12. Prevalence, incidence and severity of a new root rot disease of cowpea caused by Macrophomina phaseolina (Tassi) Goid in Northern Ghana

Cowpea is an important economic crop in northern Ghana. Following reports of a new cowpea root rot, disease in northern Ghana (Northern, Upper East and Upper West regions), surveys were conducted in 2016 and 2017 with the aim of determining the causal organism, prevalence, incidence and severity of the disease across northern Ghana under rain fed and irrigated conditions. Seventeen locations were surveyed and symptomatic plants were taken to the Plant Pathology laboratory in CSIR- Savanna Agricultural Research Institute (SARI), Nyankpala for pathogen identification. The disease was prevalent in all the locations surveyed. There was no significant difference (P > 0.05) between disease incidence and severity (1‒9 scale) under rain fed and irrigated conditions for each year. Disease incidence and severity were however significantly different (P < 0.05) amongst locations surveyed under both rain fed and irrigated production for 2016 and 2017. Under rain fed conditions for 2016, Nyankpala recorded the highest incidence (43.8%), with Feo recording the lowest (17.8%). For the same period, Manga recorded the highest severity (4.3) with Silbelle recording the least (2.1). Under dry season cultivation for 2016, Asumsapeliga recorded the highest disease incidence (44.5%) with Silbelle recording the lowest (11.4%). Sakpari, however, recorded the highest disease severity (3.8) with Feo recording the lowest for the same period. Under rain fed conditions for 2017, disease incidence was highest in Nyankpala (47.7%) and lowest in Lawra (8.7%). For the same period, however, Manga and Yendi recorded the highest severity (4.3) with Lawra recording the lowest (1.6). Under dry season cowpea production for 2017, Sakpari (64.8%) recorded the highest incidence and Silbelle (7.0%) recording the least. Disease severity for the same period was highest in Nafkluga (4.2) and lowest in Silbelle (2.3). Morphocultural characteristics and pathogenicity test confirmed Macrophomina phaseolina as the causal organism of the cowpea root rot disease.