Validação de escala diagramática para mancha foliar causada por pestalotiopsis sp. Em mudas de coqueiro

Abstract

The absence of a methodology to quantify the Pestalotiopsis sp. in coconut trees (Cocos nucifera L.) justified the elaboration and validation of a diagrammatic scale containing seven values (2%, 5%, 10%, 15%, 20%, 40% and 60%) of disease severity in sampling in natural conditions of occurrence in the field. To elaborate the diagrammatic scale, 100 leaves of Cocos nucifera L. were obtained from the experimental field of Reunidas Farm Sococo in the municipality of Santa Isabel, Pará. The images of these leaves were obtained with the aid of a digital camera. Subsequently, with the aid of Assess 2.0 APS software, the values of the disease's actual severity were obtained in percentage terms. The validation of the proposed diagrammatic scale was carried out by ten inexperienced evaluators who evaluated the projected images without the aid of the suggested scale, and later with the aid of the scale. From the data obtained from the evaluators with and without scale a linear regression analysis was performed, relating the real severity and the estimated severity. The precision of the estimates was evaluated by using the regression coefficient determition (R2) and the variance of absolute errors. The accuracy of each evaluator was determined by using the test t applied to the angular coefficient of the line (b) and the linear coefficient of the line (a), both obtained by linear regression. Through the coefficient of determination values, it is possible to verify that the use of the scale gave greater precision to 100% of the evaluators with a mean of 0.94 and a repeatability of 94%. The use of the diagrammatic stain scale for Pestalotiopsis sp. possible future works with accuracy and precision, as well as can optimize disease control practices within a management program in the nursery of coconut tree seedlings.