LACK OF CORRELATION BETWEEN FITNESS AND RESISTANCE TO STEROL BIOSYNTHESIS-INHIBITING FUNGICIDES IN PYRENOPHORA-TERES

Fitness costs associated with resistance to sterol biosynthesis-inhibi ting fungicides (SBIs) were investigated by calculating correlations b etween SBI-resistance phenotypes and fitness phenotypes in Pyrenophora teres. Correlations between resistance to the SBIs triadimenol and pr opiconazole and two components of fitness were estimated with P. teres isolates randomly sampled from populations in North Dakota and Bavari a, Germany. The fitness components, latent period (the time from inocu lation to the first appearance of a conidium) and sporulation (total s porulation per lesion), were determined quantitatively with detached b arley 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 inoc ulation and sporulation from 0 to 50,000 conidia per lesion. Significa nt genetic variation (P < 0.05) in fitness components was detected amo ng P. teres isolates from both populations in three of four separate e xperiments. Significant genetic variation in resistance to triadimenol and propiconazole (P < 0.001) was detected among P. teres isolates fr om both populations. However, no significant correlation between fitne ss and resistance was obtained in any of the experiments. Therefore, w e could not detect any fitness costs associated with resistance to tri adimenol or propiconazole in these populations and conclude that SBI-r esistance management strategies cannot depend upon the existence of fi tness costs.