Comparative epidemiology of three Colletotrichum species complex causing Glomerella leaf spot on apple

Glomerella leaf spot (GLS) is an apple disease that is causing concern to growers in Brazil due to the increases in severity over the years and the difficulties in control. To date there are few studies on the temporal progress of this disease specially comparing species of Colletotrichum. In Brasil the main species is C. fructicola followed by C. nymphaeae. It is not known the contribution of each species to the more or less aggressive behavior of the epidemic related to the different regions of apple production in Brazil. This study aimed to evaluate the temporal progress of GLS and to compare epidemiological differences between Colletotrichum species in two apple cultivars. After modeling disease progress in two plots of experiments assessing the curve for each leaf (300 curves/plot, 30 twigs with 10 leaves each), we recommend the use of the non-linear logistic model with random effects. The simulated temperature range of different producing regions in Brazil (under growth chamber) did not influence the severity of the disease caused by each species studied: C. nymphaeae, C. fructicola or C. karstii. Under controlled conditions of temperature and also in an experimental orchard, C. karstii did not cause GLS symptoms in ‘Eva’ and was less severe in ‘Gala’ when compared to C. nymphaeae and C. fructicola. Incubation period and latent period in ‘Gala’ were similar between C. nymphaeae and C. fructicola and greater when leaves were inoculated with C. karstii. In this study we demonstrated differences in GLS severity among species and between apple cultivars. We showed that the infection period and latent period are similar between C. fructicola and C. nymphaeae and they were equally severe at the same inoculation conditions. Cultivar Eva, classified as resistant to Colletotrichum spp., can be infected by C. fructicola and C. nymphaeae.