Potato

Quality factors

Potato is a useful crop because it is grown in many regions, and in a relatively short time it produces a large quantity and high quality of food per unit area. Other characteristics include storability, ease of preparation, taste qualities with high satiety value, and broad acceptability.

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

The texture of boiled potato is greatly influenced by dry matter content, as well as 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, a high amylose-to-amylopectin ratio, small cell size and low sugar content are preferred for most types of processing and for preparation by baking or frying. Such potatoes tend to disintegrate when boiled and have a mealy texture. Potatoes with low dry matter content are best used boiled, since they usually remain whole. The starch composition of many low-dry-matter potato varieties tends to have a low amylose-to-amylopectin ratio. Such potatoes have a moist texture when baked.

In addition to water (about 78%), other components are carbohydrates and protein, usually about 18% and 2%, respectively. Potato also contains a significant amount of minerals and vitamin C. Yellow-fleshed varieties contain some carotene. When comparing the nutritional value of products, it is important to note that the high water content of potato must be taken into account when comparing with grains or other products with high dry weight. Due to relatively high consumption, potato provides a significant amount of protein and calories, despite its low absolute content.

Ancient times

The Incas used potato at least 2,000 years before the arrival of Spanish explorers. Radiocarbon dating of starch grains found in archaeological excavations has shown that potato was used at least 8,000 years ago.

In Europe and the world

Potato was brought to Europe around 1570 from South America, first to Spain, and later spread throughout all European states, which led to an unimaginable growth and spread of a new food crop with profound economic and historical consequences. From Spain, potato was brought to neighboring European countries, and in less than 100 years it was grown quite widely in many regions of Europe. Soon potato spread beyond Europe: around 1610 it was brought to India, in 1700 to China, and around 1766 to Japan. Scottish-Irish immigrants brought potato to North America in the early 1700s.

However, before the widespread spread and acceptance of potato in Europe, there was considerable skepticism regarding its edibility. When potato first appeared in Europe, it was considered poisonous due to its external similarity to nightshades (Solanum spp.). The tubers were considered unsuitable for human consumption or suitable only for the very poor and as animal feed. Acceptance was also poor due to low productivity. Andean introductions (Solanum tuberosum subsp. andigena), obtained from low-latitude regions, performed poorly because they were not adapted to European temperate latitudes, although productivity was higher in southern European regions. Herbarium specimens and drawings show that Andean rather than Chilean (Solanum tuberosum subsp. tuberosum) forms were introduced first, and that Chilean sources appeared only in the 19th century.

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

The increased dependence 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 in 1845 and 1846. Many years of extensive potato cultivation, especially in Ireland, with limited crop rotation and an increase in land area occupied by potato growing, made it highly vulnerable to disease. The late blight fungus Phytophthora infestans became established, and under favorable conditions the fungal population grew to epidemic proportions, partly because the most susceptible potato varieties grown at that time were of Andean origin. During this period, about one million people died of starvation in Ireland. Because of the famine, there was mass migration of the population, as well as significant economic shocks in Ireland and other European countries. A consequence of the crop failure was the appearance in the 19th century of better-adapted Chilean potato varieties, which replaced the original Andean ones. This formed the genetic base that is now called Solanum tuberosum subsp. tuberosum.

In Russia

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

The widespread distribution of potato in Russia was initiated by a Senate decree of 1765. In 1765–1766, the Senate considered the issue of introducing potato 22 more times. In 1765, an “Instruction” on its cultivation was published, representing an encyclopedia on potato growing consisting of 16 sections. In December 1765, an additional “Instruction” was issued on the transportation and storage of seed potatoes.

From the mid-19th century, the potato cultivation zones in Russia expanded significantly due to frequent grain crop failures. In 1881, the area occupied by potato reached 1,529 thousand ha.

In the second half of the 19th century, Russia developed its own relatively good potato varieties, bred by amateur breeders, primarily the self-taught breeder Efim Andreevich Grachev (1826–1877), who bred them in St. Petersburg Governorate and repeatedly demonstrated them at exhibitions in Russia and abroad.

In 1903, potato breeding was continued by Professor D. L. Rudzinsky of the Moscow Agricultural Institute (later the MAA named after K. A. Timiryazev), who conducted individual selection from foreign varieties. However, the scale of seed production did not at all correspond to the importance that potato had acquired in Russia by that time.

Only after the October Revolution did potato breeding receive significant development. In 1919, S. M. Bukasov began work on studying 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. Lorch and T. V. Aseeva collected a collection of some foreign and local varieties at the Korenevskaya Potato Station, which was founded in 1920 in the Ukhtomsky district of Moscow Oblast and later became the Research Institute of Potato Farming (NIIKH).

The first early potato varieties of Soviet breeding — Komsomolets and Kalitinets — were bred in the 1920s by I. A. Veselovsky; in 1922, A. G. Lorch and P. S. Gusev bred two mid-late varieties — Lorkh and Korenevsky.

In subsequent years, extensive breeding work was carried out under the leadership of P. I. Alsmik at the Belarusian Research Institute of Potato and Fruit and Vegetable Growing (BelNIIKPO). The work was aimed at creating cancer- and late-blight-resistant varieties with increased starch and protein content in tubers. Breeding work was also carried out at NIIKH, the Ukrainian Research Institute of Potato Farming (UkrNIIKH), the Northwestern Research Institute of Agriculture, and in the Baltic countries.

Root system

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

• sprout (eye), or primary, roots, which form at the beginning of tuber germination;
• stolon roots, formed throughout the growing season and arranged in groups of 4–5 near each stolon;
• stolon roots, located on the stolons.

Plants obtained asexually from tubers develop finely branched, relatively small and thread-like spreading adventitious roots, while plants grown from true seeds form a thin root with many lateral branches.

The root system penetrates the soil shallowly. About 50% of the roots are located in the arable layer, 22–38% penetrate deeper, and individual roots penetrate to 150 cm in depth.

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

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

The power of the root system depends on moisture, aeration and nutrient content in the soil.

The 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 the period of intensive tuber formation is associated with the ability to absorb nutrients even at the end of the growing season.

Tuber

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

Varieties differ in the number of buds. As a rule, there are three buds in one eye. During germination, one of them starts growing — the most developed middle (apical) one; the others remain reserve and sprout when the sprouts are damaged or broken off. Apical buds sprout first, since they suppress the germination of other buds. Such apical dominance decreases as they are removed or separated from the apical part of the tuber; low temperatures and aging of the tuber also reduce apical dominance.

The tuber bud consists of a growth cone with rudiments of future leaves, axillary buds and rootlets.

The eyes on the tuber are arranged spirally. In the upper part of the tuber, the buds are located more closely together, since the tuber grows at the apex. These eyes are more viable and sprout earlier than the lower ones.

Depending on the variety, sprouts that germinate in the light may have green, red-violet or blue-violet coloration.

The main tissues of the tuber are the periderm, cortex, vascular cylinder of phloem and xylem, as well as areas of the internal and external medulla or pith tissue.

The skin of mature tubers is a thin cork tissue that protects them from drying out and diseases. Under the cork layer are parenchyma cells of the cortex filled with starch grains, then a layer of educational tissue (cambium) and a ring of vascular-fibrous bundles connecting with the eyes. The cambium produces few secondary tissues. In the inner part of the tuber — the pith — the starch content is lower than in the cortex.

The surface of the tuber can be smooth or rough due to netting or cracking; the color of the periderm varies from brown to light brown, red or dark violet.

Respiration of tubers and evaporation of moisture occur through intercellular spaces, that is, loosely arranged cells, through lenticels — elevations on the tuber skin. Their number and size are determined by growing conditions.

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

The color of tubers can be white with a manifestation of yellowness; red with shades from light pink to intense red and blue-violet. The flesh of the tuber is usually white, to varying degrees yellowish; in some varieties red, blue-violet, dark yellow, orange.

The external color of the tuber is determined by the amount of cork substance of the cortex and the pigment contained in the cell sap of the cortex. With a thin cork layer, the color of the flesh shows through. As the cork layer thickens, the color changes from cream to brown.

The starch content in tubers can vary from 12 to 25% (sometimes up to 29%). In tubers of table potato varieties, the starch content is 12–16%; in factory (technical) varieties — 18–29%. Late varieties are distinguished by greater starchiness. For processing, potatoes with a starch content of at least 18% are used.

Stem

The stem is erect, less often deviates to the side; at first smooth, and with further growth becomes angular and branched. The color is green; in some varieties, due to the presence of anthocyanin, with a reddish-brown tint. The intensity of pigmentation is determined by varietal characteristics, cultivation conditions, light, water supply and other factors.

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

• late-ripening varieties, in which branching occurs mainly in the lower tier;
• early-ripening varieties, in which the stem does not branch from below.

The stems are ribbed, three- or four-sided, less often rounded, to varying degrees pubescent. At the junctions of the faces on the ribs, outgrowths of green tissue called wings are formed. They are a varietal distinguishing feature.

The height of stems varies from 30 to 150 cm and depends on cultivation conditions and variety. Late-ripening varieties, as a rule, have taller stems and more internodes.

The bush usually consists of 2–8 leafy stems. Their number is determined by the variety, the size of planted tubers, and the number of sprouted buds. Plants grown from large tubers usually have more stems. The number of stems in a bush to a certain extent affects tuber yield. To increase the number of sprouting buds, techniques are used, for example, making transverse cuts in tubers or treating planting tubers with growth substances.

In the underground part of the stem, shoots called stolons form from axillary buds. At their ends, tubers, or thickenings, form. One stem can form 6–8 stolons, which can additionally branch. The thickness of stolons is less than that of stems. The length of stolons varies: shorter in early varieties, longer in late ones.

Leaves

The leaves that appear during germination of tubers or seeds are simple, entire-margined. As the plant develops, interrupted-odd-pinnately dissected leaves form. Each such leaf consists of several pairs of lateral lobes, which are placed opposite one another, intermediate lobules between them, and a terminal lobe. The lateral lobes and lobules are borne on stalks attached to the rachis, which passes into the petiole. The lobules, depending on their position, are divided into series: terminal, first, second, third and fourth. The first series includes all lobules borne on the stalk between the lobes of the first and second pairs, etc.

The lobules of the first and second series are important for varietal distinction. The terminal (unpaired) leaf lobe at the end of the rachis differs in shape from the lateral lobes and is often larger. The counting of lobes begins from it. In some varieties, the separation of the terminal and lateral lobes is incomplete; this phenomenon is called potato-leaf-like.

The structure and dissection of leaves is one of the varietal characteristics. According to the number and arrangement of lobules in the series, strong and weak dissection are distinguished. Medium dissection is an uncharacteristic varietal trait.

With a wide gap between lobes and lobules, the leaf is called sparsely lobed; with narrow gaps — dense, or densely lobed.

On the underside of the leaf there is a network of veins; their color is often associated with the color of the tubers. Venation decreases with the application of increased doses of potassium or increases with increased doses of nitrogen. On the stem, leaves are arranged spirally.

Flowers

Potato flowers are collected in inflorescences, which are diverging cymes located on a common peduncle of different lengths. The pedicel is articulated. The flowers are of the pentamerous type (five-lobed fused corolla). The calyx of the flower is gamosepalous, with sepals fused at the base. The corolla is wheel-shaped and includes five fused petals.

The color of the corolla can be white, blue, dark blue-violet, red-violet with various shades. The flower contains five stamens, which consist of anthers borne on short filaments, fused with each other and with the base of the petals. The anthers are orange, yellow, greenish-yellow or greenish. The pistil consists of a stigma, style and ovary. The stigma is capitate, club-shaped or dissected. The style is straight or curved. The ovary is superior, consisting of two carpels with numerous ovules.

Potato is a self-pollinating plant; most varieties are sterile, some are fertile. According to other data, lacking nectar, potato is mainly cross-pollinated, usually by wind, but pollination by insects also occurs (Rubatzky). In some varieties, flower drop often occurs, so fruiting is rare.

Fruit

The fruit is a bilocular multi-seeded juicy green or purple berry of spherical or oval shape. When ripening, the berries become white with a pleasant odor similar to that of strawberries; they are unsuitable for food 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, with a curved embryo. The weight of 1,000 seeds is about 0.5 g.

Temperature requirements

Potato reacts negatively to soil temperatures below 7–8 °C and above 25 °C.

Tops at high relative humidity and temperature of -1.5…-2.0 °C with an average frost duration of 5–6 h blacken and die. Young plants are especially susceptible to low temperatures. However, a slow decrease in temperature leads to the accumulation of sugars in plants, thereby increasing their resistance to temperatures of -2…-4 °C.

Young plants damaged by frost recover quite easily. With sufficient nutrients and moisture, they quickly increase vegetative mass. On potato plantings affected by frost, it is recommended to apply nitrogen fertilizers.

Potato tubers, as a rule, are damaged at temperatures of -1…-2 °C, which is associated with their high water content (up to 75%). However, in some years, as a result of gradual cooling of tubers in autumn and accumulation of sugars (sometimes up to 8%), they can even overwinter in the soil. Overwintered tubers awaken early, start growing and can become a place of temporary habitation for insect pests, and subsequently become weeds in the crops of the following crop.

When exposed to low temperatures down to -1 °C during storage, tubers become sweet due to the formation of sugars, but when such tubers are kept at room temperature for 5–10 days, the sugars are converted back into starch, and the 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 occurs very slowly without the formation of a root system, and the incidence of tuber diseases sharply increases. At temperatures below 3 °C and above 31 °C, growth and development of buds on tubers are delayed. Exposure to temperatures below -1…-1.5 °C and above 35 °C for several days leads to 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; at the expense of nutrient reserves, new tubers may form on them without the appearance of aboveground organs. This phenomenon can be observed when planting potatoes in cold, waterlogged soil or in too dry soil at temperatures above 25 °C.

Normal germination of tubers occurs at a soil temperature of 6–8 °C. The optimal temperature for germination is 18–20 °C (according to other data, 13–15 °C<1>); under these conditions, sprouts appear 10–12 days after planting, at a temperature of 13–15 °C — after 18–20 days, whereas at a soil temperature below 7 °C they appear only after 30–35 days, sometimes after 50 days.

For the middle zone, the optimal soil temperature for tuber formation is 16–19 °C, which corresponds to an air temperature of 21–25 °C. Cooling leads to delayed tuber growth; at 2 °C growth stops.

Increased soil temperature leads to greater formation and branching of stolons; this intensification of growth processes occurs to the detriment of tuber yield accumulation.

Prolonged heat above 30 °C causes cessation of assimilatory activity of leaves, as a result of which tuber growth stops and their skin becomes coarse. During these periods, respiration intensifies, increasing carbohydrate consumption, which inhibits tuber formation.

The sum of active temperatures above 10 °C during the growing season, necessary for the full development of potato plants, is 1,000–1,400 °C for early and mid-early varieties, and 1,400–1,600 °C for late-ripening varieties.

Autumn frosts down to -3 °C lead to the death of tops, but tubers are not damaged.

Later potato varieties are distinguished by better cold resistance.

Moisture requirements

Potato is demanding of moisture. Water consumption changes by growth phase. The critical period of water consumption is the beginning of flowering. During this period, a lack of moisture in the soil leads to a sharp decrease in yield. Even a short drought in the budding phase leads to a yield reduction of 17–23%. The tuber yield of early potato varieties is determined by atmospheric precipitation in July, mid-season varieties — by July–August, late varieties — by precipitation in July–August–September (A. G. Lorch, 1948).

Potato roots are strongly branched and located relatively shallowly. About 90% are within 50 cm of the surface, which generally increases susceptibility to soil moisture stress. A high demand for moisture arises after tuber set and during their enlargement.

Uniform moisture supply is very important, especially for tuber shape. Bumpiness, usually caused by moisture deficiency, can be especially severe in some varieties.

The transpiration coefficient of potato is 400–550, sometimes varying from 167 to 659, which indicates the high plasticity of potato plants and good adaptability to growing conditions.

On hot days, a bush can evaporate up to 4 L of water, and in southern regions even more. Therefore, for all regions with insufficient moisture, agrotechnical techniques for accumulating and preserving soil moisture are of decisive importance. With a high level of agricultural technology and sufficient nutrient supply, potato water consumption decreases.

The optimal soil moisture for growth and formation of a high yield is 70–80% of the least moisture capacity in the layer of distribution of the main mass of roots in the flowering and tuber formation phase. During starch accumulation — 60–65% of the least moisture capacity.

In the conditions of the middle zone, a decrease in soil moisture to 60% of the least moisture capacity leads to a yield reduction of 3–9%, to 40% — by 40–43%. At a moisture content of 40%, flowering is delayed by 4–6 days; at 20–30% — by 9–10 days. Tuber formation and death of tops are correspondingly delayed.

In providing moisture during the first period of growth, the moisture reserves of the mother tuber are of great importance. During the hottest hours of the day, the lack of soil moisture is compensated by these reserves. The same role during further plant development is played by newly formed tubers. Thus, potato tubers serve as a reserve storage of moisture, which is filled when water is sufficient or from which the plant takes moisture when it is deficient.

Potato has a well-developed ability to absorb air moisture through leaves. These features allow plants to withstand short droughts relatively easily.

The water requirement of crops varies greatly from 250 to more than 500 mm of water. To obtain high potato yields in the middle zone, at least 300 mm of atmospheric precipitation must fall during the growing season. With increasing evaporation of moisture from the soil surface and as crops move south, the water requirement increases, so the lack of moisture in these conditions is compensated by irrigation. With uneven precipitation in the Non-Chernozem zone, potato also responds well to irrigation.

Excessive moisture is also undesirable, as it leads to deterioration of the soil air regime, increased wateriness of tubers, reduced starchiness, poorer storage, an increased number of tuber lenticels, and excessive rain or prolonged wetting of leaves and high humidity contribute to the development of foliar diseases.

Soil air regime requirements

The potato root system consumes a large amount of oxygen from soil air during respiration. The root requirement is approximately 1 mg of oxygen per 1 g of dry matter per day. The greatest demand is noted during tuber formation.

This determines the need to maintain the soil in a loose state with a bulk density not exceeding 1–1.2 g/cm³. In loose soil, gas exchange between soil and atmospheric air proceeds more intensively. In heavily moistened, compacted or poorly cultivated soils, the oxygen content can decrease to 2% and the carbon dioxide content can increase greatly. Under such conditions, tubers begin to suffocate and rot. The optimal concentration of carbon dioxide in soil air should be no more than 1%.

Light requirements

Potato is a short-day plant (according to other data, a long-day plant<1>). A short day is not a mandatory condition, but in the middle zone it accelerates development. Potato varieties may differ in their response to day length. Under the lowered temperatures of the north, the photoperiodic response also changes.

In the middle zone, a short day leads to acceleration of the onset of tuber formation and shortening of the growing season, including the duration of tuber formation and growth.

In the early stages of tuber formation, tuber mass under a short day is greater than under a long day. However, a long day promotes the formation of tops, on whose vigor the productivity of photosynthesis and the formation of substances necessary for tuber growth depend. Therefore, tuber yield under a long photoperiod is usually higher, but this does not mean that potato can be classified as a long-day plant.

In early and late potato varieties, more prolonged and intensive top growth is noted under long-day conditions, but the efficiency of tuber formation, that is, the ratio of tuber mass to top mass, is significantly greater under a short day. This is also evidenced by the fact that the most intensive tuber formation for most varieties occurs in the second half of summer, when day length decreases.

Potato is a light-loving plant. Even a slight decrease in illumination leads to yellowing of tops, elongation of stems, weakening or complete absence of flowering, and reduced yield.

The yield and quality of tubers are influenced by row direction. Illumination of rows with north-south, northwest and southeast directions is more uniform, in contrast to west-east. Thus, with rows directed from north to south, potato yield was higher by 1.6–2.0 t/ha, and starch content by 1–2% (MAA named after K. A. Timiryazev).

After digging, tubers exposed to light for several days turn green due to chlorophyll formation. Under the action of direct or diffuse sunlight, the solanine content in tubers increases to 30–40 mg per 100 g of tubers, whereas its usual content is 2–10 mg per 100 g. Then solanine is converted into solanine glycoside, which has an antiseptic effect. Therefore, greening seed potatoes helps protect tubers from diseases and rodents during autumn-winter storage.

Greening tubers intended for food or feed is unacceptable, since potato acquires a bitter-astringent taste and becomes poisonous.

Soil requirements

Potato prefers loose soils. The respiration intensity of the root system is 7–12 mL of oxygen per hour per 1 g of dry root matter, which is 5 times greater than the respiration intensity of the roots of sunflower and other crops. This determines the increased demand of potato for soil porosity. Roots grown in loose soil with a density of 1.10 g/cm³ branch better, penetrate the entire arable layer, and go into the subsoil. The optimal soil density for growing potato is 0.9–1.2 g/cm³. On looser soils, moisture losses become too great. Soil structure and soil compaction have a strong influence on tuber shape, as well as on yield and quality.

Well-drained soils with a deep arable layer and medium to coarse-grained structure are preferred.

Loose soil is necessary for good development of stolons and formation of young tubers; in compacted soil they are small and severely deformed.

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

Potato grows well on fertilized sandy loam and loamy chernozem soils. In the Non-Chernozem zone, cultivated sod-podzolic and gray forest soils are suitable for it; on light sandy loam soils, organic fertilizers are applied. Cultivated peatlands are also suitable, primarily for seed plantings.

Soils that are light in granulometric composition are also suitable for growing potato; tubers are obtained with high taste qualities provided sufficient fertilizers are applied.

Due to the high absorptive capacity of the root system, potato can also grow on relatively poor soils, but the yield remains low.

Heavy loamy, clayey, strongly compacted, waterlogged soils, primarily with a close occurrence of groundwater, are unsuitable for potato cultivation. On such soils, free development of tubers is difficult, and due to excessive moisture, plant disease incidence increases. Saline soils are also unsuitable, since potato tolerates salinity poorly.

When organic fertilizers are applied, potato tolerates slightly acidic soils relatively well. The optimal soil acidity value is 5–6. According to other data, slightly acidic soils with pH 5.5–6.5 are optimal (Rubatzky). Soil pH below 5.4 helps control common potato scab (Streptomyces scabies).

Nitrogen

A lack of nitrogen in the soil leads to weak development of aboveground organs of potato plants, reduced leafiness, reduced productivity of the leaf apparatus, and decreased yield and starchiness of tubers.

Excess nitrogen leads to excessive top growth, delayed tuber formation and ripening, lengthening of the growing season, and reduced plant resistance to diseases. Optimal nitrogen nutrition promotes better assimilation of potassium and phosphorus.

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

Phosphorus

Sufficient phosphorus supply to potato helps accelerate plant development, starting from the appearance of sprouts; other developmental phases, including tuber formation, occur faster; the rate of root system formation, yield and starch content of tubers increase; their keeping quality and seed properties improve.

A lack of phosphorus in the soil leads to disruption of normal plant development: bush branching decreases, budding, flowering and tuber formation begin later. Brown spots form on tubers, starchiness and taste qualities decrease.

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

Since phosphorus is well absorbed by the soil, small doses of phosphorus fertilizers are ineffective.

Potassium

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

A lack of potassium leads to disruption of potato growth and development, affects morphological structure, and mechanical tissues and the root system develop poorly. With potassium deficiency, tubers elongate, become small, and store poorly in winter.

The effect of potassium depends on the form of nitrogen fertilizers used. Nitrate nitrogen has little effect on its action, ammonium nitrogen has a strong effect. Chlorine-containing potassium fertilizers reduce the starchiness of tubers.

The content of available potassium in the soil for potato is variable and depends on soil moisture. The higher the moisture, the more available potassium, so the effect of potassium fertilizers on yield is stronger in dry years.

Excessive potassium nutrition reduces the likelihood of diseases with macrosporiosis and ring rot.

Tuber formation

Tuber formation begins with the cessation of stolon elongation and starch accumulation, which leads to an increase in volume and weight. Tuber formation is collectively influenced by day length, temperature, photosynthetic reserves and variety. High light intensity and low nitrogen level in the plant promote tuber formation.

The three phases of tuber formation are as follows: initiation, occurring as differentiation of the bud on the stolon into the tuber primordium; enlargement, recognized by rapid cell division accompanied by starch accumulation; and maturation, which occurs when the tuber enters the dormant stage. Tuber enlargement has priority over vegetative growth and the initiation of new tubers. Simultaneously with tuber maturation, leaf aging occurs.

Tuber yield is influenced by many factors; the main influence is the duration of the growth period until leaf wilting. Late-ripening varieties usually give a greater yield than early-ripening ones due to the ability of the foliage to produce a large amount of photosynthate.

Accelerated propagation of potato varieties

For rapid propagation of promising potato varieties, accelerated propagation techniques are used: cutting tubers and cutting into parts, rooting stem tips, layers, and cuttings.

Good results are obtained by propagating potato by layers and rooting tips that have grown from plant layers (NIIKH, Filippov, 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 the sprouts reach a length of 5–8 cm, they are separated from the tubers and planted one at a time in vegetative gauze or film houses. Separation of layers from tubers can be done up to 5 times. From plants whose layers have grown to 25–40 cm, the stem tips up to 10 cm are cut off. The cut tips for rooting are immersed halfway for 6–7 h in a heteroauxin solution (0.75 mg per 1 L of water), after which they are planted in the soil. Periodic watering of plants is carried out. To reduce moisture evaporation, the planted tips are covered with polyethylene film until rooting, then it is removed. The propagation coefficient by this method reaches 212.

Another method of accelerated propagation involves placing tubers after harvest for long sprouting at room temperature (U. Hamann, East Germany). After sprouts of 1.5–2 cm appear, the tubers are kept in a gibberellin solution (2 mg/L) to stimulate growth, then sprouted under the same conditions with alternating lighting at a periodicity of 8 days until long branching sprouts appear. To prevent tubers from shriveling, the air humidity in the chamber is maintained at 80–90%. As sprouts grow, they are separated and cut into segments with one rudimentary bud. The segments are placed on moistened filter paper until roots form, which usually appear after 4–5 days. Rooted segments are planted in boxes with moistened peat. After 2 weeks, a normal plant 8–10 cm high forms from each segment, ready for transplanting into the soil. The propagation coefficient by this method for the variety Rannyaya Rosa was 1,064 (L. N. Trofimtsev).

Storage of seed tubers

An important aspect of propagation is the storage of seed tubers. Since freshly harvested potatoes do not sprout, tubers intended for propagation must be stored after harvest in order to pass through a dormant period.

The dormant state (internal dormancy) can last from 5 to 20 weeks, depending on variety, storage temperature and tuber maturity. Freshly harvested tubers usually do not sprout, even if conditions favorable for sprouting (temperature and moisture) are provided. The dormant period can be shortened at high temperatures (21–27 °C), storage at high humidity, low oxygen concentration, and also by wounding or cutting tubers. In most situations, dormancy disappears over time. Absence of growth differs from dormancy in that the former is caused by unfavorable environmental conditions.

The appearance of sprouts and subsequent growth depend on the storage period and temperature; variability is observed among varieties. Tubers are stored at low temperature, 3–4 °C, and high, 90%, relative air humidity with proper ventilation to maximize storage life and minimize premature sprout development. A storage period of 6 weeks is usually sufficient for most varieties to satisfy the dormancy requirement, although some may need longer. Temperatures below 2 °C can damage subsequent sprouts. Tubers stored at 12–22 °C have a shorter dormant period and also demonstrate stronger apical dominance compared with tubers stored at low temperatures. Exposure to light during low-temperature storage causes plants to produce many small tubers, while storage in darkness at high temperatures causes plants to produce fewer but larger tubers.

In a warm climate, the use of natural diffuse light is an inexpensive alternative to controlled-temperature storage. Exposure of tubers to diffuse light has the same effect as low temperature, limiting sprout growth and reducing apical dominance. Under these conditions, sprout elongation is suspended. In some European countries this practice is called “roguing” or greening. Greening and solanine formation are not a concern, since the tubers are not used for food.

True potato seed in commercial production

Research, mainly at the International Potato Center in Peru, has led to increased reliability of using true potato seed (TPS) for propagation. The use of TPS ensures freedom from transmission of most viruses during propagation and makes it possible to avoid the disadvantages associated with handling, storing and transporting bulky seed tubers. Therefore, TPS opens up great prospects, especially for developing countries. One hundred grams of TPS is equivalent for propagation to 2–3 tons of seed tubers. However, TPS varieties often do not differ in uniformity of tuber size, shape, color and quality and give low yield. Parental lines are currently being developed that are distinguished by better uniformity. Although the quality and use of TPS will continue to improve, these obstacles must be overcome.

Since TPS is in a dormant state, it is first used to obtain seedlings rather than sown directly in the field. Seedlings are planted after 4 or 5 weeks, when they better tolerate possible unfavorable growing conditions. Such a delay leads to lengthening of the growing season by several weeks. TPS is also sown at high density in nurseries to obtain seed tubers, which, because of their small size, are usually planted whole.

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

Degeneration

Potato degeneration is a progressive decrease in yield and quality of tubers in subsequent reproductions, which is associated with viral diseases of this 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, an important point was the discovery of the infectious nature of one of the typical forms of degeneration — leaf curl. Later, the viral nature of other degeneration diseases was established.

Degeneration manifests in:

• premature awakening of buds in tuber eyes;
• formation of elongated sprouts;
• development of small, usually diseased tubers;
• sharp decrease in plant productivity;
• damage by diseases, primarily viral.

There are several versions explaining 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 links this phenomenon with unfavorable growing conditions and disruption of plant nutrition. First of all, this is caused by high temperature and lack of moisture in the soil during tuber formation.

The viral theory assumes that the cause of degeneration is viruses. In this case, environmental conditions only strengthen or weaken the effect of viral diseases.

…there is no natural degeneration, there is pathological degeneration.

A. A. Yachevsky, Diseases of Potato Degeneration, 1925.

Potato can be affected by viruses X, S, A, Y, M, L, R. However, modern research indicates that potato degeneration is probably associated with the influence of both these factors at once: ecology and viral diseases.

…we do not need to argue whether it is ecology or virus, but must once and for all learn that it is ecology and virus. We must know when we are dealing with a virus and when with ecological degeneration.

M. S. Dunin. Results and New Tasks of Obtaining and Using Antiviral Sera for the Improvement of Seed Potatoes, 1960.

A potato plant can be infected by one or several viruses. In the latter case, plant suppression and yield losses increase. Thus, in the variety Prisekulsky Ranny when affected by viruses X and S, the yield reduction is 8%, and by viruses X, S and Af — 19%. Similar examples have been obtained for many other varieties.

According to the nature of symptoms appearing on plants, morphological characteristics of pathogens and methods of spread, viral diseases are divided into mosaics and yellows.

Degeneration can be of a non-infectious type, for example, thread-like sprouts and tuber sprouting. 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 weaken or disappear completely when plants are provided with favorable growing conditions.

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

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

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

The cause of degeneration may be the use of physiologically old tubers for seed purposes and planting potatoes in late spring. Potato varieties differ in resistance to degeneration.

Regular improvement of planting material is not always possible, as it is associated with the constant replacement of old varieties with more resistant ones. At present, the organization of seed production is underway in the northern and mountain regions of Russia, where elite material not infected with viruses is grown, with control over the propagation of promising clones. Modern achievements in biotechnology make it possible to use the results of meristem culture.

Improvement of seed material

The technology of growing seed potatoes includes the same set of agricultural practices 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 fully ripen; this especially applies to early varieties. Earlier harvesting reduces the probability of infection: the earlier harvesting is done, the more likely it is that the virus has not penetrated from the leaves into the tubers.

Also, a technique for improving potato seed material is summer planting, which reduces tuber degeneration and increases yield. When planted in late June — early July, tuber formation occurs in the cooler time (September), when abundant precipitation falls, nights become cool, and day length shortens. Overall, this favorably affects tuber formation, whereas with spring planting it occurs during the hottest period of summer, which leads to deterioration of the seed qualities of tubers.

Summer planting of potatoes has proven especially good in the North Caucasus, the Middle Volga region, the Central Chernozem zone, and also in southern Ukraine.

Repeated summer plantings and their alternation with spring plantings help maintain the yielding properties of tubers and slow down their aging as a vegetatively propagated plant.

In southern Russia, for obtaining high-quality seed material, the two-harvest culture is of importance, which involves growing two vegetative generations in one season, mainly early and mid-early potato varieties. For the second (summer) planting, freshly harvested tubers from the spring planting crop are used. For these purposes, zoned varieties with a short dormant 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 harvest when planting freshly harvested tubers, special techniques are used to artificially break the dormant period, observing certain features of agricultural technology.

Germination of tubers is related to their maturity. Physiologically young tubers, under the influence of stimulants, awaken faster and produce uniform sprouts in a shorter time. Therefore, harvesting potatoes in spring planting is carried out immediately after flowering, when tubers reach a mass of 30–50 g. Before harvesting, the tops are cut with top-removing machines or treated with a 3–5% solution of magnesium chlorate.

The dug young tubers are immediately prepared for planting. For this, they are sorted, removing small, deformed and spindle-shaped ones, washed with water for more effective chemical treatment, and treated with a 2% solution of thiourea and gibberellin at the rate of 1–2 mg of the preparation per 1 L of solution for 30–60 min. Large and medium tubers are cut into 2–3 parts of at least 20 g each, leaving 2–3 eyes on them. Small tubers are cut to a depth of 5–10 mm to stimulate germination.

When preparing tubers, sunlight must not fall on the seed material, as this can cause burns on young tubers, which subsequently leads to their rotting.

The plot for planting freshly harvested tubers should be clean of weeds, loose and sufficiently moist. Autumn and pre-planting soil cultivation is the same as for ordinary potato plantings. Black fallow or early-harvested crops, such as vegetable pea, pea-oat mixture for green fodder, and winter rapeseed, are suitable as predecessors. If there is a lack of moisture in the soil, pre-planting irrigation is carried out 5–6 days before planting so that a soil layer 50–60 cm deep is well moistened.

Fertilizers are applied under autumn plowing or after harvesting the predecessor. Fertilizer application rates: 15–20 t/ha of rotted 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.

Planting dates are chosen taking into account the climatic zone and weather conditions. Freshly harvested tubers are planted using ordinary potato planters to a depth of no more than 8–10 cm. The planting rate is 70–85 thousand tubers (parts) per 1 ha; the planting scheme is 70×15–20 cm.

Since tuber germination is slowed, it is important to ensure optimal conditions for accelerated emergence of sprouts. In particular, maintaining soil moisture at 75–85% of field moisture capacity during the period when visible sprouts appear on tubers, and 90–95% in the following two weeks until mass sprouts.

The first sprinkler irrigation is carried out immediately after planting, with a water consumption rate of 250–400 m³/ha. Subsequent irrigations are done at intervals of 4–6 days. After each irrigation, as the soil dries, harrowing with light harrows along the planting or inter-row loosening with a cultivator with goosefoot shares is carried out. It is optimal to carry out irrigation in the morning, evening or night hours. During the period of sprout emergence and until the end of the growing season, 5–6 irrigations, 2 inter-row loosenings and 1–2 hillings are done.

A technique for improving the seed and yielding qualities of potato tubers is growing them on drained peaty and floodplain soils, which are usually fertile, sufficiently moist and loose; they do not experience sharp temperature fluctuations, which rarely rise above 18–20 °C. Tubers grown on peaty soils have a thicker cork layer, fewer lenticels, a longer dormant period, and 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 obtained on peaty soils give a yield 3.5–5.0 t/ha higher when planted on mineral soils than seed tubers grown on mineral soils (NIIKH, MAA named after K. A. Timiryazev).

Improvement of planting material with an increase in its yielding qualities also occurs when growing potatoes in mountain conditions.

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

Selection of varieties

When selecting potato varieties for the conditions of a specific zone, it is advisable to simultaneously use 2–3 varieties with different earliness.

NIIKH recommends for farms specializing in potato the following ratio of varieties, in % of the total area under potato: early and mid-early varieties — 40%; mid-season varieties — 35%; mid-late — 25%. With such a ratio of varieties, it is possible to shift harvesting dates to an earlier period (August) and harvest the bulk of the potato under favorable conditions, reducing yield losses and preserving its quality.

Classification

By purpose, potato varieties are divided into:

• table varieties, distinguished by good taste qualities, non-darkening flesh and even tuber shape;
• technical (factory) varieties, with increased starch content;
• universal (table-factory) varieties, characterized by good taste qualities, even tuber shape with non-darkening flesh and increased starchiness and protein content.

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

By ripening time, varieties are divided into:

• early (50–65 days);
• mid-early (65–80 days);
• mid-season (80–100 days);
• mid-late (100–110 days);
• late (more than 110 days).

Early varieties

Priekulsky Ranniy. The variety was bred by the Priekule Experimental Breeding Station. Resistant to cancer; distributed in the central and northwestern regions of Russia, Western Siberia, the Far East, also in the Baltic states, some regions of Ukraine, and Moldova.

Belorussky Ranniy. The variety was bred by BelNIIKPO. High yield, resistant to cancer, medium resistance to viral diseases. Good taste qualities, satisfactory keeping quality. Cultivated in Altai Krai, Kaliningrad, Moscow and Oryol Oblasts, also in Belarus, some regions of Ukraine and Estonia.

Prigozhy 2. Bred by BelNIIKPO. Resistant to cancer and potato nematode. Late blight damage is above average, viral diseases — weak. Cultivated in Bryansk, Vladimir, Tver and Kaluga Oblasts, also in Belarus.

Borodyansky.

Varmas.

Pirminės.

Sedov.

Kharkovsky Ranniy.

Khibinsky Ranniy.

Priobsky.

Volzhsky.

Vesna.

Vyatka.

Iskra.

Falensky.

Uralsky Ranniy.

Zhukovsky Ranniy (1993).

Izora.

Mid-early varieties

Volzhanin. The variety was bred by the Ulyanovsk State Regional Agricultural Experimental Station. High yield, drought-resistant table variety with good taste qualities. Grown in the Middle and Lower Volga region, North Caucasus and Western Siberia.

Lyubimets. A table variety bred by NIIKH. High yield, with high taste qualities. Resistant to cancer. Cultivated in Moscow Oblast, Stavropol Krai, Chechnya and Ingushetia.

Penzenskaya Skorospelka. Bred by the Petrovsk Selection Experimental Station of the Research Institute of Agriculture of the Southeast. A table variety with high taste qualities, good keeping quality. Resistant to drought and cancer. Cultivated in Lipetsk, Penza, Ryazan, Tula, Tver Oblasts, also in some regions of Kazakhstan.

Kolpashevsky. The variety was bred by the Narym State Breeding Station. A table variety with good taste. Resistant to cancer. Grown in Krasnoyarsk Krai, Kamchatka and Sakhalin Oblasts, Bashkiria, Komi and Tuva Republics.

Ulyanovsky. A table variety bred by the Ulyanovsk State Regional Agricultural Experimental Station. High yield, drought-resistant. Increased resistance to ring rot. Grown in the Middle and Lower Volga region, southern Urals and North Caucasus.

Petrovsky.

Detskoselsky.

Laimdota.

Pioner.

Polessky Rozovy.

Arina.

Agria.

Nevsky (1982).

Mid-season varieties

Gatchinsky. A table variety bred by the Northwestern Research Institute of Agriculture. High yield. Good taste qualities, with good and excellent keeping quality of tubers. Resistant to cancer. Cultivated in the northwestern regions of Russia and Ukraine.

Kameraz. A universal variety bred by VIR. High yield, good taste qualities and keeping quality. Resistant to cancer. Grown in Kaliningrad, Leningrad, Novgorod, Pskov, Sakhalin Oblasts.

Ogonyok. A table variety bred by BelNIIKPO. Good taste qualities and keeping quality. Resistant to cancer, relatively resistant to late blight. Cultivated in North Ossetia, also in Belarus, Cherkasy and Chernihiv Oblasts of Ukraine.

Stolovy 19. A table variety bred by the Northwestern Research Institute of Agriculture. High yield, medium starchiness. Good keeping quality and taste qualities. Resistant to cancer and late blight. Grown in the west and northwest of the Non-Chernozem zone, also in Ukraine.

Anar.

Alma.

Katadin.

Mechta.

Ostrovsky.

Peredovik.

Zarechny.

Krasnopolsky.

Lugovskoy (1987).

Lybid.

Mid-late varieties

Lorkh. A universal variety bred by NIIKH in 1931. One of the most widespread varieties. High yield and taste qualities. Good keeping quality. Starchiness up to 22%. Resistant to late blight, ring rot and other diseases, except cancer. Cultivated in Russia, Ukraine, and Central Asian countries.

Sulev. A table-factory variety bred at the Jõgeva Experimental Breeding Station of the Estonian RI of Agriculture and Land Reclamation. Medium and increased starch content. Good taste qualities and keeping quality. Resistant to cancer, relatively resistant to late blight, affected by scab and rhizoctonia. Grown in Vladimir and Pskov Oblasts, also in the Baltic states and Ukraine.

Yantarny. A table variety bred by the Bolshevik experimental farm of VIR. Medium starchiness. Satisfactory and good taste qualities, good keeping quality. Resistant to cancer, weakly affected by late blight and rhizoctonia. Grown in Moscow Oblast.

Vita.

Ideal.

Istrinsky.

Loshitsky.

Biryusa.

Verba.

Ramensky.

Filatovsky.

Late varieties

Temp. A universal variety bred by BelNIIKPO. High yield and starchiness. Excellent taste qualities, cooks well. Good keeping quality. Resistant to aggressive races of cancer, slightly affected by late blight, relatively resistant to common scab. Cultivated in Bryansk, Tver, Ryazan Oblasts, also in Belarus and Ukraine.

Razvaristy. A universal variety bred by BelNIIKPO. Can be grown on peat-bog soils of Vitebsk, Gomel and Minsk Oblasts of Belarus.

Pavlinka. A table-technical variety bred by BelNIIKPO. High starchiness. Good keeping quality. Resistant to cancer, relatively resistant to late blight. Grown in Minsk Oblast.