1a. Objectives (from AD-416)
The objective of this cooperative research is to identify, characterize and control soilborne pathogens of wheat and barley, such as Fusarium, Pratylenchus and/or Heterodera, which cause root and crown rot diseases; to identify the effects of cropping system on root pathogen populations and diversity, and on disease epidemiology; and to identify wheat germplasm with performance against root pathogens.
1b. Approach (from AD-416)
Root and crown rot diseases will be identified and characterized through a combination of laboratory, greenhouse and field studies. The ecology of root pathogens and effects of cropping system on pathogen populations and diversity, and disease epidemiology will be determined using classical plant pathology and microbiology methods and molecular techniques. Wheat germplasm will be screened for resistance or tolerance to root and crown pathogens in the field and greenhouse. Practical root disease control will be accomplished through a combination of agronomic practices, and biological and chemical treatments.
3. Progress Report
This project aligns with objective 1 on parent project. As management practices change from an intensively cultivated to a conservation-oriented system the prevalence and severity of diseases also change. ARS collaborators at Oregon State University, Pendelton evaluated root and crown diseases in a long-term cropping systems experiment and found that yields of spring and winter wheat were inversely correlated with density of root-lesion nematodes over a seven-year experiment. Nematode density was not affected by the intensity of tillage but was much lower following barley compared to wheat, canola, mustard or winter pea. Extraction of water stored in the soil profile was inversely correlated with the density of these nematodes. These observations indicate a need to monitor and to reduce populations of root-lesion nematodes in Pacific Northwest wheat fields. As a result, crop management recommendations were modified and published as a Pacific Northwest Extension Bulletin. Identification of Root-lesion Nematode Species. Management of root-lesion nematodes continues to be based upon the identity of the species present in each field. Most commercial diagnostic laboratories do not identify individual species due to high cost, degree of difficulty, and financial liability that could be associated with an erroneous species designation. ARS collaborators at Oregon State University, Pendelton and ARS scientists at Pullman, WA and Beltsville, MD developed species-specific primers to detect the Pratylenchus species of importance in dryland agriculture in the Pacific Northwest and developed a multiplex assay of soil to simultaneously quantify and identify each species from a single DNA extract using real-time PCR. Validation tests with naturally-infested soils demonstrated that the real-time PCR procedures for P. thornei provided much more accurate results than conventional extractions and identifications of lesion nematode species done at four commercial nematode testing laboratories. The P. thornei procedure was used to eliminate contamination (species mixtures) of cultures used in greenhouse screening trials and is being used for nematode distribution surveys and greenhouse screenings in Oregon and Washington. These molecular methods will become the standard approaches for identifying these nematodes in at commercial and research laboratories. Progress on this project will be monitored by conversations with the collaborator at professional meetings, through conference calls and by visits to Pullman or Pendelton.