2012 Annual Report
Alternate Hosts of Root-lesion Nematodes. Root-lesion nematodes reduce profitability of wheat production throughout the PNW but nothing was known about the hosting ability (rate of nematode multiplication) of specific varieties of non-cereal crops, weed species, and CRP grasses and broadleaf plants. Each of these groups of plants must be screened before more profitable management strategies and reasonable risk projections can be developed to provide further management guidelines for rotation of crops, for development of bio-fuel crops, for takeout of CRP, and for enhancing soil water-use efficiency. During 2011 and 2012, ARS collaborators at Oregon State University, Pendleton screened 75 plant entries each year representing 53 plant species for resistance to the two most important species of root-lesion nematodes that occur in PNW fields. As compared to the resistant and susceptible wheat controls, surprisingly few plant species allowed significantly high rates of nematode reproduction. Several plant species allowed P. neglectus but not P. thornei to reproduce, and the converse also occurred, underscoring the need to identify the nematode species in each field before developing a management strategy for these parasites. 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 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 the nine years of that experiment. Different crops selected for different species of this nematode over the life of the experiment; winter wheat selected for P. neglectus and spring wheat selected for P. thornei. Nematode density was not affected by 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 PNW wheat fields. QTL 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 PNW wheat varieties. Imported landrace wheat lines AUS28451R and Persia 20 expressed high levels of resistance to both species and resistances from both parents were transferred into PNW varieties. Greenhouse assays to select wheat lines with resistance to these nematodes are laborious and expensive. Molecular markers could be used to reduce the time required to identify plants carrying the resistance genes. ARS collaborators at Oregon State University, Pendleton extracted DNA from seedlings of resistant parents and resistant and susceptible crosses of six mapping populations and succeeded in identifying 15 potential resistance gene analog polymorphism (RGAP) markers. These 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 (QTLs) 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 Heterodera 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. ARS collaborators at Oregon State University, Pendelton used polymerase chain reaction (PCR) and restriction fragment-length polymorphism (RFLP) procedures to identify these species in infested soils and used the PCR-RFLP procedure to screen soil samples. Some sites were found to be infested with mixtures of H. avenae and H. filipjevi but only H. avenae was detected in most fields sampled.
Accomplishments from this project align with Component 1, Problem Statement 1, Components 2, Problem Statement 2C, Component 3 Problem Statement 3B of NP 303.