Pyrimethanil sensitivity and fitness in Botrytis cinerea populations from Shanxi Province, China

Abstract

Pyrimethanil is a fungicide that is highly active against the plant pathogen Botrytis cinerea. The sensitivity of B. cinerea to pyrimethanil and the risk of resistance were investigated in Shanxi, China. A total of 169 B. cinerea isolates from decayed cucumber leaves were collected and tested for their sensitivity to pyrimethanil based on mycelial growth inhibition. The EC50 values ranged from 0.09 to 12.26 μg/ml (average = 3.19 μg/ml, SD = 0.95) for pyrimethanil. Sensitive isolates (54.4%) had EC50 values of <1.0 μg/ml, whereas 29 highly resistant isolates had EC50 values ≥9.17 μg/ml. This resistance persisted after 10 generations of successive incubations on fungicide-free potato dextrose agar. A fitness study of pyrimethanil-resistant strains showed that all resistant isolates had sporulation and pathogenicity similar to the sensitive strains, but they had lower rates of mycelial growth and spore germination and lower competitive ability. The fitness of resistant isolates was lower than that of sensitive strains, but treatment of B. cinerea with pyrimethanil could produce a resistant population. EC50 values for pyrimethanil and cyprodinil were positively correlated, and no cross-resistance was found between other fungicides included in this study.