Effect of fungicides on epiphytic yeasts associated with strawberry

We studied the effect of two commonly used fungicides on the epiphytic yeast
community of strawberry. Greenhouse and field experiments were conducted
applying Switch (cyprodinil plus fludioxonil) or Signum (boscalid plus pyraclostrobin) to strawberry plants. Yeasts on leaves and fruits were assessed on
treated and untreated plants at several time points via plating and denaturing
gradient gel electrophoresis (DGGE) analysis. The yeast counts on plates of the
treated plants were similar to the control plants. Unripe fruits had 10 times
larger yeast concentrations than ripe fruits or leaves. Some dominant yeast
types were isolated and in vitro tests showed that they were at least 10 times
less sensitive to Switch and Signum as compared with two important fungal
strawberry pathogens Botrytis cinerea and Colletotrichum acutatum, which are
the targets for the fungicide control. DGGE analysis showed that the applied
fungicides had no effect on the composition of the yeast communities, while
the growing system, strawberry tissue, and sampling time did affect the yeast
communities. The yeast species most commonly identified were Cryptococcus,
Rhodotorula, and Sporobolomyces. These results point toward the potential
applicability of natural occurring yeast antagonists into an integrated disease
control strategy for strawberry diseases.