Abstract
In Brazil, the production of sweet oranges has been threatened by the Citrus Variegated Chlorosis (CVC) incited by the gram-negative bacterium Xylella fastidiosa (Wells). Commercial citrus groves in two counties at the Northwestern Paraná state were evaluated to estimate the disease progression by using parameterizations of nonlinear models. Groves of Citrus sinensis Osbeck, variety “Pêra”, “Valência”, “Natal” and “Folha Murcha” had all the plants evaluated for the presence of disease symptoms. Thereafter, different parameterizations of the Logistic and Gompertz models were fitted to these data. The goodness of fit was evaluated by the intrinsic (IN) and parameter-effects (PE) curvatures of Bates and Watts, the bias of Box and the Hougaard measures of skewness. In Loanda, the best model was the Fermi-Dirac, and in Nova Esperança the data were best fitted to the parameterization L5, which is also a parameterization from the Logistic model.
Highlights
In Brazil, the sweet orange production has been threatened by the Citrus Variegated Chlorosis incited by Xylella fastidiosa (Wells) which is a gramnegative bacterium detected in the plant xylem (GARCIA JUNIOR et al, 1995; ROSSETTI; DE NEGRI, 1990)
The intrinsic-effects of Logistic and Gompertz parameterizations were nonsignificant for data sets from varieties, except for those data collect at Nova Esperança from the cv
Most of the Hougaard measures of skewness were lower than 0.25, and the best responses were found for the FermiDirac parameterization which was the best model fitted to these data
Summary
In Brazil, the sweet orange production has been threatened by the Citrus Variegated Chlorosis incited by Xylella fastidiosa (Wells) which is a gramnegative bacterium detected in the plant xylem (GARCIA JUNIOR et al, 1995; ROSSETTI; DE NEGRI, 1990). The CVC symptoms are foliar chlorosis that becomes dark-brown and necrotic, clusters with four up to ten small units of hard rind fruit, slowly plant growth, branch die-back, and premature leaf abscission (GARCIA JUNIOR et al, 1995; ROSSETTI; DE NEGRI, 1990). Laranjeira et al (1998) studied the spatial and temporal progression of the CVC in eleven groves of sweet orange. These groves were bi-monthly sampled, and the Logistic was considered the best model for representing the disease progression
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