VIEW ARTICLE

Resistance

Partial Rust Resistance in Sweet Corn Hybrid Seedlings. J. K. Pataky, Assistant professor, Department of Plant Pathology, University of Illinois, Urbana 61801; Phytopathology 76:702-707. Accepted for publication 9 February 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-702.

Partial resistance in corn (Zea mays) to Puccinia sorghi, causal agent of common rust, was evaluated in seedlings in greenhouse experiments. In preliminary experiments, 11 sweet corn hybrids and two dent corn inbreds were differentiated on the basis of the number of sporulating uredinia per plant when inoculation techniques and replications were adequate. The components of the infection cycle through which partial resistance was expressed were evaluated further using five sweet corn hybrids: Miracle (moderately resistant), Gold Cup (intermediate), and Sweet Sue, Florida Staysweet, and Stylepak (susceptible). No differences were observed among the five hybrids for time-related components (latent period, infectious period, and rate of occurrence of sporulating uredinia in time). Latent period was about 6 days and infectious period was about 28 days. The maximum number of sporulating uredinia occurred about 20 days after inoculation. Components of partial resistance related to P. sorghi reproduction (number of lesions, number of sporulating uredinia, number of uredinia per lesion, size of uredinia, and urediniospore production) varied among the hybrids. The partial resistance of Miracle was expressed as a reduction in all reproduction-related components. Gold Cup also had fewer uredinia and urediniospores than the susceptible hybrids but was not as resistant as Miracle owing to an increased number of chlorotic lesions per leaf. Florida Staysweet had fewer lesions than Sweet Sue and Stylepak but more uredinia per lesion. Size of uredinia and urediniospore production per uredinium were less on Sweet Sue than on Florida Staysweet and Stylepak. Consequently, partial rust resistance can be detected at the seedling stage and is expressed as reductions in various components of the infection cycle. Although screening for various components of resistance may be impractical in most breeding programs, detection of partial resistance at the seedling stage could be potentially beneficial if selections for resistance could be made before anthesis.