Analysis of factors affecting latent infection and sporulation of Monilinia fructicola on prune fruit

Two studies were conducted to determine the effects of water content (WC) o n sporulation on thinned fruit and the effects of wetness duration, inoculu m density, and temperature on secondary infection of prune fruit by Monilin ia fructicola, the main causal pathogen of brown rot in California. In the first study, sporulation intensity and duration of sporulation of the patho gen were tested on inoculated thinned fruit with five levels (67.2, 53.8, 4 0.3, 26.9, and 13.4%) of WC. Regression analyses showed that both sporulati on intensity and duration of sporulation increased as WC of thinned fruit i ncreased. The predicted difference in duration of sporulation between fruit with 13.4 and 67.2% WC was about 3 days. In the second study, three inocul um concentrations (8,000, 16,000, and 24,000 conidia per milliliter) of M. fructicola were atomized onto prune fruit on trees in an orchard. Inoculate d fruit and shoots were covered with plastic bags to maintain wetness durat ion for 4, 8, 12, or 16 h. An overnight freezing and incubation technique w as used after harvest to determine the proportion of fruit with latent infe ction. Regression analysis demonstrated that inoculum concentration and wet ness duration were significant factors affecting secondary infection. Tempe rature was less important. Increased inoculum concentration and wetness dur ation increased the percentage of fruit with latent infections. Increased t emperature decreased the percentage of fruit with latent infections.