FITNESS OF ISOLATES OF ERYSIPHE-GRAMINIS FSP TRITICI WITH REDUCED SENSITIVITY TO FENPROPIMORPH

Under crowded infection conditions, isolates of Erysiphe graminis f.sp . tritici with reduced sensitivity to fenpropimorph displayed a lower competitive ability than wild type isolates. The lower competitive abi lity could not be ascribed to changes in germination, latent period, c olony forming ability or production of conidia, but seems to be a comp lex change in phenotype that cannot be assessed easily by characteriza tion of individual fitness components. Using mildew isolates containin g fungicide-sensitivity and virulence markers to study survival, some isolates with reduced sensitivity to fenpropimorph survived the winter . The competitive ability of these isolates seemed to be slightly lowe r than that of the mildew population that migrated naturally into the experimental field. Results described indicate that in practice, in pe riods without selection pressure, the frequency of isolates with reduc ed sensitivity to this compound may decrease. Copyright (C) 1996 Elsev ier Science Ltd