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摘要
Effects of 2 (1-6 ppb ambient), 25, 50 and 75 ppb SO2 for 5 h (alternate day for 3 months) on the vulnerability of ten cultivars of Indian mustard, Brassica juncea to the infection of Altemaria brassicae and vice versa were investigated in open-top exposure chambers placed in an open field during two consecutive years. Four weeks old plants were sprayed with a spore suspension of A. brassicae (10(5) spores/ml, 5 ml/plant) 2 days before the gas exposures started. Among the three SO2 concentrations, only 75 ppb incited visible foliar injury and suppressed the plant growth, yield, oil contents and leaf pigments of mustard cultivars (P <= 0.05). Fungus inoculated plants developed brown to black necrotic lesions (spots). Severity of the blight, increased on plants exposed to 25 or 50 ppb SO2 with greater fungal sporulation, but decreased at 75 ppb SO2. The interaction between the gas and the fungus was found dependent on SO2 concentration and cultivar reaction to the fungus. The 25 or 50 ppb SO2 promoted pathogenesis by A. brassicae on the fungus susceptible cultivars. The combined treatments of 50 ppb SO2 and A. brassicae reduced the yield of cv. Pusa Bold by 31% against the sum of yield declines caused by the gas and fungus separately (23%). At 75 ppb SO2, the sporulation of A. brassicae was suppressed and the interactive effect of the gas and fungus was equal to their individual effects on the susceptible cultivars. The cvs. BS-2 and Rohini, expressing tolerance to the fungus became susceptible due to gas exposure, and exhibited greater leaf necrosis and plant growth reductions at 50 and 75 ppb SO2. The study has demonstrated that the leaf spot disease may become severe in areas polluted with 25-50 ppb SO2, and the fungus resistant cultivars may become susceptible to the disease at higher concentrations of the gas.
- 出版日期2015-1-1
