Genetic variances, heritabilities and genetic correlations of grain yield, harvest index and yield components for common bean (Phaseolus vulgaris L.) in sole crop and in maize/bean intercrop

Breeding of common bean (Phaseolus vulgaris L.) for intercropping with maize (Zea mays L.) is usually done in bean sole crop nurseries. However, bean cultivar evaluations have identified significant cultivar x cropping system interactions. The objective of this study was to determine whether intercrop and sole cropping systems have different effects on phenotypic and genetic variance components of bean populations. Unselected F-2 and F-3 populations of 16 crosses of common bean were evaluated in the two cropping systems at Elora and Woodstock, Ontario, Canada, in 1993 and 1994. Significant population x cropping system interaction was found for grain yield and pods per plant. Genetic correlations between cropping systems were lowest for grain yield and pods per plant and highest for seed weight and seeds per pod. There were few differences between cropping systems for genetic variances. Genotype x location variance was higher in intercrop than in sole crop. Broad-sense heritabilities and narrow-sense heritabilities for most traits were comparable between cropping systems. The exception was pods per plant, which showed greater heritability in sole crop. Realized heritability of grain yield was greater in intercrop. We conclude that single plant selection as done with the pedigree system of breeding should be effective in intercrop.