2005 Annual Report 4d.Progress report. This report serves to document research conducted under a Specific Cooperative Agreement between ARS and Oregon State University. Additional details of the research can be found in the report for the parent project 5348-22000-012-00D, Plant Disease Research. Rhizoctonia root rot and Fusarium crown rot were the most damaging diseases and root-lesion nematodes and cereal cyst nematodes were the most damaging plant-parasitic nematode species in annual spring cereal cropping systems. Changing patterns for disease occurrence and severity must be monitored during the transition from traditional winter wheat-summer fallow rotations to conservation-oriented systems such as annual spring cropping. ARS collaborators at Oregon State University, Pendleton evaluated diseases in two long-term cropping system transition studies performed at low-rainfall sites in Oregon and Washington, and shared data with up to 14 participating scientists representing nine disciplines. Growers, lending institutions, agronomic advisors and regulatory agency personnel have shown keen interest in the successes and failures of each treatment in these large-scale field studies. Early-generation wheat lines with superior tolerance to crown rot were acquired from CIMMYT and Australia, the volume of seed was increased for testing under conditions in the Pacific Northwest, and portions of the seed were distributed to wheat breeders in Oregon and Washington. This wheat germplasm is needed to improve levels of crop tolerance to chronic and occasionally acute (up to 35%) yield losses caused by a crown rot complex (Fusarium pseudograminearum, F. culmorum, Bipolaris sorokiniana, and others) in low-rainfall environments. Enhanced tolerance to crown rot appears achievable and will help to address the continual requests by growers and their advisors for access to varieties with higher levels of field-based tolerance to this crown rot disease. Multiple isolates of crown rot pathogens from Oregon and Washington were shown to have variable levels of pathogenicity that were as high within species as between species, and individual isolates were determined to be influenced in different ways by changes in environmental variables over successive years. This study was designed to identify reasons why field tests with native populations and with artificial inoculum of individual isolates of crown rot pathogens (Fusarium pseudograminearum, F. culmorum and Bipolaris sorokiniana) often have inconsistent results among similar tests performed at multiple locations and years. Multiple isolates of the three primary crown rot pathogens were evaluated individually over two years in field tests at the Columbia Basin Agricultural Research Center’s stations at Pendleton (16-inch annual precipitation) and Moro (11-inch), locations that span the range of rainfall environments in which 80% of the wheat acreage occurs in Oregon and Washington. Results of these tests show clearly that multiple isolates of each pathogen must be used in inoculation experiments to properly represent the range in pathogenicity within strains of each species. In a sand-based genetic-resistance testing system, wheat and barley lines without symptoms of crown rot occurred at very low percentages (<1%) for each of the three principal crown rot pathogens, Fusarium pseudograminearum, F. culmorum and Bipolaris sorokiniana. Genetic tolerance to crown rot is based on yield performance evaluations in the field, but varieties and lines with highest levels of tolerance often fail to protect wheat from yield loss during years characterized by particularly stressful climatic conditions, leading to the need for genetic resistance as well as tolerance. Approximately 1,600 wheat and barley entries from Oregon State University and Washington State University breeders were screened for resistance to each of the three pathogens in a sand-based bioassay at the Columbia Basin Agricultural Research Center at Pendleton, and seed from plants without symptoms was retested multiple times to determine if those lines are resistant or simply escaped being infected during one or more tests. The objective of this work is to determine if resistant genotypes can be identified as potential parents for use in wheat and barley breeding programs in areas where crown rot causes chronic and sometimes acute damage to wheat and barley yields. Facilities, equipment and staff were upgraded for research to improve tolerance of wheat to high populations of the root-lesion nematodes Pratylenchus neglectus and P. thornei. Root-lesion nematodes occur in high densities and cause yield reductions as high as 50% in many annual spring conservation cropping systems in the Pacific Northwest. A nematode extraction facility was constructed, microscopes and other equipment were purchased, technical staff participated in an intense nematology short course, and an experienced nematologist/wheat breeder was hired at the Columbia Basin Agricultural Research Center at Pendleton to develop lesion nematode management strategies including genetic resistance and/or tolerance. Additional research and education for controlling root-lesion nematode densities in conservation systems is likely to become an important adjunct to improvement of air, water and soil quality in the Pacific Northwest. Pure cultures of Pratylenchus neglectus and P. thornei are being developed for use in screening studies to identify genetic resistance in wheat. Field tests to evaluate genetic resistance and tolerance are essential but require a full season, whereas early generation tests and particularly the application of marker-assisted selections can be performed on higher numbers of test plants and with greater speed in precisely controlled greenhouse and plant growth rooms. Thousands of individual lesion nematodes were manually picked from water extracts, identified, and transferred to develop pure cultures for each species in redundant in vivo cultures (open pots in the greenhouse) and in vitro cultures (pre-sterilized carrot slices in an incubator) at the Columbia Basin Agricultural Research Center at Pendleton. Pure cultures are difficult to maintain and a loss of a culture can lead to suspension of screening activities for periods up to two years while cultures are regenerated, leading us to develop redundant culture systems to reduce the risk in our future research. Wheat lines and distant relatives of wheat with potential genes for resistance to root-lesion nematodes Pratylenchus thornei and P. neglectus were acquired from CIMMYT and Australia, and are being increased for crossing with wheat varieties locally adapted to the Pacific Northwest. Root-lesion nematodes occur in high densities and cause yield reductions as high as 50% in many annual spring conservation cropping systems in the Pacific Northwest. Strong linkages and germplasm exchanges were developed with Pacific Northwest and international wheat breeding and nematology programs where wheat and wheat relatives of interest have been developed. Advanced screening of the newly introduced germplasm will begin as soon as sufficient seed is increased, with the anticipation that lines identified as being resistant will be of interest to wheat breeders throughout the western USA. Densities of root-lesion nematodes with soil depth varied among sites, with some locations having highest density near the soil surface and other locations having very low density near the soil surface and peak density at depths as great as three feet in fields cropped annually to spring wheat. Previous lesion nematode surveys and research in the Pacific Northwest were based on soils sampled at depths from 4 to 10 inches, resulting in apparent high levels of spatial variability in nematode density, periodic failures to associate high populations of nematodes with reduced yield, and the conclusion that root-lesion nematodes were not affecting productivity of winter wheat rotated with summer fallow. Soils at 100 sites in Oregon and Washington were sampled at 15-cm increments to 5-ft depth to determine whether spatial variability and variable responses to nematodes at different locations could be attributed to the shallow sampling depths used in previous research. The finding that peak nematode populations often occurred far below the depths for all earlier soil samplings was immediately communicated to scientists initiating similar lines of inquiry in Washington, Idaho, Montana and Colorado, and the finding also leads us to conclude that damage from root-lesion nematodes in annually cropped fields may be more intense than previously thought, and that similar investigations must now be initiated to determine if lesion nematodes influence growth of winter wheat rotated with summer fallow. Experiments are being performed to identify the pathotypes (equivalent to “races”) of the cereal cyst nematode, Heterodera avenae, that occur in the Pacific Northwest. Cereal cyst nematodes are widely dispersed in wheat and barley production regions in the western USA, can reduce winter wheat yield as much as 50%, and can cause total destruction of spring wheat and barley. ARS collaborators at Oregon State University, Pendelton are collecting cyst nematode samples from various locations across the Pacific Northwest and are making progress in overcoming technical challenges associated with uniformly hatching large populations of nematode eggs under controlled conditions, as required for determining the pathotype and therefore identifying the appropriate resistance genes by screening wheat, barley and oat lines in the International Cereal Cyst Nematode Pathotype Screening Nursery. Identification of the pathotypes will allow acquition of germplasm with appropriate resistance genes for introduction into varieties currently adapted for maximum performance in the Pacific Northwest.