الفهرس 
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Abstract
Potato (Solatnum tuberosum L.) is considered one of the most important vegetable crops in Egypt and in most countries all over the world. Total cultivated area of potatoes in Egypt reached 439, 504 feddans annually produced 7529022 tones/year, 427907 tonnes of total production were approved for foreign destinations (FOA., 2016). Worldwide losses of potato yield; due to diseases such as bacterial, fungal, and viral. Rhizoctonia solani is an important soil borne pathogen of potato, causing black scurf on tubers and shoot/stolon canker on young plants. Black scurf disease considered the most destructive disease and reduce productivity of potato. Objectives: Survey collection and Isolation of stem and root cankers Isolation from potato tubers Pathogenicity tests Biochemical study characterization of the causal pathogen Anastomosis group test Molecular characterization Virulence of R. solani isolates and potato varietal susceptibility Effect of biological control and chemical agent on R. solani in vitro Comparing between effect of biological control and chemical under greenhouse conditions Methods & results: Eight Egyptian governorates (Aswan, Behera, Dakahlyia, Gharbia, Giza, Ismailia, Menofyia, and New Valley) were examined on vegetative and tuber of four potato cultivars (Diamant, Hermes, Lady Rosetta and Spunta) during 2012-13 and 2013-14 seasons. Representative infected samples of Diamant, Hermes, Lady Rosetta and Spunta cultivars were collected randomly from different conventional, past free aria and organic farms. 255 isolates were collected and subdivided into 14 group based on the morphological examination. Pathogenicity test of the 50 selected isolates were revealed that all isolates were pathogenic. The anastomosis test on the same 50 isolates produced four different interactive groups (C0-C3). Sequence analysis was performed on the internal transcribed spacer (ITS) 18s rDNA of 50 selected isolates and confirmed the identified groups. These results of great applications at the level of potato black scurf disease characterization in Egypt. Eleven potato cultivars (Enova, Diamant, Arizona, Erika, Angria, Cara, Lady Rosetta, Hermes, Mondale, Spunta and Bellini) were screened for resistance or susceptibility to black scurf caused by three isolates of R. solani (RS1, RS2, and RS3) under greenhouse conditions. Hermes and Diamant cvs. Show resistant to three isolates of R. solani mentioned above, while Bellini and Lady Rosetta showed susceptible to the same isolates. Biological Control of Rhizoctonia solani in vitro was investigate activity of certain isolates of Trichoderma spp with the most radial growth inhibition to Rhizoctonia solani isolates that isolate T12-1 was the most effective in inhabiting of tested Rhizoctonia isolates. in vitro studies of the effect of different salt concentrations on radial growth of Rhizoctonia solani isolates showed that The most suppressive salt treatment was potassium silicate at 8000ppm for the three isolates , the lowest suppressive salt treatment was potassium thiosulfate for isolates no R1and R2,while potassium sulfate saltswas the lowest for isolates. as Ascorbic acid, Citric acid, Salicylic acid and Boric acid, subsequently. The most suppressive acid treatment was Boric acid and Salicylic acid at 500, 1000 and 2000ppm for the three isolates. as Cinnamon, carnation, Camphorand Castor, subsequently. The most suppressive oil treatment was carnation at 1250,2500 ppm for the three isolates while the lowest suppressive treatment was oil Castor. Conclusion: The results of this study indicate the identified isolates in current study can be used as new pathogenic testers for R. solani in Egypt. In organic cultivation, the recommended potato cultivar is the resistant Hermes and the susceptible Lady Rosetta cultivar should be avoided. In the conventional cultivation, the recommended potato cultivar is the resistant Diamant and the susceptible Lady Rosetta cultivar should be avoided. The molecular differences found in our study can be used as marker progenitors to characterize the Egyptian R. solani isolates.