Genotype and cropping system effects on cowpea growth and yield.

Genotype X cropping system interactions may complicate the plant breeders' task of increasing crop yields, since selection and improvement in one cropping system may not result in improved performance in a different cropping system. Field experiments were conducted in 1990 and 1991 to examine the effects of cowpea (Vigna unguiculata (L.) Walp.) genotypes and cropping systems on cowpea yield, yield components, biomass, and leaf area. When cowpea was grown in sole crop and in intercrop with pearl millet (Pennisetum americanum (L.) Leeke), a significant genotype X cropping system interaction for seed yield occurred in both years. In sole crop, 'California Blackeye 46' (CB46) yielded more than 'Tohono O'odham' (TOC). By contrast, in intercrop, there was no difference in yield between genotypes in 1990, but TOC outyielded CB46 in 1991. More vegetative biomass and leaf area was produced by TOC than CB46 and more was produced in sole crop than intercrop. In intercrop, TOC produced more leaf area in the furrow and higher in the intercrop canopy than CB46. TOC had a more negative effect on millet than CB46. In intercrops differing in row-spatial arrangement (within- and between-row intercrops), TOC outyielded CB46 in both the within- and between-row intercrops, and more yield was produced in the between-row than within-row intercrop. To identify plant traits associated with cowpea seed yield under intercropping, three F₂ cowpea populations were grown in intercrop with millet. All three yield components (pod number, seeds per pod, and mean seed weight) were significantly correlated with cowpea seed yield. The number of pods accounted for most of the variation in seed yield. There was a negative association between seeds per pod and mean seed weight. Plant length, number of nodes, and number of branches were also correlated with seed yield, as were the number of pods produced on basal and distal branches and from the longest (> 10 cm) internode category. Plant traits associated with yield in intercrop may differ from those associated with yield in sole crop. Hence, selection criteria for indirectly selecting yield will differ between cropping systems