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.