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Lack of Correlation Between Fitness and Resistance to Sterol Biosynthesis-Inhibiting Fungicides in Pyrenophora teres. Tobin L. Peever, Department of Plant Pathology, Cornell University, Ithaca, NY 14853; Michael G. Milgroom, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 84:515-519. Accepted for publication 25 January 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-515.

Fitness costs associated with resistance to sterol biosynthesis-inhibiting fungicides (SBIs) were investigated by calculating correlations between SBI-resistance phenotypes and fitness phenotypes in Pyrenophora teres. Correlations between resistance to the SBIs triadimenol and propiconazole and two components of fitness were estimated with P. teres isolates randomly sampled from populations in North Dakota and Bavaria, Germany. The fitness components, latent period (the time from inoculation to the first appearance of a conidium) and sporulation (total sporulation per lesion), were determined quantitatively with detached barley leaf sections inoculated with P. teres conidia in the greenhouse. Resistances to triadimenol and propiconazole were measured as radial growth (proportion of the control) on a single discriminatory dose of each fungicide. The latent period varied from 5 to 11 days after inoculation and sporulation from 0 to 50,000 conidia per lesion. Significant genetic variation (P < 0.05) in fitness components was detected among P. teres isolates from both populations in three of four separate experiments. Significant genetic variation in resistance to triadimenol and propiconazole (P < 0.001) was detected among P. teres isolates from both populations. However, no significant correlation between fitness and resistance was obtained in any of the experiments. Therefore, we could not detect any fitness costs associated with resistance to triadimenol or propiconazole in these populations and conclude that SBI-resistance management strategies cannot depend upon the existence of fitness costs.

Additional keywords: DMIs, fungal resistance.