Study of biology and epidemiology of Uncinula necator caused powdery mildew disease

This study was carried out during 2007 and 2008 in the vineyards of Ardebil province of Iran to study the biology and the epidemiology of Uncinula necator the causal agent of grape powdery mildew disease. The study concentrated on the survival and the initiation of primary inoculum of the fungal causal agent. Results of histopathological experiments indicated that U. necator survived as mycelium in the dormant buds of the grapes during winter season. Results of study on the effect of environmental factors on fungus biology showed that the pathogenic activity of the fungus began when the temperature was between 16-19 C with a relative humidity more than 50%. It was also found that optimum temperature and relative humidity for the sporulation of U. necator was 20-25 C and 50-100% respectively. According to the results, fungal conidia were trapped during formation of 5-6 true leaves and first disease symptoms were observed on the clusters on late June after fruit formation. Fungal cleistothecia were observed abundantly at the end of season on the leaves, petioles and twigs but they were not able to survive during winter. Formation of ascospores on young leaves was proved but their role as the primary inoculum was not supported by the results of this study. Results of this study and the new findings on the biology and epidemiology of U. necator may be of national and international interests for the management of powdery mildew disease which is one of the most destructive diseases around the world including Iran.