Location: Sugarbeet and Potato Research2012 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:
This report documents progress for Project 5442-22000-047-00D, which started in March 2012 and continues research from Project 5442-22000-042-00D. Progress was made in all three Objectives and their Sub-objectives. The ability to reliably reproduce sugarbeet diseases in controlled settings is foundational for studying pathogen biology and disease resistance screening. In Sub-objective 1a, protocols were optimized for the inoculation of beet soilborne mosaic virus, an important viral disease of sugarbeet. Protocols were optimized for inoculation of Cercospora beticola, the most important foliar pathogen of sugarbeet. In Sub-objective 2a, RNA and genome sequencing of A. cochlioides was initiated, which will facilitate the identification of secreted proteins that are involved in pathogenicity. In Sub-objective 3a, jasmonic acid treatments were previously identified that reduced root rot to three important pathogens of sugarbeet. To identify genes important for this resistance response, next generation sequencing was utilized to quantify sugarbeet genes differentially expressed after exposure to jasmonic acid. Gene expression of selected genes was validated using real-time PCR.