Early generation testing of common bean (Phaseolus vulgaris L.) populations in sole crop and in maize/bean intercrop

Few plant-breeding studies have examined methodology for improving common bean (Phaseolus vulgaris L.) yields by selecting in an intercrop situation. We hypothesized that early-generation testing would be as useful in a maize (Zea mays L.)/bean intercrop as in sole crop for identifying superior bean populations for yield. F₂ to F₅ bulks of six selected crosses and their F₅-derived advanced lines were evaluated in sole crop or intercrop. The F₂ and F₅ bulks were evaluated together in a preliminary trial in one location, while the advanced lines were evaluated with the F₃s in one location, and with the F₄s in two locations. Within sole crop, selection of the best three populations, based on F₂ performance, provided 67% of the top advanced lines. The rank correlation between average bulk yield across generations and the average line yield was positive and significant. Within intercrop, selection of the best three populations provided 56% of the top advanced lines. The rank correlation between advanced line yield and bulk yield across generations was positive but not significant. Also, the top three F₂ populations selected in sole crop produced 89% of the top advanced lines in intercrop. Advanced line performance showed a positive significant correlation with mean F₄ bulk performance for grain yield, 100-seed weight and seeds per pod within sole crop, while positive significant correlation was seen with pods per plant and seeds per pod in intercrop. Results indicate that F₂ bulk yields can be used to discard the least promising crosses in both cropping systems.