Influence of relative virulence and latent infections on the development of Monilinia to Greek peach orchards

Brown rot is a very important disease of stone fruit worldwide. Host specificity has important implications for disease management. In this study, the pathogenicity and relative virulence of Monilinia laxa and M. fructicola isolates from peach on different hosts were evaluated. The results of this study showed that all the isolates of M. laxa and M. fructicola originated from peach were pathogenic on the excised shoots of cherry, peach, plum, apricot, apple and pear shoot segments and the fruit on plum, apple and pear. The behavior of each species was not the same in different crops and there was no evidence for the predominance of either Monilinia species. In addition, the incidence of latent infections on peach and nectarine cultivars was investigated. This study showed that there was no latent infection in bloom stage in 2013. In contrast, the percentage of latent infection during the fruit development stage was between 4 and 13% in peach cultivars and 2-15% in nectarine cultivars. Latent infections were only found in bloom stage of peach cultivars in 2015, but not in the different fruit development stages tested. It is possible that the percentage of latent infections on peach and nectarine flower and fruit may different from year to year depending on the weather conditions and cultivar. Finally, the significance of leaving thinned peach fruits in the orchard on the appearance of latent infection was examined. It was found that the percentage of latent infections on fruit was significantly higher in the untreated control compared with a treatment with thiophanate methyl or when the fruits were thinned. No significant difference was found between fruit treated with thiophanate methyl and thinning of fruits. Generally, the results of this study could help on the better management of brown rot disease.