APS Abstract of Presentation
The status of powdery scab disease on potatoes in Egypt
A. TOHAMY (1) (1) Plant Pathology Research Institute, Giza,12619, Egypt Phytopathology 98:S156 Powdery scab of potato caused by Spongospora subterranean f. sp. subterranea has become an important disease in Egypt during winter season (export season) and summer season (seed production season). The disease was observed on potato tubers harvested from potato growing fields in Behira, Ismailiya and Sharkiya governorates during 200506 and 200607 seasons. The disease became endemic in potato fields after planting powdery scab-infected potato seeds which led to soil contamination with the powdery scab pathogen. In addition, variations in some edaphic factors such as soil types, soil pH, temperature and moisture favor the development of the disease. Symptoms of powdery scab on tubers were assessed visually by following the progress of the development of the powdery scab lesions on the infected tubers. The pathogen was identified microscopically according to the morphological features of cystosori (sporeballs) of the pathogen present in the developed lesions on the infected tubers. The effects of edaphic factors, (soil types, moisture, temperature, and pH) on the incidence and severity of powdery scab disease were investigated on potato grown in greenhouse conditions. Both sandy and loamy soils encouraged the development of powdery scab symptoms on potato tubers while clay soil did not. Continuous soil moisture resulted in greater disease severity compared to a fluctuating moisture regime. Disease symptom development was highest in a range of 1218°C. In addition, the optimum soil pH for the powdery scab disease development ranged between 6 and 7 while at pH 8 the disease symptoms were not noticed. According to the available literature, this is the first record of powdery scab disease in Egypt.
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