Breeding corn for adaptation to two diverse intercropping companions

Intercropping is an agricultural system widely practiced in the tropics and becoming more widespread in temperate regions. The vast majority of varieties currently grown in intercrop have been developed in and for monoculture, although some breeding programs specifically focused on intercrop systems have beer initiated. It is not clear if selection in monoculture is adequate to identify varieties adapted to intercrop, nor is it clear if varieties selected for intercrop performance with one companion will be adapted to another crop combination. The aims of this study were to determine the extent to which selection of corn in monoculture would identify types adapted to growth in corn-bean or corn-clover intercrop, and to determine how selection in one of the intercrops (corn-bean or corn-clover) would compare with selection in the other. The corn used consisted of two groups that had been selected in monoculture, and two that had been selected in corn-bean intercrop. All groups were evaluated in monoculture, corn-bean intercrop, and corn-clover intercrop. Analysis of variance showed that the ranking of the four selection groups was not significantly different when the two intercrops were compared, but was significantly different (P < 0.05 for comparison of clover intercrop and monoculture, and P = 0.07 for comparison of bean intercrop and monoculture) when either of the two intercrops was compared with monoculture. Correlation analysis of corn traits and corn yield in the three cropping systems revealed more similarities between the intercrops than between either intercrop and monoculture. Plant height and leaf area index were more strongly negatively correlated with days to flower in both intercrops than in monoculture. Correlation analysis also revealed some differences between the intercrops, particularly with bean and clover yields. Clover yields were not adversely affected by early growth and maturity of corn, but bean yields were. We conclude that selection of corn in monoculture is not ideal when lines adapted to corn-clover intercrop or corn-bean intercrop are desired. Furthermore, selection in either intercrop will identify corn types adapted to the other, as early vigor and maturity allow best corn performance in both crop combinations. Thus, individualized breeding programs may not be required to adapt a crop to growth in association with relatively different companions.