Cowpea reactions to Striga gesnerioides II. Effect on grain yield and nutrient composition

Two field trials (early planting (EPT) and late planting (LPT)) were conducted in 1994 to determine the effect of Striga gesnerioides on the grain yield, yield components and nutrient composition of 16 cowpea varieties. These included 11 resistant varieties, 2 tolerant varieties and 3 susceptible varieties. The pod number and weight and grain yield of some of the resistant cowpea varieties were increased in the early planted trial (EPT), but most varieties exhibited varying degree of reduction in yield components in the late planted trial (LPT), caused by Striga infestation. In the LPT, there was a reduction in the pod weight and grain yield in two resistant varieties that hardly support Striga growth. The percentage reduction in the grain yield among cowpea varieties was lower in the EPT than LPT, and among the resistant than the susceptible varieties. However, S. gesnerioides showed low-percent reduction of grain protein in cowpea varieties. Generally, the percent change in grain protein and TSC content in cowpea varieties, due to Striga infestation varied among varieties with sowing dates and yield. This study showed that, the negative impact of Striga infestation on cowpea grain yield and nutrient composition can be alleviated when resistant varieties are planted early in the growing season.