A diagrammatic scale of Alternaria Brown Spot in citrus was developed in order to standardize disease severity assessments. The scale was built taking into consideration the distribution, shape and frequency of lesions as well as minimum and maximum severity levels found in the field. Two types of symptoms widely observed at field were represented in the diagrammatic scale: small circular or irregular lesions (0.1 1 2.5 5 11 and 25%) and large circular lesions (1 2.5 5 10 and 17%). The validation of the scale was accomplished in two stages. Firstly, four experts estimated the severity of disease in 79 photographs of citrus fruits with symptoms without using the diagrammatic scale. Secondly, the experts estimated the severity of the disease on the same fruits, by using the scale. When the scale was not used, the coefficient of determination (r²) was 0.69, the intercept (a) 1.42 and the angular coefficient (b) 0.77, while by using the scale these parameters were 0.84, 1.59 and 0.84, respectively. The scale was shown to be appropriate for severity assessment of Alternaria Brown Spot on citrus fruits.
Alternaria alternata; pathometry; disease evaluation
