In our institute garden of Jyothy Institute of Technology (Bangalore), we found bean leaves infected with some disease. On the leaf surface there were dark black spots surrounded by yellow zones.
Fig: Bean leaves with necrotic spots
It is leaf spot. This fungal disease, caused by Cercospora species, occurs primarily on the lower leaves of plants as irregular, tan spots. Severe infection causes excessive leaf drop and stunting of the plant. Infection is worse during periods of extended rainfall, high humidity.
Infected leaf part, mycelium and spores were observed under foldscope and following pictures were taken.
Fig: Spores of Cercospora
Fig: Necrotic part on leaf observed unser foldscope
We found some tetrad like structures while observing this sample and we couldn’t identify it.