Fruit number in relation to pollen production and viability in groundnut exposed to short episodes of heat stress

Hot days and warm nights are important environmental factors limiting fruit yields of groundnuts in the semi-arid tropics. The objective of the presen t research was to quantify the effects of short episodes of heat stress on pollen production and viability, and fruit yield. Plants of cultivar 'ICGV 86015' were grown at a day/night temperature of 28/22 degrees C from sowing until 9 d after flowering. Cohorts of plants were then exposed to a factor ial combination of four day (28, 34, 42 and 48 degrees C) and two night (22 and 28 degrees C) temperatures for 6 d. Thereafter, all plants were mainta ined at 28/22 degrees C until final harvest 9 d later. Number of flowers pe r plant (FN), the proportion of flowers setting pegs (fruit-set), the numbe r of pegs and pods per plant (reproductive number, RNt), pollen production per flower and pollen viability were determined during the 6 d stress perio d. There were strong negative linear relations between day temperature over the range of 28 to 48 degrees C and FN (slope, -1.1 degrees C-1), fruit-se t (-2.8%degrees C-1), RN, (-0.90 degrees C-1), and pollen production (-390 degrees C-1) and viability (-1.9%degrees C-1). Warmer night temperature (28 vs. 22 degrees C) had no effect on FN, but reduced fruit-set (31 to 19%), RNt (8 to 5), and pollen production (4389 to 2800) and viability (49 to 40% ). There were no significant interactions between day and night temperature . Reduced fruit-set was a consequence of fewer pollen grains and reduced po llen viability. The threshold day temperature for pollen production and via bility was 34 degrees C and there were strong negative linear relations bet ween both pollen production and pollen viability and accumulated temperatur e >34 degrees C. (C) 1999 Annals of Botany Company.