45Potato: Production Strategies under Abiotic StressJoginder Singh Minhas

Potato production is rapidly expanding in tropical and sub-tropical environments.The population density in these areas is high and potato with its high productivity ofedible energy per unit area and time has the potential to alleviate hunger andmalnutrition. However, the crop is exposed to various kinds of abiotic stresses likedrought, heat, salinity etc. in these environments which are important limitingfactors for potato productivity. The average tuber yield in these areas is less than halfcompared to temperate climates. With increased human activity impacting climatechange, these stresses are likely to be experienced in higher magnitude and moreareas. Genetic variability exists for tolerance to these stresses in potato and relatedspecies germplasm and can be exploited for developing abiotic stress tolerantvarieties. Moreover, it is important to understand stress tolerance mechanismsoperating in different plant species, and utilize our knowledge of agronomy,physiology, genetics and molecular biology to develop new genotypes capable ofgiving good yields under stressful environments.

45.1

Introduction

Although cultivated potatoes originated in highlands of South America, full potentialof the crop was exploited in the temperate countries through organized breedingwork. From these countries, potato was introduced to the tropical and subtropicalareas of the world. As of now, potato is one of the most important food crops, both indeveloped and in developing countries. Owing to high protein–calorie ratio (17 gprotein:1000 kcal) and short vegetative cycle, potato yields substantially more edibleenergy, protein, and dry matter per unit area and time than many other crops. In2005, potato production by the developing countries overtook production by thedeveloped countries. Most of these countries lie in tropical and subtropical zones ofthe world and are prone to various abiotic stresses such as drought, salinity, and hightemperature. Abiotic stresses reduce the potential crop yields to a large extent and

Improving Crop Resistance to Abiotic Stress, First Edition.Edited by Narendra Tuteja, Sarvajeet Singh Gill, Antonio F. Tiburcio, and Renu Tuteja� 2012 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2012 by Wiley-VCH Verlag GmbH & Co. KGaA.

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present a major challenge to sustainable food production. Water is recognized as themost crucial natural resource for agricultural productivity. Water stress relatedproblems are aggravating all over the world since droughts are becoming a commonoccurrence in rain-fed agriculture, more so, because of global weather changes.Scanty rainfall or inadequate irrigation creates drought-like situation resulting inreduced water availability to the crops. Loss of water due to high temperature alsocontributes to drought and leads to symptoms typical of dehydration or desiccation.Physiological drought is caused by high osmolarity (due to excessive salinity) of thesoil because of which plants cannot utilize water even if available. Salinity directlyaffects ionic balance in the cells resulting in reduced growth and dry matterproduction. Temperature has profound effect on plant growth and development.Low temperatures lead to reduced photosynthesis and frost injury.High temperaturehas direct and indirect effects that reduce plant productivity. Direct effects arereduced photosynthesis and increased respiration leaving little photosynthate forgrowth and development. Indirectly high temperature disturbs partitioning of sugarsamong different organs affecting yield; for example, in potato, translocation of sugarsis diverted to aboveground parts leading to severe yield reduction even at mild nighttemperatures.

Physiologically, stress tolerance canbe defined inmanyways like ability of the plantto survive under severe stress through osmotic adjustment and reducedmetabolism,percentage yield reduction under stress compared to control, seed setting understress, and so on, but from agronomic point of view, total commercial crop yieldunder stress is the only criterion. Therefore, the aim of the agricultural scientist is todevelop stress-tolerant varieties and agrotechniques to maximize crop productivityunder stressful environmental conditions.

45.2Drought Stress

Drought is considered to be the major limiting factor for yield in the world potatoproduction [1] influencing negatively not only yield but also tuber quality. Insufficientwater supplymay occur almost anywherewhere potatoes are grown. In arid regions (e.g., subtropics), where potato production is possible only with irrigation, short periodsofdrought oftenarisebecause of inadequate irrigation techniquesor shortage ofwater.Even with good irrigation practices, water stress may occur because of high transpi-ration rates, especially duringmid-day, when root system cannot completely meet thewater requirements of the plant, leading to increased water potential and consequentreduction in the rate of photosynthesis [2]. In the temperate climatic zones, both shortand long periods of drought may occur almost every year due to irregular rainfall,particularly on soils with low water holding capacity. Taking into account productionconditions and the present yield levels, it is estimated that the average potato yield inthe world could be increased by at least 50% if the water supply to the crop could beoptimized. Introduction of drought tolerance in potato through breeding and bio-technological means should therefore receive high priority.

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45.2.1Potato Growth and Production

Droughtmay affect potato growth and production in three ways: (1) by reducing theamount of productive foliage, (2) by decreasing the rate of photosynthesis per unitof leaf area, and (3) by shortening the vegetative growth period. Drought afterplantingmay delay or even inhibit germination. Drought after planting is generallyexperienced by the potato crop under rain-fed conditions. Bansal and Nagarajan [3]found that water stress caused reduction in leaf growth in all the eight cultivarstested by them, although the extent of reduction varied within the varieties. Evenmild water stress of �3 to �5 bars greatly reduced leaf expansion in potatoes [4].Similar results on reduction of leaf growth under water stress were obtained byother workers [5–7]. Insufficient water supply in the period between the emergenceand the beginning of tuber bulking may therefore lead to a limited growth rate offoliage and to small leaves and small plants. As a consequence, soil cover with greenfoliage will often be incomplete and yields will be below optimum. Decline in therate of photosynthesis is fast and substantial even at relatively low water potentialsof �3 to �5 bars [8, 9]. Even in the irrigated crop, plants experience water stressduring the mid-day as the roots are not able to fully meet the transpirationaldemands of the plants. Mid-day depression in the rate of photosynthesis in well-irrigated crop was reported by Minhas and Sukumaran [2]. Plants respond to waterstress by closing their stomata, thus shutting out the supply of CO2. Sugarconcentration within the leaf tissue increases to increase the osmotic potentialof the plant, thus leading to feedback inhibition of photosynthesis [10]. Sensitivityof the potato crop to water stress varies with the developmental stage of the crop.Various authors have defined these stages as per their convenience; however, thestage between stolon initiation and early tuber development is the most sensitive,and stress at this stage causes maximum reduction in tuber yield [11–14]. Waterstress during the tuber bulking stage caused a reduction in the leaf expansion rate,but to a lesser extent, compared to plants before tuber initiation. The presence of thetubers probably increased the water capacitance of the plants [10, 15] leading toreduced effect of water stress. Apart from reduction in leaf growth, water stressduring tuber bulking stage accelerates plant senescence resulting in decreased LAI.At first, lower leaves start to wilt and drop off, while drought simultaneouslyinhibits the development of new leaves [16].

45.2.2Drought and Tuber Quality

Drought stress also affects tuber quality characteristics such as shape, dry mattercontent, and reducing sugar content. Tuber shape defects such as dumbbell-shaped,knobby, or pointed end tubers are caused by short periods of drought during the tuberbulking stage. Misshapen tubers can also occur due to secondary growth, which isespecially likely to occur in dry soils where temperature can go high [17]. Thisphenomenon may also result in poor cooking quality (glassiness) in some of the

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tubers or jelly end or translucent end tubers. All these tubers have high content ofreducing sugars, which makes them unfit for the processing industry. Tubers ofwater-stressed plants often have higher content of total sugars than well-irrigatedplants [18]. Some studies have shown that the drymatter and starch content of potatotubers grown under low soil moisture was higher than the well-watered plants, thusimproving the quality [19–21]. Other studies have shown that dry matter declinesupon exposure to drought [22]; however, there were varietal differences for thischaracter [18]. Tuber starch content has been reported to increase under droughtstress [5].

45.2.3Coping with Drought Stress

With the spread of potato cultivation to tropical and subtropical areas, the crop islikely to be exposed to increasing incidences of drought stress. Therefore, to copewithit, the first line of defense is the development of drought-tolerant varieties. Geneticvariability exists in the potato germplasm, varieties, and wild species for tuber yieldunder drought stress [23–25]. Newer techniques such as heavy carbon isotope (13C)discrimination based on D13C values indicate water use efficiency of the plant.Screening of potato germplasm for D13C showed good genetic variability for thischaracter and can be utilized for breeding drought-tolerant varieties [26]. Screeningtechniques have also been developed by variousworkers on the basis of leaf extensionafter relief of stress [3], root mass in in vitro plantlets [27, 28], isotope discriminationratio [29], and field screening using line source principle [30]. Using these techni-ques, some of the drought-tolerant varieties have already been developed/screened [18, 23, 24, 31].

Along with developing tolerant varieties, drought stress can be managed to someextent by various agronomic, chemical, and biological means. Soil water stresscombined with higher atmospheric evaporative demand leads to severe stressaffected yield losses [32]; therefore, crop under limited water supply can be grownwhen atmospheric evaporative demand is low. Mulching with agricultural wasteduring periods of drought helps in conservation of water, better crop stand andyields [33]. Plastic mulch on the ridges helps in rainwater harvesting and conser-vation between the ridges leading to better tuber yields [34]. Potassium application tothe soil [35, 36] and spray of potassium humate [37] improves crop performanceunder drought stress. The use of gel polymers in the soil under water-limitingconditions improves water availability to the crop and tuber yield [38]. Somerhizobacteria contain the enzyme 1-aminocyclopropane-1-carboxylase (ACC) deam-inase that degrades the ethylene precursor ACC and promotes plant growth,particularly under unfavorable environmental conditions such as drought. Thesebacteria can attenuate the growth inhibition caused by water deficit [39]. Better tuberyield can be obtained under water-limiting conditions by using drip irrigationcombined with appropriate placement of drip tapes. While Onder et al. [40] foundsurface and subsurface drip equally effective, Patel and Rajput [41] reported a distinctadvantage of subsurface drip irrigation at 10 cm for obtaining maximum tuber yield

1158j 45 Potato: Production Strategies under Abiotic Stress

at 100 and 80% irrigation levels. A combination of drought-tolerant varieties coupledwith modern water saving irrigation techniques can be used to successfully producepotatoes in arid and semiarid zones of the world.

45.3Heat Stress

Potato originated and evolved in the tropical highlands of Andes and hence preferscool climate (17 �C) for optimum tuber yield [42]. Higher temperature may inhibityield by overall reduction of plant development due to heat stress or by reducedpartitioning of assimilates to tubers. Minimum night temperature is very impor-tant for potato crop. Whether or not potato will tuberize depends largely on theminimum night temperature and not on the average daily temperature. Tuberiza-tion is reduced at night temperatures above 18 �C and there may not be anytuberization at night temperature of 25 �Cand above, even though potato plants cantolerate day temperature of about 35 �C without much deleterious effect. Hightemperature induces development of plants with thin stems, small leaves, and longstolons, increase in the number of internodes, inhibition of tuber development anda decrease in the ratio of tuber freshweight to total freshweight [43–46]. Heat stressaffects many plant processes, and some of them are discussed in the followingsections.

45.3.1Photosynthesis and Respiration

Optimum temperature for dark respiration is 16–20 �C [47] and for photosynthesis itis 24–28 �C [48]. Higher temperature increases the rate of dark respiration andreduces the rate of photosynthesis in plants. Bushnell [42] measured the rate of nightrespiration in potato plants at different temperatures and found doubling ofrespiration with every 10 �C increase in temperature. So, as the temperatureincreases, more and more carbohydrates are used up as respiratory substrate andless and less are synthesized and are available for translocation to the tubers. Atcertain temperature (30 �C according to Burton [49]), there is no net assimilation.However, chlorophyll fluorescence studies showed that photosynthetic apparatus inpotato is stable up to 38 �C, but beyond that there is a drastic reduction inphotosynthetic efficiency [50].

45.3.2Tuberization

The most prominent effect of high temperature is on the partitioning of assimilatedcarbon between leaves and tubers. The inhibition of tuberization at high temperaturehas often been demonstrated since the early study by Bushnell [42]. Gregory [51]found that tubers were initiated under short days over a long range of day tempera-

45.3 Heat Stress j1159

tures, but initiation was depressed at high night temperatures (over 26 �C). Underlong days, the temperature range for tuberization was greatly restricted, with thenecessity for lower night temperatures (10–17 �C). This interaction suggests that thehigh-temperature inhibitionmay operate through similarmechanism to the long-dayinhibition and perhaps is subject to manipulation by the control of hormonelevels [52]. Further proof of this hypothesis is provided by the increased synthesisof GA in apical buds exposed to high temperature and its transport to stolons where itinhibits tuberization [53] and that manual disbudding increased tuberization [54].Wolf et al. [55] studied the partitioning of 14C at 32/22, 32/12, 27/22, 27/12, and 22/12 �C day/night temperature. Neither the total plant productivity nor the export ofcarbon from the source leafwas affected by temperatures.More of assimilated carbonwas partitioned to vegetative parts at high temperature, while at lower nighttemperature most of the assimilated carbon was partitioned to the tubers. Theyconcluded that the main effect of high temperature is on assimilate partitioning andnot on total plant productivity. Basu and Minhas [56] studied the partitioning ofassimilated carbon within the source leaf into starch and sucrose in three heat-tolerant and three heat-susceptible varieties. They found that in heat-tolerant varieties20–25% of the assimilates were converted to sucrose and 40–45% into starch,whereas in heat-susceptible varieties about 5% of the assimilates were convertedto sucrose and 80–85% were converted to starch. Exposure of potato plants to heatstress alters the hormonal balance between roots and shoots, thus affecting tuber-ization and bulking.When potato plants are exposed to high temperature, gibberellincontent in the leaves increases promoting haulm growth and inhibiting tuberiza-tion [53]. Basu andMinhas [57] studied gibberellins and abscisic acid concentrationsin heat-tolerant and -susceptible genotypes and found that GA/ABA ratio was low inshoots of heat-tolerant genotypes and high in the shoots of heat-susceptible geno-types. GA-like substances decreased in the shoots and tended to accumulate in theroots of heat-sensitive genotypes during tuber bulking stage, whereas substantialamounts of GA-like substances remained in the shoots of heat-tolerant genotypes.They suggested that tuberization at high temperaturemay be related to high levels ofABA-like inhibitors in the roots during tuber induction.

45.3.3Tuber Quality

Apart from the effects of heat stress on plant growth, development and yield, tuberquality is also affected by high temperature. Physiological disorders such as internalnecrotic brown spots, chocolate spots, or internal rust spots in tuber parenchyma arelinked to hot dry weather during tuber bulking [58]. Similarly, brown discoloration ofthe vascular ring or heat necrosis occurs at high soil temperature and varies with theseverity of the stress, tuber development stage, and cultivar [59]. High temperatureduringharvest causes tuber rot in the irrigated soil [60].High temperature also causestuber shape disorders such as misshapen tubers, chain tubers, field sprouting, andreduced dry matter content [43, 61]. High temperature may cause preharvestsprouting and is linked to increased GA/ABA ratio [62].

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45.3.4Coping with Heat Stress

Potato prefers cool climate for optimum tuber yield. Therefore, the world over, thecrop is grown during cool summer days in temperate zones or during short winter insubtropical zones. Most of the suitable temperature niches for potato cultivation intropical and subtropical zones have already been occupied, leading to spatial andtemporal concentration for its cultivation. To bring more area under potato, the onlyoption available is to extendpotato cultivation to less suitable areas and seasonswherethe crop is likely to experience high-temperature stress. Potato productivity isdrastically reduced when grown under high temperatures. Therefore, developmentof heat-tolerant varieties is the foremost requirement for extending potato cultivationto new areas.

Genetic variability for heat tolerance exists in cultivated potato, primitive and wildspecies, and intergroup hybrids [63, 64]. Along with genetic variability, a goodscreening technique is also required for a successful breeding project. Variousworkers have developed screening techniques such as those based on tuberization inleaf bud cuttings, where single-node cuttings are exposed to high temperature for 3weeks and then checked for tuberization [65] and ratio of internode length in two-node cuttings grown at high and normal temperature [66], and glasshouse screeningtechnique for seedling populations based on their capacity to tuberize at hightemperatures [67]. A combination of these screening techniques has been used byvarious workers for the successful development of heat-tolerant potato varieties [68,69]. These heat-tolerant varieties have been able to extend potato cultivation towarmer nontraditional areas of Israel and India. These varieties are also a timelytool formitigating the ill effects of global warming on potato production in the world.

Apart from heat-tolerant varieties, heat stress can also be mitigated by agronomicpractices. Soil treatments like covering the soil with reflectants such as white chalklayer reduced daytime soil temperature by 7 �C, hastened emergence, foliage devel-opment, and tuber yield by more than 50% [70]. Mulch also had beneficial effects inreducing soil temperature, decreasing weed population, and increasing yield underhot dry conditions [71, 72]. Intercropping with shade crops such as maize have alsoshownbeneficial effect; for example, shadingwithmaize (one rowofmaize:three rowsof potato) improved potato yield with additionalmaize yield coming as bonus [73, 74].Application of calcium as fertilizer also improved the performance of potato varietiesexposed to heat stress [75]. Therefore, heat stress can be successfully managed by acombination of heat-tolerant varieties and suitable agronomic practices.

45.4Salinity Stress

Owing to an excessive use of irrigation, salinity problem in soils is increasing theworld over. Moreover, vast tracts of saline soils are present in all the continents of theworld. Salinity is a major cause of low crop production in many regions. Increasing

45.4 Salinity Stress j1161

population and industrialization are taking a heavy toll on fresh water resources, andthe quantity and quality of water available for agriculture are likely to decline infuture. Therefore, we need to look for alternative water resources and crops that cantolerate lower quality water.

45.4.1Ionic Imbalance in Soil

Salinity adversely affects growth and productivity ofmany crop plants. Soil salinity orthe use of saline water results in higher osmotic potential in the soil solution, thusreducing water uptake by roots. Saline soils also have the problem of waterinfiltration, aeration, and root respiration [76]. Excessive concentration of certainions such as Na, Cl, Ca, Mg, B, and SO4 in the soil solution can cause physiologicaldisorders in plants. In saline soils, there is an increase in adsorbed Na, a decrease inadsorbed Ca and Mg, and precipitation of Ca and Mg carbonates [77]. Saline waterincreases the proportion of exchangeable sodium ions in the soil solution leading toformation of sodium bicarbonate, thus raising soil pH. Resulting alkaline conditionsreduce availability of nutrients such as PO4, Fe, Mn, Zn, and so on to the plant. Incalcium carbonate-rich soils, this damaging process is inhibited. This phenomenonhas been exploited for saline soil reclamation by addition of gypsum. At cellular level,salinity-induced nuclear degradation in root meristematic cells was alleviated byaddition of calcium to the growth medium [78].

45.4.2Crop Growth and Yield

Affects of salinity stress are aggravated if it is combinedwith heat stress, water stress,high light intensity, and low humidity as encountered in natural environments[79, 80]. Crops have been rated for salt tolerance on the basis of two parameters, thatis, the maximum salinity up to which there is no yield reduction and the percentageyield decrease per unit of salinity increase. According to these parameters, potato hasbeen classified as moderately sensitive to soil salinity [81, 82]. Plant height, leaf area,and dry weight accumulation in potato are significantly reduced by salinity. Tuberyield is reduced through reduced tuber number and weight per tuber [83, 84].

Potato leaves are very sensitive to saline water and are severely damaged bysprinkler irrigation [82]. Uptake of sodium and chlorine induces toxicity as evidentfrom leaf burn along the margins. Salinity adversely affects relative water content,stomatal conductance, and transpiration rate in potato. It also leads to changes inchloroplast ultrastructure such as thylakoid swelling and decreased grana stacking,affecting photosynthesis and reducing growth and dry matter production [85].Irrigation with saline water during tuber germination caused greater depression inyield (59%) than when it was applied well after plant establishment (22–31%) [86].High salinity levels (EC > 10 dS m�1 in the root zone) may cause coarse russettingand furrowing of tubers accompanied by severe browning of the surface, thusreducing tuber quality [87].

1162j 45 Potato: Production Strategies under Abiotic Stress

45.4.3Field Selection for Salt Tolerance

Genetic variability for plant response to salinity has been found inwild potato speciesand potato varieties. Solanum chacoense, S. kurzianum, S. juzepczuckii, and S.curtilobum have been found to be salt tolerant in various experiments involvingirrigation with saline water, glasshouse trials, and production of microtubers in thepresence of NaCl in the growthmedium [88, 89]. Screening for salinity tolerance hasbeen carried out in the field by irrigation with saline water or by growing the crop insaline soils and salt-tolerant varieties such as Patrones, Norland, Red Lasoda, Cara,Serrana Alpha, Arica, and so on have been identified. These varieties fall in allmaturity groups, and earliness or lateness is not related to salt tolerance [86, 90, 91].Some of the Israeli varieties such as Almera,Hermes, andMaris Peer are not affectedby moderate level of salinity, and the Peruvian variety Serrana is most salttolerant [87].

45.4.4Laboratory Selection for Salt Tolerance

Salt-tolerant potato lines have also been developed using recurrent in vitro selection ofcell lines over a number of generations by exposing them to increasing saltconcentration. Whole plants regenerated from salt-tolerant calli accumulated morefresh and dry weight whenwatered with 90mMNaCl and also producedmore tubersper plant [92]. The known salt-tolerant variety Serrana produces profuse root mass inMS medium containing 154mM NaCl; so, plants have been screened in vitro bymeasuring root growth in culture medium containing high NaCl concentration[93, 94]. In vitro selection for salt tolerance has also been reported by Burgutinet al. [95]who identified 38 somaclones thatmaintained superior performance infieldtests over many years.

45.4.5Coping with Salinity

Salt-tolerant varieties have been selected using field and laboratory screeningmethods and are being regularly grown in many countries where good-quality waterfor irrigation is not available. In central Negeve desert, the underground water, toosaline for irrigation, is beingmixedwith freshwater from the Sea of Galilee to controlsalinity level before applying it for irrigation to different crops [87]. Thismodel can beeasily replicated in other areas of the world facing similar problems. Sensitivity of thepotato crop to salinity varies with the growth stage of the plant. Some stages aremoresensitive to salinity than others [86]. Therefore,more sensitive stages can be irrigatedwith better quality water and the rest of the stages can be irrigated with poor-qualitywater to get optimumyield. In saline areaswhere freshwater is available, excesswatercan be used to leach down the salts from the top layer. In such cases, depletion of thenitrate from the root zone should be taken care of for optimum yields. Proper

45.4 Salinity Stress j1163

fertilizer management can reduce metabolic disturbances brought about by salinity.Potassium nutrition stands out in increasing plant tolerance to salinity. It has beenshown that potassium application up to 600 kg ha�1 increased the tuber yield of fourcultivars irrigated with saline water with 9.38 dS m�1 electrical conductivity [96].

45.5Reactive Oxygen Species and Abiotic Stress

Reactive oxygen species (ROS) are generated under abiotic stresses such as drought,salinity, and oxidative stress. ROS are produced in the chloroplast due to oxidativestress and is scavenged by superoxide dismutase (SOD). ROS, when produced inhigh amounts, cause severe damage to plant cell membranes. It has been shown thatsalt tolerance in potato varieties is linked to high activity of antioxidant enzymes suchas peroxidase (POD) and SOD [97]. When frost-tolerant Andean potato species S.curtilobum and frost-sensitive S. tuberosum were exposed to PEG-mediated waterstress, SOD activity increased by more than twofold in stress-tolerant variety and itwas highly correlated with chlorophyll fluorescence parameter fv/fm indicatingprotection of PSII from ROS generated by water stress [98]. Other chemicals thatscavenge ROS have also been found to enhance yield and provide protection againstabiotic stresses; for example, cobalt in the culture medium provided protection topotato seedlings during osmotic stress [99]; treatment with diphenylamine, a potentantioxidant, increased potato yield by 27–47% [100]; and potato plants sprayed withantiozonant ethylenediurea (EDU) had higher amount of reduced glutathion,protected leaves against ozone damage, and increased tuber yield [101]. Treatmentof plants with chlorocholine increased SOD, POD, and catalase activities, improvedP, K, Ca, Mg, Fe, Mn, and Zn content, and enhanced tuber yield under suboptimalconditions [102]. Transgenic potato plants carrying bacterial catalase gene impartedsalt tolerance to potato [103], proving beyond doubt the role of antioxidant enzymes inamelioration of abiotic stresses.

45.6Conclusions

Potato produces highest amount of edible energy, protein, and dry matter per unitarea and time compared to other food crops. Therefore, the crop has the potential tofeedmore people per unit area than any other crop. Already, more potatoes are beinggrown in developing countries in the tropics and subtropics than in developedcountries in the temperate zones. The major limitations to potato production intropics and subtropics are high temperatures, scarcity of water, and salinity. Withincreasing population and industrialization in these countries, quality and quantityof water available for agriculture are going to go down with each passing decade.These problems are likely to aggravate with impending global warming. Therefore,the study of abiotic stresses in potato crop has assumed substantial significance. It is a

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challenge for scientists to use their understanding of stress tolerance mechanismsandmodern technologies to developnew varieties capable of giving good yields understressful environments. Given the genetic diversity available in potato germplasmand increased knowledge of physiology and molecular biology, the prospects arepromising for our ability to improve potato yield in nontraditional environments andmake more food available to millions.

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