Evaluation of St. Augustinegrass Accessions and Cultivars for Resistance to Sclerophthora macrospora. R. W. Toler, Professor, Department of Plant Sciences, Texas A&M University, College Station 77843. B. D. Bruton, Research Plant Pathologist, USDA, ARS, Weslaco, TX; and M. P. Grisham, Assistant Professor, Department of Plant Sciences, Texas A&M University, College Station 77843. Plant Dis. 67:1008-1010. Accepted for publication 18 March 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-1008.

Sixty-four St. Augustinegrass accessions and cultivars were tested for resistance to downy mildew in the field and laboratory in 1981 and 1982, and 47 of these showed from a trace to 95% infection. In 1982, 15 accessions and cultivars had ratings of 25% or greater and 23 had ratings from a trace to 25%. The fact that infection of artificially inoculated plants ranged from 14.5 to 36.3% suggests that the inoculum potential was too high to detect low levels of resistance. A Floratam mutant, Mut 10, was rated as uninfected in the field, whereas artificial inoculation resulted in 21% infection. Two accessions, Tx 33 and PI 410355, which were rated as 90 and 64% infected, respectively, under conditions of natural inoculum in 1982, were rated as only 27 and 30% infected when artificially inoculated. Artificial inoculation with Sclerophthora macrospora by current techniques does not provide adequate discrimination among resistant and susceptible St. Augustinegrass accessions and cultivars, but reaction to natural infections provides a more reliable means of evaluation.

Keyword(s): Stenotaphrum secundatum, turfgrass.