HEAT TOLERANCE AND ASSIMILATE TRANSPORT IN DIFFERENT POTATO GENOTYPES

Six potato genotypes with different degrees of heat tolerance were grown in pots at 38/25-degrees-C maximum/minimum temperature at 14 h daylength under natural light glasshouse conditions. Prior to sampling, the plants were given a 14 h dark period. Photosynthesis was measured at 28-degrees-C and at a saturating light intensity of more than 1200-mu-E m-2 s-1. During the optimum photosynthetic period (09.00-12.30 h), the leaves of heat-tolerant potato genotypes (DTO-28, Norchip, and Desiree) had 4-5 times more soluble sugars (mainly sucrose) and higher sucrose-phosphate synthase activity than the leaves of the heat-susceptible genotypes (Kufri Jyoti, Kufri Chandramukhi, and Kufri Muthu). However, starch accumulation in leaves of susceptible genotypes was about twice that in tolerant genotypes. All susceptible genotypes showed a low rate of assimilate transport from leaves and a higher shoot/root ratio which indicated that the shoot remained the predominant sink for photosynthate. Activities of amylase and invertase in leaves were also higher in susceptible genotypes. It is suggested that the poor yield of heat-susceptible genotypes at high temperature and long day conditions is related to insufficient availability of the transportable sugar, sucrose.