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Increased populations of Heterodera avenae in southeastern Idaho are associated with increased planting of susceptible cereal cultivars and lack of crop rotation. Identifying high-yield, resistant spring wheat cultivars with tolerance requires testing new genotypes and susceptibility assessments of marketed cultivars. We conducted two experiments to determine whether cultivars with putative resistance could maintain acceptable yield in the presence of H. avenae . We also evaluated the tolerance response in relation to previously tested cultivars. Seven spring wheat cultivars were planted in two irrigated commercial fields that were naturally infested with high populations of H. avenae . Measures of resistance, tolerance, and grain yield were assessed in aldicarb-treated versus nontreated plots. In aldicarb-treated plots in both years, grain yield of the susceptible cultivars Snow Crest, WestBred 936, WB9411, Patwin-515, and WB9668 was significantly increased. The expected yield increase with aldicarb was limited for the moderately susceptible Expresso due to water stress. 'WB-Rockland', carrying the Cre5 resistance gene, maintained its standard yield, while none of the other cultivars in the experiment showed resistance or tolerance. Our results indicated that aldicarb improves wheat grain yield in irrigated crop production systems, and although removed from the market, it is effective and has utility for research. The results also support the hypothesis that high yield susceptible cultivars can mask the effect of H. avenae on grain yield when managed appropriately., Competing Interests: The author(s) declare no conflict of interest.

Heterodera avenae , a globally distributed plant-parasitic nematode, is one of the most significant pests on cereal crops. In China, it is widely distributed in cereal-growing areas of 16 provinces and causes serious yield losses. In the present study, a total of 98 populations of H. avenae were collected from major wheat-growing regions in China and six other countries. The mitochondrial COI genes were amplified and analyzed. Forty-one mitochondrial COI haplotypes were identified, suggesting a high genetic diversity and endemism level of H. avenae in China. Phylogenetic analysis showed that H. avenae populations in China were divided into four clades. Significant evolutionary and genetic differences were found between Chinese (except Hubei) and foreign populations. Hap1, the most widely distributed haplotype, was considered to be a separate evolutionary origin in China. The gene flow of H. avenae from the northwestern region to the north China region and Huang-Huai-Hai region was significant, so as the direction between north China and Huang-Huai-Hai region. We speculate that water flowing from the Yellow River and mechanical harvesters promoted gene exchange among these groups. A distance-based redundancy analysis showed that genetic distances observed among H. avenae populations were explained foremost not only by geographic distance but also by temperature and precipitation. This study provides theoretical support for the origin and spread of H. avenae populations in China and elsewhere in the world.

Economic loss from Rhizoctonia bare patch, caused by Rhizoctonia solani AG-8, was estimated in two 50-ha fields on a single farm. A winter wheat crop was managed as a conventionally cultivated 2-year wheat/fallow rotation and a spring barley crop was managed as a no-till annual crop. Aerial photographs revealed that the patch-affected area was nearly double in barley (17%) compared with wheat (9%). Yield inside patches was reduced by 73 and 68% for wheat and barley, respectively. Grain produced on each field was reduced more for winter wheat (21.6 metric tons [t], valued at US$5,080) than for spring barley (16.8 t, valued at US$2,784). More precise estimates of economic damage and more robust management practices for Rhizoctonia bare patch must be developed.

Root-lesion nematodes ( Pratylenchus spp.) are parasites that invade and deteriorate roots, thereby reducing the efficiency of water and nutrient uptake. Pratylenchus neglectus and P. thornei are the two species that are most prevalent and cause reduced yields of rainfed wheat and barley in semiarid regions of the Pacific Northwest. They are particularly damaging where wheat and barley are produced without irrigation in areas receiving less than 450 mm (18 in.) of precipitation annually. This review is focused on the biology and management of P. neglectus and P. thornei in semiarid rainfed agriculture. Characteristics of climates, soils, and crop production systems are described as a preface to constraints placed upon management options. Discussions include the economic importance, host ranges, and protocols for sampling and species identification. Discussion of disease management options include crop rotation, genetic resistance and tolerance, planting date, trap and biofumigant crops, crop nutrition, chemical and biological nematicides, and tillage. Predictions for rainfed agriculture in a period of changing climate are presented, as are suggestions for important areas of research including crop genetics, nematode testing, and communication of results, Pratylenchus biology, mechanisms of resistance, the phytobiome, and closing the "yield gap" between actual and attainable yields.

Fusarium crown rot becomes most severe when wheat is stressed for water near the time of anthesis. This research examined the potential to study crown rot in the gradient of resource competition near a tree windbreak. Winter wheat was planted for 2 years into a field infested by Fusarium pseudograminearum and bordered by 17-m-high Austrian pines. Crown rot, plant growth and yield, and soil water content were evaluated at six distances (5 to 46 m) perpendicular to the tree line in strip plots inoculated or not inoculated with the pathogen. Crown rot was minor (<5% whiteheads) in noninoculated strips and greater in inoculated strips (26 to 35%) in a 21-m zone from 9 to 30 m from the tree line (0.5-1.8 times the tree height; 0.5-1.8H). At 46 m (2.7H), crown rot was similar in noninoculated and inoculated strips (2 to 5% whiteheads). Whiteheads and culm browning were roughly the reverse of soil water depletion by tree roots. Grain yield at 23 m compared with 46 m was reduced by 33 to 35% in noninoculated plots and by 43 to 49% in inoculated plots. It is possible to study associations between water stress and Fusarium crown rot in the zone of resource competition near windbreaks.

Assessments of Fusarium crown rot are often made in field trials inoculated with Fusarium pseudograminearum or F. culmorum . Factors affecting the efficiency of two inoculation procedures were evaluated. Pulverized Fusarium -colonized wheat plus oat grain inoculum mixed with the wheat seed caused more seedling damping-off compared with equal rates of colonized whole millet seeds placed 2 cm above the wheat seed. Both inoculation systems increased the incidence and severity of crown rot. The efficiency of F. pseudograminearum -colonized millet seed inoculum was not reduced when wheat seed was treated with difenoconazole. Crown rot in inoculated plots became greater when starter fertilizer was applied with or below the wheat seed and when soil below the wheat seed was disrupted by a seed drill with an opener that creates a groove or trench directly below the seed. No biologically important associations were detected between whiteheads and other measures of crown rot, grain yield, or grain test weight. The millet seed inoculation system was the most efficient for wheat production systems in the semiarid U.S. Pacific Northwest.

Symptoms of Fusarium crown rot of wheat include premature death of inflorescens (whiteheads), lesions on subcrown internodes, and rotting of crown tissue and lower stem internodes. Each symptom type is influenced by a different set of environmental conditions. Whiteheads are the easiest symptom to quantify and are frequently reported in the Pacific Northwest U.S.A. The objective of this research was to examine factors associated with whitehead expression and relationships with wheat yield and test weight. Incidence of whiteheads differed for inoculations with different isolates of F. pseudograminearum and F. culmorum , and over years due to weather factors. Whiteheads became less as planting dates for winter wheat were delayed until after September, and incidence was increased with increasing nitrogen application rate. Dates of initial and greatest expression of whiteheads differed among cultivars, which was associated in part with the cultivar heading date. Whiteheads were not correlated with subcrown internode lesions or browning of crown tissue. Whiteheads were also not correlated with grain test weight. Whiteheads were sometimes negatively associated with grain yield, but that relationship was variable and could not be considered a reliable, recurrent, or accurate measure of crown rot severity. These results indicate the need for caution in reporting whiteheads as a sole indicator of cultivar susceptibility to Fusarium crown rot.

Small grain cereals have served as the basis for staple foods, beverages, and animal feed for thousands of years. Wheat, barley, oats, rye, triticale, rice, and others are rich in calories, proteins, carbohydrates, vitamins, and minerals. These cereals supply 20% of the calories consumed by people worldwide and are therefore a primary source of energy for humans and play a vital role in global food and nutrition security. Global production of small grains increased linearly from 1960 to 2005, and then began to decline. Further decline in production is projected to continue through 2050 while global demand for these grains is projected to increase by 1% per annum. Currently, wheat, barley, and oat production exceeds consumption in developed countries, while in developing countries the consumption rate is higher than production. An increasing demand for meat and livestock products is likely to compound the demand for cereals in developing countries. Current production levels and trends will not be sufficient to fulfill the projected global demand generated by increased populations. For wheat, global production will need to be increased by 60% to fulfill the estimated demand in 2050. Until recently, global wheat production increased mostly in response to development of improved cultivars and farming practices and technologies. Production is now limited by biotic and abiotic constraints, including diseases, nematodes, insect pests, weeds, and climate. Among these constraints, plant-parasitic nematodes alone are estimated to reduce production of all world crops by 10%. Cereal cyst nematodes (CCNs) are among the most important nematode pests that limit production of small grain cereals. Heavily invaded young plants are stunted and their lower leaves are often chlorotic, forming pale green patches in the field. Mature plants are also stunted, have a reduced number of tillers, and the roots are shallow and have a "bushy-knotted" appearance. CCNs comprise a number of closely-related species and are found in most regions where cereals are produced.

Soil-borne pathogens of the Pacific Northwest decrease yields in both spring and winter wheat. Pathogens of economic importance include Fusarium culmorum , Pratylenchus neglectus , P. thornei , and Rhizoctonia solani AG8. Few options are available to growers to manage these pathogens and reduce yield loss, therefore the focus for breeding programs is on developing resistant wheat cultivars. A recombinant inbred line population, LouAu (MP-7, NSL 511036), was developed to identify quantitative trait loci (QTL) associated with resistance to P. neglectus and P. thornei This same population was later suspected to be resistant to F. culmorum and R. solani AG8. This study confirms partial resistance to F. culmorum and R. solani AG8 is present in this population. Six major and 16 speculative QTL were identified across seven measured traits. Four of the six major QTL were found within the same genomic region of the 5A wheat chromosome suggesting shared gene(s) contribute to the resistance. These QTL will be useful in breeding programs looking to incorporate resistance to soil-borne pathogens in wheat cultivars., (Copyright © 2017 Thompson et al.)

The cereal cyst nematode Heterodera avenae reduces wheat yield in the Pacific Northwest. Resistance and tolerance traits among spring wheat cultivars were poorly defined. Screening trials were conducted with 39 cultivars over a 2-year period in irrigated commercial fields that were infested by H. avenae. Comparisons were made between drill strips treated or untreated with aldicarb at the time of planting. Root sampling at the time of plant anthesis indicated that cultivars differed greatly in susceptibility to H. avenae, with numbers of newly produced white H. avenae females ranging from <5 to 70 per plant. Aldicarb reduced mean numbers of white females as much as 99% on the most susceptible cultivar ('Glee') and increased mean grain yield as much as 77% for the least tolerant cultivar ('Cataldo'). Density of H. avenae eggs in untreated soil following harvest was significantly higher than the density in aldicarb-treated plots. Agronomically acceptable traits of resistance plus tolerance were identified in one cultivar of hard red spring wheat ('WB-Rockland') and two cultivars of hard white spring wheat ('Klasic' and 'LCS Star') but in none of the soft white spring wheat cultivars. This is the first report of spring wheat cultivars expressing the dual traits of resistance plus tolerance to H. avenae.

Rainfed experiments operated continuously for up to 84 years in semiarid eastern Oregon are among the oldest agronomic trials in North America. Disease incidence and severity had been quantified visually but quantification of inoculum density had not been attempted. Natural inoculum of 17 fungal and nematode pathogens were quantified for each of 2 years on eight trials using DNA extracts from soil. Crop type, tillage, rotation, soil fertility, year, and their interactions had large effects on the pathogens. Fusarium culmorum and Pratylenchus thornei were more dominant than F. pseudograminearum and P. neglectus where spring crops were grown, and the opposite species dominances occurred where winter wheat was the only crop. Bipolaris sorokiniana and Phoma pinodella were restricted to the presence of spring cereals and pulse crops, respectively. Helgardia spp. occurred in winter wheat-fallow rotations but not in annual winter wheat. Gaeumannomyces graminis var. tritici was more prevalent in cultivated than noncultivated soils and the opposite generally occurred for Rhizoctonia solani AG-8. Densities of Pythium spp. clade F were high but were also influenced by treatments. Significant treatment effects and interactions were more prevalent in two long-standing (>50-year) annually cropped experiments (29%) than two long-standing 2-year wheat-fallow rotations (14%). Associations among pathogens occurred mostly in an 84-year-old annual cereals experiment. This survey provided guidance for research on dynamics of root-infecting pathogens of rainfed field crops and identified two pathogens (Drechslera tritici-repentis and P. pinodella) not previously identified at the location.

Heterodera avenae is a cereal cyst nematode that reduces wheat yields in the Pacific Northwest of the United States. Barley is also susceptible but there were no previous reports of resistance or tolerance to H. avenae in the United States. Spring barley cultivars were assayed in H. avenae-infested fields over 2 years. Cultivars were planted in plots treated or not treated with aldicarb. Forty-five cultivars were evaluated for the market classes of two- and six-row feed barley cultivars and two- and six-row malt barley cultivars. One two-row feed barley ('Lenetah') was ranked as resistant and four were tolerant or very tolerant. In total, 1 two-row malt barley ('Odyssey') was very resistant and 10 were tolerant or very tolerant. Two six-row feed and two six-row malt barley cultivars were tolerant or very tolerant but none were resistant. Seven feed barley cultivars were ranked as having a balance of at least moderate resistance plus moderate tolerance: 'Champion', Lenetah, 'Xena', 'Idagold II', 'Transit', 'Millennium', and 'Goldeneye'. This is the first report of resistance and tolerance of barley in H. avenae-infested fields in the Pacific Northwest. Barley productivity can be improved by planting resistant plus tolerant cultivars or by using highly resistant and highly tolerant cultivars as parents in barley improvement programs.

The cereal cyst nematode Heterodera avenae suppresses wheat production in the western United States. A second species of cereal cyst nematode, H. filipjevi, was identified in eastern Oregon during 2008. This paper reports the discovery of H. filipjevi-infested fields in eastern Washington, thereby extending the known distribution of H. filipjevi in the United States. The identity of H. filipjevi was determined and confirmed by species-specific polymerase chain reaction (PCR), PCR-restriction fragment length polymorphism (RFLP), sequencing, and cyst morphology. Soils that were collected from naturally infested fields in Washington were used to compare the virulence of H. avenae and H. filipjevi on six spring wheat cultivars under controlled-environment conditions. Noninfested soils from nearby fields were used as controls. Cultivars Ouyen and WB Rockland were resistant to H. avenae and susceptible to H. filipjevi. Cultivars Sönmez and SY Steelhead were resistant to H. filipjevi and susceptible to H. avenae. Cultivars Louise and WB 936 were susceptible to both species. The resistance of SY Steelhead to 'H. avenae', reported in a previous paper, is corrected as resistance to H. filipjevi due to an earlier misidentification of H. filipjevi. Management guidelines that include crop rotations and resistant cultivars are presented. Discovery of additional infestations of H. filipjevi are anticipated when DNA-based tests become used routinely in commercial diagnostic laboratories.

Thirty crop species and cultivars were assayed in the greenhouse for efficiency as hosts of Pratylenchus neglectus and P. thornei. Hosting ability ratings were assigned using the ratio of final versus initial nematode density and also by comparing the final nematode density to that of a susceptible wheat control. Good hosts of both Pratylenchus spp. included oat 'Monida', chickpea 'Myles', and lentil 'Athena' and 'Morton'. Good hosts of P. neglectus but not of P. thornei included 10 Brassica spp. (5 canola, 2 mustard, and 3 camelina cultivars), chickpea 'Sierra', sudangrass 'Piper', and sorghum/sudangrass hybrid 'Greentreat Plus'. Good hosts of P. thornei but not of P. neglectus included lentil 'Skyline' and pea 'Granger', 'Journey', and 'Universal'. Poor or minor hosts of both Pratylenchus spp. included chickpea 'Dwelley', pea 'Badminton', safflower 'Gila', 'Girard', and 'KN 144', sunflower '2PD08', flax 'Pembina', eastern gamagrass 'Pete', and switchgrass 'Blackwell'. Results of these assays will provide guidance for improving crop rotation and cultivar selection efficiencies.

Eighteen rangeland plants and 16 weed species were assayed in the greenhouse for efficiency as hosts of Pratylenchus neglectus and P. thornei. Hosting ability ratings were assigned using the ratio of final versus initial nematode density and by comparing the final nematode density to that of susceptible wheat controls. Good hosts of both Pratylenchus spp. included thickspike bluegrass 'Critana', smooth brome 'Manchar', seven wheatgrasses, and jointed goatgrass. Good hosts of P. neglectus but not P. thornei included two hairy vetches, western wheatgrass 'Rosana', big bluegrass 'Sherman', tall wheatgrass 'Alkar', green foxtail, kochia, large crabgrass, palmer amaranth, redroot pigweed, tumble mustard, and wild oat. Good hosts of P. thornei but not P. neglectus included hard fescue 'Durar', sheep fescue 'Blacksheep', downy brome, and rattail fescue. Poor or minor hosts of both Pratylenchus spp. included two alfalfas, dandelion, horseweed, lambsquarters, prostrate spurge, and Russian thistle. These assays will provide guidance for transitioning rangeland into crop production and for understanding the role of weeds on densities of Pratylenchus spp. in wheat-production systems.

Pratylenchus neglectus and P. thornei reduce wheat yields in the Pacific Northwest of the United States. Resistant landrace cultivars have been identified using controlled environments. Field resistance and tolerance characteristics were compared over 3 years and two locations for four spring wheat cultivars: the susceptible 'Alpowa' and 'Louise' and the resistant landraces AUS28451 and Persia 20. Proportions and densities of P. neglectus and P. thornei differed across seasons and locations. Resistance was evaluated by comparing preplant and postharvest densities of nematodes in soil. Tolerance was evaluated by comparing grain yield and grain quality in plots treated or untreated by the nematicide aldicarb. Alpowa was susceptible and intolerant, Louise was susceptible and moderately tolerant, AUS28451 was resistant and intolerant, and Persia 20 was moderately susceptible and moderately intolerant. The species dominance shifted from P. neglectus to P. thornei in one field over a period of 3 years in apparent response to cultivars and crops planted. Estimates of economic loss caused by Pratylenchus spp. ranged from $8 to $20/ha. Economic benefits appear to be achievable by developing a spring wheat genotype with tolerance plus resistance, such as with a cross between AUS28451 and Louise.

Heterodera avenae and H. filipjevi are economically important cyst nematodes that restrict production of cereal crops in the Pacific Northwest United States and elsewhere in the world. Identification of these two species is critical for recommending and implementing effective management practices. Primers were designed from the internal transcribed spacer (ITS) regions of H. avenae and H. filipjevi ribosomal DNA. The primers were highly specific when examined on target isolates but did not amplify DNA from nontarget Heterodera, Globodera, Meloidogyne, Pratylenchus, and other nematode species tested. Polymerase chain reaction (PCR) and amplification conditions were established, and H. avenae and H. filipjevi were clearly distinguished by PCR fragments of 242 and 170 bp, respectively. Robust PCR amplification was achieved with DNA extracted from a single egg or second-stage juvenile (J2) using a laboratory-made worm lysis buffer, and DNA from 0.5 egg or J2 using a commercial kit. The PCR assays were successfully employed for differentiation of H. filipjevi and H. avenae populations collected from eight locations in three Pacific Northwest states. This is the first report of a species-specific ITS PCR assay to detect and identify H. filipjevi. The assays for both species will enhance diagnosis of cereal cyst nematode species in infested fields.

Field surveys were conducted by collecting soil samples to estimate nematode densities in soil from winter wheat, spring wheat, spring barley, and spring legumes (lentil, chickpea, and pea) fields during 2010 and 2011. Pratylenchus spp. were observed in 60% of sampled fields. However, nematodes were detected in nearly all of the survey fields in high numbers where crops were grown every year. To identify climatic variables associated with density of Pratylenchus spp. in soil, correlation and regression analyses were performed using climate data of survey sites from 1979 to 2010. Fifty-seven climate variables were significantly correlated with densities of Pratylenchus spp. All precipitation variables were significantly positively correlated with nematode abundance. Summer maximum air temperature was negatively correlated and winter minimum air temperature was positively correlated with nematode densities. In addition, both years' nematode densities were significantly correlated with cropping intensity. Five multivariate regression models for 2010 and seven models for 2011 nematode abundance levels were developed. The majority of the climate variables selected in the models were related to precipitation. Knowledge of root-lesion nematode distribution in the dryland region of eastern Washington and associated climate variables may be helpful to determine risk and apply management practices to minimize crop damage.

Fusarium crown rot (FCR) is one of the most widespread root and crown diseases of wheat in the Pacific Northwest (PNW) of the United States. Our objectives were to characterize crown rot severity and distribution throughout the PNW by conducting a survey of 210 fields covering the diverse dryland wheat-producing areas of Washington and Oregon and to utilize a factor analysis statistical approach to determine the effects of climate and geography on species distribution and disease severity. Climatic variables were based on 30-year averages and 2008 and 2009 separately (the 2 years of the survey). Mean annual temperature, mean temperature in the coldest month, mean temperature in the warmest month, mean annual precipitation, snowfall, elevation, soil type, and cropping intensity were highly intercorrelated. The factor analysis of the climate variables resulted in the development of two latent factors that could be used as predictor variables in logistic regression models for the presence or absence of Fusarium spp. and of FCR disease scores. Isolates of Fusarium spp. were recovered from 99% of 105 fields sampled in 2008 and 97% of fields in 2009. There were differences between years for responses of FCR and nodes scores, and isolations of Fusarium pseudograminearum with more significant results in 2008, due to warmer drier weather. Results of the factor analysis showed that the distribution of F. pseudograminearum occurred in a greater frequency in areas of the PNW at lower elevations with lower moisture and higher temperatures in 2008, whereas F. culmorum occurred in greater frequency in areas at higher elevations with moderate to high moisture and cooler temperatures consistently across both years. Disease scores increased with increasing levels of factors 1 (primarily temperature) and 2 (primarily precipitation). Both the frequency of pathogen species and disease scores were influenced by the year, indicating that soilborne pathogens are responsive to short-term changes in environment. This factor analysis approach can be utilized in studies to determine the effects of climate and other environmental (soil, cropping system, and so on) factors on the distribution and severity of root diseases.

Growth and yield of winter wheat are suppressed by Pratylenchus thornei and by Fusarium culmorum. Many fields in cereal production regions throughout the world are infested by both pathogens. We evaluated effects of one or both pathogens on winter wheat growth, grain yield, and disease parameters at heading and harvest stages over 2 years in inoculated, rainfed pots incubated outdoors. P. thornei nematodes were inoculated at 1, 2, or 4 nematodes/g of soil and F. culmorum was added as colonized millet seed at 0.65 g/kg of soil. At harvest, compared with the noninoculated control, the high rate of P. thornei reduced (P < 0.05) plant height, shoot weight, root weight, and grain yield by 19, 17, 48, and 31%, respectively. F. culmorum alone reduced these parameters by 15, 16, 22, and 22%, respectively. Co-inoculations caused reductions of 27, 38, 61, and 63%, respectively. The reproductive rate of P. thornei was not greatly affected by co-inoculation with F. culmorum. Disease severity ratings at both plant growth stages became amplified as the nematode density was increased, and were much greater in the presence of both pathogens. Effects of co-inoculation on grain yield were slightly greater than predicted by additive effects of the individual pathogens, suggesting a synergistic effect on yield depression.

Pratylenchus neglectus is one of the most widespread and economically important nematodes that invades plant roots and restricts wheat productivity in the Pacific Northwest. It is challenging to quantify P. neglectus using microscopic methods for studies that require large-scale sampling, such as assessment of rotation crops, wheat cultivars, and other management practices. A real-time quantitative polymerase chain reaction (qPCR) assay was developed to detect and quantify P. neglectus from DNA extracts of soil. The primers, designed from the internal transcribed spacer region of rDNA, showed high specificity with a single melt curve peak to DNA from eight isolates of P. neglectus but did not amplify DNA from 28 isolates of other plant-parasitic and non-plant-parasitic nematodes. A standard curve (R 2 = 0.96; P < 0.001) was generated by amplifying DNA extracted from soil to which nematodes were added. The soil standard curve was validated using sterilized soil inoculated with lower numbers of P. neglectus. A significant positive relationship (R 2 = 0.66; P < 0.001) was observed for nematode numbers quantified from 15 field soils using qPCR and the Whitehead tray and microscopic method but the qPCR generally tended to provide higher estimates. Real-time PCR potentially provides a useful platform for efficient detection and quantification of P. neglectus directly from field soils.

The cereal cyst nematode Heterodera avenae reduces wheat yields in the Pacific Northwest. Previous evaluations of cultivar resistance had been in controlled environments. Cultivar tolerance had not been evaluated. Seven spring wheat trials were conducted in naturally infested fields in three states over 2 years. A split-plot design was used for all trials. Five trials evaluated both tolerance and resistance in 1.8-by-9-m plots treated or not treated with nematicides. Two trials evaluated resistance in 1-m head rows where each wheat entry was paired with an adjacent row of a susceptible cultivar. Cultivars with the Cre1 resistance gene ('Ouyen' and 'Chara') reduced the postharvest density of H. avenae under field conditions, confirming Cre1 parents as useful for germplasm development. Ouyen was resistant but it was also intolerant, producing significantly lower grain yield in controls than in plots treated with nematicides. Susceptible cultivars varied in tolerance. Undefined resistance was identified in one commercial cultivar ('WB-Rockland) and four breeding lines (UC1711, SO900163, SY-B041418, and SY-97621-05). This research was the first systematic field demonstration of potential benefits to be derived through development and deployment of cultivars with resistance plus tolerance to cereal cyst nematode in North America.

There is interest in converting the 2-year rotation of rainfed winter wheat with cultivated fallow in the Pacific Northwest of the United States into direct-seed (no-till) systems that include chemical fallow, spring cereals, and food-legume and brassica crops. Eight cropping systems in a low-precipitation region (<330 mm) were compared over 9 years to determine effects of changes on diseases. Fusarium crown rot was more prevalent in wheat following cultivated than chemical fallow, and Rhizoctonia root rot was more severe when winter wheat was rotated with chemical fallow than with no-till winter pea. Take-all occurred even during the driest years and was more severe on annual spring wheat than on annual spring barley. Inoculum density (picograms of DNA per gram of soil) differed (α < 0.05) among cropping systems for Fusarium culmorum, F. pseudograminearum, Gaeumannomyces graminis var. tritici, and Pythium spp. but not for Rhizoctonia solani AG-8. Phoma medicaginis var. pinodella was detected only where winter pea was planted frequently. This is the first report of P. medicaginis as a component of the dryland stem rot complex of pea in north-central Oregon. Results of this investigation will provide guidance for developing crop species with resistance to Fusarium crown rot and black stem of pea.

There is interest in converting rainfed cropping systems in the Pacific Northwest from a 2-year rotation of winter wheat and cultivated fallow to direct-seed (no-till) systems that include chemical fallow, spring cereals, and food legume and brassica crops. Little information is available regarding effects of these changes on plant-parasitic nematodes. Eight cropping systems in a low-precipitation region (<330 mm) were compared over 9 years. Each phase of each rotation occurred each year. The density of Pratylenchus spp. was greater in cultivated than chemical fallow, became greater with increasing frequency of host crops, and was inversely associated with precipitation (R 2 = 0.92, α < 0.01). Densities after harvesting mustard, spring wheat, winter wheat, and winter pea were greater (α < 0.01) than after harvesting spring barley or spring pea. Camelina also produced low densities. Winter wheat led to a greater density of Pratylenchus neglectus and spring wheat led to a greater density of P. thornei. Density of Pratylenchus spp. was correlated (R 2 = 0.88, α < 0.01) but generally higher when detected by real-time polymerase chain reaction on DNA extracts from soil than when detected by a traditional method. Selection of different Pratylenchus spp. by different wheat cultivars or growth habit must be addressed to minimize the level of nematode risk to future plantings of intolerant crops.

A complex of fungal soilborne pathogens and plant-parasitic nematodes reduces wheat yields in the Pacific Northwest. On several other crops in nematode-infested soils, seed treatment with abamectin (Avicta) or Bacillus firmus (Votivo) or foliar application of spirotetramat (Movento) reduced root injury and improved yield. These products, along with fungicide seed treatments and aldicarb (Temik), were evaluated in 13 spring wheat trials over 3 years. During 2011, the mean wheat yield at four locations was 419 kg/ha greater (valued at $122/ha) from seed treated with fungicides and insecticide than from untreated seed, due to protection against soilborne fungal pathogens. Aldicarb increased the mean grain yield over the fungicide-plus-insecticide treatment by another 798 kg/ha (valued at $254/ha) and also reduced the density of Heterodera avenae but is not registered for use on wheat. Abamectin and B. firmus had negligible effects on grain yield and postharvest density of Pratylenchus spp. and H. avenae. Spirotetramat reduced density of H. avenae but did not improve grain yield. We conclude that management of fungal pathogens by seed protectants remains essential and that management of nematodes can be achieved through crop rotations and genetic resistance.

Fusarium crown rot (FCR), caused by Fusarium pseudograminearum and F. culmorum, reduces wheat (Triticum aestivum L.) yields in the Pacific Northwest (PNW) of the US by as much as 35%. Resistance to FCR has not yet been discovered in currently grown PNW wheat cultivars. Several significant quantitative trait loci (QTL) for FCR resistance have been documented on chromosomes 1A, 1D, 2B, 3B, and 4B in resistant Australian cultivars. Our objective was to identify QTL and tightly linked SSR markers for FCR resistance in the partially resistant Australian spring wheat cultivar Sunco using PNW isolates of F. pseudograminerarum in greenhouse and field based screening nurseries. A second objective was to compare heritabilities of FCR resistance in multiple types of disease assaying environments (seedling, terrace, and field) using multiple disease rating methods. Two recombinant inbred line (RIL) mapping populations were derived from crosses between Sunco and PNW spring wheat cultivars Macon and Otis. The Sunco/Macon population comprised 219 F(6):F(7) lines and the Sunco/Otis population comprised 151 F(5):F(6) lines. Plants were inoculated with a single PNW F. pseudograminearum isolate (006-13) in growth room (seedling), outdoor terrace (adult) and field (adult) assays conducted from 2008 through 2010. Crown and lower stem tissues of seedling and adult plants were rated for disease severity on several different scales, but mainly on a numeric scale from 0 to 10 where 0 = no discoloration and 10 = severe disease. Significant QTL were identified on chromosomes 2B, 3B, 4B, 4D, and 7A with LOD scores ranging from 3 to 22. The most significant and consistent QTL across screening environments was located on chromosome 3BL, inherited from the PNW cultivars Macon and Otis, with maximum LOD scores of 22 and 9 explaining 36 and 23% of the variation, respectively for the Sunco/Macon and Sunco/Otis populations. The SSR markers Xgwm247 and Xgwm299 flank these QTL and are being validated for use in marker-assisted selection for FCR resistance. This is the first report of QTL associated with FCR resistance in the US.

The cereal cyst nematode Heterodera avenae can be extracted from soil using several different floatation or elutriation methods. Automated methods are prohibitively expensive for use in small labs and, for optimal efficiency, floatation methods require that the soil be air dried for an extended period. A method which suspends soil particles in a water column above a fluidizing plate was reported as being most efficient with wet and dry soils. Use of the fluidizing column for extracting H. avenae has not been reported in the United States and materials to construct the column using contemporary components have not been described. Objectives of this research were to construct a column with components available in the United States, and to compare numbers of cysts and eggs plus juveniles (from cysts) extracted by the column and three other floatation methods: Fenwick can, flask, and Cobb sieving. From a soil containing recently produced (more dense) cysts, the column extracted at least 18% more cysts and 23% more eggs plus juveniles than the Fenwick and flask methods. The fluidizing column was found to be useful for small laboratories because it is inexpensive ($253 for two columns), easily and quickly constructed by nonprofessional labor, and produces adequately repeatable results.

The root-lesion nematode Pratylenchus thornei is one of the most important pests restricting productivity of wheat in the Pacific Northwest (PNW). It is laborious and difficult to use microscopy to count and identify the nematodes in soils. A SYBR Green I-based real-time polymerase chain reaction (PCR) assay was developed to detect and quantify this species from DNA extracts of soil. A primer set, designed from the internal transcribed spacer region (ITS1) of rDNA, was highly specific to P. thornei and did not amplify DNA from 27 isolates of other Pratylenchus spp., other nematodes, and six fungal species present in PNW wheat fields. A standard curve relating threshold cycle and log values of nematode number was generated from artificially infested soils. The standard curve was supported by a high correlation between the numbers of P. thornei added to soil and the numbers quantified using real-time PCR. Examination of 15 PNW dryland field soils and 20 greenhouse samples revealed significant positive correlations between the numbers determined by real-time PCR and by the Whitehead tray and microscopic method. Real-time PCR is a rapid, sensitive alternative to time-consuming nematode extractions, microscopic identification, and counting of P. thornei from field and greenhouse soils.

The cereal cyst nematode, Heterodera avenae, has the potential to reduce yields of cereal crops in the Pacific Northwest. Spirotetramat (Movento) is a foliar-applied insecticide with ambimobile translocation that reduces fecundity of sucking insects which feed on roots as well as foliage. Spirotetramat (88 g/ha) was applied to foliage during 2010 in two wheat fields infested by H. avenae near St. Anthony, ID and Palouse, WA. In Idaho, two applications at 2-week intervals during late spring to plants already exhibiting swollen white females reduced the postharvest density of H. avenae eggs plus juveniles by 35% (P = 0.03) compared to the nontreated control. In Washington, a single application before white females became apparent reduced the nematode density by 78% (P = 0.01). Grain yields and test weights were not significantly affected by application of spirotetramat at either location. In addition, symptomatic plants from the Idaho field were transplanted into greenhouse pots and treated with spirotetramat. One application (110 g/ha) reduced numbers of eggs plus juveniles/plant by 78% (P = 0.02). Spirotetramat effectively reduced H. avenae populations and warrants further evaluation as a substitute for crop rotations or long fallow periods that reduce nematode population densities in infested fields.

The cereal cyst nematodes Heterodera filipjevi and H. avenae impede wheat production in the Pacific Northwest (PNW). Accurate identification of cyst nematode species and awareness of high population density in affected fields are essential for designing effective control measures. Morphological methods for differentiating these species are laborious. These species were differentiated using polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) of internal transcribed spacer (ITS)-ribosomal (r)DNA with up to six restriction endonucleases (TaqI, HinfI, PstI, HaeIII, RsaI, and AluI). The method was validated by inspecting underbridge structures of cyst vulval cones. Grid soil sampling of an Oregon field infested by both species revealed that H. filipjevi was present at most of the infested grid sites but mixtures of H. avenae and H. filipjevi also occurred. These procedures also detected and differentiated H. filipjevi and H. avenae in soil samples from nearby fields in Oregon and H. avenae in samples from Idaho and Washington. Intraspecific polymorphism was not observed within H. filipjevi or PNW H. avenae populations based on the ITS-rDNA. However, intraspecific variation was observed between H. avenae populations occurring in the PNW and France. Methods described here will improve detection and identification efficiencies for cereal cyst nematodes in wheat fields.

Crown rot caused by Fusarium pseudograminearum reduces the yield of wheat (Triticum aestivum) in Oregon. Observations of crown rot symptoms in traditional breeding and yield testing nurseries have not been useful for describing tolerance ratings of wheat cultivars. Yield data from inoculated experiments were therefore evaluated to determine if differences in cultivar response could be identified. A comparison of yields in inoculated and noninoculated plots was made for one group of spring wheat entries and four groups of winter wheat entries. Significant differences among spring wheat entries were identified and were validated against standards for tolerance and intolerance to F. pseudograminearum in Australia. Locally adapted and Australian standards exhibited a comparable range of yield reduction due to inoculation. Spring wheat tolerance reactions can be accurately described using as few as 24 yield comparisons. However, this screening method will not be practical for winter wheat due to stronger effects of year and location on the phenotypic tolerance response, requiring about 95 yield comparisons to accurately define the crown rot phenotype of a winter wheat cultivar.

Wheat (Triticum aestivum) in low-precipitation regions of eastern Oregon and Washington is grown mostly as rainfed biennial winter wheat (10-month growing season) planted into cultivated fallow (14-month crop-free period). There are increasing trends for cultivated fallow to be replaced by chemical fallow and for spring cereals to be planted annually without tillage. Most fields are infested by the root-lesion nematodes Pratylenchus neglectus or P. thornei. A replicated multiyear experiment was conducted to compare cropping systems on soil infested by P. neglectus. Populations became greater with increasing frequency of the host crops mustard, pea, and wheat. Annual winter wheat had the highest P. neglectus populations, the lowest capacity to extract soil water, and a lower grain yield compared with wheat grown biennially or rotated with other crops. Populations of P. neglectus did not differ for cultivated versus chemical fallow. Lowest populations occurred in annual spring barley. Winter wheat yield was inversely correlated with the population of P. neglectus. Measures to monitor and to reduce the population of P. neglectus in Pacific Northwest wheat fields are recommended.

Wheat in eastern Oregon is produced mostly as a 2-year rotation of winter wheat and summer fallow. Maximum agronomic yield potential is expected with early September planting dates but actual yields are generally highest for plantings made in mid-October. Field experiments with sequential planting dates from early September to December were performed over 4 years. Associations among yield, disease incidence, and 19 moisture and temperature parameters were evaluated. Incidence of Cephalosporium stripe, crown rot, eyespot, and take-all decreased as planting was delayed. Crown rot and eyespot were negatively correlated more significantly and more frequently with temperature than moisture parameters, and take-all was more associated with moisture than temperature. Rhizoctonia root rot was unrelated to planting date and climatic parameters. Crown rot was identified most frequently (4 of 5 tests) as an important contributor to yield suppression but yield was most closely associated (R 2 > 0.96) with effects from a single disease in only two of five location-year tests. Yield was most related to combinations of diseases in three of five tests, complicating development of disease modules for wheat growth-simulation models.

Dryland field crops in the Pacific Northwest United States are commonly produced in silt loams infested by the root-lesion nematodes Pratylenchus neglectus and P. thornei. Soils at 30 sites in Oregon were sampled from 0 to 120 cm depth to examine the vertical distribution of these Pratylenchus spp. Both species were distributed through entire soil profiles of all cropping systems. Populations were generally greatest in the surface 30 cm, but sometimes high populations were detected at depths greater than 45 cm. Sampling to 30 cm depth allowed detection of more than 50% of the population in most sites, while sampling to 45 cm depth yielded more than 75% of the population in over 75% of the sites evaluated. Therefore, soil samples should be collected to 30 to 45 cm depth to accurately estimate populations of Pratylenchus spp. in dryland crops produced on silt loams in the Pacific Northwest. Populations of Pratylenchus spp. were found to be related to the most recently planted crop, with populations after barley, after wheat, and during summer fallow being detected in ascending order.

A species-specific polymerase chain reaction (PCR) method was developed to detect and identify the root-lesion nematodes Pratylenchus neglectus and P. thornei from soil. A primer set was designed from Pratylenchus 28S rRNA gene sequences of the D3 expansion domain. Primer specificity was confirmed with 23 isolates of 15 nematode species and other plant-parasitic and non-plant-parasitic nematodes typically present in the soil communities, and with six fungal species commonly associated with wheat root rot. DNA obtained using a commercially available kit and a method developed in our laboratory gave comparable amplification. PCR conditions were optimized and the two species were differentiated by PCR products of 144 bp for P. neglectus and 288 bp for P. thornei. With this assay, we detected a single juvenile in 1 g of sterile, inoculated soil. Examination of 30 field soil samples revealed that this method was applicable to a range of soils naturally infested with these two pathogens in Oregon. This PCR-based method is rapid, efficient, and reliable, does not require expertise in nematode taxonomy and morphology, and could be used as a rapid diagnostic tool for commercial and research applications for disease forecasting and management.

Plant and soil samples from an irrigated winter wheat (Triticum aestivum) field near Imbler (Union County), OR were evaluated for root diseases during April 2007. The field exhibited patches with as much as 90% plant mortality. Previous crops were winter wheat (2004), chickpea (Cicer arietinum, 2005), and spring wheat (cv. Jefferson, 2006). Stubble was baled and removed, and the field was cultivated before replanting to winter wheat cv. Chukar in October. Patches of stunted seedlings (three- to five-leaf stage) appeared in March 2007. Stunted seedlings exhibited chlorotic or necrotic lower leaves, healthy younger leaves, few or no tillers, rotting of lower culms and crowns, and light brown roots with little or no branching. Signs and symptoms of fungal pathogens (Pythium spp., Gaeumannomyces graminis var. tritici, Rhizoctonia solani AG-8, and Typhula incarnata) were present on affected plants. Most small grain fields in Union County are infested with Heterodera avenae (4) but none of the roots, on either healthy or stunted plants, exhibited the bushy branching pattern typical of sites where H. avenae females penetrate and encyst. Extraction of motile nematodes (Whitehead tray method) from soil revealed high populations of Pratylenchus neglectus (6,560/kg of soil), Tylenchorhynchus spp. (2,369/kg of soil), and a species initially thought to be H. avenae (3,098 juveniles/kg of soil). Cysts were also extracted. During PCR-restriction fragment length polymorphism identification (1) of H. avenae collected in Oregon, Washington, and Idaho, four restriction enzymes applied to amplified DNA of cysts from the Imbler field consistently revealed a pattern identical to that of a H. filipjevi DNA standard and distinct from patterns of H. avenae, H. schachtii, and H. latipons. DNA standards were obtained from R. Rivoal, INRA, Rennes, France. Morphological evidence confirmed that the specimens were H. filipjevi, a member of the 'H. avenae Group' of cereal cyst nematodes (2,3). Measurements of second-stage juveniles (n = 15) included length of body (range = 530 to 570 μm, mean = 549, st. dev. = 13.0), stylet (22.5 to 24.5, 23.2, 0.6) with anchor-shaped basal knobs, tail (52.5 to 62.5, 57.4, 2.7), and hyaline tail terminal (30 to 38, 33.5, 2.6). The lateral field had four lines of which the inner two were more distinct. Shapes of the tail, tail terminus, and stylet knobs were also consistent with H. filipjevi. Cysts (n = 10) were lemon shaped and light brown. The cyst wall had a zigzag pattern. The vulval cone was bifenestrate with horseshoe-shaped semifenestra. The cysts were characterized by body length including neck (range = 718 to 940 μm, mean = 809.7, st. dev. = 61.8), body width (395 to 619, 504, 71.2), L/W ratio = (1.1 to 2.2, 1.4, 0.3), neck length (75 to 140, 103.2, 22.1) and width (50 to 95, 71.4, 10.9), fenestra length (50 to 65 μm, 56.5, 6.6) and width (27 to 40, 29.0, 3.8), heavy underbridge (60 to 80, 69, 8.5), vulval slit (7.5 to 8.5, 7.8, 0.4), and many bullae. As described for H. filipjevi, cysts hatched much more readily and at lower temperatures than populations of H. avenae. Detection of H. filipjevi in Oregon represents a new record for the occurrence of this species in the United States and for North America. The pathotype and resistance genes for incorporation into wheat, barley, and oat are being identified. References: (1) S. Bekal et al. Genome 40:479, 1997. (2) Z. A. Handoo. J. Nematol. 34:250, 2002. (3) R. Holgado et al. J. Nematol. Morphol. Syst. 7:77, 2004. (4) R. W. Smiley et al. J. Nematol. 37:297, 2005.

Associations between stunt nematodes and yield of no-till annual spring wheat (Triticum aestivum) were examined at two eastern Oregon locations. Geocenamus brevidens was the only species detected at one location and was mixed with Tylenchorhynchus clarus at another location. Six cultivars were planted with or without application of aldicarb during 2001. Inverse correlations between yield and stunt nematode density were significant at the G. brevidens-only site (P = 0.04) but not the G. brevidens + T. clarus site (P = 0.44). Yields were inversely correlated (P < 0.01) with stunt nematode populations at both sites during 2002. Aldicarb improved grain yields at both locations during 2001 (17 and 24%, P < 0.01) but not at the single location treated with aldicarb during 2002 (10%, P = 0.06). A lack of association between yield and T. clarus in 19 previously unreported experiments is discussed. Reduced wheat yield in response to stunt nematodes in Oregon is likely due to parasitism by G. brevidens and not T. clarus. This is the first report associating G. brevidens with suppression of wheat yield in the Pacific Northwest. Further studies are needed to define cropping systems and locations where G. brevidens may cause economic damage.

Crown rot of wheat in the Pacific Northwest is caused by a complex including Bipolaris sorokiniana, Fusarium avenaceum, F. culmorum, F. pseudograminearum, and Microdochium nivale. Relative pathogenicity was examined under greenhouse conditions for 178 isolates of the five species, and under field conditions for 24 isolates of B. sorokiniana, F. culmorum, and F. pseudograminearum. In the greenhouse, all five species reduced (P < 0.05) plant height relative to noninoculated controls. Disease severity was inversely correlated with plant height for the three Fusarium spp. In one or more of four experiments with spring wheat in the field, all three species reduced stand establishment and density of mature heads and increased the incidence and severity of crown rot. F. culmorum and F. pseudograminearum caused the greatest disease severity and plant damage and were the only pathogens that reduced grain yield. Virulence ratings were variable among isolates for each species in all greenhouse and field experiments. Isolate variability was especially high for the location and year variables in field experiments. Mixtures of multiple isolates are required for future research.

Many wheat (Triticum aestivum) fields planted annually in the Pacific Northwest are infested by high populations of the lesion nematode, Pratylenchus neglectus. Spring wheat cultivars varying in tolerance and resistance to P. neglectus were treated or not treated with aldicarb to examine relationships between the nematode and growth and yield of annual direct-seeded (no-till) wheat. Increasing initial density of P. neglectus in soil was more strongly associated with declining growth and yield of intolerant (Machete and Spear) than moderately tolerant (Frame and Krichauff) cultivars. Yield suppression by P. neglectus was generally 8 to 36% for intolerant cultivars, but reached 71% in soil also harboring Heterodera avenae, Rhizoctonia solani AG-8, and Gaeumannomyces graminis var. tritici. Intolerant cultivars had lower yields than Krichauff in rainfed but not in irrigated experiments. Density of P. neglectus in mature roots was generally lower for moderately resistant Krichauff than for susceptible Machete and Spear. Aldicarb improved yields in irrigated but not in rainfed experiments, and increased plant height and reduced variability in tiller height, canopy temperature, and density of P. neglectus in roots. This is the first report of damage to wheat by P. neglectus in the Pacific Northwest. Breeding wheat for tolerance and resistance to P. neglectus is suggested.

Heterodera avenae is widely distributed in the western United States, where most wheat is grown in non-irrigated winter wheat/summer fallow rotations in low rainfall regions. Economic and social pressures have motivated growers to pursue a transition from winter wheat/summer fallow rotation to no-till annual spring cereals. Annual cereals are also planted in some irrigated fields. The impact of H. avenae on spring wheat yield in the Pacific Northwest had been observed but not quantified. Spring wheat was planted with or without aldicarb to examine relationships between H. avenae and yield under dryland and irrigated conditions in moderately infested fields. Spring wheat yields were negatively correlated (P < 0.05) with initial populations of H. avenae. Aldicarb application improved spring wheat yield as much as 24%. The infective juvenile stage of H. avenae reached a peak density during mid-spring. Yield of irrigated annual winter wheat was also negatively correlated with initial density of H. avenae. Research priorities necessary to develop control strategies include a description of the pathotype, identification of sources for genetic resistance, and integrated practices designed to manage multiple yield-reducing pests.

Crown rot of wheat and barley in the Pacific Northwest is caused by a complex of Fusarium pseudograminearum, F. culmorum, F. avenaceum, Bipolaris sorokiniana, and Microdochium nivale. Yield-loss estimates were made by evaluating yield components on tillers collected from commercial fields and sorted by disease severity classes, and by comparing yields for field plots inoculated with F. pseudograminearum with yields in naturally infested soil. Increasing crown rot severity caused an increase in grain protein content and reduction in grain yield, kernels per head, kernel weight, test weight, tiller height, and straw weight. Crown rot reduced winter wheat yield as much as 1,550 kg/ha (35%, $219/ha) in commercial fields, with a 13-field mean of 9.5% ($51/ha). Inoculation reduced yields as much as 2,630 kg/ha (61%, $372/ha) over that caused by the native pathogen flora. Rain-induced crusting of the soil surface greatly amplified preemergence damping-off caused by F. pseudograminearum. Crown rot caused the greatest losses during seasons of lowest precipitation but also damaged crops under wet conditions. Aboveground symptoms were not always apparent under conditions of moderate infection and yield constraint. Damage from crown rot in the Pacific Northwest is more widespread and damaging than previously recognized.

Pratylenchus thornei reaches high population densities in non-irrigated annual cropping systems in low-rainfall regions of the Pacific Northwest. Two spring wheat varieties with different levels of tolerance and susceptibility to P. thornei were treated or not treated with aldicarb in three experiments. Grain yield was inversely correlated (P < 0.05) with pre-plant populations of P. thornei in soil and with P. thornei density in mature roots. As population of P. thornei increased, yield of the moderately tolerant/moderately susceptible variety Krichauff was generally more stable than for the intolerant/susceptible variety Machete. The reproductive factor (Pf/Pi) was generally lower (P < 0.05) for Krichauff than Machete. Aldicarb improved wheat yield (P < 0.05) in highly infested fields by an average of 67% for Krichauff and 113% for Machete. Aldicarb increased (P < 0.05) numbers of headed tillers, plant height, and grain test weight and kernel weight, and reduced (P < 0.05) the density of P. thornei in mature wheat roots, variability in height of heads, and leaf canopy temperature. Aldicarb did not improve yield in a soil with a low population of P. thornei. This is the first report that P. thornei causes economic damage to wheat in the Pacific Northwest.

Damage caused by Hessian fly, Mayetiola destructor (Say), was quantified in spring wheat, Triticum aestivum L., trials near Pendleton and Moro, OR, during 2001 and 2002. Five field experiments were established to examine genetic resistance to Fusarium crown rot, Fusarium pseudograminearum (O'Donnell & Aoki), and economic damage by lesion nematode, Pratylenchus neglectus (Rensch, 1924) (Filipjev Schuurmanns & Stekhoven, 1941) and Pratylenchus thornei (Sher & Allen, 1941). Hessian fly became the dominant factor affecting grain yield in four experiments. Genotypes carrying the H3-resistance gene had grain yields 66 and 68% higher than susceptible genotypes in cultivar trials during 2001 and 2002, respectively. Yield reductions were detected when Hessian fly infestation rates exceeded 50% plants during 2001 and 15% plants (8% tillers) during 2002. In two trials during 2001, in-furrow application of aldicarb (Temik) at planting improved yields of four Hessian fly-susceptible cultivars by 72 and 144% (up to 1,959 kg/ha) and yields of one Hessian fly-resistant cultivar by 2 and 3%. Resistant cultivars and aldicarb improved grain quality as much as two market grades during 2001. The value of increased grain production with Hessian fly-resistant cultivars in four field experiments ranged from dollar 112 to dollar 252/ha, excluding price incentives for improved market quality. Yield reduction due to combined damage from Hessian fly and either Fusarium crown rot or lesion nematode was additive. This report seems to be the first quantitative yield loss estimate for Hessian fly in spring wheat in the semiarid environment of the inland Pacific Northwest.

Soils and roots of field crops in low-rainfall regions of the Pacific Northwest were surveyed for populations of plantparasitic and non-plant-parasitic nematodes. Lesion nematodes (Pratylenchus species) were recovered from 123 of 130 non-irrigated and 18 of 18 irrigated fields. Pratylenchus neglectus was more prevalent than P. thornei, but mixed populations were common. Population densities in soil were affected by crop frequency and rotation but not by tillage or soil type (P < 0.05). Many fields (25%) cropped more frequently than 2 of 4 years had potentially damaging populations of lesion nematodes. Pratylenchus neglectus density in winter wheat roots was inversely correlated with grain yield (r(2) = 0.64, P = 0.002), providing the first field-derived evidence that Pratylenchus is economically important in Pacific Northwest dryland field crops. Stunt nematodes (Tylenchorhynchus clarus and Geocenamus brevidens) were detected in 35% of fields and were occasionally present in high numbers. Few fields were infested with pin (Paratylenchus species) and root-knot (Meloidogyne naasi and M. chitwoodi) nematodes. Nematodes detected previously but not during this survey included cereal cyst (Heterodera avenae), dagger (Xiphinema species), and root-gall (Subanguina radicicola) nematodes.

Tilletia indica, the causal agent of Karnal bunt of wheat, was first detected and reported in the United States in 1996. Karnal bunt occurred in the southwestern United States as early as 1992. Wheat contaminated with teliospores of T. indica is likely to have been transported from the Southwest to other regions, including the Pacific Northwest, before presence of the pathogen was discovered. Teliospore and sporidial germination and infection are highly dependent on climatic conditions. The potential for T. indica to infect wheat in the Pacific Northwest has not been reported. The objective of this study was to use published information on environmental factors favorable for infection and historical climate data for the Pacific Northwest to analyze the environmental risk for Karnal bunt to occur if wheat fields in the Pacific Northwest become contaminated by T. indica. Conditions during the past four decades appeared favorable for infection in nonirrigated wheat during 1 of every 3 years at two (Corvallis, OR, and Spokane, WA) of 13 Idaho, Oregon, and Washington locations examined, and every year at all locations where wheat is irrigated. If introduced to the area, it appears possible for T. indica to become established in selected regions of the Pacific Northwest.