Spatiotemporal dynamics of brown rot epidemics and fine‐scale structure of Monilinia fructicola populations within peach tree canopies

Toyota Auditorium, Howard H. Baker Jr. Center for Public Policy

We examined the spatio-temporal dynamics of brown rot disease (caused by Monilinia fructicola) and the structure of the corresponding pathogen population within individual, intensively mapped peach tree canopies. Across 3 years, a total of 12 trees were monitored for disease development throughout the season, tagging each individual symptom (blossom blight, green fruit rot, preharvest fruit rot, and twig canker) and mapping it in three dimensions using a magnetic digitizer. In addition, M. fructicola was isolated from each of the mapped symptoms. Trees had between 126 and 739 fruit total and a final preharvest fruit rot incidence of 12.3 to 78.2%. The index of disease aggregation was negatively correlated with disease incidence (r = −0.756, P < 0.0001), i.e., the lower the disease incidence, the greater the relative degree of aggregation of affected fruit in the canopy. DNA from all 718 single-conidial isolates obtained from a subset of six trees was evaluated with 20 polymorphic SSR markers. For one tree analyzed thus far, haploid diversity for early-season blossom blight isolates was higher than that from mid-season green fruit rot and late-season preharvest fruit rot epidemics (h = 0.522, 0.355, 0.393, respectively). No spatial genetic structure was detected for either early- or mid-season periods, whereas significant autocorrelation among genetic distances was observed at spatial distances up to 1.5 m during the preharvest interval. The presence of such fine-scale patterns of M. fructicola populations within individual trees is likely due to a localized zone of influence in pathogen spore dispersal.Preliminary analysis for 84 of 176 isolates obtained from tree O’Henry 26 in 2009 was conducted. Examining Each period was also analyzed for evidence of population structure, but no structure was observed for either early- or mid-season periods, even when combined (Fig. 7 2A). Population structure was detected for the late-season fruit rot period, showing significant genetic relatedness of isolates up to 1.25 m in distance.