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Gene Dosage Effects on Monogenic Resistance to Northern Corn Leaf Blight¹

The Ht gene conditions chlorotic lesion resistance in maize (Zea mays L.) to northern corn leaf blight incited by Helminthosporium turcicum Pass.

Monoploid, diploid, triploid, and tetraploid seedlings of Zea mays were obtained for the Ht and ht alleles and inoculated at the 3- or 4-leaf stage in a humid chamber at 19 to 21 C. Disease reaction was evaluated by determining the percentage of leaf area infected.

There was no difference in resistance between monoploid (Ht) and diploid (Ht Ht) or between triploid (Ht Ht Ht) and tetraploid (Ht Ht Ht Ht) seedlings; however, three and four doses of the Ht allele conferred a higher level of resistance on seedlings than did one or two doses. Heterozygous diploid (Ht ht) seedlings were always less resistant than any of the other levels of Ht used in this study.

Diploid, triploid, and tetraploid seedlings containing two, three, and four doses, respectively, of the ht allele did not differ in their degree of susceptibility. Monoploid (ht) seedlings were much more susceptible than seedlings of the other three dosage levels.

Key Words: Monoploids • Triploids • Tetraploids • Maize

² Professor of Agronomy, Plant Science Department, University of New Hampshire, Durham, N.H. 03824, and Assistant Professor, Department of Biology, St. Francis College, Biddeford, Maine, respectively. The authors express their sincere appreciation to Dr. A. L. Hooker, University of Illinois, for materials and helpful advice and to Dr. W. E. Urban, Jr., University of New Hampshire, for assistance on statistical procedures.

Received for publication November 10, 1969.