EFFECT OF WATER-STRESS ON PHOTOSYNTHESIS IN 2 MULBERRY GENOTYPES WITHDIFFERENT DROUGHT TOLERANCE

Three-month-old mulberry (Morus alba L.) cultivars (drought tolerant S 13 and drought sensitive S54) were subjected to water stress for 15 d. Water stress decreased the leaf water potential, net photosynthetic r ate (P-N), and stomatal conductance (g(s)) in both the cultivars. Howe ver, the magnitude of decline was comparatively greater in the sensiti ve cultivar (S54). Intercellular CO2 concentration (C-i) was unaltered during mild stress, but significantly increased at severe stress in b oth cultivars. The photosystem 2 activity significantly declined only at a severe stress in both cultivars. The C-i/g(s) ratio representing the mesophyll efficiency was greater in the tolerant cultivar S13. Inv olvement of stomatal and/or non-stomatal components in declining P-N d epended on the severity and duration of stress. However, the degree of nonstomatal limitations was relatively less in the drought tolerant c ultivar.