Ozone: Changing Anthracnose (caused by Colletotrichum acutatum) Severity and Accelerating Hypersensitive Response in Pepper

The interaction effects of ozone (O₃) and anthracnose (Colletotrichum acutatum) disease were examined in green fruits and seedlings of pepper (Capsicum annuum). Pre-treatment with (O₃) as a factor causing predisposition to the disease prior to infection was investigated in green fruits and stems using an (O₃) concentration of 150 nL/L, which is easily reached in summer in Korea. (O₃) treatment increased antioxidative responses in pepper foliar tissues, and defense against anthracnose was examined in fruits and stems. Anthracnose severity on stems of the O₃-treated , ozone-sensitive 'Dabotop' cultivar was always lower than that on untreated plants, but the difference was not always significant (p=0.147). Significantly lower anthracnose severity was found on O₃-treated green 'Dabotop' fruits as compared to untreated green fruits in three of eight replicate experiments. In contrast, hypersensitive responses in 03treated seedlings were significantly accelerated compared to those in untreated seedlings by about 7.8 h (p<0.001). This confirmed previous evidence of increased transcription of plant defense genes with (O₃) treatment. (O₃) treatment significantly decreased chlorophyll concentrations in the leaves in four replicate experiments (p<0.01). (O₃) increased hypersensitive responses in the leaves of pepper seedlings, but this increase did not contribute to the control of anthracnose severity on fruits. Antioxidant reactions to (O₃) were limited to chlorosis and changes in hypersensitive responses in leaves.