Date of Award

8-2012

Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

Advisor

Stylianos M. Tavantzis

Second Committee Member

M. Susan Erich

Third Committee Member

David Lambert

Abstract

Rhizoctonia solani is an important plant pathogen affecting monocot and dicot crops alike. In potato, R. solani is an economically important pathogen causing two types of symptoms. Stem and stolon canker results from the formation of lesions on stems and stolons that can girdle and kill the plant, while black scurf is marked by the formation of sclerotia on the potato tuber surface, providing a source of inoculum in subsequent years on seed tubers, and decreasing marketability of table stock potatoes. Control of rhizoctonia disease of potato has traditionally focused on economically and environmentally costly chemical measures that are often ineffective. Therefore, the identification of novel control measures is paramount to the development of sustainable disease management strategies. The goals of this study were two-fold. The first was to gauge the success of several cultural practices at controlling rhizoctonia disease of potato. Specifically, a Brassica napus (rapeseed) rotation crop, conifer-based compost, and three biological control organisms (Trichoderma virens, Bacillus subtilis, and a hypovirulent isolate of R. solani RhslAl) were assessed at two potato production sites with contrasting management histories (organic versus conventional potato production). All of the treatments tested had significant impacts on rhizoctonia disease of potato and overall soil microbial communities in at least one year of trials. However, while the rapeseed rotation crop generally reduced rhizoctonia disease, the compost amendment had the opposite effect, and this appeared to be independent of the levels of R. solani in the soil (as measured by quantitative PCR) at summer or fall sampling dates. The second goal of this study was to enhance the understanding of the molecular mechanisms governing pathogenicity in R. solani. Through the use of a suppression subtractive hybridization cDNA library, next-generation sequencing techniques and current bioinformatics approaches, several hundred genes induced during the infection process of R. solani were identified. These genes included many with known roles in pathogenesis in fungal phytopathogens, including those involved in entry into and growth within the host. From these data, a potential model outlining the molecular processes governing the infection of potato by R. solani was constructed and tested using quantitative PCR.

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