THE EFFECT OF HIGH-TEMPERATURE ON VIGNA-RADIATA NODULATION AND GROWTH WITH DIFFERENT BRADYRHIZOBIAL STRAINS

A study was conducted to examine the effect of constant high temperatures and diurnally administered temperature regimes (day/night temperature was maintained at 30-degrees-C and increasing 2 hr temperature shocks of 36, 42 and 48-degrees-C were applied daily) on growth, nodulation and nitrogen fixation of mungbean (Vigna radiata L. Wilczek) plants and growth responses of five different cowpea bradyrhizobial strains. Mungbean genotype and bradyrhizobial strains responded differently to high temperatures. Mungbean plants survived at (1) diurnal regimens of high temperature and (2) constant root temperatures of 42 and 48-degrees-C (day and night), but germination at 48-degrees-C was reduced to 38%. The bradyrhizobial strains survived, grew and remained infective and effective after incubation at constant temperatures up to 42-degrees-C and diurnal regimen high temperatures. Two strains, Vml and Vr16, survived and multiplied at a constant temperature of 48-degrees-C. These strains were also effective on mungbean and siratro (Macroptilium atropurpureum) plants after incubation at 48-degrees-C for 5-10 days. Elevated temperatures (> 36-degrees-C) depressed nodulation and nitrogen fixation. Constant high temperatures (42 and 48-degrees-C) at the seedling stage markedly affected nitrogenase activity (ARA).