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Leaf rust is one of the most important diseases and influences the sustainable cultivation of wheat. Therefore, for the first time in Iran, the spatial pattern and temporal progress of this disease were assessed in five wheat cultivars, including Chamran 2, Star, Ofogh, Kavir, and Boolani, with different resistance levels in 2015-16 and 2016-17 cropping years. In both years, disease progress curves (DPC_S) showed a sigmoid-like shape, and the rate curves had an obvious inflection point, both the features of Gompertz and logistic models. Plots of transformed, predicted disease intensity values and residual patterns indicated that disease intensity data fit closely with Gompertz and logistic models. Gompertz and logistic models with a bit of variation gained R² above 90 % in all cultivars. Based on the results, there is no direct relationship between cultivar resistance and best-fitted models, as in both years, logistic and Gompertz models fitted properly with disease intensity data for all cultivars. In the Gompertz model, the mean rate of increase (rG) per unit of disease in the resistance (Chamran 2) and susceptible (Boolani) cultivars were 0.052 and 0.09, respectively, and in the logistic model (rL) were 0.12 and 0.144, respectively. Results indicated that in the first weeks after the appearance of the disease symptoms, the spatial pattern of diseased plants was aggregated, and the amount of the dispersion index and lloyd’s Index of Patchiness in the first and second years were 8.9, 9, and 1.3, 1.2, respectively. Three weeks after data collection, the spatial pattern became random.

 

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 In this study, the first symptom appearance of wheat leaf rust disease was monitored in Khuzestan Province every ten days from early December 2014, for three years. Also, the climate changes and their influence on the development of the disease were studied. During 2014-2015, the first symptoms, with the severity of 5 MS (Moderately Susceptible), appeared in the south and west parts in early and mid-March, respectively. In northern areas, the symptoms appeared with 10 MS severity in early May. In 2015-2016, the first symptoms appeared with the severity of 5 MS in February in the southern areas. In the west, symptoms appeared and reached 20 S (susceptible) on March 10. In the north, the disease started in late February with the severity of 10 MS and developed to 30 S. In 2016-2017, the first symptoms appeared around the Karun River with the severity of 5 MS on March 10 and eventually reached 10 MS in late March. In the western areas, the disease started in early March with the severity of 5 MS and then stopped. Symptoms appeared one week later in the north, with the severity of 5 MS, and reached 15 MS until the end of March. Based on the previous studies, the first symptoms of wheat leaf rust usually start from the west. However, now, the regional pattern of the symptom has changed dramatically, and it appears in the south near Karun River and the Sugar Cane Crop Industry. This might be due to implementation of preventive measures and dryness of a big part of Hoveyzeh Marshland.