Incidence and preliminary control of blast disease of rice in southwest Nigeria

Abstract

Studies were carried out on the occurrence of a rice blast disease in southwest Nigeria. Blast disease caused by the fungal pathogen Pyricularia oryzae which was not in existence in southwest region of Nigeria in the past is now assuming an economic dimension. Pathogenicity tests were carried out and assessment of the extent of damage in incidence and severity which caused considerable loss to the cultivation of rice were investigated and ascertained. While 35–65% incidence was obtained on the farm land, the severity ranged from 3.2 to 5.4. This was very devastating in rice production. From the studies conducted, 30–50% of yield loss in rice is recorded and this has caused untold hardship to the rice researchers and farmers in the agro-ecological region of Nigeria. A weed, Panicum maximum, was identified as the alternative host of P. oryzae which may also hinder the pathogen's control. As a preliminary control measure, aqueous extracts of three botanicals, namely Ocimum gratissimum, Gmelina arborea and Chromolaena odorata were employed at concentrations 20, 40, 60 and 80% on the growth and sporulation of P. oryzae, the causal organism of rice blast disease. G. arborea at 60% and C. odorata at 80% show some promise in reducing mycelial growth and sporulation of the causal organism. This served as a preliminary control strategy for rice blast. A single isolate is still being observed but molecular studies will be carried out to determine their variation.