SPATIAL PATTERN OF BROWN ROT WITHIN PEACH TREES RELATED TO INOCULUM OF MONILINIA FRUCTICOLA IN ORGANIC ORCHARD

Abstract

Brown rot, caused by Monilinia fructicola, is the most important peach disease in Brazil. However, there is little information about the epidemiology and spatial patterns associated with this disease in organic orchards. This study characterized the spatial distribution of blossom blight and brown rot within trees under natural infection. The study was carried out in 2007 and 2008 in an organic orchard of located in southern Brazil. The spatial pattern of diseased flowers (in a sample of 80 flowers per tree per year) and fruit (from 64 to 309 fruit per tree per year) within each peach tree was assessed using 16 quadrats per tree. The dispersion index (D) and the modified Taylor’s power law were used to characterize the spatial pattern of the disease. The conidia density of M. fructicola and the weather conditions were monitored. In both years of assessment, diseased flowers were distributed at random in 90% of the trees, and no correlation was found between the incidence of blossom blight from a given year to the incidence of blossom blight or brown rot in the previous year. The distribution of brown rot within the tree was aggregated in both years in 70% of the trees where disease incidence was lower than 90%, and a significant positive relationship was observed in disease incidence from one year to the other. Taylor’s power law was significant for blossom blight and brown rot but aggregation was verified only for brown rot. According to these results, blossom blight is not an important source of inoculum to fruits, and we suggest that the intensive chemical control during flowering in the subtropical regions of Brazil should be reviewed.