भारत में बीज आलू की गुणवत्ता को प्रभावित करने वाले कारक

Seed is a critical input in potato cultivation and accounts for about 40-50% of the total cost of cultivation. Most significant constraint in lower productivity is attributed to lack of quality seed tubers especially to small and marginal farmers in India. Varietal purity, seed health, physiological age, prevalence of pest and diseases, change in virus vector relationship and poor  knowledge of seed selection and ignorance about Seed Plot Technique are the important aspects which affect the seed potato quality.

Pre harvest and post-harvest factors viz selection of variety, area of seed production/ climatic conditions, agronomy/ agro technique of seed production, size of tuber, rouging, plant protection measures, harvesting, post harvest handling and storage are the important factors which affect quality of seed potato production.

Potato is one of the world’s most important non-cereal, high yielding horticultural food crop. Potato in India is mainly grown in the Indo-Gangetic plain, both an important staple and a cash crop. But now it is being cultivated in almost all the States of India under different agro-climatic conditions.  India has taken a giant leap in area and production of potato since independence and is the second-largest producer of potatoes in the world accounting for 11.3% of the global area and contributes 12.5% to global production (NASS, 2021). In 2020-2021, India produced more than 54.23 million tons of potatoes from 2.24 million hectares area with an average productivity of 24.12 tons/ha (FAO, 2023). 

 Sustainable potato production depends on a constantly renewed supply of disease free planting material, improving quality seed production and seed distribution. Under potato, cultivation seed is the highest cost-bearing input accounting for 40-50% of the total cost of its cultivation. More than 90% of seed potatoes in developing economies is produced in the farmer-based category and is of poor quality. Effective seed systems is providing access to quality planting material, at the time needed, at a fair price, to all who need it. In wealthier countries, greater than 90% of potato seed is obtained through formal certification systems. In developing countries like India, seed acquired informally by producing it on-farm or by sourcing from local markets, neighbors, traders. India projects to produce 70 MT of potato from an area of 2.6 million ha with a productivity of 27 t/ha by 2030. Hence there is increasing seed potato demand. To bridge the gap between demand and supply of seed potatoes, it is imperative to develop seed potato hubs at farmers' level and this would certainly help to meet the future seed requirements.

Quality seed in potato and its importance

Like other crops, high yields of potato (Solanum tuberosum L.) revolves around use of high-quality seed potatoes. Since potato is a vegetatively propagated plant, fungal, bacterial, and especially viral diseases easily affect seed tubers which are responsible for fast degeneration, requiring seed replacement after every four years. Additionally, the quality seed is either unavailable or out of the reach of poor farmers owing to high seed cost. The seed related issues are further intensified due to restricted accessibility to seed producing regions, transportability of quality seeds. One major constraint resulting in lower productivity   in   the   country   is   the use of poor-quality seeds. Quality seed can increase the yield by 15 – 20.

Seed Plot Technique

Technology that revolutionized potato cultivation in India is the innovative technique of producing healthy planting material in the sub-tropical plains of India that is popularly known as “Seed Plot Technique”. Technology is based on a simple but profound observation on population dynamics of the virus vector and basic principles of low aphid period of at least 70-75 days for growing seed crop. Essentially, the   potato   seed   production   programme  is  based  on  elimination  of  the  prevalent  viruses  in  a  given  region  from  the  seed stock and its further multiplication under vector  free  /  low  vector  pressure  conditions. Seed production is very technical aspect and needs careful attention during all stages like date of planting, spacing, fertilization, top-dressing, irrigation, roguing, weeding, earthing up, spraying of pesticides, date of dehaulming, harvesting, etc.

Factors influencing seed potato tuber quality

Seed tuber quality defined as the ability of a seed tuber to produce a healthy, vigorous plant that produces a high yield of good quality within the time limits set by the growing season into which the seed is going to be used. In India, ICAR- Central Potato Research Institute (CPRI) produces about 2,400 tons of breeder’s seed (basic seed) every year and supplies 80% of it to the states and other agencies for its multiplication. If this stock has to multiply in three stages, i.e., foundation 1, foundation 2, and certified grades (as per norms), we can produce only about 0.5 million tons of certified seed. On the assumption of a 100% seed replacement rate (SRR), it meets only 10% of the total seed requirement, leaving a deficit of about 4.9 million tons. The situation is further aggravated by the fact that the breeder’s seed supplied by ICAR-CPRI is seldom multiplied in three recommended generations by the states. Hence there is a huge gap between demand and supply of quality seed.

Farmers in India, especially the marginal and small farmers, rarely store their harvests as seeds for the next growing season. Often, they buy seed potatoes every season, making the seed replacement rate (SRR) almost 100%. Most of the farmers cited the inadequate availability and high price of certified seed as main reason for low SRR. Next in importance was the untimely availability of seed. Farmers in India often have four major sources of seed: seed purchased from a formal seed industry, seed purchased from informal seed industry, seed obtained from other farmers and self-retained seed from the previous year’s produce. There is no institutional mechanism to monitor the quality of seed potatoes. Most often, degenerated produce is sold as seed, especially to small and marginal farmers who lack finances. Non availability of quality seed was considered as major problems faced by potato growers.  Hence farmers uses self-retained seed from the previous autumn crop for potato cultivation and there is no standard seed supply system. Successive   multiplication   of   seed   tubers   in  the  field  magnifies  the  risk  of  infection  and  build-up  of  several  bacterial,  fungal,  nematode and viral pathogens. Degenerated seed lowers the productivity to the extent of about 40 per cent. Factors affecting seed are pre and post harvest are describe below

Pre Harvest Factors:

1. Agronomic Practices

The aim of crop husbandry varies between seed and ware potato production system. High rate of multiplication, maintaining health and optimum physiological quality of seed tuber are the main focus in seed potato production whereas, in ware potato production system, high yield and disease control upto economic level as well as consumption and processing quality of tubers are given priority. However, the final quality and quantity of potato yield is determined by the quality of the potato seed tuber used at the time of planting. Production of better quality seed potato could be achieved by following appropriate practices starting from site selection, timely application all inputs like nutrients, water and crop protection measures.

Soil/ field preparation

Potato grows well at pH 5.5.to 8.5 in sandy loam, sandy and clay loam soils but the best soil is with pH 6.0 to 7.0. Potato crop production demands well prepared soil since expansion of tuber needs enough amount and optimum textured soil and also for ease of harvesting. In plains, summer ploughings should be done during May-June and prepare the fields for potato planting in September-October. Three years crop rotation during seed potato production should be followed to prevent build up of soil-borne pathogens in the field. Raising and ploughing under the 45-55 days old green manuring crops of sunhemp (Crotalaria juncea) or dhaincha (Sesbania aculeata) during rainy season at least one month before potato planting for proper decomposition is beneficial in reducing pest and disease incidence. The seed crop is separated from crops meant for “ware’ purpose by a distance of at least 25 meters to avoid mixture and spread of viral diseases. An isolation distance of 05 meters is also required between different varieties of the seed crop.

Planting time and depth

An appropriate planting time is important since the growing condition, which the crop faces afterwards, determined by the time of planting. Planting before the optimum window tends to reduce yields by exposing the crop to abiotic and biotic stresses, such as unfavorable soil conditions and insect vectors particularly thrips and whiteflies which tend to reduce yield. Likewise, planting after the optimum window also reduces potential yield by reducing the days available for plant growth and tuber bulking. As per seed plot technique schedule of planting, dehaulming and harvesting for different regions is described under table1 which should be strictly followed for high quality seed potato production. Optimum planting time for potato crop is the period having temperature maximum 30-32^°C and minimum 18-20^OC. In seed crop, the aphid free period of growth is also an important consideration. Planting must be completed in a time schedule to ensure 75-85 days of low aphid period for crop growth.

Table 1 Schedule of planting, dehaulming and harvesting for different regions

Appropriate planting depth is one of the main agronomic practices required for potato production, this is because, potato tuber economical part of the crop is produced underground. Planting depth determines the time and energy the sprout requires to emerge, thereby early establishment and vigour are affected which are vital in seed potato production. Deep planting may result in delayed ground cover, may results in reduction in the number of stems also  helps to overcome tuber greening. Planting potato in shallow depth results with declined marketable yield and gross income from potato crop production. Seed tubers should placed at a depth of 5-7 cm from top of the ridges made manually or by tractor drawn implements.

Plant population/ spacing

Potato crop needs to get enough intra and inter row spacing to allow maximum initiation of number of stems / plant as well as an optimum number and better quality tuber formation. The optimizing of plant density is one of the most important subjects of potato production management because it affects seed cost, plant development, yield, and quality of the crop. An ideal combination of plant population, row width, and in-row seed spacing for a particular variety. Under Indian condition, in the plains inter-row spacing for planting seed crop manually, bullock and tractor drawn implements  may be kept at 40-45, 50-55 and 60 cm, respectively. Planting of seed-sized tubers of 30-40 g at 60 cm inter and 20 cm intra-row spacing is best for seed potato production under SPT. Adjustment of spacing according to the size of seed tubers is essential and to keep the seed rate reasonably within limits (32-35 q/ha). A plant population of about 1 to 1.1 lakhs hills/ha to ensure a stem density of 40-45/m² is adequate for best results. Plant the large size tubers by increasing the intra-row spacing from 20 to 30 cm depending upon the size of seed tubers. Small-sized tubers are planted at reduced intra-row spacing.

Seed tuber size

Size of seed tuber is an important factor to decide the seed per unit area because it affects total yield and graded or marketable tuber yields. The approximate intra-row spacing for <25, 25-60, 60-100 and > 100 g seed size tubers is 15, 20, 25 and 30 cm with inter-row spacing of 60 cm, respectively is suggested under  SPT. If seed tubers are too small, they will have a small number of stems that produce only a few tubers, thereby reducing yield. On the other hand, too big seed tubers may result in the production of too many stems, which eventually produce too many tubers that may compete for growth factors in soil and become too small.

Water/ irrigation management

A potato crop is sensitive to water shortage. Hence, to meet the water requirement and reach with high quality and quantity of final potato tuber yield, efficient and effective water management is crucial. Irrigation requirements differ with locations, soil types, and cultural practices. Regular monitoring of soil moisture content, scheduled watering and having water resource and/or irrigation system capable of providing the required amount of water are the most important factors to address effective water management in potato production and thereby to achieve the desired quantity and quality potato tuber production.

Pre-planting irrigation before land preparation is beneficial for early and uniform emergence. If omitted at the time of field preparation, irrigate the crop immediately after planting. First irrigation following planting should be light to minimize damage to the newly formed ridges. Heavy irrigation before emergence leads to anaerobic conditions resulting in rottage of seed tubers, gappy emergence and reduced tuber yields. Second irrigation is given a week after first irrigation. Subsequently, irrigate the crop at 7-10 days’ interval depending upon the requirement. Avoid flooding over the ridges while irrigating and irrigate as far as possible in morning and evening hours. In a normal season, potato seed crop 6-8 irrigations are required. Light and frequent irrigations are much better than less frequently given heavy irrigations. Stop irrigation at about 10 days before dehaulming in light soil and 15 days in heavy soils.

Nutrient Management

Maintaining the fertility of the soil is one of the most important agronomic practices needed to be followed in potato production. Application of well rotten farmyard manure (FYM) @ 20-25 t/ha or vermicompost @ 3-4 t/ha in absence of green manuring is beneficial for seed crop. The FYM/vermicompost should be incorporated into the soil 20-25 days before planting. Proper management of N, P, and K fertilizers are considered very important to maximize tuber yield and attain desirable quality. Potato is particularly sensitive to a steady supply of nitrogen fertilizer. Fertilizer N needs of seed crop are 25-30% lower than the ware crop. Crop requires a basal dose of 75 kg N, 60-80 kg P₂O5 and 100-120 kg K₂O/ha at planting. The nitrogen fertilizer demands of the potato crop varies between different growing stages which is relatively high during the periods of high tuber growth rates which warrants the importance of split application of nitrogen. Hence Split application through urea is recommended in seed potato production under SPT. The basal dose of N can also be applied through urea by incorporating into the soil at least 48 hrs before planting during field preparation. If seed crop is grown under drip irrigation, nutrient dose in general should be reduced by 25% due to increased nutrient use efficiency on account of splitting/localized applications on demand.

Roguing for healthy seed

Roguing is an essential practice in the production of healthy seed potatoes in which diseased and off type plants along with tubers and seed pieces are disposed. The affected plants may be diseased, another variety, or simply different. Only plants showing visual symptoms can be rogued. The plants infected with severe mosaic can be easily identified but it is difficult to identify the plants with mild mosaic symptoms. However, it can be identified by a person who is well trained in identification of virus symptoms. Generally, roguing should be done in the morning hours from 10 to 11 AM after drying of dew and evening hours from 3 to 5 PM. Light intensity is to be taken into consideration for better identification of mild mosaic symptoms. The first roguing is done 45 days after planting, Second roguing is done after 60 days after planting and the third is done 75 days after planting or 3-4 days before dehaulming. At each roguing, make it sure to remove the tuber and tuberlets of rogued plants.

2. Climatic factors

Climatic factors influence the production of potato by affecting three phenological phases during preharvest. Potato growth and final yield is determined by an intricate interaction between soil temperature, air temperature, solar radiation and photoperiod duration

Photoperiod /Daylength

The main climatic factors controlling tuber formation are night temperature and day length. For best yields, potato crop needs long day conditions during growth and short-day conditions during tuberization. Potato plants forms tubers on stolons if conditions for the induction, initiation and subsequent growth of tubers are favorable. Primary stolons can form branches and can have numerous potential tuber sites. One of the factors determining tuberization is the photoperiod. Tuberization is favored by days shorter than a critical photoperiod. The short-day signal triggers a leaf factor that is one of the components of the tuberization stimulus. Longer photoperiod delay the onset of tuber growth and the onset of tuber bulking, probably more at higher than at lower temperatures. Longer photoperiods also reduced the relative partitioning rate.

Air temperature and light

Potato (Solanum tuberosum L.) tuberization is a complex developmental process that requires the interaction of environmental, biochemical, and genetic factors. Low mean temperatures (15-19°C) under short photoperiod (12 h) are optimal for tuber initiation and early tuber growth. High temperatures interrupt the tuber initiation and bulking, decrease the rate of tuber growth, and assimilate partitioning to the above-ground parts is being favored. Under cool temperatures and short photoperiods, a transmissible signal is activated that triggers cell division and elongation in the sub-apical region of the stolon to produce tuber initials. Temperatures 15-19°C are optimal for tuber initiation. Tuber induction influence mainly by an interaction between cultivar and temperature. Hence planting the seed potato crop during favorable temperature is essential for high quality seed production. 

Soil Temperature and Its Management

Soil temperature has its contribution towards hastening sprout emergence. The rate of development of sprouts from planted seed pieces depends on soil temperature. Very little sprout elongation occurs at 6°C, slow at 9°C and is maximized at about 18°C. The time between planting and emergence depends on soil temperature. Accordingly, warmer soil temperature positively affects the emergence as far as the moisture content of the soil is in adequate level. Management practices, such as planting population density, use of mulch and irrigation might substantially modify the soil temperature regime within the root zone in such a way as to affect stolonization, tuber initiation and bulking, and tuber enlargement at a given site.

Atmospheric Humidity and Wind/Wind Management

Most of the contributions related to the influence of RH on potato refer to potato storage where RH is an important factor in tuber weight loss and the occurrence and severity of diseases and pests. Wheeler et al. (1989) studied the effect of two RH levels, 50% and 85%, on the physiological responses of three cultivars of potato (Russet Burbank, Norland, and Denali) in controlled-environment rooms under continuous light intensity at 20^oC. No significant differences in total plant dry weight were measured between the atmospheric humidity treatments, but plants grown under 85% RH produced higher tuber yields. Leaf areas were greater under 50% RH and leaves tended to be larger and darker green under drier than at more humid atmospheric conditions. The elevated humidity appeared to shift the allocation pattern of photosynthates to favor allocation to the tubers over leaves and stems. Wind has important effects on potato. Wind also affects transpiration rates and, therefore, photosynthetic activity and crop yield. At sites where winds are frequently strong throughout the year, increased stomatal resistance can cause reduction in potato yield. At such sites, guidelines for the sustainable management of potato cropping systems need an emphasis on windbreak development including height, porosity, and orientation.

3. Genetic factors

The appropriateness of the variety or genetic quality of the seed is the adaptability to specific growing conditions and biotic or abiotic stresses and its food and processing quality characteristics. Growers have the choice of selecting preferred cultivars prior to planting crop. In potato, a great deal of plant breeding has been done to provide a wide range of varieties with different quality attribute. This can be seen in the wide range potato varieties available to growers for planting based on shapes, sizes, productivity levels, dry matter and taste attributes vary, as well as the ripening times and rates and postharvest longevity. Potato breeding started in India in the 1950s and has contributed significantly to improving production. To date, 69 potato varieties have been released by CPRI suitable cultivation in different zones of the country. Because of the use of home saved seed, use of seed potatoes of unknown origin from local markets, limited use of resistant varieties, poor storage practices like leaving potato underground un-harvested and only limited adoption of haulm killing and selection practices by farmers, the seed tubers used by most potato producers cannot be healthy.

4. Pest and Diseases

Tubers attacked by pathogens undergo gradual degeneration. The degeneration of tubers negatively affects their quality and leads to a yield reduction in subsequent cycles of vegetative reproduction. Potato diseases are caused by fungi, bacteria and viruses, which adversely affect the productivity and quality of the produce. While insects cause direct damage to the crop, they also play an important role in the transmission of viruses. In areas where untreated seeds without proper crop rotation are used, tuber borne diseases like black scurf, common scab, dry rot etc. become serious problems. Among bacterial diseases, bacterial wilt or brown rot is the main problem in some places. Aphids, leaf hoppers, thrips, white flies, mites, potato tuber moth etc. are the typical pests of potatoes.

Earlier six  viruses  (PVS,  PVX,   PVA,   PVM,   PVY,   PLRV) and new strains of PVY (PVYⁿ, PVY^NTN)   have   either   been   introduced   or   developed  through  mutations are major cause of potato plant and tuber degeneration through vector Myzus   persicae.   Viruses infect potato leaves, stalks and tubers. These reduce the size and yield potential of the plants. Two or more viruses may infect a plant simultaneously to cause mosaic symptoms. Whiteflies are known to transmit Tomato leaf curl New Delhi virus-potato (ToLCNDV-potato), also known as potato apical leaf curl virus, posing serious threat to healthy seed potato as well as ware potato production in India.

Practicing appropriate crop protection methods are also the other important component of potato production packages to achieve a desired potato seed tuber yield and the overall benefit from the potato production. Additional plant protection measures against aphid, white flies and other vectors transmitting viral diseases are required in the seed crop. Application of granular systemic insecticide, Cartap hyhrochloride 4G @ 20 kg/ha at the time of planting and again at earthing up takes care of jassids, leafhoppers and white flies at early stages of growth up to 30-35 days. After appearance of aphids sprays of Imidacloprid 17.8% S.L. @ 0.004%, Thiamethoxam (25 WG) @ 100 g a.i./ha, Metasystox @ 1 litre/ha alternatively may be repeated at an interval of 12-15 days depending on duration of the crop and infestation. Alternate sprays of these chemicals restrict insects from developing resistance against insecticides. Drenching of the ridges with Chloropyriphos 20EC @ 2.5 litres/ha effectively controls cutworm attack during the early stages of the crop. In white grub prone areas, Chlorpyriphos 20EC @ 4.0 litres/ha should be applied either after mixing with sand or can be sprayed on the ridges before the final earthing up. For control of early and late blight, one prophylactic spray of Mancozeb @ 0.2% is given, it may be repeated at an interval of 7-14 days depending upon the weather condition. It will also take care of other foliar diseases like Phoma blight, etc. In case of persistent and severe attack of late blight, spray of systemic fungicides like Curzate M-8 @ 3.0 kg/ha or Ridomil @ 2.5 kg/ha may be given and repeat the spray after 7-10 days, if required.

Post-Harvest Factors

 After harvest, tuber quality management aims to delay dormancy break and limit weight loss and sweetening of potatoes.

1. Maturity Stage at Harvest and Time of Harvesting

There are problems in timing of the harvest because of differences in maturity between plants. Mature tubers are more desirable for seed and storage than immature ones. In the Indo-Gangetic plains potato digging should be preferably completed by 15^th February. Delayed digging beyond February promotes rotting due to soft rot and charcoal rot. Start digging in the plains 10-15 days after dehaulming, when peel is firm to withstand handling operations. Digging may be done either manually by spades or by mechanical potato digger. Exercise care to avoid bruising of tubers during harvesting, handling and transportation. After harvesting, keep potato tubers in heaps on raised beds for about 15 days for hardening of peel and shedding of adhered soil from tuber surface. Heaps of about 1.5 m high and 3.5 m broad at the base and variable length as needed are convenient, effective and economical. Cover the heaps with paddy straw or tarpaulins.

2. Post-Harvest Handling

Potato tubers are harvested, stored, packaged and transported with little care to prevent physical damage to the tuber, most likely because of the low level of knowledge about the consequence of physical damage by all stakeholder involved. Physical damage includes cuts, bruises and holes, inflicted on tubers during harvesting, storage, packaging and transportation. The tools used by farmers to dig out tubers from the soil might not be appropriate (too sharp or elongated ending). Physical damage in seed tubers may also occur during storage because of piling of one sack upon the other and lack of ventilation. Potatoes are usually packed in sacks which cannot protect tubers from any external pressure causing bruising and stabbing. Distant transportation takes place by Lorries. In this case loading and unloading is done by throwing up and down the tuber sacks. The seed tubers may be loaded with other sharp or beneath heavy materials which might cause damage to the tubers.

3. Potato Storage

Proper storage is one of the most important post-harvest criteria that must be met in order to ensure the quality of potatoes. Seed potato storage is a common practice in all potato producing areas. It is very important to save potato seeds from one crop to another, which is about 7-8 months time interval. It is considered most convenient to store seeds in cold storage. Seed potatoes harvested in February have to be stored until October. Thus cold storage is essential for the storage of seed potatoes. Seed potatoes are best stored at 2-4°C and 90-95% RH, because at this temperature, sprouting does not occur and weight loss is minimum. Under this condition, potatoes remain viable for a long period and therefore these tubers can be used as seed potatoes for planting in the subsequent season.

Ways to improve Potato seed tuber quality

There are various ways of campaign the problem of quality of potato tuber seed loss in developing countries like India. The most important of which is improving the skills and knowledge of the stakeholders with respect to Seed Plot technique and the postharvest handling of potato tuber seed. Following points should be considered in improving the quality of potato tuber seed and solving the problem associated with the quality of potato tuber seed.

1. Proper technical advice of potato producers regarding Seed Plot Techniques in potato enabling them to produce high quality seed through their own management and use of quality seed leads to increased tuber yields at farm level.
2. Top priority should be given to the improvement of seed health in all seed systems.
3. Production and supply of quality seed potato should be increased through strengthening private and public sectors enterprises so that farmers can able to replace their existing seeds with quality seed for seed potato production.
4. Development of seed potato hubs for increasing quality seed potato production.
5. To remove viral diseases, tissue culture technology (Aeroponic, Apical root cutting) should be disseminated so that farmers can get virus free potato plantlets which they can cultivate within net house for preventing insect vectors to produce quality seed potato. Awareness about Hi-tech seed production methods among farmers.
6. Research institutes should take greater initiatives to develop high yielding resistance varieties of potato.
7. In climate change scenario, virus-vector relationship is changing; hence there is a need to revisit the Seed Plot Techniques.
8. Concerned authorities and diffusion agencies should give proper attention to disseminate sustainable seed potato production technologies through arranging farmers trainings, mass media services, community lectures, demonstration farms, and school curricula followed by establishing seed potato demonstration plots at farmers field adequately.
9. Seed potato growers should be given credit facilities in easy terms and conditions to buy their input materials.
10. Besides, sufficient cold storage facilities should be developed in potato producing areas for preservation of their seed potato by utilizing cooperative effort or public private partnership approach
11. Organizing farmers into cooperatives also helps to reach more farmers in technology dissemination.

Conclusions

Seed potato tuber quality is constrained by both pre harvest and postharvest factors. Factors that are affecting the quality of potato seed tuber are; uses of traditional production technology, climatic factors, disease and insect pest, lack of improved storage and absence modern post-harvest handling technologies. Hence, improvement of the quality of seed potato within the country is very important for increasing potato production and productivity. Therefore, production system, transportation, storage, marketing and treatment methods should be improved through integrated manner.

References

1. (2023). FAOSTAT Database collection. Food and Agriculture Organization of the United Nations.
2. National Academy of Agricultural Sciences (NAAS) (2021). Innovations in potato seed production. strategy paper No.14(New Delhi: National Academy of Agricultural Sciences).
3. Sharma AK, Singh SP, Kumar D, Singh V, Buckseth T and Singh RK (2022). Seed Plot Technique. In SK Chakrabarti and Vinay Bhardwaj (eds) Potato in Subtropics: A saga of Success. International Books Periodical Supply Services, New Delhi-110034 (India) pp 34-49
4. Wheeler RM, Tibbitts TW, and Fitzpatrick AH (1989). Potato growth in response to relative Hort Science 24:482-484.

Authors:

Murlidhar J Sadawarti¹, SP Singh², Subhash Katare¹, Tanuja Buckseth³, Brajesh Singh³, Sanjay Kumar Sharma¹, RK Samadhiya¹, YP Singh¹_, Shyam Kumar Gupta¹ Surender Singh¹ and Priyadarshani Khambalkar⁴

¹ICAR- Central Potato Research Institute, RS, Gwalior, MP, ²ICAR- Central Potato Research Institute, RS, Patna, Bihar, ³ICAR- Central Potato Research Institute, Shimla, HP, ⁴Rajmata Vijaya Raje Scinidia Krishi Viswa Vidyalaya, Gwalior MP

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