EFFECT OF LUPINUS SEED DIFFUSATES ON BRADYRHIZOBIUM SP. GROWTH AND NODULATION OF LUPINE

Seeds of three species of lupine (Lupinus termis, L. triticale and L. albus) were tested to determine if the seed contains diffusable substa nces toxic to bradyrhizobia. L. albus seeds were less toxic to bradyrh izobia, followed by L. triticale. Six strains of Bradyrhizobium were e valuated for their resistance to the toxic substances in lupine seeds. Zones of growth inhibition were determined on yeast-mannitol-agar med ium surrounding surface-sterilized seed. The effect of surface sterili zation of seeds by different chemical treatments on seed toxicity was assessed. Seeds soaked in water for 1 h before placing on agar surface significantly decreased the inhibition zone. Also, the effect of soak ing seeds in water for 4 h before planting and inoculation on nodulati on, nitrogen fixation and plant growth were investigated. Addition of seed diffusate to soaked seeds significantly decreased nodulation and plant growth. Autoclaving the seed diffusate had no effect on the toxi city of the seed diffusate. Addition of the absorbent polyvinylpolypyr rolidone (PVPP) to seed diffusates significantly decreased the inhibit ory effect of seed diffusate on nodulation and plant growth. Seed diff usate substances were water-soluble, heat-stable and partially bound t o PVPP.