EFFECTS OF ENHANCED UV-B RADIATION ON THE GROWTH OF RICE AND ITS SUSCEPTIBILITY TO RICE BLAST UNDER GLASSHOUSE CONDITIONS

The effects of enhanced UV-B (280-320 nm) on the susceptibility of 18 irrigated lowland rice cultivars to rice blast (Pyricularia grisea) we re investigated. The rice cultivars were irradiated with UV-B 313 lamp s that were either filtered with cellulose acetate of 0.13 mm thicknes s (light transmission greater than 290 nm) or with Mylar D of 0.13 mm thickness (light transmission greater than 320 nm). Irradiation was fo r 6 h daily for 21 days starting at 9 days after planting. After irrad iation, plants were inoculated with one or two blast isolates. In 18 o ut of 36 measured interactions the number of lesions per plant was hig her in the presence of UV-B than in its absence. However, only two int eractions were statistically significant. In a second experiment the d ose-response relationship between the cultivars IR30 and IR72 and UV-B was established in the presence and absence of disease. Increasing le vels of UV-B significantly reduced leaf areas, dry weights, and height s of both cultivars. Disease severity was either unaffected or decreas ed by UV-B. However, disease significantly changed the effects of UV-B on plant growth and recovery from UV-B damage, IR30 but not IR72 reco vered from UV-B damage in the absence of disease within 5 days. No rec overy occurred when inoculated. IR72 suffered even greater reductions of leaf area and dry weight by UV-B when inoculated. Although the effe cts of UV-B on disease severity may be small, it appears that the tole rance of plants to disease is decreased by UV-B radiation.