Location: Sugarbeet and Potato Research2008 Annual Report
1a. Objectives (from AD-416)
Three of the most significant field diseases of sugarbeet in the U.S. are root rot, caused by Aphanomyces cochlioides; Rhizomania, caused by a fungal/viral complex; and wilt, caused by the sugarbeet cyst nematode, Heterodera schachtii, and concomitant infection by Fusarium fungi. The objectives of this project are to investigate methods to reproduce the field diseases of these pathogens in controlled environments, to develop qualitative and quantitative detection reagents and protocols for these organisms, and to determine genetic changes in viruses of the Rhizomania complex that condition heightened virulence to sugarbeet. Since the incorporation of natural genetic resistance into crops remains the most cost-effective strategy for disease control, an additional objective of the project is to obtain molecular genetic tags for disease resistance genes in sugarbeet in collaborative studies with ARS sugarbeet geneticists and pathologists.
1b. Approach (from AD-416)
Gradients of saturation across seedbeds will be tested as a means to evaluate sugarbeet varieties with known resistance to Aphanomyces cochlioides using stand loss as a measure of disease severity. Protocols for the inoculation of sugarbeet with Polymyxa betae will be modified to select for clonal isolates of the organism, an aspect lacking in past studies on this pathogen. Probe primers will be designed to perform in conjunction with specific primer sets in the development of real-time PCR (qPCR) methods for quantifying these pathogens in soil and plant samples. Disruptions (insertions) in the chromosomes of beet black scorch virus and beet necrotic yellow vein virus will be engineered in efforts to determine the role of virus genes in pathogen virulence. Plants typed for either resistance or susceptibility to the sugarbeet cyst nematode and Fusarium stalk blight will be subjected to DNA fingerprinting for generation of molecular markers linked to resistance genes.
3. Progress Report
Research to determine the optimum temperature for chemical control of Rhizoctonia solani have been initiated in collaboration with colleagues at North Dakota State University. To facilitate sugarbeet germplasm development, greenhouse methods to screen for resistance to Aphanomyces cochlioides are being developed. Research to identify effector proteins in the important sugarbeet pathogens Cercospora beticola and Aphanomyces cochlioides has been initiated and methods to isolate apoplastic fluid have been optimized. This research addresses National Program 303: Components 2 (Pathogen Biology, Virulence Determinants, and Genetics of the Pathogen) ,3 (Disease Resistance in New Germplasm), 4 (Biological and Cultural Strategies for Sustainable Disease).
5. Significant Activities that Support Special Target Populations
Bolton, M.D., Thomma, B.P.H.J. 2008. The complexity of nitrogen metabolism and nitrogen-regulated gene expression in plant pathogenic fungi. Physiological and Molecular Plant Pathology. 72:104-110.