DRY-MATTER PARTITIONING IN GROUNDNUT EXPOSED TO HIGH-TEMPERATURE STRESS

The yield of groundnut (Arachis hypogaea L.) grown in West African env ironments is often limited by high temperatures. We tested whether or not differences in the tolerance of groundnut genotypes to high temper ature episodes are due to genotypic differences in the rates of dry ma tter partitioning to yield. A high temperature tolerant (HTT) and a hi gh temperature sensitive (HTS) genotype were grown in a polyethylene-c overed greenhouse (polytunnel) at 30/25 degrees C (day/night) until af ter the start of pegging (49 d after planting, DAP). Then, cohorts of each genotype were exposed for 6 d to four different constant day temp eratures between 30 and 50 degrees C before returning to the common en vironment until harvest maturity (98 DAP). Total plant biomass and see d yield at 98 DAP were reduced by the hottest temperature episodes and were less in the HTS compared with the HTT genotype, Proportional red uction in biomass and seed yield due to high temperature stress was gr eater in the HTS than the HTT genotype, The root/total biomass ratio d eclined more rapidly after flowering in the HTS compared with the HTT genotype, The start of seed-filling was delayed by progressively hotte r temperature episodes and was 11.7 d later in the HTS than the HTT ge notype, However, the rate of increase in seed harvest index during see d filling was 0.0068 d(-1) for both genotypes and was mot affected by high temperature stress. We conclude that genotypic differences in the response of groundnut yield to episodes of high temperature stress we re due to differences in the timing of seed filling rather than to gen otypic differences in the rate of dry matter partitioning to fruits.