There are thousands of potato varieties worldwide and are available for home gardening purposes as well as for commercial growing. Genetically modified varieties are also available now.

Classification of Potato Varieties: Potato varieties are often classified based on the colour of the tuber, length of the growing season of the plant and cooking quality of tubers. Based on tuber colour, there are brown potatoes or russet potatoes (tubers have brown skin), red potatoes (tubers have red skin), white potatoes (tubers have white skin), yellow potatoes or Yukon potatoes (tubers have yellow skin) and purple potatoes (tubers have purple skin). Based on the growing season, potato varieties are categorized into Early, Medium and Late varieties. Based on cooking quality, there are baking/frying potatoes, boiling/table potatoes and chipping potatoes.

Early Varieties of Potato: These are early-maturing varieties of potato and the crop will be ready for harvesting in 2-3 months. A detailed account of some early varieties of potatoes is given below:

  • Satha is an early, low-yielding variety that can be harvested in 2 months
  • Gola is an early variety of potato with large, pear-shaped, white tubers and cream-coloured flesh
  • Up-to-Date is an early-maturing potato variety and is one of the most popular varieties in India
  • Kufri Chandramukhi, Kufri Khasi-Garo, Kufri Alankarand and Kufri Lauvkar are a few of early maturing varieties (70 -100 days) developed in India

Medium and Late Varieties of Potato: Medium varieties of potato plants will be ready in 3-4 months while late varieties will be ready for harvest in 4-6 months. Some examples of medium and late varieties of potato plants are given below:

  • Craig’s Defiance, Great Scot, and President are some English varieties of potato that need 3-4 months to mature
  • Phulwa is a late-maturing (4-5 months) European potato variety
  • Darjeeling Red Round, Kufri Kisan, Kufri Kumar, Kufri Neela, Kufri Jeewan are late-maturing Indian varieties

Based on the cooking quality, there are mainly three types of potatoes. A brief account of these potatoes is given below:

  • Baking Potatoes: Baking or frying potatoes are good for baking, roasting, and frying purposes and will have starch level between 20 and 22%
  • Boiling or Table Potatoes: Boiling or table potatoes have 16–18% starch
  • Chipping Potatoes: Chipping potatoes are good for making potato chips

While growing potato plants, selection of a suitable variety is important as well as the purpose of growing, whether for home consumption or for commercial purposes. A detailed account of various commercial growing practices for potato plants is given below:

Climatic and Soil Requirements: Potato is basically a cool season crop and is slightly tolerant to frost; heavy frost may kill the plants. Favourable temperature for plant growth and tuber production is between 18 and 20 degree Celsius. Tuber formation stops at soil temperature of 27 °C (81 °F) or more. Loose, friable and porous soils with good aeration are best for tuber production. Soil should be well drained, well aerated, deep and fertile with pH between 5 and 6.

Propagation: Potato is propagated by seed potatoes or by tuber cuttings. If tuber cuttings are used, each tuber piece should have 2-3 viable eyes and should be of 50 mm diameter in size. It should be weighing about 50 grams.

What are seed potatoes? Seed potatoes are the potato tubers that are grown as planting materials with special care in selected locations with specific growing conditions such as a location with cool environment and are free of potato pests and diseases.

Planting materials should be healthy, free from diseases and defects, firm and sound with viable sprouts. Freshly harvested tubers have a dormant period of 2 to 3 months and this dormancy can be broken by treating the tubers with specific chemicals (such as thiourea, ethylene chlorohydrin or potassium thiocynate). Rate of seed tubers varies from 1 – 1.5 tons/hectare. (Note: 1 ton = 1000 kg and 1 hectare = 10000 square meter.)

Planting: In the tropics, seed potatoes may be planted during the second half of the year when climate is moderate and cool. Recommended spacing is 45 – 60 cm x 15 – 30 cm according to the variety and size of seed tubers/tuber cuttings.

Growth Phase of Potato Plant: A detailed account of various growth phases of a potato plant is given below:

  1. Emergence of sprouts and roots from seed potatoes: This is first stage of plant growth
  2. Development of shoot system (leaves and branches) and root system: Newly emerged sprouts grow into multiple leaves and branches. Simultaneously, roots also grow into a well-defined root system
  3. Development of stolons and new tubers: Stolons start developing from the axils of lower leaves which grow downwards into the ground
  4. Tuber formation and flowering: New tubers start developing on these underground stolons; flowering may begin at this phase
  5. Tuber bulking and development: Tubers grow in size and a good tuber yield is obtained at optimum soil temperature (18 – 200C)
  6. Tuber maturity: When tubers reach maturity stage, leaves start yellowing and eventually the whole plant dies; the tuber skins harden and starch level increases (sugars in the tubers convert to starches)

Site Preparation: Site is prepared by 2-3 successive ploughings followed by levelling and incorporation of organic manures into the top soil. Potato is a shallow-rooted crop and heavy feeder and therefore, top soil should be highly fertile with lots of plant nutrients. Well-rotten FYM (farmyard manure) or compost @25-30 tons per hectare may be incorporated in the soil almost one month before planting.

Manures and Fertilizers: It is estimated that a yield of 25 tons per hectare of tuber removes 110 kg of nitrogen, 50 kg of phosphate and 225 kg of potash from the top soil. Recommended fertilizer doses for 1 hectare area is 600kg ammonium sulphate, 500kg single superphosphate and 140 kg of potassium sulphate. Of these, 400 kg of ammonium sulphate and full doses of single superphosphate and potassium sulphate are applied in furrows at planting time. Remaining 200 kg of ammonium sulphate is top-dressed just before the first earthing-up.

Earthing up and Mulching: First earthing-up should be done when the plants are about 30 cm high. Second earthing-up is done to cover the tubers in order to protect tubers from direct sunlight exposure. Tuber exposure to sunlight leads to greening of the skins and the development of solanine (a toxic compound) in the tubers. So tubers should be protected from direct exposure to sunlight. This can be done by earthing up or mulching. Earthing up is nothing but a practice of piling up soil around the base of the plant. Mulching is a practice of covering the growing area with organic mulches such as straw, saw dust or leaf mould or by plastic sheets/polythene covers.

Irrigation: As mentioned earlier, potato is a shallow-rooted crop and therefore it draws water from surface soils. Soil moisture in the surface soils are prone to evaporation loss and therefore regular watering at frequent intervals is needed to keep the soil moist always, especially during the initial growth phase of the plants. During tuber formation stage, frequent irrigations are not needed. As a general rule, when the soil moisture is below 50 % of field capacity, field should be irrigated. It is estimated that approx. 24 acre inches of water in about 6 irrigations may be sufficient for a commercial crop of potatoes.

Weed Control: Manual and mechanical weed control practices such as mulching, hoeing and earthing up are recommended. Chemical and synthetic weedicides/herbicides are to be avoided due to the health risks.

Insect-Pest Management: Major insect-pests of potato crop are aphids, tobacco caterpillars, tuber moths, leaf hoppers, white grubs and cut worms etc. Some of these are explained below:

Aphids: Aphids are tiny, pear-shaped, yellowish green or white or brownish dark coloured sucking insects that appear in clusters on plants and feed on leaf juices thus causing mottling and malformation of leaves. These insects can be organically controlled by introducing their natural enemies or predators in the field. Major predators of aphids are Lady bug beetles, Lacewing, and Syrphid flies. In less severe cases of infestations, plants may be sprayed with strong current of irrigational water which may wash of aphids from the plants.

Leaf hoppers: Potato leaf hoppers are pale-green, winged insects about 2-3mm size which suck sap from the leaves and stems. In severe cases of infestations, leaf curling occurs followed by yellowing of the leaves; leaves later turn brown and brittle. Leaf hoppers may be controlled by spraying recommended organic insecticides such as pyrethrums.

White grubs and Caterpillars: Both larvae/caterpillars and adult beetles of these pests attack and feed on tubers. They can be controlled by using light traps, and pheromone traps. Hand picking and destroying the larvae may also be effective in case of minor infestations.

Cut worms: There are both black cutworms and white cut worms. They attack on young seedlings by cutting them at the base near the soil. They can be controlled by using light traps, and pheromone traps. Hand picking and destroying the larvae may also be effective in case of minor infestations.

Potato Tuber Moth: They are winged insects attacking potato tubers by making tunnels through the tubers. They can be controlled by using light traps, and pheromone traps. Collecting and destroying the infected tubers may also be effective in case of minor infestations. Spraying biopesticide formulation involving Bacillus thuringiensis @1 kg/ha at 10 days intervals may also be effective.

Disease Management: Major diseases of potato crop are fungal diseases (blight, scab, wilt, soft rot, and wart), viral diseases (mosaic and leaf roll disease), bacterial diseases (wilt) and mycoplasma diseases (purple-top roll, witch’s broom, phyllody).

Late Blight and Early Blight: Late blight is a fungal disease caused by Phytophthora infestans. Early blight is a fungal infection caused by Alternaria solani. Symptoms include dark-brown or black leaf spots in both cases. Late blight is a severe disease where appearance of leaf spots is followed by wilting or drying of leaves and stems; in severe cases of infestations, white mildew is present on the lower surface of leaves. Control measures are same for both diseases and include use of disease-free planting materials and proper drainage of the fields as damp soils facilitate spread of the disease.

Common Scab: This is a fungal infection caused by Streptomyces scabies. It affects tubers and the affected tubers have rough corky lesions. The disease is common in soils having high pH and therefore in most cases, scab disease is controlled by maintaining the soil pH at 4.5 to 5. Planting scab-resistant potato varieties is also effective.

Verticillium Wilt: This is a fungal disease caused by Verticillium spp. and is spread through the soil. Major symptoms include wilting and discoloration of vascular tissues; sometimes ‘eyes’ of the infected tubers may turn pink. Control measures include proper soil treatment with a recommended fungicide before planting, use of disease-free planting materials, and use of resistant varieties.

Wart Disease: Black wart is a fungal disease caused by Synchytrium endobioticum. Major symptoms include abnormal growth of spherical, green to dark coloured, warts on stems, stolons, and tubers. The disease is spread through the soils. Control measures include soil sterilization by steam or sterilization of soils by using chemicals such as mercuric chloride, copper sulphate or 5% formalin solution.

Bacterial Brown Rot or Wilt: This is a soil-borne bacterial disease caused by Pseudomonas solanacearum. Major symptoms include wilting, stunting and yellowing of the foliage followed by collapse of the entire plant. Skin of the infected tubers is discoloured. Control measures include use of disease-free planting materials, soil treatment with sulphur-lime mixture and planting of resistant varieties.

Latent Mosaic Virus and Mild Mosaic Virus: Latent mosaic disease is caused by virus X and virus S. Mild mosaic is caused by virus ‘A’ alone or in combination with virus ‘X’. Virus is transmitted by aphids and white flies. Major symptoms include mottled and malformed leaves. Viral diseases are very difficult to control. Best way to control viral diseases is to control aphids and whiteflies which will prevent further spread of the diseases. Planting disease-free planting materials and mosaic-resistant varieties may be effective in some cases. Uprooting and destroying diseased plants are also found to be effective.

Rugose or Vein-Banding Mosaic Disease: Rugose mosaic is caused by virus ‘Y’ alone or in combination with virus ‘X’. Major symptoms include stunted plant growth, mottled and malformed leaves, necrotic streaks on leaves and stems and brittle leaves. Control measures are same as those of latent mosaic disease.

Leaf Roll Disease: Leaf roll is caused by virus infections and the affected leaves become cupped and rolled upwards; the leaves become leathery-textured and brittle. Leaf roll virus is transmitted by aphids and white flies and therefore the best control measures include control of these vectors. Use of disease-free planting materials and uprooting and destroying of diseased plants are also found to be effective.

Purple-Top Roll: This is a disease caused by mycoplasma and the growth of the affected plants is stunted with the upward rolling of young leaves. Later the infected leaves turn to purple to pink colour; hence the name ‘purple-top roll’. These mycoplasma pathogens are transmitted by leaf hoppers (Alebrodes spp.) and therefore the best control measure includes control of leafhoppers. Tuber development in affected plants is unhealthy and tubers remain small and aggregate around the main stem.

Witch’s Broom: This is a disease caused by mycoplasma pathogens and the plant growth is stunted in affected plants. The affected plants produce broom-like, numerous needle-like, colourless stems with small leaves in a cluster and hence the name ‘witch’s broom’ is given for this disease. The infected plants generally do not produce tubers.

Potato Phyllody: Potato phyllody is caused by mycoplasma and the affected plants produce hairy and chlorotic leaves. This mycoplasmal pathogen is transmitted through tubers and therefore the best control measure includes use of pathogen-free planting materials.

Charcoal Rot: It is a fungal infection of tubers caused by Macrophomina phaseoli. This is a storage disease of potato tubers and the best control measure includes surface disinfection of tubers with some mercurial fungicide before storage.

Root-Knot Nematodes: Golden nematode or root knot nematodes are a serious soil-borne pathogen of potato plants. Since the pathogen is spread through soils, soil treatment with a recommended nematicide is advised before planting. The infected plants form galls in the roots which adversely affect root absorption of plant nutrients from the soil and as a result, the plant growth suffers.

Harvesting and Yield: Potatoes may be harvested from the time tubers are mature and of sufficient size until the plants have fully died. Potatoes are normally dug out by using a long-handled spading fork or potato fork. For large plantations, potato harvesters are used. Average yield of early-maturing varieties is about 200 quintals/hectare and that of the late varieties is about 300 quintals per hectare. Under good cultural management practices with high-yielding varieties, a yield up to 500 quintals per hectare may be obtained.

What are Creamer Potatoes? Creamer potatoes are immature, tender, small potatoes known for their texture and taste. Creamer potatoes are harvested when the tuber is still young, small and immature and measures about 2.5 cm in diameter. Creamer potatoes have waxy skin, low starch level and high moisture content.

Curing of Potatoes: Curing is an important post-harvest operation in potatoes. Curing process involves exposing of freshly harvested tubers to warm temperatures for a few days so that tuber skins get hardened. During curing process, any wounds and injuries on the skin may be healed. Curing is done at 50 to 60OF (10 to 16OC) with high relative humidity (95% RH) and good ventilation (gas-exchange). Curing of potatoes normally last for 8 days. Cured potatoes are resistant to skinning damage during storage and post harvest handling process. Cured potatoes are resistant to post harvest pests and diseases during storage. Storage life of cured potatoes is up to 5 months at 4°C (39°F) and 95 % RH (relative humidity).

Storage at Room Temperature: Freshly harvested potatoes may be stored at room temperature for immediate consumption or for selling in the local markets. While storing the potatoes in rooms, make sure that the room is hygienic and with good ventilation. Doors and ventilators should have insect-proof wire-nets to prevent the entry of insects-pests. Potatoes can be stored in single layers on sand. Discard all infected and rotten potatoes as soon as they are spotted.

Traditional Storage in Underground Pits: Large pits (75cm deep x 2.5m long x 1m wide) are made in a cool shady location. Pits are watered to keep the soil moist; after 2-3 days, pits are lined with neem leaves (neem leaves have insect-pest repellent and disease-fighting properties). After that, the pits are fitted with bamboo chimneys or similar structures (so that moisture from stored tubers are collected in these structures and later disposed off). Later, tubers are stored in these pits (leaving 15cm space on top which is filled with dry grass or similar materials). Finally, a small roof/thatch is constructed over pits for protection from winds and rains.

Home Storage of Potatoes: At homes, potatoes can be stored at room temperature for a few weeks. Potatoes should always be stored in well-aerated containers. Jute bags, bamboo baskets, tubular nets etc are suitable for storing potatoes at homes.  Never store potatoes in plastic bags because moisture accumulated inside the plastic bags causes rotting of potatoes. Do not eat potatoes with green skin or sprouted potatoes. ‘Solanine’ a plant toxin (present in all nightshade vegetables), may be present in these potatoes and hence such potatoes are inedible.

Physiological Changes during Storage: High starch and low sugar content is desirable in potatoes and hence optimum storage conditions should always be maintained to prevent sugar formation in the tubers. Sprouting is not desirable; a pre-harvest spray of maleic hydrazide (0.3%) will be effective in controlling the sprouting.

Physiological Disorders of Potato: Major physiological disorders of potato are:

  • Black heart: Black heart is common in poorly aerated storages where proper storage temperature is not maintained
  • Freezing injury: When potatoes are stored below 00C , they suffer freezing injury and the affected tubers are discoloured and spongy

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