Populationsänderungen von Pseudocercosporella herpotrichoides mit und ohne Fungizidselektion

Population changes in Pseudocercosporella herpotrichoides with and without fungicide selection A conidium mixture of W (wheat‐type) and R (rye‐type) strains of Pseudocercosporella herpotrichoides (W:R = 1:1) was incubated on PD‐agar without fungicide or amended with the imidazole prochloraz or the triazole cyproconazole. The W:R ratio was assessed over four generations using the different benomyl sensitivity of the strains as marker. In untreated mixtures, the R strain completely dominated the population already after two generations. Similarly, in cyproconazole‐treated mixtures, the R strain increased to 100% after the second generation, whereas in prochloraz‐treated mixtures the R strain either followed the same pattern as in untreated mixtures or fluctuated around the initial proportion of 50% over four generations. The W and R strains displayed different fitness properties. The average hyphal growth rate was 8.5 mm/10 d and 4.5 mm/10 d for the W and the R strains, respectively; the sporulation capacity was 80 and 400 conidia/colony, respectively, for the two strains. The different fitness resulted in a strong dominance of the R strains both in vitro and in field populations towards the end of the vegetation period. This shift towards R‐dominance occurred about equally fast with or without fungicide selection.