Histopathology in Brassica juncea -Alternaria brassicae interaction and localization of histochemicals in Alternaria blight-infected B. juncea leaves

Conidia of Alternaria brassicae germinated on the upper epidermis of Indian mustard (Brassica juncea) leaf, by producing one or several germ tubes and penetrated the host directly without formation of appresorium. The mycelia ramified, colonized mesophyll and palisade tissue, caused necrosis of the cells by producing toxins or metabolites that resulted in the formation of necrotic spots and reduction in photosynthetic area. This infection also decreased the amount of all the cell constituents like lignin, lipids, suberin and protein, except phenolic compound in all the tissues of Alternaria-infected B. juncea leaves as compared to healthy leaves. This study showed how the pathogen A. brassicae penetrated and infected the host B. juncea and caused reduction of cell constituents by the production of toxin, which resulted in necrosis of leaf tissue. This information may further be used in order to generate detailed information for Brassica juncea -Alternaria brassicae interaction.