Nonlinear Logistic Model for Describing Downy Mildew Incidence in Grapes

摘要

Biological organism always tends to behave non-linearly contrary to linear growth as perceived in most of the data analysis procedure. In the present communication, a simple nonlinear logistic growth model has been developed to describe the populationdynamics of incidence of downy mildew in grapes (cv. Anab-E-Sahai) so as to workout quantitative information about the biological parameters concerning intrinsic infection rate and maximum mildew severity over time-epoch. Statistical analysis of diseaseseverity data over time period for three years (2004-05 to 2006-07) using non linear growth models revealed that 98% of the variability in disease progression over time-epoch was captured by nonlinear models. Nonlinear models developed were then used toconstruct area under disease progression over time period. Results showed that, in general, the rate of disease severity was maximum during fifth- sixth week after fore-pruning, calling for appropriate management strategies for controlling the disease within the period identified, thus avoiding crop loss. Before taking final conclusion about the model, the model-generated residuals were tested for their robustness using statistical techniques. SAS Programming codes were constructed to develop the nonlinear growth models.