Fruit Number in Relation to Pollen Production and Viability in Groundnut Exposed to Short Episodes of Heat Stress

Abstract

Hot days and warm nights are important environmental factors limiting fruit yields of groundnuts in the semi-arid tropics. The objective of the present 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 °C from sowing until 9 d after flowering. Cohorts of plants were then exposed to a factorial combination of four day (28, 34, 42 and 48 °C) and two night (22 and 28 °C) temperatures for 6 d. Thereafter, all plants were maintained at 28/22 °C until final harvest 9 d later. Number of flowers per plant (FN), the proportion of flowers setting pegs (fruit-set), the number of pegs and pods per plant (reproductive number, RNt), pollen production per flower and pollen viability were determined during the 6 d stress period. There were strong negative linear relations between day temperature over the range of 28 to 48 °C and FN (slope, −1.1 °C−1), fruit-set (−2.8% °C−1), RNt(−0.90 °C−1), and pollen production (−390 °C−1) and viability (−1.9% °C−1). Warmer night temperature (28 vs. 22 °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 pollen viability. The threshold day temperature for pollen production and viability was 34 °C and there were strong negative linear relations between both pollen production and pollen viability and accumulated temperature >34 °C.