EFFECTS OF EPIBRASSINOLIDE AND ABSCISIC-ACID ON SORGHUM PLANTS GROWING UNDER SOIL-WATER DEFICIT .1. EFFECTS ON GROWTH AND SURVIVAL

Spray treatment with 22R, 23R epibrassinolide (EBR, 0.1 ppm) increased the length and dry weight of both the top and root of sorghum plants under various soil water conditions, although the extent of growth promotion was small. Under well-watered conditions, abscisic acid treatment (ABA, 50 ppm) inhibited top growth but promoted root growth. However, under water-stressed conditions, ABA-treated plants grew at a higher rate than control and EBR-treated plants. The accelerated growth of ABA-treated plants was apparent both in the top and the root. Treatment with 0.1 ppm EBR + 50 ppm ABA inhibited growth even more than ABA treatment under well-watered conditions, but it increased the growth rate more than ABA alone under water stressed conditions. Treatment with EBR + ABA promoted root growth to a larger extent even than ABA treatment. From the above results, it was concluded that EBR increased the effects of ABA both under well-watered and water stressed conditions. Treatment with EBR and ABA increased the survival ability of plant and leaf under severe drought. This effect of ABA was also enhanced by EBR. Thus, synergistic interaction between ABA and EBR was observed in almost all aspects examined.