Growth and photosynthetic responses of groundnut genotypes to high temperature

Among abiotic factors, high temperature is one of the major constraints to adaptation of groundnut (Arachis hypogaea L.) in tropical and subtropical a reas. The aims of this study were (i) to evaluate three genotypes (ICG 1236 , ICGS 44, and Chico) of groundnut for their heat acclimation potential (HA P), and (ii) to examine whether the growth, yield, and photosynthetic respo nses of these genotypes to temperature related to the HAP. We defined HAP a s the change in leaf heat tolerance based on plasmalemma thermostability at 40 to 60 degrees C measured by electrolyte leakage after acclimation at 35 /30 degrees C day/night temperature. Initially, plants were raised in a gla sshouse maintained at 25/25 degrees C day/night temperature. One half of th e plants were shifted to another glasshouse maintained at 35/30 degrees C a fter the appearance of the third leaf. Heat killing time (HKT), defined as the time required to cause 50% relative injury, indicated that the three ge notypes acclimated to high temperature stress, with significant variations in HAP. All genotypes maintained greater vegetative growth and higher photo synthetic rates when grown under the higher temperature regime and genetic differences in photosynthetic rate were related to HKT. The higher temperat ure regime affected the reproductive growth adversely by increasing flower abortion and decreasing seed size, however. Differences in chlorophyll fluo rescence and membrane thermostability between growth temperature were found only after incubating the leaf tissue at temperatures of 50 degrees C or h igher. Genetic differences in HAP were small and unrelated to grow th diffe rences.