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Combining ability of tropical maize germplasm in West Africa: IV. Inheritance of resistance to downy mildew (Perenosclerospora sorghi) infection
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Response to downy mildew (DM) attack especially in improved maize varieties is usually erratic when grown in the field. There is need to have a clear understanding of the breeding behavior of maize when infected with DM. A set of diallel crosses obtainecl from nine parents, four resistant and five susceptible lines, was evaluated under artificial infection with DM spores in four environments of Nigeria from 1993 to 1995. Results obtained from these evaluations revealed a highly significant genotype by environment interaction resulting in high general and specific combing ability interaction with environment for the resistance parameters. However, the importance of this interaction is rather low when compared with the main effect, thus reflecting the overall importance of the main effects. Resistance to DM attack is polygenic, with both additive and non-additive genes being important. There was a preponderance of additive gene action for the resistance parameters. Susceptibility was dominant. High mid- and better-parent heterosis were generally obtained in the direction of susceptibility. Useful sea effect obtained in a single cross involving a line (KU 1414) from the well known DM population Suwan-1 of Thailand and a tropical maize inbred (Tzi 18) is being exploited as a commercial hybrid for the control of the disease in West and Central Africa.