Report on Phytophthora sp. Causing Corm Rot of Colocasia (Colocasia esculenta L.) from Prayagraj, Uttar Pradesh, India

Abstract

Taro [(Colocasia esculenta L.) Schott] also known as old cocoyam or true cocoyam is a water-loving herbaceous plant. Taro is affected by major diseases and pests in different parts of the world but among them taro blight and corm rot caused by a fungus-like oomycete Phytophthora colocasiae Racib is most important disease. The infected corm samples were collected from markets in two districts of Andhra Pradesh and the experiment was carried out based on Koch’s postulates in the Department of Plant Pathology, SHUATS, Prayagraj during Rabi season (2022-23). Isolation was done from collected corm samples (infected corms) for identification of the pathogen. Based on the cultural and morphological characters under microscopic examination, the pathogen was identified as Phytophthora sp. which causes corm rot and leaf blight of Colocasia. The isolated pathogen was inoculated into the healthy corms of Colocasia. At the time of corm germination, the typical symptoms were observed like downy whitish growth on the surface of the corms and on the leaf surface as small grey to brown discoloured water-soaked spots which later enlarged, became dark brown and coalesced, finally destroyed entire leaf lamina. After the examination of the symptoms, reisolation was done and pathogenecity of the fungus was proved by Koch’s postulates. Perusal of the literature revealed that Phytophthora sp. causes post and pre harvest corm rot and leaf blight in colocasia and it seems to be the first report from Prayagraj, Uttar Pradesh.