Comparative Spatial Analysis of the Sooty Blotch/Flyspeck Disease Complex, Bull’s Eye and Bitter Rots of Apples

Plant PathologyPlant Pathology, Published online 15 August 2011

P. Spolti, R. M. Valdebenito-Sanhueza, F. F. Laranjeira, and E. M. Del Ponte

“The incidence of sooty blotch/flyspeck (SBFS) and bitter and bull’s eye rots were assessed in a Fuji apple orchard during two seasons. Using a regular sampling design, 252 trees were selected and 20 fruits per tree were sampled at harvest and scored for disease incidence. For bitter and bull’s eye rots, additional assessments were made on all symptomless fruit after a 30-day period of storage. Randomness in the spatial pattern was assessed using beta-binomial analysis of incidence data for three sampling scales (one, three or six adjacent trees as sampling units) and using Spatial Analysis by Distance Indices (sadie) for disease counts for the 3-tree sampling scale. sadie was also used for testing spatial associations between a pair of diseases, between years for the same disease or between rotted and latently infected fruit. Using a toroidal-shifts procedure, 360 maps of disease counts were created based on the observed data, which were further analysed using sadie. Most datasets showed an aggregated spatial pattern, which was more consistent for the two fruit rots than SBFS, which showed distinct patterns depending on the year or method of analysis. The two fruit rots were spatially associated in most situations but SBFS and bull’s eye rot were dissociated in one season. Results from virtual orchards showed that the patterns observed in the original maps may accurately represent those in similar apple-growing areas. Hypotheses regarding aspects of ecology and epidemiology of pathogens studied and potential efficacy of control measures in the region are discussed.”