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:
Field Tolerance and Resistance to Root-Lesion Nematodes. The root-lesion nematodes Pratylenchus neglectus and P. thornei reduce yields of intolerant wheat varieties. ARS collaborators at Oregon State University, Pendleton identified genetic resistance to the nematodes in imported wheat lines and crossed the resistance into Pacific Northwest locally-adapted wheat varieties. Two imported landrace wheat lines AUS28451R (resistant to both nematode species) and Persia 20 (resistant to P. neglectus) were evaluated for the second year in the field, using large-plot conditions at two Oregon locations. These tests were repeated for a third year during 2013. The goal is to demonstrate the value of incorporating resistant wheat into cropping systems where other resistant crops (barley, safflower, flax) are of limited value to growers in the wheat-intensive cropping systems of low rainfall regions of the Inland Pacific Northwest. Identification of Root-Lesion Nematode Species. Management of root-lesion nematodes is based upon the identity of the species present in s field. Most commercial diagnostic laboratories do not identify individual species. ARS collaborators at Oregon State University, Pendleton in collaboration with ARS scientists at Pullman, Washington, and Beltsville, Maryland, developed species-specific primers and a real-time Polymerase Chain Reaction assay to quantify and identify each species from a single DNA extract from soil. These tests are intended for routine use at commercial and research laboratories. Alternate Hosts of Root-lesion Nematodes. Root-lesion nematodes reduce profitability of wheat production throughout the Pacific Northwest but little was known about the hosting ability (rate of nematode multiplication) of specific varieties of non-cereal crops, weed species, and grasses (used in the Conservation Reserve Program) and broadleaf plants. ARS collaborators at Oregon State University, Pendleton, screened 75 plant entries representing 53 plant species for resistance to the two most important species of root-lesion nematodes that occur in fields to gain further understanding of potential rotations and potential risks of overwintering weed populations on infested fields. The goal is to provide further management guidelines for rotation of crops, for development of bio-fuel crops, for takeout of Conservation Reserve Program, and for enhancing soil water-use efficiency. Some plant species favored reproduction of P. neglectus but not P. thornei, and the converse also occurred. These results highlight the need to identify the nematode species in each field before refined management strategies can be developed for these nematodes. Crop Management. As crop 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, Pendleton, evaluated root and crown diseases over the 9-year life of a long-term cropping systems experiment and found that yields of spring and winter wheat were inversely correlated with density of root-lesion nematodes. Winter wheat favored higher populations of P. neglectus and spring wheat favored an increase of P. thornei. Nematode density was less in no-till than cultivated fallow systems, and was much lower following barley, camelina or spring pea, as compared to high populations following wheat, canola, mustard or winter pea. Wheat favored an increasing inoculum density of Fusarium pseudograminearum, and barley favored an increasing density of F. culmorum. These observations indicate a need to monitor and to reduce populations of root-lesion nematodes and fungal pathogens in Pacific Northwest wheat fields. ARS collaborators at Oregon State University, Pendleton also identified a pathogen of winter pea, Phoma medicaginis var. pinodella, previously not known to occur in the Pacific Northwest. Quantitative Trait Loci Mapping for Resistance to Root-lesion Nematode. The root-lesion nematodes Pratylenchus neglectus and P. thornei reduce yields of intolerant wheat varieties. Genetic resistance is not present in Pacific Northwest wheat varieties. ARS collaborators at Oregon State University, Pendleton, showed that imported landrace wheat lines AUS28451 and Persia 20 expressed high levels of resistance to both species and resistances from both parents were transferred into Pacific Northwest varieties. Greenhouse assays to select wheat lines with resistance to these nematodes are laborious and expensive. Molecular markers can be used to reduce the time required to identify plants carrying the resistance genes. They then extracted DNA from seedlings of resistant parents and resistant and susceptible lines of six mapping populations and succeeded in identifying 15 potential molecular markers, which were then subjected to validation tests using three mapping populations from crosses between Persia 20 and the spring wheat varieties Alpowa, Louise, and Otis. Lines from the F6 generation of these mapping populations were produced in preparation for performing assays to identify quantitative trait loci for dual resistance to both P. neglectus and P. thornei. This research will provide to wheat breeders effective markers for resistances to root-lesion nematodes. Identification of Cereal Cyst Nematode Species. Two cereal cyst nematode species occur in Oregon, Heterodera avenae and H. filipjevi. These species appear to differ in the timing at which juveniles emerge from cysts and in their reactions to genes for resistance in wheat and barley. Accurate identification of these species is important for developing effective management strategies but commercial nematode diagnostic laboratories do not distinguish these species; they report population densities only at the Heterodera genus level. ARS collaborators at Oregon State University, Pendleton, in collaboration with ARS scientists at Pullman, Washington and Beltsville, Maryland, developed a rapid and simple polymerase chain reaction assay that identifies each species without the need for morphological identification procedures. This technology will be transferred for use at commercial as well as at research laboratories. This research relates to Objective 1 of the parent project “Evaluate the pathogenic diversity, host range, and geographical distribution of fungal and nematode root pathogens, and the influence of cropping systems on soilborne diseases”.