Regulation of Virulence in Rhizoctonia solani: Global Gene Expression Profile and Impact of Soil Amendments on Rhizoctonia Disease of Potato

REGULATION OF VIRULENCE IN RHIZOCTONIA SOLANI:

GLOBAL GENE EXPRESSION PROFILE AND IMPACT

OF SOIL AMENDMENTS ON RHIZOCTONIA

DISEASE OF POTATO

By Edward Bernard

Thesis Advisor: Dr. Stellos Tavantzis

A Lay Abstract of the Dissertation Presented

in Partial Fulfillment of the Requirements for the

Degree of Doctor of Philosophy

(in Biological Sciences)

August, 2012

Keywords: Microbial Communities, Rhizoctonia solani, Potato Production Practices, Pathogen Detection

Potato is a globally important food crop, ranking fourth in world production.  Rhizoctonia solani is a cosmopolitan fungal plant pathogen responsible for a wide variety of diseases in several crops, including black scurf, characterized by formation of black survival structures (sclerotia) on the potato tuber surface, and stem canker, characterized by lesion formation and necrosis on stems and stolons of potato plants.  Control of rhizoctonia disease has traditionally been achieved using costly chemical and seed treatments, which have various negative consequences.  Alternative control strategies for rhizoctonia disease must therefore be devised to effectively and safely control the disease. Several soil amendments, such as composts, biological control organisms (which naturally control pathogens), and mustard-family cover crops (including rapeseed) have demonstrated the potential to control rhizoctonia diseases in vitro.  In order to evaluate their effects on rhizoctonia disease, and the soil environment, they were tested in a field setting. 

All of the treatments utilized in the field generally lead to increased microbial activity and a healthier soil microbial population.  They also had pronounced effects on tuber diseases, with the compost amendment, rapeseed rotation crop and at least one biological control organism decreasing rhizoctonia disease.  Similarly, tuber yields were increased by both compost amendment and rapeseed rotation.  In addition, a method was devised for quick detection and quantification of R. solani within field soils, with potential future applications as a predictor for observed tuber diseases.

To devise novel control strategies and better understand the mechanisms behind virulence in R. solani, it is necessary to investigate their molecular basis.  This research uncovered several important groups of genes responsible for the disease-causing capability of R. solani.  Among these were several genes involved in recognition of the host plant, production of molecules to thwart host defenses, and breakdown and utilization of host tissue.  These processes were characterized by genes involved in important cellular signaling pathways, important metabolic pathways, and production of degradative enzymes.  Most importantly, however, these results will serve as a framework for future investigation into the processes that govern the ability of R. solani to infect potato.