Physiological mechanisms underpinning tolerance to high temperature stress during reproductive phase in mungbean (Vigna radiata (L.) Wilczek)

This study investigated the physiological factors underlying genotypic variation in response to high temperature and the role of acclimation prior to high temperature stress, in mungbean genotypes, selected based on their sensitivity to high temperature. The genotypes were subjected to three temperature regimes during the reproductive phase, i.e. normal (28 degrees C/24 degrees C, CON), acclimation temperature (35 degrees C/28 degrees C, Ac-HT) before transferring to high temperature (45 degrees C/30 degrees C), and direct exposure of non-acclimated plants to high temperature (45 degrees C/30 degrees C, NAc-HT). Environmentally controlled growth chambers were used to provide the required temperature regimes. The plants were maintained at fully watered conditions throughout the growing cycle. The average shoot biomass (including root) was reduced by 9% and 41%, and the grain yield by 31% and 50%, in the acclimated (Ac-HT) and non-acclimated (NAc-HT) treatments, respectively, compared to CON. The mean root weight in the NAc-HT treatment was reduced by 32%, while the mean root weight in Ac-HT treatment was comparable to CON, although there was genotypic variation with in the treatments. The mean root weight in the tolerant group was 48%, 180% and 130% greater than susceptible group, in CON, Ac-HT and NAc-HT treatments, respectively. There was significant variation among genotypes for root weight. A positive relationship (r(2) = 0.54**) between root and shoot weight indicated that plants with larger root weight also produced higher shoot biomass. The high temperature tolerant genotypes responded to acclimation treatment by promoting root growth while such enhanced root growth was not observed in susceptible genotypes. The study suggested that acclimation treatment followed by high temperature could be used as a technique to identify genotypes with ability to adapt to high temperature stress conditions.