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Analysis of Nuclear Genetic Resistance in Maize to Race T of Southern Corn Leaf Blight

Two maize (Zea mays L.) inbred lines, in Texas malesterile cytoplasm (Tcms), with high levels of nuclear genetic resistance to race T southern corn leaf blight (Helminthosporium maydis Nisikado and Miyake) were derived by selfing and selection from two open-pollinatedcomposite sources. The lines were confirmed to be in Tcms and were utilized in crosses with an extremely susceptible Tcms line in two generation-mean analysis experiments.

Resistance was polygenic, and additive genetic effects accounted for most of the variation among generations. Dominance effects accounted for a small but significant portion of the genetic variance in both experiments.

The results suggest that gene frequencies for resistance could be enhanced by recurrent mass selection. In a program for development of commercial hybrids, selection should be practiced in male-sterile cytoplasm in two unrelated source populations. Lines would be extracted by inbreeding and crossed. Resulting hybrids would be evaluated for disease resistance, agronomic suitability, and yield.

Key Words: Cytoplasm • Generation-means • Male sterility • Zea mays L. • Helminthosporium maydis Nisikado and Miyaki

Received for publication June 6, 1975.