Elaboração e validação de escala diagramática para quantificação da severidade de entomosporiose em folhas de pereira

Abstract

Fabraea leaf spot, caused by the fungus Entomosporium mespili, is one of the major diseases affecting pear (Pyrus sp.) in Brazil. Considering the lack of standardized methods to quantify this disease on leaves, the aim of this study was to develop a diagrammatic scale to quantify the severity of Fabraea leaf spot of pear. To standardize the assessment, we developed a diagrammatic logarithmic scale with seven levels (0.3, 1.0, 2.3, 5.1, 11.1, 22.4 and 40.0% diseased leaf area). To validate the scale, nine raters estimated the severity of 60 scanned leaf images at different severity levels. The evaluations were done in two steps: with and without the aid of the scale. The actual severity was obtained through the program Quant. v.1.0. The accuracy and the precision of raters were determined by simple linear regression between actual and estimated severity. The proposed scale provided good levels of accuracy and precision, good repeatability of estimates, and rapid and easy assessment, constituting thus a useful tool in epidemiological studies and for the development of strategies to control Fabraea leaf spot of pear.