Am. Julian et al., THE INDUCTION AND CHARACTERIZATION OF ISOLATES OF PSEUDOCERCOSPORELLA-HERPOTRICHOIDES WITH ALTERED SENSITIVITY TO THE FUNGICIDE PROCHLORAZ, Pesticide science, 41(2), 1994, pp. 121-128
Isolates of Pseudocercosporella herpotrichoides (Fron.) Deighton, caus
al agent of eyespot disease of cereals, with reduced sensitivity to th
e imidazole fungicide prochloraz were produced by spontaneous selectio
n on fungicide-amended media or by successive rounds of ultra-violet (
UV) irradiation of conidia. Resistance frequencies were similar to tho
se obtained for other sterol-biosynthesis-inhibiting (SBI) compounds.
Stability testing indicated that a large proportion of the UV-induced
mutants reverted rapidly to wild-type sensitivity levels. However, the
spontaneously selected strains, and strains produced after the third
round of mutation proved more stable. Strains produced by spontaneous
selection and from a single round of UV irradiation showed relatively
low levels of resistance, in most cases within the range shown by the
European field population. Subsequent rounds of UV irradiation raised
resistance levels by factors of between 5 and 16 times. Growth rate in
culture and sporulation ability were impaired in some, but not all, s
trains. Spontaneous mutants showed no decrease in pathogenicity to cer
eal hosts while UV-induced strains were more variable, with some givin
g significantly reduced infection scores. The spontaneous mutants, and
some of the UV-induced strains, gave higher infection scores on plant
s treated with prochloraz than on untreated plants. This may have been
due to changes in the stem base microflora resulting in reduced compe
tition. The findings from this study suggest a multi-factorial basis f
or resistance, resulting in directional rather than disruptive selecti
on for field resistance.