In Russia and other countries, local cultivars of apple, pear, currant, raspberry, and strawberry are preserved, possessing high winter hardiness and disease resistance (Trunov, 2012).

5.5. International Organizations and Initiatives

The conservation of plant genetic resources is coordinated by a number of international organizations:

• FAO (Food and Agriculture Organization of the United Nations) — develops global strategies for the conservation and use of genetic resources and monitors the state of collections.
• CGIAR (Consultative Group on International Agricultural Research) — includes a network of international research centers, such as CIP (potato), IRRI (rice), CIMMYT (maize and wheat), ICRISAT (sorghum, millet), ICARDA (dryland crops and cereals), and others.
• Bioversity International (formerly IPGRI — International Plant Genetic Resources Institute) — coordinates research and conservation of genetic resources and develops standards and protocols.
• GCDT (Global Crop Diversity Trust) — a fund supporting long-term conservation of collections, including in the Svalbard Global Seed Vault (Maxted et al., 2008; Welbaum, 2015).

According to the FAO report, about 98,284 potato samples are conserved ex situ in 174 gene banks worldwide; 39% of them are concentrated in six gene banks — in France, Russia, Peru, Germany, the USA, and Japan (Caliskan et al., 2023).

5.6. Botanical Gardens as Conservation Centers

Botanical gardens play an important role in plant conservation, including wild relatives of cultivated plants. According to BGCI, there are about 2,122 botanical gardens in the world, preserving more than 6.13 million samples representing more than 80,000 species (Pandey and Kasana, 2021).

The largest botanical gardens in the world:

• Royal Botanic Gardens, Kew (UK) — the largest plant collection in the world, including more than 68,000 samples, 27,000 taxa, 7 million herbarium specimens, the Millennium Seed Bank (92,500 collections), and DNA and Tissue Bank (58,000 samples). Kew represents about 95% of vascular plant genera and 60% of fungal genera (Pandey and Kasana, 2021).
• Missouri Botanical Garden (USA) — one of the oldest gardens in the USA, including about 51,000 plants and the largest orchid collection (6,500 plants, 89 taxa of rare and endangered species).
• Brooklyn Botanic Garden (USA) — includes more than 48,401 samples, including 19,423 living plants, about 297,000 herbarium specimens, and more than 380 rare species.
• Singapore Botanic Gardens — the first in Asia and the third in the world UNESCO World Heritage Site, including collections of giant ferns, gingers, and orchids.
• Royal Botanic Garden, Sydney (Australia) — the oldest garden in Australia, including 28,000 plants and a herbarium of 1.2 million specimens.
• Botanical Garden of St. Petersburg (Russia) — one of the oldest gardens in Russia, founded in 1714, including 25 greenhouses and collections of tropical and subtropical plants.

In Russia and CIS countries, botanical gardens also play an important role in CWR conservation. For example, in India a network of Lead Botanical Gardens has been created, including the Shivaji University Garden (Kolhapur), CSIR-NBRI (Lucknow), JNTBGRI (Kerala), and others (Pandey and Kasana, 2021).

5.7. Problems and Challenges of Conservation

Despite achievements, the conservation of genetic resources faces a number of problems:

• Limited resources — many national gene banks do not have sufficient capacity and funding for storing and distributing collections (Caliskan et al., 2023).
• Duplication and redundancy — a significant part of samples is duplicated in different collections, which diverts resources from conserving unique material (Caliskan et al., 2023).
• Genetic erosion — loss of landraces and wild populations as a result of land-use change, urbanization, and climate change.
• Lack of characterization — many samples are not characterized phenotypically or genotypically, which complicates their use in breeding.
• Legal and ethical issues — access to genetic resources and benefit-sharing are regulated by international agreements (Convention on Biological Diversity, International Treaty on Plant Genetic Resources for Food and Agriculture).

5.8. Conclusions

Ex situ and in situ conservation are two complementary approaches to preserving the genetic diversity of cultivated plants and their wild relatives. Ex situ ensures reliable long-term storage in gene banks, cryobanks, and in vitro collections but fixes only part of diversity. In situ preserves the evolutionary potential of populations and their interaction with the environment but is subject to risks. On-farm conservation supports local cultivars and related cultural practices. International organizations — FAO, CGIAR, Bioversity International — coordinate efforts to conserve and use genetic resources. Botanical gardens make a significant contribution to the conservation of rare and endangered species. The next topic — crop ↔ feral form ↔ weed — completes the review of the dynamics of genetic material in the agrosphere.

6.1. Three Categories in a Single Evolutionary Network

In the agrosphere, cultivated plants, feral forms, and weeds do not form rigidly separated categories. They are dynamic states of the same genetic material that transition into one another depending on environmental conditions, farming practices, and human activity. Understanding these transitions is necessary for the systematics of the agrosphere, because the same species may act as cultivated, feral, or weedy in different regions and at different times (Welbaum, 2015; Rubatzky and Yamaguchi, 1997; Maxted et al., 2008).

The key difference between these categories lies not in taxonomic rank but in ecological-agronomic status. A cultivated plant is a form consciously grown by humans for production. A feral form is a cultivated plant that has returned to the wild and exists without purposeful care. A weed is a form growing in agrocenoses or disturbed habitats and competing with cultivated plants for resources. All three categories may be represented by the same biological species (Gómez-Campo, 1999; Welbaum, 2015).

6.2. Domestication as a Transition from Wild to Cultivated State

Domestication represents the first and most important transition: from a wild population to a cultivated form. This process is accompanied by the fixation of traits useful to humans and the loss of traits necessary for survival in nature. Among the key changes are gigantism (increase in the size of fruits, seeds, root crops), loss of seed dispersal ability (non-dehiscing fruits, absence of shattering), reduced seed dormancy, decreased bitterness and toxicity, changes in photoperiodic response, and shortening of the life cycle (Rubatzky and Yamaguchi, 1997; Welbaum, 2015).

These changes make cultivated plants dependent on humans. For example, modern cantaloupe cultivars have fruits that do not split when ripe, and seeds often die inside the fruit without being released. Such plants cannot survive in nature without human help (Welbaum, 2015). Similarly, cultivated potato has lost the bitterness and toxicity characteristic of wild species and cannot compete with wild forms in natural conditions (Caliskan et al., 2023).

However, domestication is not irreversible. When a cultivated plant enters conditions where humans stop caring for it, it may return to a wild lifestyle — this process is called feralization.

6.3. Feral Forms: Cultivated Plants Returning to Nature

A feral form is a population of a cultivated plant that exists outside cultivation, without purposeful human care. Feralization can occur in various ways: through the spread of seeds, tubers, rhizomes, and cuttings beyond fields; through the dumping of plant residues; through accidental transport by humans or animals. Feral forms often retain traits of the cultivated plant but gradually return to a wild phenotype under natural selection (Welbaum, 2015; Gómez-Campo, 1999).

Classic examples of feral forms:

• Feral soybean (Glycine max). In regions with warm and humid climates, soybean can spread beyond fields and form self-sustaining populations. Feral soybean often has smaller seeds, shattering pods, and increased dispersal ability — traits that were lost in cultivation (Welbaum, 2015; Sadras and Calderini, 2015).

• Feral radish (Raphanus sativus). Cultivated radish and its wild relative R. raphanistrum cross easily, forming hybrid populations that can behave as weeds. In the Mediterranean and other regions, feral radish is found along roads, in wastelands, and in crops (Gómez-Campo, 1999).

• Feral sunflower (Helianthus annuus). In North America, feral sunflower populations are widespread in disturbed habitats; they often cross with cultivated cultivars and wild species, forming complex hybrid complexes (Welbaum, 2015).

• Feral carrot (Daucus carota). Cultivated carrot and wild carrot are the same species. Feral carrot forms are found in Europe, Asia, and North America; they have a thin, woody root and are often regarded as weeds (Gómez-Campo, 1999).

• Feral potato (Solanum tuberosum). In some regions, potato tubers survive in the soil after harvest and give rise to new plants. Feral potato forms can transfer genes from cultivated cultivars into wild populations (Caliskan et al., 2023).

Feral forms play a dual role. On the one hand, they can become weeds competing with the crop. On the other hand, they serve as a reservoir of genetic diversity and can be a source of alleles for breeding. In addition, feral forms are a “bridge” for gene flow between cultivated and wild populations (Welbaum, 2015; Maxted et al., 2008).

6.4. Weeds: An Ecological-Agronomic Characteristic, Not a Taxonomic Rank

A weed is a plant growing in an agrocenosis or disturbed habitat and causing harm to cultivated plants through competition for light, water, and nutrients, as well as through allelopathy, shading, lodging, and spread of diseases and pests. Weeds are not a taxonomic but an ecological-agronomic category (Nayda, 2021; Welbaum, 2015).

The key consequence of this position: the same species can be cultivated, weedy, or feral under different conditions. For example:

• Brassica rapa — in Europe and Asia it is cultivated as turnip, fodder turnip, pak choi, and Chinese cabbage; at the same time, in crops and on disturbed lands it occurs as a weed — wild mustard, field mustard (Gómez-Campo, 1999; Welbaum, 2015).

• Daucus carota — cultivated carrot and wild carrot; the wild form grows as a weed along roads and in crops (Gómez-Campo, 1999).

• Raphanus sativus — cultivated radish and weedy radish; feral forms occur in crops and wastelands (Gómez-Campo, 1999).

• Sorghum halepense (Johnson grass) — in some regions it is cultivated as a forage crop, in others it is a noxious weed (Welbaum, 2015).

• Avena fatua (wild oat) — a close relative of cultivated oat (Avena sativa); it occurs as a weed in cereal crops but can be used as a forage plant (Welbaum, 2015).

Weeds are classified by ecological and agronomic traits: by life span (annual, biennial, perennial), by mode of reproduction (seed, vegetative), by habitat (field, meadow, ruderal), by harmfulness (quarantine, especially harmful, slightly harmful). Detailed weed management is assigned to other disciplines — agronomy, plant protection, herbology (Nayda, 2021; Welbaum, 2015).

6.5. Genetic Exchange Between Crops, Feral Forms, and Weeds

Between cultivated plants, feral forms, and weeds there is a constant gene flow. This flow can be directed both ways: from the crop to wild and weedy forms (through pollen, seeds, vegetative propagules) and from wild and weedy forms to the crop (through introgression, hybridization, accidental selection).

Main mechanisms of gene flow:

• Cross-pollination. In cross-pollinated crops (maize, sunflower, beet, brassicas, cucurbits), pollen can be transferred to weedy and feral forms, forming hybrids. For example, cultivated sunflower crosses easily with wild species of Helianthus and with feral forms (Welbaum, 2015; Maxted et al., 2008).

• Seed dispersal. Seeds of cultivated plants can enter the soil, be transported by wind, water, animals, and humans, and give rise to feral populations. In some crops (for example, sorghum, millet, rice) there are “weedy” races that mimic cultivated plants in morphology but shatter and contaminate crops (Welbaum, 2015).

• Vegetative reproduction. Tubers, rhizomes, and bulbs of cultivated plants can survive in the soil and give rise to feral forms. For example, potato can survive in the soil as tubers and sprout the following year (Caliskan et al., 2023).

• Introgression from CWR. Genes of wild relatives can enter cultivated cultivars through spontaneous hybridization, as well as through breeding programs. In turn, genes of cultivated plants can enter wild populations, changing their genetic structure (Maxted et al., 2008; Sadras and Calderini, 2015).

Particularly intensive gene flow is observed in regions where cultivated plants grow near their wild relatives. For example, in the Andes cultivated potato coexists with wild species of Solanum, creating conditions for hybridization and introgression (Caliskan et al., 2023; Campos and Ortiz, 2020). In the Mediterranean, cultivated and wild forms of Brassica and Raphanus form complex hybrid complexes (Gómez-Campo, 1999).

6.6. Weeds as a Source of Genes for Breeding

Weeds are often regarded as an undesirable element of the agrocenosis, but they can serve as a source of genes for breeding. Weedy forms often possess traits that may be useful to cultivated plants:

• Resistance to diseases and pests. Weedy relatives of cultivated plants may carry resistance genes that were lost in cultivation. For example, weedy forms of Brassica and Raphanus can be sources of resistance to clubroot, fusarium, and nematodes (Gómez-Campo, 1999).

• Resistance to abiotic stresses. Weedy forms growing in marginal conditions may possess resistance to drought, salinity, cold, and poor soils. These traits can be introgressed into cultivated cultivars (Maxted et al., 2008).

• Allelopathic properties. Some weeds release substances that suppress the growth of other plants; these properties can be used to create crops resistant to weeds (Welbaum, 2015).

• Genetic diversity. Weedy forms maintain genetic diversity in agroecosystems and can serve as a reservoir of alleles for future breeding (Maxted et al., 2008).

However, the use of weeds in breeding is associated with risks: weedy forms may be carriers of undesirable traits (small seeds, shattering, bitterness, toxicity), and their introgression into cultivated cultivars may lead to the appearance of “weedy” traits in cultivated plants.

6.7. Feral Forms as a Threat and as a Resource

Feral forms can pose a threat to agriculture because they compete with cultivated plants, spread diseases and pests, and can transfer herbicide resistance genes into weed populations. For example, feral radish can cross with cultivated cultivars and transmit wild traits to them (Gómez-Campo, 1999).

However, feral forms can also be a resource. They preserve genetic diversity that may be lost in cultivation. Feral populations of potato, soybean, and sunflower may carry alleles useful for breeding for resistance to diseases and abiotic stresses. In addition, feral forms serve as a model for studying the adaptation of cultivated plants to the wild environment (Welbaum, 2015; Maxted et al., 2008).

6.8. Legal and Ethical Aspects

Gene flow between cultivated, feral, and weedy forms has legal and ethical consequences. In particular, the spread of transgenic crops can lead to the transfer of transgenes into wild and weedy populations, which raises concerns among regulators and the public. The Convention on Biological Diversity and the Cartagena Protocol on Biosafety regulate transboundary movement of genetically modified organisms and require risk assessment (Maxted et al., 2008; Taiz et al., 2023).

In addition, access to genetic resources and benefit-sharing are regulated by the International Treaty on Plant Genetic Resources for Food and Agriculture (ITPGRFA). This treaty recognizes the sovereign rights of states over their genetic resources and establishes mechanisms for access and benefit-sharing (Maxted et al., 2008).

6.9. Conclusions

Cultivated plants, feral forms, and weeds form a single evolutionary network in which genetic material constantly passes from one category to another. Domestication converts wild forms into cultivated ones; feralization returns cultivated forms to the wild; weedy forms arise as a result of adaptation to disturbed habitats and agrocenoses. The same species can be cultivated, feral, or weedy under different conditions. Weeds are not a taxonomic but an ecological-agronomic category. Genetic exchange between crops, feral forms, and weeds can be both a threat and a resource. Weedy and feral forms can serve as a source of genes for breeding, but their use requires caution. The next topic — the significance of phylogeny for searching for resistance donors — shows how systematics and phylogenetics help purposefully search for useful alleles in this complex network.

7.1. Taxonomic and Ecological Categories: A Fundamental Difference

In plant systematics, the basic unit is the species, and larger categories — genus, family, order — reflect the phylogenetic relationship of organisms. These categories have an objective biological basis and are regulated by international codes of nomenclature. The concept of “weed” has a completely different status. It is not part of the taxonomic hierarchy and does not designate any natural group of kinship. A weed is an ecological-agronomic characteristic that describes the position of a plant in an agrocenosis and its interaction with cultivated plants (Nayda, 2021; Welbaum, 2015).

The same species can be cultivated, weedy, feral, or wild depending on growing conditions and human activity. For example, Daucus carota is both cultivated carrot and wild carrot, which often behaves as a weed along roads and in crops. In a classic work on the systematics of crucifers, it is directly noted that “weedy and cultivated Daucus carota are the same species,” and many modern weeds are cultivated plants that have escaped from cultivation (Gómez-Campo, 1999). Similarly, Medicago sativa (alfalfa) can be a valuable forage crop and at the same time a feral or weedy plant depending on context (Gómez-Campo, 1999).

Thus, “weed” is not a rank but a role that a species plays in a particular agrocenosis. This role can change over time, space, and depending on agricultural practices. That is why in the systematics of the agrosphere it is important to distinguish the taxonomic affiliation of a plant and its ecological-agronomic status.

7.2. One Species — Different Statuses: The Example of Brassica rapa

The most illustrative example is Brassica rapa L. (syn. B. campestris). This species includes many cultivated forms: turnip, fodder turnip, pak choi, Chinese cabbage, leaf mustard, and oilseed forms (rapeseed, turnip rape). In some regions, B. rapa is grown as an important vegetable and oilseed crop; in others, it occurs as a weed in crops, wastelands, and along roads (Gómez-Campo, 1999; Welbaum, 2015). Taxonomically, it is the same species. Differences between cultivated and weedy forms are often determined by a few genes, not by species affiliation.

A similar situation is characteristic of many crucifers. Raphanus sativus (radish) and Raphanus raphanistrum (wild radish) cross easily, forming hybrid populations that can behave as weeds. In the Mediterranean and other regions, feral radish occurs in crops and on disturbed lands (Gómez-Campo, 1999). Sinapis arvensis (field mustard) is a noxious weed of cereals but at the same time a close relative of cultivated mustards and a potential source of resistance genes (Gómez-Campo, 1999).

7.3. Weedy Races of Cultivated Plants

A special category consists of weedy races of cultivated plants — forms that morphologically mimic the cultivated plant but possess traits allowing them to survive in the agrocenosis. A classic example is weedy races of rice (Oryza sativa), which mimic cultivated rice in height, leaf shape, and inflorescence, but have shattering grains and increased dispersal ability. Such races can cause significant yield damage and are difficult to separate from cultivated forms (Welbaum, 2015). Similar weedy races are known in sorghum, millet, flax, and oat.

Weedy races arise as a result of natural selection in the agrocenosis: plants that are morphologically closer to cultivated plants are less likely to be removed during weeding, while traits of shattering and seed dormancy ensure their survival. This process is an example of agroecological evolution — evolution driven by agricultural practices (Welbaum, 2015; Nayda, 2021).

7.4. Ecological Plasticity and Adaptation of Weedy Forms

Weeds possess a set of ecological and biological features that allow them to compete successfully with cultivated plants. These include:

• High seed productivity — one plant can produce tens and hundreds of thousands of seeds.
• Diversity of dispersal methods — by wind, water, animals, humans, machinery.
• Long-term preservation of seed viability — seeds can remain in the soil for years and even decades, forming a “seed bank.”
• Extended germination period — seeds do not germinate simultaneously, which complicates weed control.
• Ability for vegetative reproduction — by rhizomes, tubers, bulbs, and shoots.
• High ecological plasticity — ability to survive in a wide range of conditions.
• Allelopathic properties — release of substances suppressing the growth of other plants (Nayda, 2021; Welbaum, 2015).

These traits are not taxonomic; they arise independently in different families and genera. For example, high seed productivity is characteristic of many annual weeds from different families — Asteraceae, Brassicaceae, Poaceae, Amaranthaceae. That is why “weed” is not a taxonomic group but an ecological strategy.

7.5. Classification of Weeds by Ecological-Agronomic Traits

In agronomy and geobotany, weeds are classified by traits that have no taxonomic significance:

• By life span: annual, biennial, perennial.
• By mode of reproduction: seed, vegetative, mixed.
• By habitat: field, meadow, ruderal, aquatic.
• By harmfulness: quarantine, especially harmful, slightly harmful.
• By response to agricultural practices: typical, facultative, accidental (Nayda, 2021; Welbaum, 2015).

In phytocenology, weeds are considered a component of the agrophytocenosis — a plant community created by humans. In the agrophytocenosis, cultivated plants are dominants and edifiers, while weeds are the second participant, which appears independently of humans. The species composition of weeds depends on the level of agricultural technology, nutrient reserves in the soil, moisture supply, and preceding crop (Nayda, 2021). These characteristics also have no taxonomic rank.

7.6. Weeds as a Source of Genes for Breeding

Because weeds are often close relatives of cultivated species, they can serve as a source of genes for breeding. Weedy forms often possess resistance to diseases, pests, and abiotic stresses, as well as allelopathic properties. For example, weedy forms of Brassica and Raphanus can be sources of resistance to clubroot, fusarium, and nematodes (Gómez-Campo, 1999). Weedy cereals may carry genes for resistance to rust, powdery mildew, and drought (Maxted et al., 2008).

However, the use of weeds in breeding is associated with risks: they may be carriers of undesirable traits — small seeds, shattering, bitterness, toxicity — and their introgression into cultivated cultivars may lead to the appearance of “weedy” traits in cultivated plants. Therefore, when using weedy forms in breeding, careful selection and multiple backcrosses are required (Maxted et al., 2008; Sadras and Calderini, 2015).

7.7. Weed Management Is Assigned to Other Disciplines

It is important to emphasize that detailed weed management — agrotechnical, chemical, biological, and mechanical methods — is assigned to other disciplines: agronomy, plant protection, herbology, and farming. Within the systematics and taxonomy of the agrosphere, we are interested primarily in the identification of weedy species, their relationships with cultivated plants, and their role in genetic exchange. Systematics makes it possible to distinguish a weedy species from a cultivated one, determine its taxonomic affiliation, and assess its potential as a source of genes (Nayda, 2021; Maxted et al., 2008).

7.8. Conclusions

“Weed” is an ecological-agronomic characteristic, not a taxonomic rank. The same species can be cultivated, weedy, feral, or wild depending on conditions and farming practices. Weeds are classified by ecological and agronomic traits, not by kinship. Weedy races of cultivated plants arise as a result of agroecological evolution. Weeds can serve as a source of genes for breeding, but their use requires caution. Weed management is assigned to other disciplines; in the systematics of the agrosphere it is important to identify weedy species, understand their relationships, and assess their role in genetic exchange. The next topic — the significance of phylogeny for searching for resistance donors — shows how systematics and phylogenetics help purposefully search for useful alleles in the complex network of cultivated, wild, and weedy forms.

8.1. Phylogeny as a Navigation Map for Searching for Donors

Phylogeny is the history of evolutionary relationships between species, genera, and larger taxa. A phylogenetic tree shows which species are close relatives and which are distant; which lineages diverged recently and which millions of years ago. For the plant breeder and geneticist, phylogeny serves as a navigation map: it makes it possible to determine where to look for donors of economically valuable traits, how likely crossing with a particular species is, and what methods will be required for gene transfer (Maxted et al., 2008; Sadras and Calderini, 2015).

The law of homologous series in hereditary variation, formulated by N. I. Vavilov, establishes that genetically close species and genera possess similar series of hereditary variation. If a trait is found in one species — resistance to a disease, a certain color, fruit shape — then with high probability an analogous trait can be found in related species. Thus, phylogeny makes it possible to predict where to look for the needed allele (Rubatzky and Yamaguchi, 1997; Korovkin, 2023; Sadras and Calderini, 2015).

Modern phylogenetics relies not only on morphology but also on molecular data — DNA, RNA, and protein sequences. This makes it possible to construct more accurate and reliable phylogenetic trees than classical morphological systematics. For example, for the genus Capsicum (peppers), phylogenetic studies based on molecular markers and cytogenetic analysis made it possible to identify three species complexes — C. annuum, C. baccatum, and C. pubescens — which are regarded as independent domestication lineages (Rêgo et al., 2016). For the genus Brassica, molecular data revealed two main lineages — “nigra” and “rapa/oleracea” — which made it possible to refine the relationships between cultivated species and their wild relatives (Gómez-Campo, 1999).

8.2. From Phylogeny to Genetic Resources: The Logic of Search

The strategy for searching for resistance donors based on phylogeny includes several stages:

1. Construction of a phylogenetic tree for the cultivated species and its wild relatives. This makes it possible to determine which species are closest relatives and which are more distant.

2. Identification of gene pools (GP1, GP2, GP3) for each potential donor. This determines whether direct crossing is possible or whether special methods will be required.

3. Search for the trait in species belonging to the corresponding gene pool. The law of homologous series suggests which species should be searched for the needed trait.

4. Assessment of donor potential — phenotyping, genotyping, checking for the target allele.

5. Introgression — transfer of the allele into the cultivated gene pool using methods corresponding to the gene pool.

6. Selection and stabilization — marker-assisted selection, backcrosses, evaluation of economically valuable traits (Maxted et al., 2008; Sadras and Calderini, 2015).

Phylogeny makes it possible to narrow the search: instead of checking all wild species one by one, the researcher focuses on those most likely to carry the needed allele. This saves time and resources and accelerates the creation of new cultivars (Maxted et al., 2008).

8.3. Examples of Successful Use of CWR

8.4. Strategies for Searching Donors Based on Phylogeny

The modern strategy for searching donors based on phylogeny includes the following approaches:

1. Phylogenetic analysis based on molecular markers. The use of DNA markers (SSR, SNP, AFLP) and sequencing makes it possible to construct an accurate phylogenetic tree and determine relationships between the cultivated species and its wild relatives. For example, for the genus Capsicum, phylogenetic analysis based on cytogenetic and molecular data made it possible to identify three species complexes and determine a strategy for searching for disease resistance donors (Rêgo et al., 2016).

2. Vavilov’s law of homologous series. This law makes it possible to predict which species should be searched for the needed trait. If rust resistance is found in one cereal species, it should be sought in related cereals (Rubatzky and Yamaguchi, 1997; Korovkin, 2023).

3. Ecological and geographical data. Phylogeny in combination with ecological and geographical data makes it possible to determine in which regions and habitats donors should be sought. For example, species growing in arid regions are more likely to carry drought resistance genes (Maxted et al., 2008).

4. Allele mining. Mass sequencing of target genes in a large number of samples makes it possible to identify new alleles conferring resistance. For example, allele mining in wheat made it possible to identify new powdery mildew resistance alleles at the Pm3 locus (Sadras and Calderini, 2015).

5. FIGS (Focused Identification of Germplasm Strategy). This strategy combines ecological and phenotypic data to identify samples most likely to carry the needed trait. For example, with the help of FIGS, wheat samples carrying new powdery mildew resistance alleles were selected (Sadras and Calderini, 2015).

6. Genomic approaches. Genome sequencing, GWAS, and genomic selection make it possible to identify loci associated with resistance and predict the potential of wild species as donors (Sadras and Calderini, 2015; Taiz et al., 2023).

8.5. Molecular Methods in Phylogeny and Donor Search

Modern phylogenetics uses a wide range of molecular methods:

• DNA sequencing — determination of nucleotide sequences of genes and genomes. It makes it possible to construct accurate phylogenetic trees and identify relationships.
• Microsatellites (SSR) — short tandem repeats, highly polymorphic and codominant. Widely used to assess genetic diversity and relationships.
• SNP (single nucleotide polymorphisms) — single-nucleotide substitutions, the most abundant type of polymorphism. Used for GWAS, genomic selection, and phylogenetic analysis.
• AFLP, RAPD, ISSR — dominant markers used to assess genetic diversity and phylogenetic relationships.
• FISH, GISH — cytogenetic methods allowing visualization of chromosomes and their segments. Used to study polyploidy, introgression, and hybridization (Vreugdenhil, 2007; Rêgo et al., 2016).
• Cryopreservation and in vitro — methods for conserving genetic resources, ensuring the availability of donors for breeding (Caliskan et al., 2023).

8.6. Problems and Limitations

Despite achievements, the search for donors based on phylogeny is associated with a number of problems:

• Incompleteness of phylogenetic data. For many genera and species, phylogenetic trees have been constructed only partially; relationships remain unclear.
• Hybridization and polyploidy. Complex polyploid complexes (potato, wheat, cotton) complicate the construction of phylogenetic trees and the determination of relationships.
• Linkage drag. Linked inheritance of undesirable alleles with the target gene requires multiple backcrosses and marker-assisted selection.
• Genetic barriers. Hybrid sterility, incompatibility, and different levels of ploidy and EBN require special introgression methods.
• Limited availability of CWR. Many species grow in hard-to-reach regions, are endangered, and are not represented in gene banks.
• Lack of knowledge about genetic potential. Many CWR are not characterized phenotypically or genotypically, and their useful alleles remain unknown (Maxted et al., 2008; Sadras and Calderini, 2015).

8.7. Conclusions

Phylogeny is a navigation map for searching for resistance donors. It makes it possible to determine where to look for the needed allele, how likely crossing with a particular species is, and what methods will be required for gene transfer. Vavilov’s law of homologous series makes it possible to predict the presence of traits in related species. Successful examples of CWR use include wheat resistance to rust, tomato resistance to diseases and nematodes, potato resistance to nematodes and late blight, rice resistance to drought, barley resistance to powdery mildew, and soybean resistance to nematodes. Modern strategies for searching donors include phylogenetic analysis based on molecular markers, allele mining, FIGS, and genomic approaches. Molecular methods — sequencing, SSR, SNP, FISH, GISH — make it possible to construct accurate phylogenetic trees and identify useful alleles. However, the search for donors is associated with problems: incompleteness of phylogenetic data, hybridization and polyploidy, linkage drag, genetic barriers, limited availability of CWR, and lack of knowledge. The next topic — conclusion — summarizes the significance of genetic diversity, systematics, and phylogeny for food security.

9.1. Genetic Diversity — A Strategic Resource of Humanity

Throughout the lecture, we consistently developed one central idea: the genetic diversity of cultivated plants and their wild relatives is a strategic resource of humanity, comparable in importance to soil, water, and energy. This is not an abstract statement but a concrete conclusion from the analysis of domestication history, the current state of breeding, and the challenges facing the food system (Maxted et al., 2008; Sadras and Calderini, 2015).

Domestication, which began about 10,000 years ago, led to the emergence of cultivated plants from wild ancestors. However, this process was accompanied by a sharp reduction in genetic diversity — the so-called “bottleneck.” Humans selected only a small part of individuals possessing desired traits, thereby narrowing the genetic base of future cultivars. Subsequent breeding, especially intensive in the 20th–21st centuries, further strengthened this trend: modern elite cultivars often derive from a limited number of parental lines and carry a similar set of alleles (Rubatzky and Yamaguchi, 1997; Welbaum, 2015; Caliskan et al., 2023).

A narrow genetic base makes agrocenoses vulnerable to biotic and abiotic stresses. The appearance of a virulent pathogen strain, the spread of a new pest, drought, or frost can lead to mass yield losses if all cultivated cultivars are genetically uniform. Examples include the Irish famine of the 19th century, caused by potato late blight, and modern outbreaks of new races of Phytophthora infestans that overcome previously effective resistance genes (Mattoo, 2017; Caliskan et al., 2023). That is why the conservation and use of genetic diversity is not only a scientific but also a strategic task, on the solution of which the food security of humanity depends.

9.2. Vavilov’s Doctrine and Its Modern Development

N. I. Vavilov’s doctrine of centers of origin of cultivated plants became a turning point in understanding the geography and evolution of the cultivated flora. The eight main centers — Chinese, Indian, Central Asian, Near Eastern, Mediterranean, Ethiopian, South American, and Central American — cover the vast majority of the most important food, industrial, medicinal, and ornamental crops (Rubatzky and Yamaguchi, 1997; Welbaum, 2015; Nayda, 2021; Meshkov, 2017). The law of homologous series in hereditary variation makes it possible to predict the presence of useful traits in related species and thereby guide the search for donors (Korovkin, 2023; Sadras and Calderini, 2015).

Modern science has supplemented Vavilov’s doctrine with ideas about the non-coincidence of centers of origin and diversity, the polyphyletic origin of many crops, and the role of hybridization and polyploidy. For potato, a primary center in the Andes and a secondary center in Chile are distinguished; for maize, the center of origin is Mexico, but secondary centers of diversity arose in the Andes and other regions (Caliskan et al., 2023; Welbaum, 2015). These refinements are important for practice: they show that the search for donors should rely not only on historical centers of origin but also on modern centers of diversity, where unique adaptations have formed under natural and artificial selection.

9.3. CWR and Gene Pools: A Conceptual Framework

The concept of crop wild relatives (CWR) and gene pools GP1–GP3 is a tool for understanding the degree of genetic closeness between cultivated species and their wild relatives. GP1 includes forms with which crossing is possible without barriers; GP2 — species with which crossing is difficult but possible using special methods; GP3 — species whose genes can be transferred only with the help of biotechnologies (Maxted et al., 2008; Sadras and Calderini, 2015).

The use of CWR in breeding has made it possible to create cultivars resistant to diseases, pests, and abiotic stresses and to improve product quality. Examples include wheat resistance to rust, tomato resistance to diseases and nematodes, potato resistance to nematodes and late blight, rice resistance to drought, barley resistance to powdery mildew, and soybean resistance to nematodes (Mattoo, 2017; Caliskan et al., 2023; Sadras and Calderini, 2015). However, the use of CWR is associated with problems: linkage drag, genetic barriers, limited availability, and lack of knowledge about the genetic potential of many species. To overcome these problems, embryo culture, chromosome doubling, bridge crosses, somatic hybridization, 2n gametes, and EBN analysis are used (Campos and Ortiz, 2020; Vreugdenhil, 2007).

9.4. Hybridization, Polyploidy, Introgression

Hybridization, introgression, and polyploidy are interrelated mechanisms determining the evolution of cultivated plants and their genetic diversity. Hybridization creates new combinations of alleles; introgression transfers useful alleles from wild relatives into cultivated cultivars; polyploidy increases the number of genomes and creates new adaptive possibilities. Autopolyploids (potato, alfalfa, banana) and allopolyploids (wheat, cotton, rapeseed, tobacco) are widely represented among cultivated plants (Taiz et al., 2023; Welbaum, 2015). Synthetic amphiploids, such as triticale, demonstrate the possibilities of purposeful creation of new cultivated forms (Taiz et al., 2023).

2n gametes and EBN determine the success of interspecific crosses and are used to overcome barriers between species. Bridge species, embryo culture, somatic hybridization, and other methods make it possible to involve GP2 and GP3 species in breeding (Campos and Ortiz, 2020; Caliskan et al., 2023). These mechanisms underlie modern breeding for resistance, productivity, and adaptability.

9.5. Ex Situ and In Situ Conservation: Complementary Approaches

The conservation of genetic diversity is carried out in two complementary ways: ex situ and in situ. Ex situ ensures reliable long-term storage in gene banks, cryobanks, and in vitro collections but fixes only part of diversity. In situ preserves the evolutionary potential of populations and their interaction with the environment but is subject to risks of natural disasters and anthropogenic impact. On-farm conservation supports local cultivars and related cultural practices (Maxted et al., 2008; Caliskan et al., 2023).

The largest gene banks in the world — VIR in St. Petersburg, the Svalbard Global Seed Vault, the Millennium Seed Bank, NCGRP, and CGIAR collections — ensure the conservation of seeds, clones, tissues, and DNA. Botanical gardens make a significant contribution to the conservation of rare and endangered species, including CWR (Pandey and Kasana, 2021; Welbaum, 2015). International organizations — FAO, CGIAR, Bioversity International, GCDT — coordinate efforts to conserve and use genetic resources.

9.6. Crop, Feral Form, Weed: A Single Evolutionary Network

Cultivated plants, feral forms, and weeds form a single evolutionary network in which genetic material constantly passes from one category to another. Domestication converts wild forms into cultivated ones; feralization returns cultivated forms to the wild; weedy forms arise as a result of adaptation to disturbed habitats and agrocenoses. The same species can be cultivated, feral, or weedy under different conditions — for example Brassica rapa, Daucus carota, Raphanus sativus (Gómez-Campo, 1999; Welbaum, 2015).

“Weed” is not a taxonomic but an ecological-agronomic characteristic. Weeds are classified by ecological and agronomic traits, not by kinship. Weedy races of cultivated plants arise as a result of agroecological evolution. Weeds can serve as a source of genes for breeding, but their use requires caution (Nayda, 2021; Welbaum, 2015; Maxted et al., 2008).

9.7. Phylogeny as a Tool for Donor Search

Phylogeny is a navigation map for searching for resistance donors. It makes it possible to determine where to look for the needed allele, how likely crossing with a particular species is, and what methods will be required for gene transfer. Vavilov’s law of homologous series makes it possible to predict the presence of traits in related species. Successful examples of CWR use include wheat resistance to rust, tomato resistance to diseases and nematodes, potato resistance to nematodes and late blight, rice resistance to drought, barley resistance to powdery mildew, and soybean resistance to nematodes (Mattoo, 2017; Caliskan et al., 2023; Sadras and Calderini, 2015).

Modern strategies for searching donors include phylogenetic analysis based on molecular markers, allele mining, FIGS, and genomic approaches. Molecular methods — sequencing, SSR, SNP, FISH, GISH — make it possible to construct accurate phylogenetic trees and identify useful alleles (Sadras and Calderini, 2015; Rêgo et al., 2016; Vreugdenhil, 2007). However, the search for donors is associated with problems: incompleteness of phylogenetic data, hybridization and polyploidy, linkage drag, genetic barriers, limited availability of CWR, and lack of knowledge.

9.8. Systematics and Taxonomy of the Agrosphere as an Integrative Discipline

Systematics and taxonomy of the agrosphere occupy a special position among biological disciplines. They do not duplicate botany, zoology, or genetics but integrate their data to solve applied problems: identification of cultivated plants and their wild relatives, determination of their relationships, assessment of genetic potential, and planning of breeding programs. The taxonomy of the agrosphere relies on morphological, cytogenetic, biochemical, and molecular data; it uses the concepts of gene pools, EBN, polyploidy, and introgression to describe the diversity of the cultivated flora and its wild relatives (Maxted et al., 2008; Sadras and Calderini, 2015; Rêgo et al., 2016).

For the agrosphere, it is especially important to distinguish taxonomic rank and ecological-agronomic status. A cultivated plant, a feral form, and a weed may belong to the same species but play different roles in the agrocenosis. Systematics makes it possible to identify these forms, determine their taxonomic affiliation, and assess their potential as sources of genes (Gómez-Campo, 1999; Welbaum, 2015). That is why the systematics of the agrosphere is not an academic discipline but an instrument of food security.

9.9. The Future of Food Security

The future of food security depends on the competent management of genetic diversity. Climate change, population growth, urbanization, soil degradation, and biodiversity loss — all these challenges require new cultivars resistant to diseases, pests, drought, salinity, and extreme temperatures. Such cultivars can be created only on the basis of broad genetic diversity preserved in gene banks, in situ, and on-farm (Maxted et al., 2008; Sadras and Calderini, 2015).

Modern technologies — NGS, GWAS, genomic selection, CRISPR-Cas — open new possibilities for using genetic diversity. They make it possible to identify useful alleles, accelerate introgression, predict phenotypes, and create new combinations of genes (Taiz et al., 2023; Sadras and Calderini, 2015). However, these technologies do not replace the need to conserve and study CWR, landraces, and old cultivars. Without genetic diversity, breeding loses material for work; without systematics and phylogeny, it loses navigation.

9.10. Final Provisions

1. Genetic diversity is a strategic resource of humanity. Its conservation and use are a condition of food security.

2. Vavilov’s doctrine of centers of origin and the law of homologous series remain the methodological basis for searching for donors of economically valuable traits.

3. CWR and gene pools GP1–GP3 are a conceptual framework for understanding the degree of genetic closeness and choosing introgression methods.

4. Hybridization, polyploidy, introgression, 2n gametes, and EBN are mechanisms underlying the evolution of cultivated plants and their breeding improvement.

5. Ex situ and in situ conservation are complementary approaches; their combination provides reliable insurance against loss of diversity.

6. Cultivated plants, feral forms, and weeds are a single evolutionary network; “weed” is an ecological-agronomic, not a taxonomic, category.

7. Phylogeny is a navigation map for searching for resistance donors; it makes it possible to purposefully search for useful alleles and plan breeding programs.

8. Systematics and taxonomy of the agrosphere are an integrative discipline, an instrument of food security linking fundamental knowledge about plant diversity with the practical tasks of breeding.

Cultivated plants, their wild relatives, and weedy forms are not separate categories but a single evolutionary network in which genetic material constantly passes from one form to another. Understanding this network, its taxonomic structure, and phylogenetic relationships is a necessary condition for the conservation and use of genetic diversity. Systematics and phylogeny are tools that allow humanity to manage this diversity, direct it into the channel of breeding, and ensure sustainable food production in a changing world. The future of food security depends on how competently we can preserve, study, and use the genetic heritage created by nature and humans over ten thousand years of agriculture.