First Report of Phytophthora sansomeana (E.M. Hansen) Causing Leaf Blight of taro (Colocasia esculenta (L.) Schott) in South Eastern Nigeria

Abstract

Leaf blight and corm rot of taro (Colocasia esculenta (L.) Schott) caused by Phytophthora colocasiae Raciborski is the most disparaging disease of taro inducing severe losses in yield and quality of taro corms. Investigations were carried out in Umudike in 2016 and 2017 to determine the pathotypes present in that locality with a view to screening them on available taro genotypes for resistant cultivars. Symptomatic taro plant samples were collected from Taro Project Farm of the National Root Crops Research Institute, Umudike. Leaf tissue sections were excised from the periphery of lesions on symptomatic leaf, surface sterilized in 10% Sodium Hypochlorite solution for 2 minutes, rinsed in three changes of sterile distilled water and plated on Water Agar (WA). Mycelia emerging from diseased tissues after incubation were aseptically transferred to Corn Meal Agar (CMA). A total of 15 fungal isolates under 6 groups of species were obtained and these isolates were transferred to Carrot Agar (CA) from time to time until pure cultures were obtained. Based on varied cultural patterns, morphological characteristics and microscopic examination, the isolates were identified as Phytophthora sp, Fusarium sp FSSC, Fusarium solani, F. oxysporum and F. equiseti. Pathogenicity test confirmed that only Phytophthora sp induced leaf blight on detached leaf of taro plant. Molecular characterization of the isolates via Internal Transcribed Spacer (ITS) sequence analyses confirmed that the already implicated Phytophthora species was Phytophthora sansomeana. This is apparently the first report of P. sansomeana as a taro leaf blight pathogen in addition to the already known P. colocasisae.