WASHINGTON
USDA-ARS, WHEAT GENETICS, QUALITY, PHYSIOLOGY AND DISEASE RESEARCH UNIT
361 Johnson Hall, Washington State University, P. O. Box 646430, Washington State University, Pullman, WA 99164, USA.
Xianming Chen, David A. Wood, Laura Penman, and Paul Ling.
Monitoring rusts, predicting epidemics, assessing yield
losses, and identifying races of Puccinia striiformis
f. sp tritici. Wheat stripe rust, leaf rust, and stem
rust were monitored throughout the Pacific Northwest (PNW) using
trap plots and field survey in 2004. The diseases were accurately
predicted for the PNW using monitoring data and predictive models
based on resistance of wheat cultivars and environmental factors
such as temperature and precipitation. Through coöperators
in many other states, wheat stripe rust was monitored throughout
the United States. In 2004, wheat stripe rust occurred in 17 or
more states including Alabama, Arkansas, California, Colorado,
Indiana, Kansas, Louisiana, Minnesota, Missouri, Nebraska, Ohio,
Oklahoma, Oregon, South Dakota, Texas, Washington, and Wisconsin.
Wheat stripe rust was much lighter and its damage was much less
in the Great Plains in 2004 than in 2003. However, the disease
continued destructive in the Pacific West (California, Oregon,
Washington, and Idaho). Stripe rust alerts were sent to growers
through E-mails and news releases to implement control with fungicide
applications. As a result, most of fields grown with susceptible
or moderately susceptible cultivars were appropriately sprayed
with fungicides in the PNW. The on-time application of fungicides
prevented major losses. The wheat yield losses by stripe rust
in Washington State were estimated as 1.5 % for winter wheat and
3 % for spring wheat. A total yield loss of 11,756,000 bushels
of wheat by stripe rust in the United States was estimated in
2004 (http://www.cdl.umn.edu). In the PNW, leaf rust occurred
in some areas but the severity levels were low except in northwestern
Washington. Stem rust was not observed.
The epidemic impact of wheat stripe rust and benefit of fungicide
control were assessed based on our experimental data and disease
survey. In 2004, we evaluated yield reduction by stripe rust and
yield increase by fungicide application with 24 winter wheat and
16 spring wheat cultivars in field experiments of randomized split-block
design with four replications. Yield losses caused by stripe rust
were up to 44 % on susceptible winter wheat and up to 49 % on
susceptible spring wheat. Fungicide spray increased yield up to
42 bu/acre for susceptible winter wheat cultivars such as Hatton
and 12 bu/acre for susceptible spring wheat cultivars such as
Zak. Yield differences between the sprayed and unsprayed plots
were not statistically significant for resistant and moderately
resistant cultivars, showing effectiveness of stripe rust resistance,
especially high-temperature, adult-plant (HTAP) resistance, in
major cultivars in the PNW.
In 2004, 278 wheat stripe rust samples were obtained from 17 states. These samples were evaluated for the virulence/avirulence patterns on 20 wheat genotypes that are used to differentiate races of P. striiformis f. sp. tritici. Of 32 races detected from these samples, nine (5 % of the samples) were races first identified before 2000. Each of these old races had a frequency less than 1 %. Fourteen races (85 % of the samples) were those first detected from 2000 to 2003. Nine races (10 % of the samples) were first identified in 2004. Each of the new races had a frequency less than 3 %. One of the new races had virulence only on Chinese 166 (Yr1), Stephens (Yr3a, YrSte and YrSte2), and AVS-Yr8 (Yr8). This race (named PST-110) is the second race avirulent on Lemhi (Yr21). All other new races are new variants of the race group exampled by PST-78 (first identified in 2000; virulent on Lemhi, Heines VII, Lee, Fielder, Express, AVS-Yr8, AVS-Yr9, Clement, and Compair) and PST-100 (first identified in 2003; virulent on Lemhi, Heines VII, Produra, Yamhill, Stephens, Lee, Fielder, Express, AVS-Yr8, AVS-Yr9, Clement, and Compair). Some of the new races have the virulences of PST-100 plus virulences on Moro (Yr10 and YrMor), Paha (YrPa1, YrPa2, and YrPa3), Tres (YrTr1 and YrTr2), and/or Hyak (Yr17). PST-100 was the most predominant race throughout the U.S. Genes Yr5 and Yr15, which confer all-stage (often called seedling) resistance, were still resistant to all the races. HTAP resistance, which is nonrace specific and in wheat cultivars like Madsen, Stephens, Daws, Rod, Druchamp, Nugaines, Jagger, and the AVS-Yr18 single gene line, is still effective.
Test wheat germ plasm and breeding lines for rust resistance. In 2004, more than 13,000 entries of wheat germ plasm and breeding lines from the National Germplasm Collection Center, various regional nurseries, and public and private wheat breeders in the United States were evaluated for stripe rust resistance in fields under natural infections and in the greenhouse with selected races to cover all possible virulences. All nurseries were evaluated for resistance in both Pullman and Mt. Vernon, WA, and some of the nurseries were also evaluated in Walla Walla and Lind, WA. The germ plasm nurseries and some entries of the regional and breeding nurseries also were evaluated in the greenhouse for resistant to selected races and for HTAP resistance. The wheat entries also were evaluated for resistance to leaf rust, powdery mildew, and physiological leaf spot in field sites when these biotic and abiotic diseases occurred. Disease data of regional nurseries were provided to all breeding and extension programs in that region, whereas data of individual breeders nurseries were provided to the individual breeding programs. Through the germ plasm screening, new cultivars with adequate resistance were released and resistant germ plasm was selected to establish a collection for stripe rust resistance. The current collection has more than 4,000 entries, which should be valuable sources of stripe rust resistance for further characterization of resistance and for development of wheat cultivars with superior resistance.
Determining genetics of resistance, developing molecular markers, and cloning genes for resistance to stripe rust. Most wheat genotypes are resistant to barley stripe rust (P. striiformis f sp. hordei, PSH) and most barley cultivars are resistant to wheat stripe rust (PST). The wheat genotype Lemhi, which is susceptible to most PST races, is resistant to all tested PSH races. Similarly, the barley cultivar Steptoe, which is susceptible to all PSH races, is resistant to all tested PST races. To determine genetics of the Lemhi resistance to PSH and the Steptoe resistance to PST, crosses were made between Lemhi and PI 478214, a wheat genotype susceptible to all tested PST and PSH races, and between Steptoe and Rusell, a barley cultivar susceptible to some PST races and all tested PSH races. Seedlings of parents and F1, BC1, F2, and F3 progeny from the wheat cross were tested with races PSH-14, PSH-48, and PST-21, and those from the barley cross were tested with races PST-41 and PST-45 under controlled greenhouse conditions. Genetic analyses of infection type data showed that Lemhi had a dominant gene (provisionally designated as RpsLem) for resistance to the PSH races and the gene was closely linked to Yr21, a previously reported gene for resistance to PST-21; and that Steptoe had a dominant gene and a recessive gene (provisionally designated as RpstS1 and rpstS2, respectively) for resistance to PST-41 and PST-45. For each of the crosses, genomic DNA was extracted from the parents and 150 F2 plants that were tested for rust reaction and production of the F3 progeny that were tested with the races to confirm the phenotypes and determine genotypes of the F2 plants. The phenotypic data and polymorphic markers identified using the resistance gene analog polymorphism (RGAP) technique were analyzed with the Mapmaker computer program to map the resistance genes. A linkage group for the genes in Lemhi was constructed with 11 RGAP markers and a linkage group for the dominant gene in Steptoe for resistance to PST races was constructed with 12 RGAP markers. Using an RGAP marker that was linked to the resistant alleles in repulsion and the set of nulli-tetrasomic Chinese Spring lines, the linkage group for RpsLem and Yr21 was mapped on wheat chromosome 1B, which confirmed that chromosomal location of Yr21. The dominant gene in Steptoe for resistance to PST races was mapped on barley chromosome 4H using a microsatellite marker HVM68. These genes may provide effective resistance against appropriate pathogens when introgressed into appropriate hosts from inappropriate hosts.
To identify genes for HTAP, as well as for all-stage, resistance and develop molecular markers for the resistance genes, we made crosses among Alpowa, Express, IDO377s, Zak, and Avocet Susceptible (AVS). In 2004, F3 progeny and parents of the crosses were phenotyped for resistance to stripe rust. Seed of F4 were harvested and the generations were advanced to F5. The mapping populations will be evaluated in multiple field locations for determining the genetics of resistance, identifying genes and developing molecular markers.
Through collaborating with other wheat geneticists and breeders, markers of Yr5 and Yr15 were used to combine these genes and incorporate the genes into wheat cultivars. Genes for HTAP resistance were identified from winter wheat 'IDO444' and from T. turgidum subsp. dicoccoides. Molecular markers were identified for QTL on chromosome 6B controlling HTAP resistance in Stephens.
To clone stripe rust resistance genes, a BAC library for hexaploid wheat was constructed. The BAC library consists of 410,000 clones with an average insert size of 130 kb, and covers approximately 3.3X wheat genome equivalents. Using the BAC library, 12 positive BAC clones containing molecular markers for Yr5 were identified. A full-length cDNA library consisting of 42,000 clones with an average cDNA length of 1.5 kb also was constructed to facilitate the Yr gene cloning.
Determining the effectiveness and use of foliar fungicides for rust control. Fungicides were evaluated for controlling stripe rust in experimental fields near Pullman, WA. Susceptible winter wheat cultivars Hatton and PS 279 were planted on 22 October, 2003, and spring wheat Lemhi was planted on 22 April, 2004, using a completely randomized block design with four replications. Six treatments with four fungicides (Quilt, Tilt, Stratego, and Headline) were tested with nontreatments as checks. Fungicides were sprayed on 6 June in the winter plots when the plants were at the boot stage with 1 % stripe rust and on 19 June in the spring plots when the plants also were at the boot stage with 10 % stripe rust. A second spray was only used for one of the treatments with Quilt. Severities of stripe rust were recorded three times after fungicide application. Test weight and yield were recorded for each plot at the time of harvesting. All of the fungicide treatments effectively reduced stripe rust severity. Stripe rust started redeveloping about 1 month after the application and therefore the fungicides kept effective for about 1 month. The treatments increased yield by 30-50 bu/acre (46-67 %) for PS 279, 36-42 bu/acre (50-58 %) for Hatton, and 7-18 (18-48 %) for Lemhi. The two-applications of Quilt best controlled stripe rust, but did not significantly increase yield compared to the one-application of Quilt and some other fungicides.
Daniel Z. Skinner, Kwang-Hyun Baek and Brian S. Bellinger.
A BAC constructed from hexaploid wheat and containing a gene encoding manganese superoxide dismutase was identified. The region containing the gene was sequenced. The gene consisted of five introns and six exons, similar to MnSOD genes from other plants and animals. The promoter region contained several stress- and hormone-responsive elements, suggesting wheat MnSOD is directly responsive to environmental conditions and is subject to hormonal regulation.
Daniel Z. Skinner, Kwang-Hyun Baek and Brian S. Bellinger.
That wheat accumulates additional phospholipid in the cell membranes in response to exposure to cold temperatures is well known. We investigated the dynamics of the structural composition of the acyl side chains during a 5-week exposure of five winter wheat cultivars to vernalizing temperatures. The proportion of phospholipids with mismatched acyl chains decreased concomitantly with an increase in total phospholipids during the first week of cold exposure. Proportions of mismatched acyl chains then increased, while total phospholipid content varied little. Newly-synthesized phospholipids with equal-length acyl chains appear to form a part of the initial response to cold temperature; they are then modified to contain near-initial levels of mismatched acyl chains during acclimation.
Daniel Z. Skinner, Kwang-Hyun Baek and Brian S. Bellinger.
Microarrays were printed with 95 oligonucleotides (60 mers)
representing 41 wheat genes. The microarray was interrogated with
cDNA from hexaploid wheat roots and shoots from a near-isogenic
lines (NIL) pair differing at the vrn1-Fr1 locus, and a
commercial cultivar. The wheat lines were challenged with cold
temperature, hot temperature, or the biological control bacterium
Pseudomonas fluorescens. Self-complementarity of
the oligonucleotides was negatively correlated with signal intensity
in 23 of 54 arrays (39%; P <0.01). Tyramide signal amplification
was essential for signal generation and detection. Genes involved
in signal transduction pathways responded similarly following
exposure to cold, heat and P. fluorescens, suggesting intersection
of the pathways involved in response to these disparate stress
factors.