Identification and etiology of visible quiescent infections of Monilinia fructicola and Botrytis cinerea in sweet cherry fruit

Visible quiescent infections were detected as small (<1 mm) necrotic flecks on green cv. Bing cherry fruit and as reddish halos surrounding tannish sp ots (1 to 2 mm) on immature, yellow-pink cv. Rainier cherry fruit in commer cial orchards in California. Monilinia fructicola or Botrytis cinerea, the fungal pathogens causing brown rot and gray mold of cherry fruit, respectiv ely, were isolated from most of the viable infections. M. fructicola was is olated more frequently from quiescent infections than B, cinerea in two yea rs of the study, whereas similar isolation frequencies for both fungi were obtained in the other two years of sampling from one commercial Rainier che rry orchard. Using immature-pink Bing fruit that were inoculated in the lab oratory, significantly more visible quiescent infections than active decay were reproduced in 6-, 9-, or 12-h wetness-period treatments after inoculat ion as compared to 18- or 24-h wetness periods where more active decay deve loped. Non-visible quiescent infections of M. fructicola or B. cinerea of i mmature Bing and Rainier fruit collected 2 weeks before harvest were identi fied on surface-sterilized, paraquat-treated fruit. in both years of the st udy, significantly more brown rot and gray mold occurred on the surface-ste rilized, paraquat-treated fruit than on the nontreated or surface-sterilize d fruit, indicating the presence of non-visible quiescent infections by the se fungi in cherry fruit. Thus, for the first time, we demonstrated the pre sence of visible quiescent infections caused by M. fructicola and B. cinere a and we confirmed the occurrence of non-visible quiescent infections in sw eet cherry fruit in California.