INOCULUM AND INFECTION DYNAMICS OF THE SOOTY BLOTCH AND FLYSPECK COMPLEX OF APPLES IN SOUTHERN BRAZIL
P. Spolti, R.M. Valdebenito-Sanhueza, M.L. Gleason, E.M. Del Ponte
The objectives of this study were to assess the relationship of infection of apple by sooty blotch and flyspeck (SBFS) to environmental conditions during fruit developmental stages and to monitor the chronology of increase in SBFS incidence in an orchard of southern Brazil. Seven “infection windows” (IWs) were simulated by exposing developing fruit (cv. Fuji) for predetermined periods of time and covering them with fruit bags during the rest of the season. Check treatments included fruit that were either surface-disinfested and covered or disinfested and uncovered. SBFS incidence was recorded after harvest on the fruits from each treatment, after incubating them in a moist chamber, and correlation analysis was used to assess association with moisture-related variables during each IW. In a separate experiment, timing of disease appearance was monitored by sampling non-covered fruit weekly until harvest. SBFS signs were observed on the fruits from all IW and check treatments. Average incidence ranged from 15 to 65% across the IWs, whereas incidence was >95% in fruits that were not covered during the experiment. SBFS infections were detected at harvest in the partially covered check treatment, thus suggesting that inoculum was present before the fruit was first covered 31 days after petal fall. Linear relationships were observed between SBFS incidence, rainfall and leaf wetness duration recorded within an IW. The period between fruit inoculation and appearance of the disease in the field was about 49 days.