ABSTRACT
Gray mold caused by Botrytis cinerea severely threatens the yield of ginseng (Panax ginseng). Various categories of fungicides have been utilized to control gray mold on this crop. In this study, the resistance of 102 isolates of B. cinerea from 11 commercial ginseng-growing regions in China to fungicides was examined. A total of 32.4% were resistant to boscalid, with EC50 values that ranged from 12.26 to 235.87 µg/ml, and 94.1% were resistant to pyraclostrobin, with EC50 values that ranged from 5.88 to 487.72 µg/ml. Except for sdhA and sdhD, the amino acid substitutions of P225F, P225L, N230I, H272Y, and H272R in the sdhB subunit from 24 (4 sensitive [S] and 20 resistant [R]), 5 (1 S and 4 R), 1 (S), 1 (R), and 8 (4 S and 4 R) strains, respectively, and the concurrent amino acid substitutions of G85A + I93V + M158V + V168I in the sdhC subunit from 5 (4 S and 1 R) strains were identified. A G143A substitution in cytochrome b was identified in 96 isolates that were resistant to pyraclostrobin and three that were sensitive to it. The Bcbi-143/144 intron was identified in the other three isolates sensitive to pyraclostrobin, but it was absent in the isolates that harbored the G143A mutation. The results showed that the populations of B. cinerea on ginseng have developed strong resistance to pyraclostrobin. Therefore, it is not recommended to continue using this fungicide to control gray mold on P. ginseng. Boscalid is still effective against most isolates. However, to prevent fungicide resistance, it is recommended to use a mixture of boscalid with other categories of fungicides.
ABSTRACT
This study aimed to establish the baseline sensitivity of Botrytis cinerea from Panax ginseng to prochloraz, and ensure the fitness of prochloraz-resistant mutants and the cross-resistance of B. cinerea to prochloraz and commonly used fungicides for the prevention and control of gray mold including boscalid, pyraclostrobin, iprodione, and pyrimethanil. The sensitivity of B. cinerea from P. ginseng to fungicides was determined by the mycelial growth rate method. The prochloraz-resistant mutants were screened out through fungicide domestication and ultraviolet(UV) induction. The fitness of resistant mutants was determined through the stability of subculture, mycelial growth rate, and pathogenicity test. The cross-resistance between prochloraz and the four fungicides was determined by Person correlation analysis. The results showed that all B. cinerea strains tested were sensitive to prochloraz, and the EC_(50) value ranged from 0.004 8 to 0.062 9 µg·mL~(-1), with an average of 0.022 µg·mL~(-1). The sensitivity frequency distribution diagram showed that 89 B. cinerea strains were located within the main peak with a continuous single peak curve, and the average EC_(50) value of 0.018 µg·mL~(-1) was taken as the baseline sensitivity of B. cinerea to prochloraz. The fungicide domestication and UV induction obtained 6 resistant mutants, among which 2 strains were unstable and the other 2 strains showed decreased resistance after multiple generations of culture. Furthermore, the mycelial growth rate and spore yield of all resistant mutants were lower than those of their parents, and the pathogenicity of most mutants was lower than that of their parents. In addition, prochloraz had no obvious cross-resistance with boscalid, pyraclostrobin, iprodione, and pyrimethanil. In conclusion, prochloraz has great potential for controlling gray mold in P. ginseng, and the resistance risk of B. cinerea to prochloraz is low.