Interactions of genotypes of bush beans (Phaseolus vulgaris L.) with planting system and cropping season were evaluated on the CIAT station at 1,000 m elevation in Colombia. The objective was to determine if selection in monoculture can result in genetic progress for yield in complex multiple cropping systems. Cultivars of bush beans, defined as non‐climbing and including both determinate and indeterminate plant types, were tested in monoculture and associated with maize (Zea mays L.) in three seasons in 1975 and 1976.Significant correlations of bean yields were obtained for these cultivars grown in monoculture and in association with maize. Higher yields and greater absolute differences among cultivars in monoculture favor this system as most efficient for early generation genotype selection and yield testing. Late generation yield evaluation of promising lines may be necessary in more than one system to evaluate adaptation to a wider range of cropping systems.Season ✕ cultivar interactions in either system could complicate selection and rapid elimination of large numbers of progeny in a breeding program. Early generation selection for yield must be practiced with care, and most decisions on promising families delayed until replicated trial data are available from two to three generations in one location or several locations in one season.

Maize (Zea mays L.) in monoculture and in association with bush and climbing beans (Phaseolus vulgaris L.) was evaluated at CIAT in the Cauca Valley, Colombia (1,000 m elevation, 4° N lat). Since small farmers in the Andean zone plant maize at low densities in association with beans, the objectives were to measure the effects of the associated legume crop on maize yields and net returns.Maize yields did not differ significantly between monoculture and associated cropping at harvest densities from 3 to 4 ✕ 104 plants/ha, in trials with different bean cultivars, bean plant densities, planting systems, and relative dates of planting of the two crops. There were no significant differences between systems in the following maize components: ear length, ear and cob diameter, row number, shelling percent, weight per 100 seeds, harvest index, prolificacy index, total biological yield, or plant height. Lodging was less severe in an associated culture of maize, wiht an average of 16.4% in association compared to 28.7% in monocrop over six trials. Less fall armyworm (Spodoptera frugiperda Smith) attack was observed in associated crop maize than in monoculture. Efficiency of land use increased with addition of beans to the system, and highest net income was achieved with associated cropping systems. These results may help to explain why small farmers continue to utilize associated cropping systems in the tropics of Latin America.

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