Potato ⋆ Horticulture

Potato are one of the most important food, fodder, and technical row crops. According to the classification adopted in horticulture, potatoes are referred to starch-bearing crops, earlier – to tuber crops.

In foreign practice it is often called Irish potato or white potato.

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Horticulture

Strach crops
- Potato (Русская версия)

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Horticulture

Strach crops
- Potato (Русская версия)

Economic importance

The potato ranks among the first in world agriculture along with rice, wheat and corn.

The chemical composition of potato tubers is 75-80% water, 20-25% dry matter, including 14-22% starch, 1.4-3% protein, about 1% fiber, 0.2-0.3% fat, 0.8-1.0% ash substances, 20 mg% vitamin C, B1, B2, B6, PP and K and carotenoids. The highest vitamin content is in young tubers.

Potatoes have different purposes, the main one is food, they are also called second bread. In European cuisine more than 200 potato dishes are known.

Potatoes are also used for fodder purposes. In terms of digestibility of organic matter, which is 83-97%, it is comparable with fodder root crops. Raw or steamed tubers, as well as ensilaged haulm, are used as fodder. Products of potato processing (mash and bard), also a good feed for livestock and pets.

Feed value of 100 kg:

raw tubers – 29.5 fodder units;
green tops silage – 8.5 fodder units;
fresh barda – 4 fodder units;
dried barda – 52 fodder units;
fresh pulp – 13.2 fodder units;
dried pulp – 95.5 fodder units.

With a tuber yield of 15 t/ha and haulm of 8 t/ha the total fodder value of potatoes is about 5500 fodder units.

However, the peel and the greened tubers contain a poisonous substance, solanine, which content usually varies from 0.005 to 0.01% and is partly decomposed during thermal treatment. The tubers that have turned green and have sprouted in daylight or artificial light are not suitable for food or fodder purposes without careful heat treatment. Potato tops and berries have a solanine content of up to 0.25%.

Potato tubers are a raw material for the production of alcohol, starch, dextrins, glucose and rubber. Starch is one of the main products of potato processing used in the food, textile and paper industries.

From 1 tonne of tubers with a starch content of 17.6% yield 112 litres of ethyl alcohol, 0.39 litres of soursop oils and 1,500 litres of bard, or 170 kg of starch and 1 tonne of pulp, or 80 kg of glucose and 65 kg of hydrol. The yield of alcohol from 1 hectare of potatoes is 3-5 times higher than from the same area of cereal crops.

Potato in agriculture has agrotechnical and agroeconomic importance: after it the fields remain in a loose and clean condition from weeds, so it serves as a good precursor in the rotation for all crops, including spring wheat, corn, legumes, beets. In many regions, potatoes can be cultivated as a fallow-occupied crop and be a predecessor of winter cereals.

Quality factors

Potatoes are a useful crop because they are grown in many areas and produce large quantities and high quality food per unit area in a relatively short time. Other characteristics include storability, ease of preparation, palatability with a high satiety value, and broad acceptability.

Important tuber quality factors include appearance, size, shape, rind texture and pigmentation, flesh color, depth and number of eyes, defects and, very importantly, dry matter.

The relationship of specific gravity and total dry matter to potato texture and utilization.

Specific gravity	Dry matter content, %	Texture	Optimum intended use
<1.06	<16	Very juicy	Pan frying, salads, canning
1,06-1,07	16-18	Juicy	Pan frying, salads, boiling and preserving
1.07-1.08	18-20	Waxy	Cooking, pureeing, making chips or preserving
1.08-1.09	20-22	Mealy, dry	Good for baking, potato chips, and french fries; some varieties tend to split when cooked
>1.09	>22	Very floury or dry	Good for baking, chips and fries; more prone to brittleness and delamination when cooked

The texture of cooked potatoes is greatly influenced by the dry matter content as well as the tuber cell size and the ratio of amylose to amylopectin starch. These characteristics affect culinary and technological use. In general, tubers with high dry matter content, high amylose to amylopectin ratio, small cell size and low sugar content are preferred for most types of processing and for cooking by baking or frying. Such potatoes tend to delaminate when cooked and have a floury texture. Potatoes with low dry matter content are best used when boiled because they usually remain whole. The starch composition of many low dry matter potatoes tends to have a low amylose to amylopectin ratio. Such potatoes have a moist texture when baked.

In addition to water (about 78%), the other components are carbohydrates and protein, usually about 18% and 2% respectively. Potatoes also contain significant amounts of minerals and vitamin C. Yellow-fleshed varieties contain some carotene. When comparing the nutritional value of foods, it is important to note that the high water content of potatoes should be considered when comparing them to cereals or other foods with a high dry weight content. Because of their relatively high intake, potatoes provide a significant amount of protein and calories despite their low absolute content.

Toxic compounds

Potato plants and tubers contain toxic glycoalkaloids, alpha-solanine and alpha-chaconine, which act as cholinesterase inhibitors. When the tubers are exposed to light, chlorophyll is synthesized along with the glycoalkaloids. The amount of glycoalkaloids formed depends on the duration of exposure, the intensity and quality of the light (mainly ultraviolet light), and the temperature; little is synthesized at temperatures below 5°C. These compounds taste bitter and ingestion can cause illness and, in extreme cases, death; toxicity depends on the amount of food ingested. Mechanical trauma also causes the formation of these substances.

Generally, the greatest amounts of glycoalkaloids are found in tissues with high metabolic activity, such as sprouts and flowers. The content in foliage and stems is higher than in tubers. The rind of the tuber (periderm) has the highest concentration of glycoalkaloids; the rind removes most of the glycoalkaloids, but not all. Mature tubers contain 2-6 mg/100 g fresh weight. Their content is high in the early stages of tuber development; the highest values (14-28 mg/100 g) are found in small immature tubers. Heat does not destroy these substances, although some of them may be leached by boiling. The content of glycoalkaloids varies from variety to variety. The introduction of some new varieties, promising in many useful characteristics, has been prevented because of their high glycoalkaloid content. An acceptable concentration is less than 20 mg/100 g; at this level, the bitter taste is very noticeable.

Origin and domestication

The supposed place of origin of the potato is South America, the Andes (Chile, Peru, Bolivia). In 1925-1932, Soviet scientists S.M. Bukasov, S.V. Yuzepchuk and others made an expedition to various parts of America, where they collected a large number of wild species, confirming that this is where potatoes were cultivated at least 1-2 thousand years BC.

In the middle part of Chile and on the island of Chiloé, local wild tetraploid species (2n = 48) were introduced into cultivation, which gave rise to the species Solanum tuberosum. It was this species that became the basis of the varietal diversity of potatoes in Europe (more than 2000 varieties, 600 of which are in use). At present, other species are also involved in breeding work – over 160 in total.

Potatoes, both wild and cultivated, survive well locally because the tubers have a high moisture content as well as stores of starch and other nutrients that allow for regeneration. Unharvested tubers may remain dormant in the soil and germinate when growth conditions become favorable; thus, continued survival is assured. In the early stages of development and in primitive conditions, the ability to store and preserve harvested tubers increased their usefulness as a food crop. For example, chuno, a dehydrated stored potato product, was made by trampling and naturally drying the tubers through repeated freezing and thawing in some high mountain areas of the Andes.

The name “potato” is thought to be derived from the Incan “papa”; a similar-sounding name for yams is also thought to be the sweet potato of the Caribbean Indians. The association with Ireland is thought to be responsible for the name “Irish potato,” which has survived despite the fact that potatoes are grown in many countries. White potatoes are the most common name. Although some varieties have white flesh and white rind (periderm), this name does not account for the internal and external color variations that occur. Nevertheless, although neither “white” nor “Irish” is accurate, this association persists.

History of the crop

Ancient times

The Incas had been using potatoes for at least 2,000 years before Spanish explorers arrived. Radiocarbon dating of starch grains found in archaeological excavations has shown that potatoes were used at least 8,000 years ago.

In Europe and the world

The potato was introduced to Europe around 1570 from South America, first to Spain and later to all European countries, resulting in unimaginable growth and diffusion of a new food crop with profound economic and historic results. From Spain, the potato was introduced to neighboring European countries, and in less than 100 years it was grown quite widely in many regions of Europe. Soon the potato spread beyond Europe: around 1610 it was introduced to India, in 1700 to China, and around 1766 to Japan. Scottish-Irish immigrants introduced the potato to North America in the early 1700s.

However, before the potato’s widespread adoption in Europe, there was considerable skepticism about its edibility. When the potato first appeared in Europe, it was considered poisonous because of its outward resemblance to the nightshade (Solanum species). The tubers were considered unfit to eat or suitable only for the very poor and as animal feed. Adoption was also poor because of low productivity. Andean introductions (Solanum tuberosum subsp. andigena) from low-latitude regions performed poorly because they were not adapted to European temperate latitudes, although productivity was higher in southern European regions. Herbar specimens and drawings show that Andean rather than Chilean (S. tuberosum subsp. tuberosum) was the first to be introduced, and that Chilean sources did not appear until the 19th century.

During its early introduction, rural populations and tenant farmers in some European countries were encouraged and sometimes even forced by landowners to produce potatoes. At the beginning of the industrial era, the crop became a staple food for the peasant population. Its value as a human food was soon recognized, as well as its ability to produce more calories at a lower cost than cereal crops. Therefore, potatoes began to be cultivated more and more frequently to meet the food needs of the growing European population.

Increased reliance on this food source led to an expansion of production areas, which contributed to the severity of the potato crop failure and the resulting Irish famine of 1845 and 1846. The perennial extensive cultivation of the potato, especially in Ireland, with limited crop rotation and increased acreage devoted to potato production, made it highly susceptible to disease. The late blight fungus Phytophthora infestans took root and, under favorable conditions, the fungus population grew to epidemic proportions, in part because the most susceptible potato varieties grown at the time were of Andean origin. During this period about a million people died of starvation in Ireland. Because of the famine there was a mass migration of people, as well as considerable economic disruption in Ireland and other European countries. A consequence of the crop failure was the emergence in the 19th century of more adapted Chilean potato varieties to replace the original Andean varieties. This formed the genetic base that is now called S. tuberosum subsp. tuberosum.

In Russia

The appearance of potatoes in Russia is associated with Peter I, who sent a sack of tubers from Holland. However, in the literature on the history of the appearance of the potato in Russia there is also information about its penetration to Russia from the East – through Kamchatka and Alaska, where this crop, according to the academician P.S. Pallas (1785) and G.I. Shelekhov (1842), was a “common staple” for the local population.

The widespread dissemination of potatoes in Russia was established by a decree of the Senate in 1765. The Senate 22 more times considered the introduction of the potato. In 1765 was published “Instruction” on its breeding, which was an encyclopedia on potato growing, consisting of 16 sections. In December 1765 a supplementary “Instruction” on transportation and storage of seed potatoes was issued.

Since the mid-19th century, the area of potato cultivation in Russia significantly expanded due to frequent cereal crop failures. In 1881 the area cultivated with potatoes reached 1529 thousand hectares.

In the second half of the 19th century Russia had its own relatively good potato varieties produced by amateur breeders, first of all by the amateur breeder Efim Andreyevich Grachev (1826-1877), who bred them in the St. Petersburg Province and repeatedly demonstrated them at exhibitions in Russia and abroad.

In 1903, the potato selection was continued by D.L. Rudzinsky, professor of the Moscow Agricultural Institute (which later became the Moscow Agricultural Academy), who conducted individual selection from foreign varieties. However, the scale of seed production did not correspond at all to the importance that potato had acquired in Russia by that time.

Only after the October Revolution, potato breeding received a significant development. In 1919, S.M. Bukasov started to study potato varieties in the Bureau of Applied Botany of the Agricultural Scientific Committee, which was later transformed into the All-Union Research Institute of Plant Industry named after N.I. Vavilov (VIR).

A.G. Lorkh and T.V. Aseeva collected some foreign and local varieties at the Korenevskaya potato station, which was founded in 1920 in the Ukhtomsky district of the Moscow region and later became the Research Institute of Potato Agriculture (NIIKKh).

The first early Soviet potato varieties – Komsomolets and Kalitinets – were bred in the 1920s by I.A. Veselovsky, in 1922 by A.G. Lorkh and P.S. Gusev – two medium-late varieties – Lorkh and Korenevsky.

In the following years, much breeding work was carried out under the direction of P.I. Alsmik in the Belarusian Research Institute of Potato and Fruit and Vegetable Growing (BelNIIKPO). The work was conducted in the direction of creation of cancer- and phytophthora-resistant varieties with increased content of starch and protein in tubers. Also, breeding work was carried out in the Research Institute of Plant Breeding, Ukrainian Potato Research Institute (UkrNIIKh), North-West Research Institute of Agricultural Industry, and the Baltic countries.

Area of cultivation

In terms of production, the potato ranks fourth among the world’s major food crops after wheat, corn and rice. Protein and carbohydrate production from potatoes per unit area of land per day exceeds that of any other cereal crop. Moreover, the potato’s high nutritional value has boosted its production in many areas, even where it is less productive.

Because of its good adaptability to growing conditions, the potato is grown all over the world. It is grown as far north as 71°N and as far south as 46°S. It is also cultivated in mountainous areas. It is cultivated on all continents in many countries. The total area planted in the world in 1981 was 17.9 million hectares, with a gross harvest of 257 million tons (FLO). Its average yield was 16 tonnes per hectare.

More than 35 percent of the world’s cultivated area is potatoes in Europe, and 28 percent in Asia. In 1981, the leading potato producers in Europe were Poland (2.26 million ha), the GDR (0.5 million ha), Germany (0.28 million ha), France (0.2 million ha) and the Czech Republic (0.2 million ha). In the USA the area under potato planting was 0.5 million hectares.

China, Poland, and the USA produce more than 15%, 8%, and 7%, respectively. More extensive use of production technologies, crops, disease and pest control is responsible for much higher yields in Western European countries and the USA compared to the former Soviet Union republics and China.

In the USSR, potatoes were cultivated from the Polar region to the southern borders of Central Asia and Transcaucasia, the total area in 1981 amounted to The total area was 6.8 million hectares. The largest areas were concentrated in Russia, Ukraine, Belarus and the Baltic States.

If we look at potato production statistics in the former Soviet Union as a whole, it was remarkable in that for many years it produced more than 25% of world production. Even now, three former republics – the Russian Federation, Ukraine and Belarus – are among the top 10 potato producing countries, together accounting for more than 22 per cent of world output.

Russia’s main potato plantings are concentrated in the Non-Black Soil Zone, with gross output of over 30 million tonnes per year in this zone. There are also large areas in the Central Black Earth zone, the Volga region, Siberia, the Urals and the Far East. In the south, especially in the southwestern regions of the steppe zone, potatoes are less common, because potatoes do not tolerate the summer heat.

In 2001-2005 the Russian potato area was 3.2-3.4 mln ha, gross output – 35.1 mln tons, 92% of which is produced by household farms. The average yield was 11.1-11.7 t/ha.

Total global production has been on a downward trend for several decades, with the decline more pronounced in industrialized countries. The overall decline has been most noticeable in the decline in the consumption of table potatoes, while the use as processed products has increased. According to FAO statistics, the global use of current production is 45% for human food, 30% for animals, 15% for seed, 2% for starch, and about 8% as waste.

Temperate countries are now the largest producers and consumers of potatoes, while tropical and subtropical countries, which include many less economically developed countries, produce and consume less. Obstacles to production in these regions include high day and night temperatures, high susceptibility to diseases and pests, and poor soils. In addition, difficulties in obtaining clean adapted seed stocks, adequate storage and other problems associated with introducing a new crop are obstacles that must be addressed before production can expand. Breeders continue to research for greater adaptation in other regions, such as the lowland tropics.
For many years, the International Potato Research Center (CIP) in Peru has developed and implemented valuable research findings. The efforts of CIP and other institutions will ensure that the importance of the potato as a staple food remains.

Yield

The average yield of potatoes during Soviet times was 11.7-12.0 t/ha, and the gross yield was 70-72 million tonnes. With proper agrotechnics, varietal renovation, yields in most potato growing areas can be stable in the range of 20-25 t/ha. For example, in the Dmitrov district of the Moscow Region, the potato yield in 1983 was 19.5 t/ha from an area of 5026 ha, in the Ramensky district – 19.3 t/ha from an area of 4290 ha. The maximum yields in 1983 were:

in Dmitrovsky district of Moscow region (state farm Rogachevsky) – 24.6 t/ha from an area of 850 ha;
in Ramensky district of Moscow region (collective farm Borets) – 34.1 t/ha on an area of 350 hectares;
in Gatchina district of Leningrad region (collective farm Plamya) – 21.5 tons/ha on the area of 610 ha;
in Novozybkovsky district of Bashkiria region – 17,4 t/ha on the area of 8522 ha;
in Pogarsky district of Bryansk region – 19.1 t/ha on an area of 6430 ha;
in Kasimovsky district of Ryazan oblast (collective farm “Zavety Ilyicha”) – 22.0 t/ha on the area of 785 ha;
in North Ossetia by industrial technology – 32.0 t/ha from an area of 1500 hectares received 32 t/ha of tubers;
in Tomsk region (B.N. Sidorenko farm) – 23.5 t/ha from an area of 350 ha.

In Belarus, the average yield was about 15 t/ha.

Potato yields in European countries average 35 t/ha, in Great Britain, Germany, Switzerland, Belgium, and the Netherlands – up to 40-50 t/ha.

Taxonomy

The nightshade (Solanum) is a large and diverse genus with over 1,500 species, about 90 of which are tuberous and only a few are cultivated. The range of wild tuberous Solanum species extends from the southwestern United States to the highlands of Mexico, Central America and the Andes, with extensions into Chile and Argentina. The tubers of wild species are usually small and bitter tasting because of the alkaloids they contain.

The greatest genetic diversity of potatoes is found in the Andean regions of Peru and Bolivia. Wild tuberous and primitive cultivated species provide a large diverse gene pool for expanding adaptations to disease resistance and other inherited characteristics to improve cultivated species, especially S. tuberosum.

The wild diploid S. leptophyes found in north central Bolivia may have been the primary ancestor of cultivated species. The diploid S. stenotomum is probably a cultivar of S. leptophyes, which through natural introgression (hybridization) with other species and possibly some human involvement in cultivation, has resulted in other cultivars, one of which is S. tuberosum, which does not occur in the wild state.

S. tuberosum subsp. tuberosum, the world trade potato, is a tetrapioid (2n = 2X = 48). In addition to S. tuberosum subsp. andigena, other recognized cultivated species are S. anjanhuiri (2X), S. chaucha (3X), S. curtilobum (5X), S. juzepczukii (3X), S. phureja (2X), S. stenotomum (2X) and S. goniocalyx (2X). In the genus Solanum, about 70% of the wild forms are diploid (2n = 24), which are mostly self-incompatible, and about 15% are tetrapioid, most of which are self-fertile.

S. tuberosum originated in the southern Peruvian and Bolivian highlands. Under cultivation conditions by prehistoric Indians, it is thought to have evolved as a tropical highland subspecies, classified as S. tuberosum subsp. andigena, and a temperate lowland subspecies, identified as S. tuberosum subsp. tuberosum. The latter, which has a long-day tuberous response, is better adapted to the temperate climate of Europe. However, S. tuberosum subsp. andigena is known to be able to adapt to the long day due to breeding.

Botanical description

Potato is a perennial dicotyledonous herbaceous tuberous plant of the Solanaceae family, genus Solanum, which includes several dozen wild and cultivated species. In culture it is used as an annual, since the entire life cycle begins with the germination of a tuber and ends with the formation of mature tubers, which occurs in a single growing season.

Potatoes are usually propagated vegetatively by tubers, parts of tubers, sprouts and cuttings. In breeding practice, seed multiplication is used.

The most used species Solanum tuberosum L., other species that are distinguished by valuable biological and economically useful features are used in breeding for the development of new varieties.

Such species include:

S. andigenuin Iuz. et Buk. – is a cultivated tetraploid species native to Argentina (2n = 48 = 4x). It is considered related to the species S. tuberosum;
S. leptostigma Iuz. – is a tetraploid cultivated species, originating from Chiloé Island. Characterized by increased starch content and resistance to cancer;
S. phureja Iuz. et Buk. S. rubinii is a cultivated diploid species (2l = 24 = 2x), distributed in South America. Characterized by increased protein content and resistance to scab;
S. demissum Lindl. – wild self-fertile hexaploid species (2n = 72), originating in Mexico;
S. stoloniferum is a self-fertile wild allotetraploid species native to the high Andes. It grows in Peru, Bolivia, and Argentina. It is noted for its frost tolerance.

Root system

The root system when grown from a tuber is fibrous, consisting of root systems of individual stems. It includes:

sprouting (eye), or primary, roots, which are formed at the beginning of tuber sprouting;
roots at the stolons, which are formed throughout the growing season and are arranged in groups of 4-5 near each stolon;
stolon roots, located on the stolons.

Plants obtained asexually from tubers develop thinly branched, relatively small and filamentous spreading adventitious roots, while plants grown from true seeds form a thin root with many lateral outgrowths.

Root system penetrates into the soil shallowly. Approximately 50% of roots are located in arable layer, 22-38% penetrate deeper, some roots reach up to 150 cm deep.

The depth of root penetration into the soil varies among varieties. Usually in late-ripening varieties it penetrates to a greater depth. According to V.R. Rotmistrov, horizontally, the roots extend 50 cm into the soil. According to Böhme, 37% of all roots spread sideways by 30 cm and 1% by 90-120 cm.

The root system is poorly adapted to overcoming the mechanical resistance of the soil.

Root system capacity depends on moisture, aeration, and nutrient content of the soil.

Root system is characterized by active absorption capacity, primarily of phosphorus.

The most intensive growth of the root system occurs during budding – the beginning of flowering. High root activity during intensive tuberization is associated with the ability to absorb nutrients even at the end of the growing season.

Tuber

The tuber is morphologically a shortened, thickened, fleshy stem. At an early age, it has small scaly leaves without chlorophyll. In the axils of these leaflets, dormant buds are laid, forming so-called ocelli. Later, the scale-like leaves atrophy, leaving a leaf trace or eyebrow.

Varieties vary in the number of buds. Generally, there are three buds in a single ocellus. During germination, one of them, the most developed middle one (apical), starts growing; the others remain in reserve and germinate if sprouts are damaged or broken. Apical buds germinate first, as they suppress germination of other buds. This apical dominance decreases as the tuber is removed or separated from the apical part; low temperatures and aging of the tuber also reduce apical dominance.

The tuber bud consists of a growth cone with future leaf buds, axillary buds, and stubs.

The eyes on the tuber are arranged spirally. At the top of the tuber, the buds are more closely spaced because the tuber is growing with its top. These buds are more viable and germinate earlier than the lower buds.

Sprouts sprouting in the light may be green, red-violet, or blue-violet, depending on the variety.

The main tissues of the tuber are the periderm, bark, phloem and xylem vascular cylinder, and parts of the inner and outer medulla or core tissue.

The rind of mature tubers is a thin cork tissue that protects them from drying out and disease. Under the cork layer are parenchyma cortex cells filled with starch grains, followed by a layer of educational tissue (cambium) and a ring of vascular-fiber bundles connecting to the ocelli. The cambium produces few secondary tissues. The inner part of the tuber, the core, has less starch content than the cortex.

The tuber surface may be smooth or rough due to reticulation or cracking, and the color of the periderm varies from brown to light brown, red, or dark purple.

Tuber respiration and moisture evaporation occurs via intercellular, that is, loosely arranged cells through lenticels, elevations on the tuber’s rind. Their number and size are determined by growing conditions.

The shape of tubers is varied and is a varietal trait. It is usually determined by ratios of length to width and width to thickness. Depending on these ratios, tubers are round, round-oval, oblong-oval, long, flat, and oval.

The color of tubers is white with the appearance of yellowing; red with shades of light pink to intense red and blue-purple. Tuber flesh is usually white, yellowish to varying degrees, in some varieties red, blue-purple, dark yellow, orange.

The outer color of the tuber is determined by the amount of bark cork and pigment contained in the juice of the bark cells. With a thin cork layer, the coloring of the pulp is translucent. As the cork layer thickens, the coloring changes from creamy to brown.

The starch content of the tubers may vary from 12 to 25% (sometimes up to 29%). In the tubers of table varieties of potato, the starch content is 12-16% starch, and in factory (technical) varieties it is 18-29%. Late varieties have a higher starch content. Potatoes with a starch content of at least 18% are used for processing.

Stem

The stem is erect, less often deflected to the side, smooth at first, then becoming angular and branched with further growth. The coloring is green, with some varieties having a reddish-brown tint due to the presence of anthocyanin. The intensity of pigmentation is determined by varietal characteristics, cultivation conditions, light exposure, water availability, and other factors.

Plant growth varies from compact to spreading. According to the nature of stem branching, potato varieties are divided into:

late maturing varieties, in which branching occurs mainly in the lower tier;
early maturing varieties which do not branch from below.

Stems are ribbed, three- or four-sided, less often rounded, pubescent to varying degrees. At the junction of the edges, green tissue outgrowths called wings are formed. They are a variety distinguishing trait.

Stem height varies from 30 to 150 cm and depends on cultivation and variety. Late maturing varieties usually have a taller stem and a greater number of internodes.

A shrub usually consists of 2 to 8 foliated stems. Their number is determined by the variety, the size of the planting tubers, and the number of sprouted buds. Plants grown from large tubers usually have more stems. The number of stems in a bush affects the tuber yield to a certain extent. The number of sprouting buds can be increased by various methods, such as cross-cutting the tubers or using growth aids on the planting tubers.

In the underground part of the stem, axillary buds form shoots called stolons. On their ends, tubers, or thickenings, are formed. One stem may produce 6-8 stolons, which may additionally branch. The thickness of stolons is less than that of stalks. Stolons vary in length: early cultivars have shorter stolons and later cultivars have longer stolons.

Leaves

The leaves, which appear when tubers or seeds germinate, are simple, entire-edged. As the plant develops, they form intermittent, unpaired, pinnately dissected leaves. Each such leaf consists of several pairs of lateral lobes, which are placed one opposite the other, intermediate lobes between them, and an terminal lobe. The lateral lobes and lobules are planted on pedicels attached to a stem that transitions into a petiole. The lobes, depending on their position, are divided into series: terminal, first, second, third, and fourth. The first series includes all lobules planted on the stem between the lobes of the first and second pairs, etc.

The lobules of the first and second series are significant for varietal distinction. The final (unpaired) leaf lobe at the end of the stem is different in shape from the lateral lobes and is often larger. The counting of the lobes begins from there. In some varieties, the separation of terminal and lateral lobes is incomplete; this phenomenon is called ivy-leafiness.

The structure and dissection of the leaves is one of the varietal traits. According to the number and location of lobes in the series, there are strong and weak cleavage. Average cleavage is an uncharacteristic varietal trait.

A leaf with a wide gap between lobes and lobules is called sparsely lobed; a leaf with narrow gaps is called dense or thickly lobed.

The underside of the leaf has a network of veins, their coloration often being related to that of the tubers. The veining decreases with higher doses of potassium or increases with higher doses of nitrogen. Leaves are arranged in a spiral pattern on the stem.

Flowers

The flowers of the potato are gathered in inflorescences, which are divergent whorls located on a common flower stalk of different lengths. The peduncle is articulated. Flowers are of the five-lobed (five-lobed, fused corolla) type. Flower calyx is spainopatilliform, with sepals fused at the base. The corolla is wheel-shaped, with five fused petals.

The corolla can be white, blue, dark blue-violet, red-violet with various shades. The flower contains five stamens, which consist of anthers planted on short filaments that fuse with each other and with the base of the petals. The anthers are orange, yellow, greenish-yellow or greenish-yellow. The pistil consists of an ovary, a stigma and an ovary. The stigma is cephalic, club-shaped or split-lobed. Styrofoam is straight or curved. The ovary is an upper one, consisting of two peduncles with numerous testicles.

Potatoes are self-pollinating; most varieties are sterile, some are fertile. According to others, without nectar, potatoes are mostly cross-pollinated, usually by the wind, but insect pollination is common (Rubatzky). In some varieties, flower drop often occurs, so fruiting is rare.

Fruit

The fruit is a two-seeded, multiseed, juicy green or purple berry of globular or oval shape. When ripe, the berries turn white with a pleasant smell similar to that of strawberries; they are not edible because of the solanine (glycoalkaloids) they contain.

The number of seeds in the fruit varies from a few to several hundred, enclosed in the pulp.

Seeds are oval or kidney-shaped, light yellow or yellowish-brown, small, flat, and have a bent germ. The weight of 1,000 seeds is about 0.5 g.

Ecological requirements

Outside of its origin, the potato plant has adapted well and can grow in most temperate regions up to 60° latitude. The lack of high-temperature adaptation limits production in the tropics. The interaction of photoperiod and temperature is the most important factor affecting plant and tuber development. Photoperiod has a direct effect on tuber formation. This effect can be modified by temperature, although the response of cultivars to day length and/or temperature can also vary.

Temperature requirements

Potatoes react negatively to soil temperatures less than 7-8°C and more than 25°C.

The leaves turn black and die at high relative humidity and temperatures -1.5 … -2.0 ° C with an average frost duration of 5-6 hours. Young plants are especially susceptible to low temperatures. However, a slow decrease in temperature leads to accumulation of sugars in plants, thus their resistance to temperatures of -2 … -4 °C increases.

Young plants damaged by frosts are quite easy to recover. With a sufficient supply of nutrients and moisture, they quickly build up vegetative mass. On plantings of potatoes that have been affected by frosts, it is recommended to give nitrogen fertilizers.

Potato tubers, as a rule, are damaged at -1 … -2°C because of their high water content (up to 75%). But in some years, as a result of gradual cooling of tubers in autumn and the accumulation of sugars (sometimes up to 8%), they may even overwinter in the soil. Overwintered tubers wake up early, begin to grow, and may become a temporary habitat for insect pests, later becoming clogged crops of the subsequent crop.

When tubers are exposed to low temperatures down to -1°C during storage, they become sweet because of the formation of sugars, but during keeping such tubers at room temperature for 5-10 days, the sugars transform into starch again, and their taste becomes normal.

Germination of tubers after the dormant period and planting in the soil, begins at a temperature of 3-5 ° C, but the process is very slow without the formation of the root system, and the morbidity of tubers increases sharply. At temperatures less than 3°C and more than 31°C, the growth and development of buds on tubers are delayed. Temperatures below -1 … -1,5 °C and above 35 °C for several days result in damage to the buds.

Root formation begins at soil temperatures above 7 °C. At lower temperatures, planted tubers lie in the soil for a long time, and new tubers may form on them at the expense of nutrient reserves, without the appearance of above-ground organs. This phenomenon may occur when planting potatoes in cold, overwatered soil, or in too dry soil at temperatures above 25°C.

Normal tuber germination occurs at soil temperatures of 6-8 °C. The optimum temperature for germination is 18-20 ° C (according to other reports 13-15 °C^[1]V.V. Kolomeychenko. Plant breeding/textbook. – Moscow: Agrobiznescentr, 2007. – 600 с. ISBN 978-5-902792-11-6. Page. 406), under these conditions shoots appear in 10-12 days after planting, at 13-15 °C – in 18-20 days, while at soil temperatures less than 7 °C they appear only in 30-35 days, sometimes in 50 days.

For the midlands, the optimal soil temperature for tuber formation is 16-19 °C, which corresponds to an air temperature of 21-25 °C. A cold snap leads to delayed tuber growth, and at 2 °C, growth stops.

Increased soil temperature leads to greater formation and branching of stolons, this enhancement of growth processes is to the detriment of accumulation of tuber yields.

Lingering heat above 30 °C causes leaf assimilation activity to cease, which halts tuber growth and coarsens the skin. During these periods, respiration intensifies, resulting in increased consumption of carbohydrates, which inhibits tuber formation.

The sum of active temperatures above 10 °C during the growing season, necessary for the complete development of potato plants, is 1000-1400 °C for early and mid-early varieties, 1400-1600°C for late ripening ones.

Autumn frosts as low as -3°C cause the tops to die, but tubers are not damaged.

Later potato varieties are better cold-resistant.

Moisture requirements

Potatoes are water-intensive. Water consumption varies by growth phase. The critical period of moisture consumption is the beginning of flowering. During this period, the lack of moisture in the soil leads to a sharp decrease in yield. Even a short-term drought in the phase of budding leads to a decrease in yield by 17-23%. The tuber yield of early potato varieties is determined by atmospheric precipitation in July, mid-maturing varieties by July-August, and late varieties by precipitation in July-August-September (A.G. Lorch, 1948).

Potato roots are highly branched and relatively shallow. About 90% are within 50 cm of the surface, which tends to increase susceptibility to soil moisture stress. High moisture requirements occur after tubers are set and during tuber enlargement.

Uniformity of moisture supply is very important, especially for tuber shape. Bumpiness, which is usually caused by lack of moisture, may be particularly severe in some cultivars.

The potato transpiration coefficient is 400-550, sometimes ranging from 167 to 659, indicating that potato plants are very plastic and well adapted to their growing conditions.

On hot days, the bush can evaporate up to 4 litres of water, in southern regions even more. Therefore, for all regions with insufficient moisture the decisive importance is given to agronomic techniques of accumulation and preservation of soil moisture. A high level of agrotechnics and a sufficient supply of nutrients the water consumption of potatoes decreases.

Optimal soil moisture for growth and the formation of high yields is 70-80% of the lowest moisture content in the layer of the spreading of the main mass of the roots in the phase of flowering and tuber formation. During starch accumulation it is 60-65% of the lowest moisture capacity.

In the conditions of the average strip reduction of soil moisture to 60% of the lowest moisture capacity leads to a decrease in yield by 3-9%, up to 40% – 40-43%. With 40% moisture content, flowering is delayed by 4-6 days, with 20-30% – by 9-10 days. Accordingly, tuber formation and haulm death is delayed.

The moisture supply during the first period of growth is very important for the mother tuber. During the hottest hours of the day, the lack of soil moisture is compensated by these reserves. The same role in the further development of the plant is played by new tubers formed. Thus, the potato tubers serve as a storehouse of moisture, which is filled when there is enough water, or from which the plant takes moisture when there is a lack of water.

Potatoes have a well-developed ability to absorb air moisture through their leaves. These characteristics make it relatively easy for the plant to withstand short-term droughts.

The moisture requirements of crops vary greatly from 250 to more than 500 mm of water. To obtain high yields of potatoes in the conditions of the average strip during the vegetation period should fall not less than 300 mm of atmospheric precipitation. With increasing evaporation of moisture from the soil surface and with the advance of crops to the south, the need for water increases, so the lack of moisture in these conditions is compensated by irrigation. With uneven precipitation in the Non-Black Soil Zone, potato also responds well to irrigation.

Excessive moistening is also undesirable, as it leads to deterioration of the soil air regime, increased water content of tubers, reduced starchiness, storage is worse, the number of lentils of tubers increases, and excessive rains or prolonged wetting of leaves and high humidity contribute to the development of foliar diseases.

Requirements for soil air regime

The potato root system consumes large amounts of oxygen from the soil air during respiration. The root requirement is approximately 1 mg of oxygen per 1 g of dry matter per day. The highest requirement is during the tuber formation period.

This is the reason why the soil should be kept friable with a volume weight not higher than 1-1.2 g/cm³. Loose soil is more intensive gas exchange between soil and atmospheric air. In very moist, compacted or poorly tilled soils, oxygen content may be reduced to 2%, and carbon dioxide content increases greatly. In these conditions, the tubers begin to suffocate and rot. The optimum concentration of carbon dioxide in the soil air should be no more than 1%.

Light requirements

The potato is a plant of short (according to other data long^[2]V.V. Kolomeychenko. Crop production/textbook. – Moscow: Agrobiznescenter, 2007. – 600 с. ISBN 978-5-902792-11-6. Page. 406) of daylight hours. A short day is not a prerequisite, but in the Russian midlands it speeds up development. Potato varieties may differ in their response to the duration of daylight hours. The photoperiodic response also varies under conditions of low temperatures in the north.

In the Russian midlands, a short day leads to an acceleration of the onset of tuber formation and a reduction in the duration of the growing season, including the duration of tuber formation and growth.

In the early stages of tuber formation, the weight of tubers in a short day is greater than in a long day. However, a long day favors the formation of haulms, the power of which determines the productivity of photosynthesis and the formation of substances necessary for tuber growth. This is why long day yields tend to be higher, but it does not mean that potatoes can be classified as long day plants.

Early and late potato varieties have longer and more intensive haulm growth in long-day conditions, but their tuber formation efficiency, that is the ratio of tuber weight to haulm weight, is significantly higher in short-day conditions. This is evidenced by the fact that the most intensive tuber formation for most varieties occurs in the second half of summer, when the length of daylight is reduced.

Potatoes are a light-loving plant. Even a slight decrease in light leads to the yellowing of foliage, elongation of stems, weakening or complete absence of flowering, reduced yield.

Yield and quality of tubers is influenced by the direction of rows. Illumination of rows in the north-south, northwest and southeast directions is more uniform, in contrast to the west-east. Thus, at the direction of rows from north to south, the potato yield was higher by 1.6-2.0 t/ha, the starch content – by 1-2% (Moscow Agricultural Academy).

Tubers after digging when staying in the light for a few days turn green due to the formation of chlorophyll. Under direct or diffused sunlight, tubers’ solanine content increases to 30-40 mg per 100 g, while the normal content is 2-10 mg per 100 g of tubers. Solanine is then converted to solanine glycoside, which has an antiseptic effect. Therefore, the greening of seed potatoes contributes to the protection of tubers from diseases and rodents during the autumn and winter storage period.

Greening potatoes intended for food purposes or for fodder is not allowed, as it acquires a bitter-tart taste and becomes poisonous.

Soil requirements

Potatoes prefer loose soils. The intensity of root respiration is 7-12 ml of oxygen per hour per 1 g of root dry matter, which is 5 times higher than the respiration intensity of the roots of sunflower and other crops. This is the reason why potatoes are very demanding in terms of soil porosity. The roots growing in loose soil with a density of 1.10 g/cm³ branch better, penetrate to the depth of the entire arable layer, going into the subsoil. The optimum soil density for growing potatoes is 0.9-1.2 g/cm³. On looser soils the loss of moisture becomes too great. Soil structure and compaction have a strong effect on tuber shape as well as on yield and quality.

Well-drained, deep-bodied soils with a medium to coarse-grained structure are preferred

Loose soil is necessary for good stolon development and young tuber formation, in compacted soil they are small and strongly deformed.

Sprouts on compacted to 1.35-1.50 g/cm³ loamy soils appear 5-6 days later than on soils with a density of 1.10-1.20 g/cm³.

Potatoes grow well on fertilized sandy loam and loamy chernozem soils. In the Nonchernozem zone for him suitable cultivated sod-podzolic, gray forest soils, light loamy soils with organic fertilizers. Cultivated peatlands are also suitable, especially for seed crops.

Soils with light granulometric composition are also suitable for potato growing, the tubers are obtained with high taste qualities, provided sufficient fertilization.

Due to the high digestive capacity of the root system, potatoes can also grow on relatively poor soils, but the yields remain low.

Not suitable for potato cultivation are heavy loamy, clayey, strongly compacted soils, swampy, especially with a close occurrence of groundwater. On such soils, the free development of tubers is hampered, and due to excessive moisture, plant disease increases. Also, saline soils are not suitable, as potatoes poorly tolerate salinity.

When organic fertilizers are applied, potatoes are relatively well tolerated slightly acidic soils. The optimal value of soil acidity is 5-6. According to other data, soils with a pH of 5.5-6.5 (Rubatzky) are optimum. Soil pH less than 5.4 helps to control common potato scabies (Streptomyces scabies).

Nutrition of potato

In the dry matter of potato plants 26 chemical elements are found, but the main in the plant nutrition for the majority of soil and climatic zones of Russia are nitrogen, phosphorus and potassium.

In one ton of harvest tubers and the corresponding amount of haulm, which is 0,4 t, and root residues contains 4,5 kg N, 2,2 kg P₂O₅, 10,3 kg K₂O (A.G. Lorch).

According to generalized and averaged data, from 10 tons of tubers and the corresponding amount of potato leaves 50 kg N, 20 kg P₂O₅, 90 kg K₂O, about 40 kg СаО and 20 kg MgO are taken out of soil. Thus, potassium is the main nutrient consumed by this crop, followed by nitrogen and less by phosphorus.

Increased yields are interrelated with increased nutrient requirements, but not directly proportional. At a low level of agrotechnics and low yields, potatoes consume more nutrients per unit yield. That is, nutrients are used more sparingly as conditions for plant growth and development improve, and hence tuber yields (Potato Research Institute).

With the same tuber yield, more intensive haulm development is associated with greater removal of mineral elements from the soil. Total nutrient removal is determined by varietal characteristics, weather conditions, and farming practices.

Potatoes remove significantly more minerals from the soil than cereals, but yield about 2-2.5 times more economically valuable products per unit area.

Potatoes do not consume many nutrients at the beginning of vegetation. The maximum consumption is during the periods of intensive growth of above-ground mass (flowering phase) and tuber formation. Nutrient intake decreases towards the end of the growing season, ceasing completely at the beginning of leaf desiccation.

Sometimes the entire fertilizer rate is applied at planting, although it is more effective to apply it gradually at certain stages of plant growth. Delayed tuber formation, tuber maturation and can be the result of over-fertilization, especially nitrogen fertilization.

By the time of flowering, potatoes consume 55-60% of nitrogen, a little less phosphorus and over 50% of potassium of the total requirement (Experimental station of field and flax farming of Moscow Agricultural Academy).

Nutritional regime more than other factors of plant life influences technological, food and seed quality indicators of tubers. Sufficient and timely supply of potatoes with nutrients, including micronutrients, allows reducing the negative effects of adverse conditions and getting a high yield of good quality.

Pre-planting soil analysis is useful for evaluating fertilizer requirements. Tissue analysis is also useful for determining the nutrient status of the plant. The recommended levels of nitrogen in potato leaf petiole tissues that are sufficient for good growth depend on the growth stage of the plant. Nitrogen levels for dry petiole tissue at the beginning of the growth season should be about 12,000 ppm, phosphorus about 2,000 ppm, and potassium about 11%. During tuber growth, the corresponding levels are 5,000 ppm N, 1,000 ppm P, and 6% K.

Nitrogen

Deficiency of nitrogen in the soil leads to poor development of the above-ground organs of potato plants, reduced foliage, reduced productivity of the leaf apparatus, yield and starchiness of tubers fall.

Excessive nitrogen leads to excessive growth of haulm, delayed tuber formation, prolongation of the growing season, reduced plant resistance to diseases. Optimal nitrogen nutrition contributes to better absorption of potassium and phosphorus.

Nitrogen from soil is consumed by potatoes in the form of nitrates and ammonium ions.

Phosphorus

Sufficient supply of potatoes with phosphorus helps to accelerate the development of plants, starting from the emergence of seedlings, other phases of development, including tuberization, begin faster, the rate of formation of the root system, the yield and starch content of tubers increase, their keeping quality and seed properties improve.

Deficiency of phosphorus in soil leads to disturbance of normal plant development: branching of bush decreases, budding, flowering and tuber formation start later. Brown spots form on tubers, starchiness and palatability decrease.

Deficiency of phosphorus is often manifested in acidic podzolic loamy soils. Interacting with mobile forms of aluminum and iron in the soil, it passes into inaccessible to plants phosphates. Liming of acidic soils, reduces the aluminum and iron content of the soil solution, thereby increasing the availability of phosphorus.

Also keep in mind that phosphorus is well absorbed by the soil, so small doses of phosphorus fertilizer are ineffective.

Potassium

Potassium is involved in photosynthesis, protein and carbohydrate metabolism, affects yield and quality, especially starchiness of tubers, increases resistance to disease. It is of great importance in the water regime of plants: it increases cell turgor and maintains the internal pressure in plant tissues.

Potassium deficiency leads to impaired growth and development of potatoes, affects the morphological structure, poorly developed mechanical tissues and root system. Tubers with potassium deficiency elongate, become small, poorly stored in winter.

The effect of potassium depends on the form of nitrogen fertilizer used. Nitrate nitrogen has little effect on its action, ammonium – strongly. Chlorinated potassium fertilizers reduce starchiness of tubers.

The content of available potassium in the soil for potatoes is not constant and depends on soil moisture. The higher the moisture content, the more potash is available, and therefore the impact of potash fertilisers on yields is stronger in dry years.

An excessive potassium supply reduces the likelihood of macrosporiosis and ring rot diseases.

Vegetation

Potatoes are mainly a temperate climate crop.

The growing season varies from 60 to 180 days: it is 60-90 days for early varieties and 140-180 days for late ripening varieties.

The vegetation phase:

sprouts;
inflorescence formation;
flowering begins 30-35 days after sprouting;
withering of the haulms.

The growth cycle of potatoes is conventionally divided into three periods:

from sprouting to the beginning of flowering, during this period there is an increase in the weight of the haulm, the growth of tubers is small;
flowering – the cessation of tops growth (practically till the beginning of withering), in this period there is an intensive growth of tubers;
cessation of haulm growth – natural withering. Tuber growth during this period continues, but less intensively.

The duration of the periods depends on the varieties and their early maturity. In early-ripening varieties, the first period lasts 27-36 days before flowering, depending on the weather, medium-ripening – 38 days, late-ripening – 46-48 days.

The duration of the second period is for early-ripening varieties – 26-28 days, medium-early – 34-36 days, medium and late-ripening – 43-45 days. The third period has the same pattern.

The second period is considered the most important: during this time 65-75% of the crop is formed, which depends strongly on weather conditions. Average daily tuber growth can be from insignificant to high depending on weather conditions. During the period of maximum tuber formation, the maximum growth can reach 2.5-2.8 t/ha. Gains of 1-1.5 t/ha in some, relatively short periods, are observed almost annually. The tuber weight gain of one bush may reach 30-35 g per day in August-September, the starch content gain is 0.3-0.5%. In the European part of Russia, the highest growths occur from July 25 to September 10.

Tuber formation begins at the end of the phase of budding and at the beginning of flowering, and the number of tubers is also determined in this period. Finally, the number of tubers depends on weather conditions in July and August and the availability of moisture.

When potatoes are grown from seed, a sprout with two cotyledons and a germinal stem root first appears. Then roots are formed from the underground part of the stem and stolons, just as in vegetative propagation.

Some varieties may only form buds; they do not flower and later fall off.

The above-ground part dies off only in early-ripening varieties, in late-ripening ones it is preserved and continues to be vital until the autumn frost.

Physiology of growth stages

Leaf growth increases rapidly after emergence of seedlings and stems, and mass accumulation occurs rapidly and often linearly for 90-100 days, and sometimes longer for late maturing varieties (Fig.). Thereafter, the growth rate decreases and ceases with leaf senescence or when growth ceases due to frost or harvest.

Leaf growth responds more to temperature than to photoperiod, but regardless of day or night temperatures, long days have a much greater effect than short days. This effect is maximized when daytime temperatures are moderate to high (20-30°C) and nighttime temperatures are low (10-17°C).

Long days increase the photosynthetic period, resulting in larger plants and greater tuber yields. Even in the northern countries of Finland, Norway, and Sweden, where days are very long but the growing season is short, yields reach 20-30 t/ha. Conversely, short days limit the length of the photosynthesis period, and therefore the plants are small and less productive. Prolonged periods of high temperature (over 35°C) may cause damage to the plants.

Although potatoes are considered a short-day plant with respect to tuber formation, the interaction with temperature cannot be ignored. Long days delay tuber initiation and limit the number of tubers; warm temperatures (25-30°C) enhance tuber initiation, and temperatures above 30°C usually prevent tuber initiation. However, long days and temperatures below 20°C increase tuber initiation; temperatures around 12°C are optimal.
Cultivars vary in their response to photoperiod/temperature. An example of this is in the middle latitudes, where days are relatively long and summer temperatures are moderate, providing a climate ideal for growing potatoes. Tubers usually set about 45 days after planting. After tuberization, tuber enlargement ideally occurs at an average temperature of 17°C or slightly lower.

High day and night temperatures reduce the net assimilation; the amount of dry matter distributed among the tubers is reduced because of the high respiration rate. Although an average daytime temperature of 20°C to 30°C is most favorable for leaf growth, optimal temperatures for maximizing yield (starch accumulation) range from 16°C to 18°C. High night temperatures are more often the cause of low tuber yields than high daytime temperatures. The main reason for the poor adaptation of potatoes to subtropical and tropical conditions is the predominance of high night temperatures.

In general, temperatures between 20°C and 30°C promote stem and leaf growth but are less favorable for tuber formation and development. Temperatures below 20°C are favorable for tuber initiation and growth. Low nighttime temperatures (10-17°C) may partially compensate for the effect of high daytime temperatures (25-30°C) on tuber initiation and tuber development.

Neither photoperiod nor temperature are completely independent in their influence, and each has a different effect on above-ground and below-ground growth. Differences between varieties often play an important role in the different response to photoperiod and temperature.

Cultivation of potatoes

Main article: Potato cultivation

Propagation

In potato breeder terminology, seed refers to seed tubers, not botanically true seed. Being highly heterozygous, true seeds often produce plants and tubers that do not resemble those of the parent plant, and their use has largely been limited to breeding purposes. Recently, as a result of research in plant breeding, the use of true seeds for propagation has increased. Vegetative propagation using whole tubers or corms remains the primary method; stem cuttings are rarely used.

Although vegetative propagation has the advantage of conforming precisely to type, the main disadvantages are large mass and the possibility of disease transmission. Dependence on vegetative propagation makes it essential to have sufficient disease- and pest-free material.

For most of the world’s production, growers use tubers from the previous crop. Chronic cases of disease in propagative material result in the need to produce disease free stocks. For this purpose, seed tubers are usually produced in cool regions that are unfavorable for disease emergence, where virus vector insects are few or absent. Also, under such conditions, the symptoms of some leafborne virus diseases usually appear more quickly, and since the seed tubers fields are inspected, diseased plants can be removed (thinned out). Other diseases, such as bacterial wilt and early blotch, show up better in hot conditions. In addition to field tests, there are laboratory tests to detect viruses and other diseases. Tissue culture procedures using heat therapy and/or meristem micropropagation are used to produce initially disease-free plant stocks. Subsequent regenerations are usually used to produce seed tubers. In some countries, governments or other organizations certify seed tubers to be disease free.

The conditions of seed tubers during their production, processing and storage can have an important effect on subsequent performance. Planting, harvesting and storage temperatures affect the “physiological age” of a seed tuber. Late planted and/or early potatoes grown for a shorter time are physiologically young; a late harvest increases the age of the tubers. Physiologically old seed tubers usually produce plants with more stems and more small tubers. Conversely, physiologically young seed tubers produce plants with fewer stems and fewer but larger tubers.

High temperatures during plant growth can increase the physiological age of tubers. Such tubers, when used for seed, can affect subsequent plant growth and yield. For example, plants grown from seed tubers grown under cool conditions (13-14°C) usually produce higher yields than plants grown from tubers grown under warm conditions (26°C); however, this response depends on the variety. Accelerated senescence may occur if the tubers are stressed during growth and/or physically damaged during post-harvest handling and storage.

Storage of seed tubers

An important aspect of propagation is the storage of seed tubers. Since freshly harvested potatoes do not germinate, tubers intended for propagation must be stored after harvest to go through a dormancy period.

Dormancy (internal dormancy) can last from 5 to 20 weeks, depending on the variety, storage temperature, and maturity of the tubers. Freshly harvested tubers usually do not germinate, even if they are kept in favorable temperature and humidity conditions. The hibernation period may be shortened by high temperatures (21-27°C), storage at high humidity, low oxygen concentration, and tubers being wounded or cut. In most situations, dormancy will eventually disappear. Lack of growth differs from dormancy in that the former is caused by unfavorable environmental conditions.

Emergence of sprouts and subsequent growth depend on storage period and temperature; there is variability in different varieties. The tubers are stored at a low temperature, 3-4°C, and a high, 90% relative humidity, with proper ventilation to maximize the storage period and minimize premature sprout development. A storage period of 6 weeks is usually sufficient for most varieties to meet the dormancy requirement, although some may require a longer time. Temperatures below 2°C may damage subsequent seedlings. Tubers stored at 12-22°C have a shorter dormancy and resting period, and show stronger apical dominance than tubers stored at low temperatures. Exposure to light during low temperature storage results in plants producing many small tubers, while storage in the dark at high temperatures results in plants producing fewer but larger tubers.

In warm climates, the use of natural ambient light is an inexpensive alternative to temperature-controlled storage. Irradiating tubers with diffused light has the same effect as low temperature, limiting shoot growth and reducing apical dominance. Under these conditions, elongation of sprouts is suspended. In some European countries, this practice is called “thinning” or sprouting greens. Greening and solanine formation are not a concern because the tubers are not eaten.

True potato seed in commercial production

Research, mainly at the International Potato Center in Peru, has led to increased reliability in the use of true potato seed (TPS) for propagation. The use of TPS ensures freedom from transmission of most viruses during propagation and avoids the disadvantages associated with handling, storage and transport of bulky seed tubers. Therefore, TPS holds great promise, especially for developing countries. One hundred grams of TPS is equivalent to 2-3 tons of seed tubers for propagation. However, TPS varieties often lack uniformity in tuber size, shape, color and quality and give low yields. Parent lines are now being developed that have better uniformity. Although the quality and use of TPS will continue to improve, these obstacles must be overcome.

Because TPS are dormant, they are first used to produce seedlings rather than sown directly into the field. Seedlings are planted after 4 or 5 weeks, when they are better able to tolerate possible adverse growing conditions. This delay extends the growing season by several weeks. TPS is also sown at high density in nurseries to produce seed tubers, which because of their small size are usually planted whole.

In developing countries, the cost of seed tubers is a large part of production costs. Hand pollination and other costs of TPS production are high, but are expected to be lower than for conventional seed tubers. TPS has the potential to expand potato production in areas where seed tubers as propagation material are limited.

Varieties

Variety selection

When selecting potato varieties for a particular zone, it is advisable to simultaneously use 2-3 varieties with different early maturity.

The Potato Research Institute recommends for potato specialization farms the ratio of varieties, in % of the total area under potatoes: early and medium-early varieties – 40%; medium varieties – 35%; medium-late varieties – 25%. With such a ratio of varieties, there is an opportunity to shift the harvesting dates to an earlier period (August) and to harvest the bulk of the potatoes under favorable conditions, reducing crop losses and preserving its quality.

Classification

According to the purpose of the potato varieties are divided into:

table varieties, characterized by good taste qualities, non-darkening flesh and aligned shape of the tuber;
technical (factory potatoes), which have a high starch content;
universal (table-factory) varieties with good taste and shape of tubers with non-darkening flesh and high starch and protein content.

Among the varieties used, 60% are table varieties, 30% are universal and 10% are technical.

Varieties are subdivided according to their maturity date into:

early (50-65 days);
middle-early (65-80 days);
middle-ripening (80-100 days);
middle-late (100-110 days);
late (more than 110 days).

Accelerated reproduction of potato varieties

For the rapid reproduction of promising potato varieties, accelerated propagation techniques are used: cutting tubers and cutting into parts, rooting stem tops, shoots, cuttings.

Good results are obtained by the reproduction of potatoes by shoots and rooting of the tops of plants grown from shoots (Potato Research Institute, Filippov and Postnikov, 1971). Tubers intended for propagation by this method are cut crosswise, and the halves are planted in the soil of vegetative houses or greenhouses. When seedlings reach 5-8 cm in length, they are separated from tubers and planted one by one in vegetative gauze or film houses. Separation of shoots from tubers can be done up to 5 times. In the outgrown to 25-40 cm of plant offshoots cut off the stem tops to 10 cm. Cut tops for rooting dipped in half for 6-7 hours in a solution of heteroauxin (0.75 mg per 1 liter of water), and then planted in the ground. Water the plants periodically. To reduce moisture evaporation, planted tops are covered with polyethylene film until rooting, then it is removed. The multiplication rate with this method reaches 212.

Another method of accelerated reproduction involves laying the tubers after harvesting for prolonged germination at room temperature (W. Hamann, GDR). After emergence of 1.5-2 cm of shoots, the tubers are kept in gibberellin solution (2 mg/l) to stimulate growth, then germinated in the same conditions with alternate lighting at intervals of 8 days until the appearance of long branching shoots. To prevent the tubers from shriveling, the humidity in the chamber is kept at 80-90%. As the sprouts grow, they are separated and cut into segments with one rudimentary bud. The segments are spread out on dampened filter paper until roots form, which usually appear after 4-5 days. Rooted segments are planted in boxes with moistened peat. After 2 weeks, each segment forms a normal plant 8-10 cm high, ready for transplanting into soil. Multiplication coefficient by this method for Early Rose variety was 1064 (L.N. Trofimtsev).

Degeneration

Potato degeneration is a progressive decrease in yield and tuber quality in subsequent reproductions that is attributed to viral diseases of the crop. It was first mentioned by the Englishman Maxwell in 1757. In Russia, information about this disease appeared in 1801.

In the study of this phenomenon, the discovery of the infectious nature of one of the typical forms of degeneration – leaf curl. Later the viral nature of other diseases of degeneration was also established.

Degeneration is manifested in:

premature awakening of tuber eye buds;
the formation of elongated sprouts;
the development of small, usually diseased tubers;
a sharp decrease in the productivity of the plant;
disease infestation, especially viral disease.

There are several versions of the explanation of the causes of degeneration: ecological, viral, physiological aging, toxin theory, and mycorrhizal. The first two are considered the most likely.

The ecological theory of degeneration attributes this phenomenon to unfavorable growing conditions and plant nutrition disorders. This is primarily caused by high temperatures and a lack of moisture in the soil during tuber formation.

The viral theory assumes that viruses are the cause of degeneration. In this case, ecological conditions only enhance or weaken the effect of viral diseases.

“…there is no natural degeneration, there is pathological degeneration.”
A.A. Yachevsky, “Diseases of Degeneration of the Potato,” 1925.

Potatoes can be affected by viruses X, S, A, Y, M, L, R. However, modern research indicates that potato degeneration is probably due to the effects of two of these factors at once: ecology and viral diseases.

“…we don’t need to argue about whether it’s ecology or virus, but we need to learn once and for all that ecology and virus. We must know when we are dealing with a virus and when we are dealing with ecological degeneration.”
M.S. Dunin. “Results and New Tasks of the Production and Application of Antiviral Sera for the Health of Seed Potatoes,” 1960.

A potato plant may be infected by one or more viruses. In the latter case, plant depression and yield losses increase. Thus, in the variety Priskulski Early, when infected with viruses X and S, the yield reduction is 8%, and with viruses X, S and Af- 19%. Similar examples were obtained for many other varieties.

According to the nature of symptoms manifested on plants, morphological signs of pathogens and ways of spreading, viral diseases are subdivided into mosaics and jaundice.

Degeneration can be of the non-infectious type, such as filamentous sprouts and tuber outgrowth. A property of this type of degeneration is that the symptoms are not transmitted to healthy plants through infection. This type of degeneration is reversible: symptoms can subside or disappear completely when plants are provided with favorable growing conditions.

Thus, potato degeneration is the result of the combined effect of unfavorable conditions and viral infection on the vegetatively propagated potato plant. Under certain conditions, one or the other form of degeneration becomes dominant.

High temperatures and soil dryness during tuber formation negatively affect plant growth and development. This is caused by the fact that at temperatures above +25°C the protein composition of tubers changes, which intensifies their degeneration. Degeneration is particularly strong in warm regions of Russia.

Viral degeneration can often be carried by aphids, and the spread of viral diseases can also be caused by soil and climatic conditions, varietal characteristics, and agricultural technology.

The use of physiologically old tubers for seed production and the planting of potatoes in late spring can also lead to degeneration. Potato varieties differ in their resistance to degeneration.

Regular improvement of planting material is not always possible because it is associated with the constant replacement of old varieties by more resistant ones. At present, seed production is being organized in the northern and mountain regions of Russia, where elites are grown that are not infected with viruses, while controlling the multiplication of promising clones. Modern advances in of biotechnology make it possible to use the results of meristem culture.

Improvement of seed material

The technology of cultivation of seed potatoes includes the same set of agricultural techniques that are used to obtain food potatoes, taking into account the zone of the country. However, it is supplemented by some special techniques aimed at obtaining high-quality seed material.

To obtain high quality seed potatoes, harvesting begins before the tubers are fully ripe, especially the early varieties. Earlier harvesting reduces the chance of infection: the earlier the harvesting, the more likely it is that the virus has not penetrated the tubers from the leaves.

Also a technique for improving potato seed production is summer planting, which reduces tuber degeneration and increases yields. When planting in late June or early July, tuber formation occurs during cooler times (September) when heavy rainfall, cool nights and shorter daylight hours occur. In general, this has a positive effect on tuber formation, while spring planting is at its hottest during the summer, which leads to a deterioration in the seed quality of tubers.

Summer planting of potatoes is particularly well-proven in the North Caucasus, the Middle Volga region, the Central Black Earth zone, as well as in the south of Ukraine.

Repeated summer planting and their alternation with spring planting help maintain the yield properties of tubers, slow its aging as a vegetatively reproduced plant.

In the south of Russia, a two-harvest crop, which involves growing two vegetative generations in one season, mainly of early and medium-early potato varieties, becomes important for obtaining quality seed material. In the second (summer) planting, freshly harvested tubers of the spring planting crop are used. For these purposes, varieties with a short dormancy period are better suited. For example, for the North Caucasus, these varieties include Ulyanovsky, Yuzhanin, Lorkh, in Moldova and the steppe zone of Ukraine – Lorkh, Ulyanovsky; in Central Asia – Lorkh.

To obtain a second crop, when planting freshly harvested tubers, use special techniques of artificial interruption of the dormancy period with observance of some peculiarities of agrotechnics.

Germination of tubers is related to their maturity. Physiologically young tubers under the influence of stimulants wake up faster and give uniform sprouts in a shorter time. Therefore, when potatoes are planted in spring, they are harvested immediately after flowering when the tuber weight reaches 30-50 grams. Before harvesting, tops are cut by topshooters or treated with a 3-5% solution of magnesium chlorate.

Excavated young tubers begin to prepare immediately for planting. To do this, they are sorted by removing small, ugly and spindle-shaped tubers, washed with water for more effective treatment with chemicals, and treated with 2% thiourea and gibberellin solution at a rate of 1-2 mg of the preparation per 1 l of solution for 30-60 minutes. Large and medium-sized tubers are cut into 2-3 pieces at least 20 g each, leaving 2-3 eyes on them. Small tubers are incised to a depth of 5-10 mm to stimulate sprouting.

When preparing the tubers, do not allow sunlight to reach the seed material, because it may cause burns on young tubers, which later leads to their rotting.

Plot for planting freshly picked tubers should be clean from weeds, loose and sufficiently moist. Autumn and preplanting soil treatment is the same as for conventional potato planting. As a precursor suitable black fallow or early harvested crops such as vegetable peas, pea-oat mixture for green fodder, winter rape. With a lack of moisture in the soil 5-6 days before planting, conduct preplanting watering so that the soil layer depth of 50-60 cm is well soaked.

Fertilizers are applied under autumn plowing or after harvesting the predecessor. Fertilizer application rates: 15-20 t/ha of decomposed manure or humus, 45-60 kg/ha of nitrogen in the form of ammonium sulfate, 60-90 kg/ha of phosphorus in the form of superphosphate, 60-90 kg/ha of potassium in the form of potassium chloride or potassium salt.

When preparing the tubers, do not allow sunlight to reach the seed material, because it may cause burns on young tubers, which later leads to their rotting.

The timing of planting is chosen according to the climatic zone and weather conditions. Freshly harvested tubers are planted using conventional potato planters to a depth of no more than 8-10 cm. Norm of planting is 70-85 thousand tubers (parts) per 1 hectare, the scheme of planting – 70×15-20 cm.

Since the germination of tubers is slow, it is important to ensure optimal conditions for the accelerated emergence of sprouts. In particular, the maintenance of soil moisture of 75-85% field capacity during the period of tubers’ appearance of visible sprouts, 90-95% in the next two weeks before the mass sprouts.

The first sprinkling irrigation is carried out immediately after planting, with the rate of water consumption of 250-400 m3/ha. Subsequent waterings are done at intervals of 4-6 days. After each irrigation as the soil dries out, harrowing with light harrows along the planting or inter-row loosening with a cultivator with lancet tines is carried out. It is optimal to irrigate in the morning, evening or night hours. During emergence of seedlings and till the end of vegetation 5-6 waterings, 2 inter-row loosening and 1-2 hilling are done.

A technique for improving seed and yield qualities of potato tubers is its cultivation on drained peat and poem soils, which are usually fertile, sufficiently moist and friable, they are not observed abrupt changes in temperature, which rarely rise above 18-20 °C. Tubers grown on peat soils have a stronger cork layer, have a longer dormancy period, and have a higher content of nitrogenous substances. When planted, these tubers form more stems and develop a powerful root system, the productivity of such bushes is higher. Seed tubers produced on peat soils yield 3.5-5.0 t/ha more when planted on mineral soils than seed tubers grown on mineral soils (Potato Research Institute, Moscow Agricultural Academy).

Improvement of planting material with increase of its yielding qualities also takes place at potato growing in mountainous conditions.

The way of improvement of planting material is also the breeding of varieties resistant to degeneration, including viral diseases, and organization of seed production of potatoes obtained on a virus-free basis with control over the reproduction of promising clones.

Breeding

In the early stages of potato development its improvement was largely confined to breeding, and this was done largely by laymen rather than by the structured activities of public or private breeders. For example, the variety ‘Russet Burbank’ was selected from botanical seed offspring before 1890, was rapidly and widely introduced, and is still a major variety in North America. Similarly, the ‘Bintje’ variety, bred around 1910, also continues to be widely cultivated in Europe. Early advances were based on somatic mutations, most of which were not useful. Consequently, relatively few large varieties emerged. Traditional breeding is based on crossing two varieties with complementary traits and selecting in a segregating population. The probability of obtaining improved varieties was very low. This is probably due to the complex patterns of inheritance of tetra-somal traits. Sexual breeding of potatoes is a relatively recent development that provides an opportunity to expand the development and introduction of improved varieties. An interesting example is the late scab-resistant variety Greta, which was bred by interspecific hybridization with S. demissum, a Mexican wild species.6

The use of true seed has many potential advantages, with 2n gametes and cytoplasmic male sterility providing a potential procedure for hybrid seed production. Modern cultivated S. tuberosum spp. tuberosum potato has a narrow genetic base but lends itself to many biotechnological manipulations, such as embryo rescue, protoplast fusion, transformation, and anther culture, which should result in improved germplasm for breeding purposes. Further exploitation of wild species should expand the genetic base. Major collections of germplasm are held at the International Potato Research Center in Peru, as well as in Russia, the United States, Germany, and several other countries.

Sources

V.V. Kolomeychenko. Horticulture/Textbook. – Moscow: Agrobiznesentr, 2007. – 600 с. ISBN 978-5-902792-11-6.

Horticulture/P.P. Vavilov, V.V. Gritsenko. Vavilov. ed. by P.P. Vavilov, V.S. Kuznetsov et al. – M.: Agropromizdat, 1986. – 512 p.: ill. – (Textbook and Tutorials for Higher Education Institutions).

Fundamentals of Technology of Agricultural Production. Farming and plant growing. Under the editorship of Niklyaev V.S. – Moscow: “Bylina”, 2000. – 555 с.

World vegetables: principles, production, and nutritive values / Vincent E. Rubatzky and Mas Yamaguchi. — 2nd ed. 1997.

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Potato

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Economic importance

Quality factors

Toxic compounds

Origin and domestication

History of the crop

Ancient times

In Europe and the world

In Russia

Area of cultivation

Yield

Taxonomy

Botanical description

Root system

Tuber

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Ecological requirements

Temperature requirements

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Nutrition of potato

Nitrogen

Phosphorus

Potassium

Vegetation

Physiology of growth stages

Cultivation of potatoes

Propagation

Storage of seed tubers

True potato seed in commercial production

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Variety selection

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Accelerated reproduction of potato varieties

Degeneration

Improvement of seed material

Breeding

Sources