ANALYSIS OF PROGRESS CURVES OF SUGARCANE SMUT ON DIFFERENT CULTIVARS USING FUNCTIONS OF DOUBLE SIGMOID PATTERN

The progress of smut on the sugarcane cultivars NA56-79, SP71-799, SP71-1406, SP71-6163, and SP70-1143 was quantified with artificial and natural inoculation during five consecutive years at Primeiro de Maio, Parana, Brazil. The annual progress curves were fitted by the generalized monomolecular y(t) = p1 {1 - exp[-(p2 + p3t + p4t2 + p5t3)]} and the generalized Gompertz y(t) = p1 exp{-exp[-(p2 + p3t + p4t2 + p5t3)]} functions, in which the dependent variable y(t) was disease severity (whips per hectare) and the independent variable t was time (days after harvest). Estimates of the upper asymptote, the mean infection rate, the transition time between growth waves of the annual disease progress curve, and the latent period, based on the generalized Gompertz function, were utilized to compare cultivars. None of the time-related curve elements, i.e., the transition time between growth waves and latent period, differentiated the cultivars because the values were similar for all cultivars. Cultivars NA56-79 and SP71-799 showed the highest and lowest upper asymptote, respectively, differing statistically (P < 0.05) from the others.