Components Contributing to Partial Resistance in Maize to Puccinia polysora. Natale Zummo, USDA-ARS, Department of Plant Pathology and Weed Science, Mississippi State University, Mississippi State 39762. . Plant Dis. 72:157-160. Accepted for publication 2 September 1987. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1988. DOI: 10.1094/PD-72-0157.

Four uredinial characteristics (incidence, size, tumescence, and sporulation) of infection of corn (Zea mays) by Puccinia polysora were studied under greenhouse and field conditions to determine their usefulness in differentiating among corn genotypes for partial resistance to southern corn rust. Evaluation scales were used so that corn genotypes could be compared under divergent environments. Corn genotypes differed significantly in response to the fungus with regard to these characters. There was some variation in expression of these rust components among individual corn genotypes inoculated in the field, humidity chamber, and spore settling tower, but the ranking of genotypes for these components remained constant. Inoculated plants of a susceptible genotype (Pioneer Brand 3369A) consistently had greater numbers of uredinia, which were significantly larger and more tumid and sporulated more readily than those on corn genotypes with partial resistance. The consistent relationship of these characteristics on plants in the field and greenhouse indicates that greenhouse studies could be useful for identifying corn genotypes with partial resistance to P. polysora. This would allow screening for resistance to southern rust in areas where epidemics do not normally occur or in years when environmental conditions do not favor rust development in the field.