Effect of intermittent exposures of SO2 on the leaf blight caused by Alternaria brassicicola on Indian mustard

▶ The mustard germplasm has been found susceptible to Alternaria brassicicola and SO2 at concentrations relevant to ambient environment. ▶ The mustard cv. Kalamoti demonstrated tolerance against the A. brassicicola and did not exhibit blight and significant reduction in plant growth and yield. ▶ Due to exposure to 143μgSO2m−3 the cv. Kalamoti became susceptible to the fungus. ▶ In general, 71.5 and 143μgSO2m−3 promoted the pathogenesis of the fungus whereas as 214.5μgSO2m−3 suppressed the blight. Effects of low levels of SO2 were investigated on the Alternaria blight on Indian mustard cultivars under artificial treatment condition. Ten cultivars of Indian mustard, Brassica juncea L. viz., Alankar, BS-2, Kalamoti, Karishma, Kranti, Mahyco Bold, Pusa Bold, Rohini, Swarna and T-59 were exposed to 5.7 (ambient), 71.5, 143 and 214.5μgSO2m−3 concentration for 5hday−1 on alternate days for 3 months in open top exposure chambers to evaluate resistance/tolerance against the gas. SO2 at 71.5 and 143μgm−3 concentrations did not incite any measurable injury to mustard cultivars. However, 143μgSO2m−3 caused visible injuries to all cultivars screened and led to a significant reduction in plant length, yield, and oil contents (P≤0.05). Effects of intermittent exposures of SO2 on leaf blight caused by A. brassicicola on the mustard cultivars were also studied. The fungus inoculated plants developed dark brown to almost black necrotic circular lesions, and severity of the blight increased on plants exposed to 143μgSO2m−3, but decreased at 214.5μgSO2m−3. The interaction between the gas and the fungus was found to be dependent of SO2 concentration. The gas at 71.5 and 143μgSO2m−3 promoted pathogenesis of A. brassicicola with result the cv. Kalamoti, expressing tolerance to the fungus, becoming susceptible and exhibiting greater blight and plant growth reductions at 143μgSO2m−3; the gas injury was also relatively greater in this treatment. The gas promoted sporulation of the fungus. Interaction of 214.5μgSO2m−3 concentration and A. brassicicola was found to be antagonistic. The cv. Kalamoti showed resistance to A. brassicicola and did not exhibit significant suppression in the yield. The exposures especially 143μgm−3 apparently broke the tolerance reaction of the cv. Kalamoti and greater lesions (32%) developed on the leaves of inoculated plants, fungus inoculation, however, did not influence the sensitivity of the cultivars to SO2. Synergistic interaction between 143μgSO2m−3