RECURRENT SELECTION FOR RESISTANCE TO EXSEROHILUM-TURCICUM IN 8 SUBTROPICAL MAIZE POPULATIONS

There are few reports on the progress achieved through recurrent selection for quantitative resistance to diseases in tropical or subtropical maize (Zea mays L.) populations. The objective of this study was to evaluate the progress achieved after four cycles of full-sib S1 recurrent selection in eight subtropical populations from the International Maize and Wheat Improvement Center (CIMMYT). Selection was primarily for improving polygenic resistance to the northern corn leaf blight (NCLB) induced by Exserohilum turcicum (Pass.) Leonard & Suggs, and the common rust (Puccinia sorghi Schw.). Evaluations were made under three environments (high, medium, and no disease pressure) represented by two locations each. A very rapid increase in resistance was obtained for both diseases (19 and 6% cycle-1 for NCLB and rust, respectively) without changing the maturity of the populations or reducing grain yield potential as measured by planting under relatively disease-free conditions. Under disease pressure, yield was found to be associated with resistance to NCLB (r = 0.52**; significant at P = 0.01), reduced stalk lodging (r = -0.51**), and greater number of ears per plant (r = 0.60**). Results suggest high heritability values for polygenic resistance to NCLB. It was also demonstrated that the full-sib S1 recurrent selection methodology employed was highly effective in achieving the initial breeding objectives in all the populations involved.