Seiya Saito and Chang-Lin Xiao, Citrograph
Gray mold caused by the fungus Botrytis cinerea has recently become a major post-harvest fruit rot disease of California mandarins after extended storage. B. cinerea historically has not been among the target pathogens in post-harvest disease control programs for citrus.
To develop post-harvest disease control programs for gray mold, information is needed about whether isolates of B. cinerea from mandarins are resistant to the currently registered post-harvest fungicides that are known to be effective against this fungus such as azoxystrobin, pyrimethanil, fludioxonil and thiabendazole.
We found that B. cinerea resistance to azoxystrobin, pyrimethanil and thiabendazole is widespread, but no resistance to fludioxonil was detected.
B. cinerea isolates from mandarin demonstrated five different fungicide-resistance phenotypes¹ including the most prevalent one that is triple resistant to azoxystrobin, pyrimethanil and thiabendazole.
In efficacy tests, azoxystrobin, pyrimethanil and thiabendazole failed to control gray mold on mandarin fruit inoculated with the respective fungicide resistant isolate.
However, fludioxonil remained effective as no fludioxonil resistance was detected in the current populations.
Efficacy of natamycin, a newly registered biofungicide (*), also was evaluated for gray mold control. Natamycin effectively controlled gray mold on mandarin fruit, regardless of B. cinerea fungicide resistance phenotypes. Natamycin appears to be a promising tool for fungicide resistance management and post-harvest disease control programs.
(*) E235 is the identification as food additive
Gray mold fungicide resistance in the pathogen Botrytis cinerea and its impact on control
Seiya Saito and Chang-Lin Xiao
Citrograph Vol. 12, No. 4 | Fall 2021