Reactions of Improved Cowpea Genotypes to Some Major Diseases in a Sorghum-Based Cropping System in the Sudan Savanna of Nigeria

Abstract

The study was carried out to investigate the susceptibilities of some improved cowpea genotypes to infection and damage due to bacterial blight, smut and cowpea aphid-borne mosaic virus CABMV in a sorghum-based cropping system during 1999 and 2000 at Minjibir, Kano, Nigeria. Treatments consisted of six (6) genotypes made up of one (1) local Danila and five (5) improved (IT90K-277-2, IT95K-1090-3, IT95K-222-14, IT96D-666 and IT96D-759) and in a four (4) row arrangements (1S:1C, 2S:2C, 1S:2C, and 2S:4C, reflecting millet to cowpea rows). These were laid out in a split plot design with three replications. There was a significant effect (P < 0.05) of cowpea genotype on bacterial blight. In both seasons IT96D-666 recorded the highest for bacterial blight and smut damage. In 1999, Danila along with improved genotypes recorded lower ratings for blight, while in 2000 only Danila and IT95K-277-2 recorded the highest protection against bacterial blight. For smut with the exception of IT96D-666, the other (Danila, IT95K-277-2, IT95K-1091-3, IT95K-222-14 and IT96D-759) recorded statistically comparable lower damage ratings. In both seasons IT95K-277-2 recorded the least incidence and severity of leaf virus. Although the other genotypes had virtually similar and higher ratings in both or one of the two seasons, Danila and IT95K-1091-3 recorded consistently higher values. In the two seasons Danila produced significantly higher Total Dry Matter (TDM) and the other semi-determinate genotypes had comparable values. In both seasons IT95K-222-14 consistently out-yielded the other genotypes but it had statistically similar grain yield with IT95K-277-2 in 2000. Row arrangement had a significant effect on bacterial blight in 1999, whereas planting cowpea at 1S:1C recorded the least infection while the highest rating was obtained at 2S:4C row arrangement. Incidence and severity of leaf virus were not affected by row arrangement. In both seasons TDM and grain yields were significantly higher at 2S:4C while the least values were recorded at 1S:1C row arrangement was superior to the row arrangement. The genotype and row arrangement interaction indicated that planting of IT95K-222-14 at 2S:4C row arrangement produced the highest grain yield.