بررسي روند پيشرفت بيماري لكه گرد برگ چغندر با استفاده ازمدلهاي اپيدميولوژيكي

MODELING OF DISEASE PROCRESS IN CERCOSPORA LEAF SPOT OF SUGAR BEET

Progress of Cercospora leaf spot (CLS) caused by Cercospora beticola was studied in the field,at Safi-Abad Research Station during two successive growing seasons (2000-2002), using completely randomized block design experiments with 4 replicates.In the first year one variety, Monondera, and 4 sugarbeet lines: 7112,261, 191 and 236, were used. In the second year var. Monondera was replaced with Var. HM-1836. Plants were artificially inoculated using spore suspention.Disease progress was recorded according to a numerical scale ofO to 5 as soon as the first disease symptoms appeared on the outermost leaves. Data were analyzed and fitness of epidemiological models monomolecular, logistic, log - logistic, Gompertz and Weibllil were evaluated. The results indicated that, in the first year the logistic and log-logestic models showed the best fitness with the actual disesae progress observed whereas in the second year logistic, log logistic and Gompertz were more efficient models in determining disease progress. Combined analysis of the results for the two years of this study showed that the logistic model was the most efficient in defining disease progress, whereas the monomolecular and Weibul modle were inefficient. This study revealed that cercospora leaf spot appears in early March and the disease progressively increases until early June. To reduce the damage caused by the disease it is recommended to give priority to harvesting date of infected fields.