Divergent selection of corn (Zea mays) in monoculture and intercrop

• Main Author: O'Leary, Niamh
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1995
• Subjects: Agronomy; Genetics
• ISBN: 9798516936913

This study investigated the role of breeding in improving corn (Zea mays L.) for intercrop with bean (Phaseolus vulgaris L.). The objectives included an assessment of variability in adaptation of corn to monoculture and corn-bean intercrop. The effects of selection environment, selection criteria, and type of recombination on intercrop yields were also investigated. A final objective concerned the efficacy of selecting in corn-bean intercrop for performance in corn-clover intercrop. The breeding methods consisted of divergent recurrent selection in two cropping systems: monoculture and corn-bean intercrop. Selection criteria used were leaf angle and corn yield in monoculture; and leaf angle and system yield in corn-bean intercrop. Selected materials were recombined in two ways: full sib recombination and half sib recombination. Selection groups were evaluated at two locations for two years. Divergent selection revealed a significant interaction between full sib families and cropping systems. This suggests sufficient variability does exist in these families to merit selection in intercrop, and to allow gain from this selection. In general, leaf angle selection in monoculture was superior to system yield selection in intercrop at improving overall intercrop yields. However, families selected for high leaf angle in monoculture generally had higher corn yield and lower bean yield than those selected in intercrop. Thus it is the importance of bean yield which should determine the choice of selection environments and selection criteria. Full sib recombination of selection groups resulted in higher corn and bean yields than half sib recombination. This suggests full sib recombination is a more appropriate choice in breeding programs aimed at increasing overall production from a corn-bean intercrop. Relative performance of the selection groups was similar in corn-bean and corn-clover (Trifolium pratense L.) intercrops. However, groups selected in monoculture out yielded those selected in corn-bean intercrop when grown in corn-clover intercrop. Therefore it seems that cycles of selection in corn-bean intercrop may result in decreased yield potential, and ultimately select families which yield lower in clover intercrop than monoculture-selected materials.