Prevalence and distribution of Penicillium expansum and Botrytis cinerea in apple packinghouses across Washington State and their sensitivity to the postharvest fungicide pyrimethanil
Blue and gray molds, caused by Penicillium expansum and Botrytis cinerea, respectively, are the two major postharvest diseases of apple worldwide. To evaluate their prevalence and distribution in Washington State, decayed apples were collected from 140 grower lots (50 fruit per lot) distributed throughout 10 counties in central Washington from February to May of 2016 on fruit harvested in 2015. Blue- and gray-mold symptomatic fruit collected from the packinghouses were used to isolate P. expansum and B. cinerea on Petri plates containing potato dextrose agar (PDA) acidified to pH 3.5. Isolates were purified and identified using key morphological traits. Overall, P. expansum was found in 137 (98.5%) of the 140 lots surveyed versus 119 lots (85%) for B. cinerea. Interestingly, only one of the two pathogens was predominant in a single grower lot. Differences in geographic distribution of the two pathogens were observed. In total, 860 P. expansum isolates and 780 B. cinerea isolates were collected, stored as purified cultures and tested for their sensitivity to the anilinopyrimidine-pyrimethanil using a germ tube elongation inhibition assay. The sensitivity of P. expansum was assessed on l-asparagine agar amended with 0.5 µg mL‑1 pyrimethanil and for B. cinerea on 0.5% sucrose agar amended with 1 and 25 µg mL‑1 pyrimethanil. The overall statewide resistance frequencies were 13.5 and 20.4% in P. expansum and B. cinerea, respectively. Resistant populations of P. expansum and B. cinerea were found in 48 and 56% of the grower lots surveyed, respectively, at frequencies ranging from 2.6 to 100%. These two pathogens are continuous threats to apple storability and the increasing selection for populations resistant to pyrimethanil can result in major control failure unless adequate rotation programs are implemented quickly.
Amiri, A., Ali, M.E., De Angelis, D.R., Mulvaney, K.A. and Pandit, L.K. (2021). Prevalence and distribution of Penicillium expansum and Botrytis cinerea in apple packinghouses across Washington State and their sensitivity to the postharvest fungicide pyrimethanil. Acta Hortic. 1323, 167-172
Malus domestica, blue mold, gray mold, fungicides, resistance, postharvest