Symptomatological, morphological and molecular validation of Colletotrichum gloeosporioides (Penz.) Sac. associated with leaf spot disease of arecanut

Abstract

The outbreak of leaf spot disease of arecanut caused by Colletotrichum spp. created havoc in hill and coastal zones of Karnataka. Colletotrichum is one among the top ten widespread plant-pathogenic fungi. The symptoms which are predominant on leaves were also noticed on nuts with circular or oblong to irregular brownish spots surrounded by larger yellow halo. Cultural characteristic of the isolated pathogen on potato dextrose agar produced dense, cottony, whitish to slight greyish mycelium with even margin without any zonation. Microscopic observation revealed that conidia with single celled, hyaline and cylindrical with rounded ends besides that length of the conidia varied from 12.06 to 12.30 µm and width 3.8 to 4 µm having 2-3 oil globules. The ITS based sequence analysis revealed that Colletotrichum gloeosporioides is associated with leaf spot disease of arecanut. It is concluded that the C. gloeosporioides was found predominant among the isolated cultures and sole responsible for epidemic of leaf spot disease.