Interactive effect of drought and high temperature on physiological traits of soybean ( Glycine max )

A pot culture experiment was conducted under controlled condition to assess the effect of drought, high temperature and their combined effects during flowering and pod initiation stages in four soybean genotypes. Reponses of genotypes were measured in terms of physiological traits including gas exchange parameters, chlorophyll content, osmotic potential and relative water content. Invariably, drought, high temperature and combination of stresses significantly affected all the physiological parameters studied. Interestingly, differential responses were observed among the genotypes for the physiological parameters which were used to identify the tolerant and susceptible genotypes under drought, high temperature and combination of stresses. In case of photosynthetic rate, high temperature stress showed two-fold reduction, while drought stress displayed more serious effect leading to three-fold reduction in the photosynthetic rate of soybean genotypes. Transpiration rate increased under elevated temperature than control conditions while it decreased in drought and combined stress in all the genotypes. Chlorophyll fluorescence (Fv/Fm) in ADT 1 and CAT 1260 showed least reduction under stress condition indicating the ability to withstand the stress, while susceptible genotypes CAT 2084 showed drastic reduction. Higher stability of chlorophyll under stress was observed in the genotypes ADT 1 followed by CAT 1260 and least in CAT 2084. Relative water content and osmotic potential was found higher in ADT 1 indicating the tolerance to individual and combined stresses. These findings suggest that maintenance of higher transpiration rate and lower leaf temperature under drought, high temperature and combination of stress, as adaptive traits associated with tolerance of ADT 1 and CAT 1260. These identified genotypes can be used directly for the region where the drought and high temperature is predominant or they can be used as parents in breeding program to develop tolerant varieties under combined stresses of drought and high temperature.