Associations Between Stewart's Wilt Ratings and Maturity of Sweet Corn Hybrids. J. K. Pataky, Department of Plant Pathology, University of Illinois, Urbana 61801. Suparyono, J. A. Hawk, M. L. Gardiner and M. H. Pauly. Department of Plant Pathology, University of Illinois, Urbana 61801; Department of Plant Science, University of Delaware, Newark 19717-1303; and Rogers Brothers Seed Company, 6338 Highway 20-26, Nampa, ID 83687. Plant Dis. 74:792-796. Accepted for publication 15 March 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0792.

The time at which sweet corn hybrids were evaluated for reactions to Erwinia stewartii and the method of evaluation affected the degree to which Stewart's wilt ratings and relative maturity of hybrids were associated. Maturity and severity of Stewart's wilt symptoms were related when inoculated plants were evaluated as seedlings and when inoculated or naturally infected plants were evaluated near anthesis. Correlations ranged from –0.25 to –0.41 for maturity and ratings of inoculated seedlings and from –0.34 to –0.71 for maturity and ratings made near anthesis. Maturity was not correlated with incidence of naturally infected seedlings. When inoculated plants were evaluated for severity of symptoms from seedling stages until the fresh-market harvest stage, correlations between ratings and maturity increased from –0.24 to –0.65 with each of five weekly evaluations. Conversely, there was no correlation between ratings and maturity when all hybrids were evaluated at the midsilk growth stage. Thus, early-maturing hybrids were rated more susceptible to E. stewartii at the later evaluations than at seedling stages, and late-maturing hybrids were rated more resistant at the later evaluations than at seedling stages. As a group, early-maturing hybrids were more susceptible to E. stewartii than mid- or late-maturing hybrids, although resistant and susceptible hybrids were identified in all three classes of maturity.