Prevalence of rice blast and varietal screening in Ghana

Abstract

Surveys were conducted in farmers' fields, participatory varietal selection (PVS) nurseries and researchers' fields during 2000-2002 cropping seasons to assess the incidence of rice blast (Pyricularia oryzae) in Ghana. Screenhouse artificial inoculation studies and field trials were also carried out on some of the rice varieties to assess their response to blast. Blast was recorded in 264 fields in the countrywide surveys. The incidence of blast varied considerably across the country and areas of blast scores of 0-3 (low), 4-6 (moderate) and 7-9 (high) have been identified. No blast was observed in Brong Ahafo, Greater Accra and Upper West Regions. Farmers at some of the high blast areas notably Fodome, Hohoe, Santrokofi and Datano reported complete devastation of their rice fields due to blast infection. The survey results suggest that Datano, Hohoe and Nyankpala are blast prone areas and key sites for resistance screening. The PVS rice varieties, with a few exceptions, had low blast severity scores at the key screening sites under natural field conditions, while the improved varieties had shown varying degrees of resistance to the dominant Ghanaian blast lineage representatives under screenhouse conditions. These improved varieties need to be tested sufficiently at other major rice-growing areas across the country to benefit the low-resourced farmers where improved varieties are not available or where local varieties are susceptible to the blast disease.