Influence of Host Resistance and Growth Stage at the Time of Inoculation on Stewart’s Wilt and Goss’s Wilt Development and Sweet Corn Hybrid Yield. Suparyono , Department of Plant Pathology, University of Illinois, Urbana 61801. J. K. Pataky, Department of Plant Pathology, University of Illinois, Urbana 61801. Plant Dis. 73:339-345. Accepted for publication 9 December 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0339.

Stewart’s and Goss’s bacterial wilts were similar in symptomatology, disease development, and effects on sweet corn yield. The severity of the two bacterial wilts and their effects on sweet corn yield depended on the level of host resistance and on the host growth stage at which plants were inoculated. Disease development was greatest when sweet corn hybrids at the three- to five-leaf stage were inoculated with Erwinia stewartii and Clavibacter michiganense subsp. nebraskense. Disease severity was less when plants were inoculated at later growth stages, although disease development was affected less by plant age in susceptible and moderately susceptible hybrids than in resistant and moderately resistant hybrids. Yields of susceptible and moderately susceptible hybrids were significantly reduced by both diseases when plants were inoculated at the three- to five-leaf or the five- to seven-leaf stage. The yield of a moderately resistant hybrid inoculated at the three- to five-leaf stage was reduced in 2 of 3 yr. The yield of a resistant hybrid was not significantly affected by either disease. A damage threshold of approximately 40% severity (i.e., a disease rating above 6, which corresponds to systemic infection and stunting) 1 wk before harvest was observed for both diseases on the susceptible and moderately susceptible hybrids. Beyond this threshold, sweet corn yield decreased 17 and 19%, by weight and number of ears, respectively, for each 10% increase in severity.