G. A. Mbong, C.N. Fokunang, A. M. Emechebe, O Alabi4, M. D Alegbejo, D. A. Fontem ,
Field experiments were conducted during the 2004, 2005 and 2006 cropping seasons at the Institute for Agricultural Research farms at Samaru and Shika, Zaria (110 111N; 070 381E and 686m above sea level) to evaluate the contribution of scab infected plant parts caused by Sphaceloma sp to cowpea yield. Three varieties of cowpea were chosen for this study, TVx 3236, SAMPEA-6 and IT93K452-1. Data obtained from the different scab infected plant parts and grain yield were correlated and path coefficients analyses were also run to determine the direct and indirect effects as well as the percentage contributions of scab infected plant parts to grain yield. The results showed that scab infected plant parts of susceptible varieties directly or indirectly reduced grain yield of cowpea. SAMPEA-6 showed the highest percent contributions of scab infection to grain yield in all the years of investigation, followed by IT93K452-1, while TVx 3236 had the least scab infection to grain yield. Cowpea variety TVx 3236 showed no direct and indirect, percent individual and combined contributions of scab infection on the leaves in all the years of investigation. Yield reduction attributed to scab was more significant on SAMPEA-6 and IT93K452-1 and it ranges from 41.3-66.9% and 35.9%-67.1% respectively while variety TVx 3236 showed a lower yield reduction of only 13.7%- 29.5%. Cowpea scab can cause yield reduction through the different plant parts up to 67% in susceptible varieties if not controlled. The use of resistance varieties or non-photosensitive medium early or medium maturing varieties would result in lower infections from scab under northern Nigerian conditions. The studies also serve as a data base of information for formulation of an integrated control strategy for the management of scab disease in Nigeria.
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