Behavior of European pear cultivars under different quince rootstocks to 'Entomosporium' leaf spot in southern Brazil

The Entomosporium leaf spot (ELS) is caused by the fungus Fabreae maculata (anamorph: Entomosporium mespili) and affects most of the pear cultivars and quince rootstocks in Brazil. The aim of this study was to characterize the behavior of European pear cultivars (Rocha, Abate Fetel e Santa Maria) under quince rootstocks (Quince A and Quince Adams) to ELS in southern Brazil, during the crop season of 2009/2010 and 2010/2011. The incidence and severity were quantified weekly from the first symptoms appearance in 100 randomly leaves distributed in four medium-height branches per plant on each eight replications per treatment. Curves of ELS progress were constructed and the epidemics compared according to: a) the beginning of symptoms appearance (BSA); b) the time to reach the maximum disease incidence and severity (TRMDI and TRMDS); c) the maximum value of disease incidence and severity (Imax and Smax); and d) area under the incidence and severity disease progress curve (AUIDPC and AUSDPC). The incidence and severity data were analyzed by linear regression and adjusted for three empirical models: Logistic, Monomolecular and Gompertz. All combinations of cultivars and rootstocks were susceptible to E. mespili. However, there were significant differences in ELS intensity among cultivars. The highest ELS intensity was observed in Santa Maria cultivar and the lowest in Rocha and Abate Fetel cultivars, independent of rootstocks evaluated. The Logistic and Gompertz epidemiological models were the most appropriates to describe the ELS progress in the edafoclimatic conditions of southern Brazil. The results of the study showed that the Abate Fetel cultivar under Quince A was the best combination when BSA was taken into account as differentiated variable.