Identification and Etiology of Visible Quiescent Infections of Monilinia fructicola and Botrytis cinerea in Sweet Cherry Fruit

Abstract

Visible quiescent infections were detected as small (<1 mm) necrotic flecks on green cv. Bing cherry fruit and as reddish halos surrounding tannish spots (1 to 2 mm) on immature, yellow-pink cv. Rainier cherry fruit in commercial orchards in California. Monilinia fructicola or Botrytis cinerea, the fungal pathogens causing brown rot and gray mold of cherry fruit, respectively, were isolated from most of the viable infections. M. fructicola was isolated more frequently from quiescent infections than B. cinerea in two years of the study, whereas similar isolation frequencies for both fungi were obtained in the other two years of sampling from one commercial Rainier cherry orchard. Using immature-pink Bing fruit that were inoculated in the laboratory, significantly more visible quiescent infections than active decay were reproduced in 6-, 9-, or 12-h wetness-period treatments after inoculation as compared to 18- or 24-h wetness periods where more active decay developed. Non-visible quiescent infections of M. fructicola or B. cinerea of immature Bing and Rainier fruit collected 2 weeks before harvest were identified on surface-sterilized, paraquat-treated fruit. In both years of the study, significantly more brown rot and gray mold occurred on the surface-sterilized, paraquat-treated fruit than on the non-treated or surface-sterilized fruit, indicating the presence of non-visible quiescent infections by these fungi in cherry fruit. Thus, for the first time, we demonstrated the presence of visible quiescent infections caused by M. fructicola and B. cinerea and we confirmed the occurrence of non-visible quiescent infections in sweet cherry fruit in California.