Early generation yield testing in beans in monoculture and intercropped with maize

As part of an effort to evaluate different breeding methods, two trials were planted at CIAT (3 degrees 31' N, mean temp. 24 degrees C) with families of beans in F3 and F4 generations, from single plant selections made in the F2 (F2 progeny method). The value of early generation yield testing was examined, particularly with regard to the performance of the materials in different cropping systems. These included sole cropping (monoculture) and intercropping with three maize genotypes varying in height from tall to short. Families had been separated on the basis of growth habit in the F2. These differences were maintained in F3 and F4, as shown by differences in main stem node number, days to flowering, and specific leaf weight (leaf dry weight/100 cm(2)). Specific leaf weight was also affected by the cropping system, an effect of shading by the maize. Bean yield was lowest with the tall maize (La Posta) and highest in sole cropping. The best combined yields of beans and maize were obtained in both generations with climbing beans (type IV) with La Posta (tall) or Suwan-1 (intermediate). Correlation coefficients between sole cropping and intercropping were generally higher for bush beans (types I, II and III) than for climbers (type IV). Bean and maize yields were negatively correlated in F3 and F4, with an average regression slope of -1, indicating that one kilo of maize was lost for every extra kilo of bean. Since the price ratio of the two crops is approximately 3:1 in Latin America, this regression slope is favourable for intercropping. The regressions among bean families from F3 to F4 were positive and significant both in sole cropping and intercropping. Two families of climbers (type IV) and one family of types II/III could be selected as exceptionally promising in both generations, in sole cropping and intercropping. It was concluded that the method of yield testing progenies from F2 single plants in two generations gave highly promising selections for yield and yield stability in different seasons and cropping systems.