Effect of Drought Stress on Traits Related to N2 Fixation in Eleven Peanut (Arachis hypogaea L.) Genotypes Differing in Degrees of Resistance to Drought

Abstract

The aim of this study was to determine the effects of drought stress on nitrogenase activity, nodule number and nodule dry weight of eleven peanut (Arachis hypogaea L.) genotypes with different degrees of drought resistance. The relative values of these nitrogen fixation traits were evaluated under well watered and water-stressed conditions. Eleven peanut genotypes were tested in a split-plot design with four replications under field conditions in 2003/2004 and 2004/2005 in Northeast Thailand. Main-plot treatments were three water regimes [Field Capacity (FC), 2/3 Available soil Water (AW) and 1/3 AW] and sub-plot treatments were 11 peanut lines. Data were collected on nodule number, nodule dry weight and nitrogenase activity (acetylene reduction assay) at 30, 60 and 90 Days After Emergence (DAE). Severe drought stress reduced nitrogenase activity, nodule number and nodule dry weight about two times greater than did mild drought stress, causing uniform performance of peanut genotypes for nitrogenase activity under severe drought conditions. However, differences among peanut genotypes in nodule traits were found at all water levels. Tifton-8 and KK 60-3 in general performed better than the drought resistant lines from ICRISAT for all traits. Nodule dry weight was closely related with nitrogenase activity under drought conditions. High nitrogenase activity under mild drought conditions was related to high nitrogenase activity under well watered conditions (potential) and to a low rate of reduction in nitrogenase activity in response to stress. The contribution of the potential was lower under more severe drought conditions. Selection for high nitrogenase activity as a surrogate trait to improve nitrogen fixation under drought conditions should be more effective under mild than severe stress.