Cowpea scab disease (Sphaceloma sp.) in Uganda.

Abstract

Cowpea (Vigna unguiculata L. Walp) is the third most important legume food crop in Uganda. It is the main legume food crop in the Eastern and Northern regions of the country, however, its mean yield is less than 400 kg ha1. Scab (Sphaceloma sp.) which is a seed-borne disease is one of the major constraints of cowpea production in the country, capable of causing yield losses of up to 100%. Cowpea scab is the anamorph of Elsinoe phaseoli in common bean (bean scab). The disease affects all the above ground parts of the cowpea plant. A study was conducted in the country to determine the incidence, severity and distribution of scab disease in 17 cowpea growing districts across three agro-ecological zones over a two-year period. The results indicated that scab disease was widespread in all the districts with mean incidence ranging between 35 and 70% and mean severity 2e4. Tororo and Amuria districts had the highest incidence and severity, while Bukedea and Arua districts recorded the least disease incidence and severity. Cowpea fields located at altitudes above 1200 m.a.s.l had the highest mean disease incidence (82%) and severity (score ¼ 3.4), while fields located on altitudes lying between 771 and 990 m.a.s.l registered the least disease incidence (64.7%) and severity (score ¼ 2.7). The type of cultivar grown and cropping system practiced influenced the incidence and severity of the scab disease. The results of this study also showed that scab had high incidence and severity across districts and altitudes in Uganda suggesting the need to develop resistant cultivars. This indicates the need to establish the variability of the pathogen to inform the breeding programme for development of resistant varieties.

Keywords: Vigna unguiculata, Sphaceloma sp., Elsinoe, Incidence, Severity, Distribution