Biology and infection mechanisms of Cryptosporiopsis spp fungus causing blight disease on cashew (Anacardium Occidentale L.)

Abstract

Efficient isolation, purification and identification techniques of a new pathogenic fungus of cashew were developed. In the study, aspects related to identification, characterization of conidial morphology and infection of the Cryptosporiopsis spp fungus were investigated. Macroscopic observations of symptoms and signs of cashew blight disease as well as isolation, culturing and morphological characterization of its causative agent were carried out. Cryptosporiopsis spp fungus penetration and infection mechanisms on susceptible cashew leaves were studied. Cashew leaves were inoculated with fungal suspensions by pricking with pin, clipping with scissors and painting a fungal suspension onto the leaves with a paintbrush. Pathogenecity assays were performed on cashew leaves, nuts and apples. Irregular spot lesions, with a brown margin, formed on leaves especially on the young leaves. Direct conidial transfer was found to be the efficient method of isolation because it was less prone to contamination. Blight macroconidia are typical of Cryptosporiopsis having ellipsoidal, rounded at the apex, tapering into a scar at the base. Stomatal penetration of Cryptosporiopsis spp was visible through the simple staining technique using lactophenol solution. Penetration was by germinating conidia through a cuticle that caused an infection in leaves. Paint brush method of inoculation was found to be more effective as compared to other two methods based on the lesion size. Leaves inoculated with Cryptosporiopsis spp isolate began curling after 72 h thereafter developed dark, irregularly shaped spots with brown margins. An increased understanding of cashew blight is important for developing strategies for its management. Keywords: Cryptosporiopsis spp, Macroscopic, Penetration, Cashew