WASHINGTON
USDA-ARS, WHEAT GENETICS, QUALITY, PHYSIOLOGY AND DISEASE RESEARCH UNIT AND WASHINGTON STATE UNIVERSITY
Departments of Crop & Soil Sciences, Food Science and Human Nutrition, and Plant Pathology, Washington State University, Pullman, WA 99164, USA.
R.E. Allan (USDA-ARS).
Development has been completed on four sets of backcross-derived NILs for winter and spring growth habit governed by four vernalization response genes. The genes are Vrn1 (Vrn-A1), Vrn2 (Vrn-B1), Vrn3 (Vrn-D1), and Vrn4 (Vrn-B4). Recurrent parents were semidwarf SWWW Daws and Stephens, nonsemidwarf SWWW Brevor; and nonsemidwarf HRWW Wanser. The nonrecurrent parents contributing the Vrn genes were the Triple Dirk lines developed by A.T. Pugsley. All NILs are BC6-derived F5:8 lines selected for winter or spring growth habit.
Several spring-growth habit lines of each Vrn gene and cultivar set were evaluated in spring-sown tests at Pullman during 2000 and 2001. Differences among NILs of the four Vrn genes occurred within each cultivar set for heading date, grain yield, test weight, and plant height. Interactions occurred between Vrn genes and cultivars for these traits. All of the spring habit Vrn NILs had later heading (5-16 d) than spring check cultivars Calorwa and Alpowa. Heading dates varied by 4, 5, 7, and 10 d among NILs of the four Vrn genes for Wanser, Brevor, Stephens, and Daws, respectively. NILs with Vrn1 were usually earlier than NILs of the other Vrn genes. An exception was Stephens Vrn4 which was 3 d earlier than Stephens Vrn1. NILs with Vrn2 were the latest heading in three cultivar sets but Daws Vrn4 was extremely late and headed 4 d later than Daws Vrn2.
Grain yields among the four Vrn NILs of each cultivar set differed by 20-115 %. Ranges in grain yield (g/m^2^) of the four Vrn gene NILs were 330-400 (Brevor), 435-530 (Wanser), 325-455 (Stephens), and 210-455 (Daws). Except for Brevor, the Vrn1 NILs were among the highest for grain yield. NILs of Brevor Vrn3 , Stephens Vrn3, and Stephens Vrn4 also were high yielding. NILs having Vrn2 generally had low yields. The Vrn4 NILs were the most variable with high and low yields occurring for Daws and Stephens, respectively. Wanser Vrn3 NILs had low yield potential while other Vrn3 NILs had medium to high yields. Several of the spring growth habit Vrn NILs had grain yields equal to or greater than those of Calorwa and Alpowa. Daws Vrn1, Stephens Vrn4, Wanser Vrn1, and Wanser Vrn3 yielded 10-30 % more than the checks.
Test weights of spring habit Vrn NILs of Daws and Stephens were low varying from 712-737 and 688-719 g/l, respectively. The test weights of Brevor and Wanser NILs were adequate ranging from 771-785 and 781-798 g/l, respectively. In general Vrn1 NILs had the highest test weights, whereas the Vrn2 NILs had the lowest test weights. Both Vrn1 and Vrn2 NILs of Brevor had low test weights, however. It seems likely that the very late heading of some Daws and Stephens Vrn NILs contributed to their low yields and test weights.
Plant height differences occurred among spring habit NILs of the four Vrn genes in all cultivar sets. The Brevor and Stephens Vrn NILs only varied 5 % for plant height, whereas Vrn NILs of Daws and Wanser differed by 10 to 15 %. The Vrn1 and Vrn2 NILs usually had tall and short heights, respectively. Across the cultivar sets, the Vrn3 and Vrn4 genes had variable effects on plant height.
Limited data is available from autumn plantings of both the winter (vrn) and spring (Vrn) sibs of the four Vrn gene and four cultivar sets. Differences in heading date occurred for seven of the 16 comparison between spring versus winter sib pairs. The spring sibs were 2 to 3 d later than their winter sibs in six comparisons. Yield differences occurred between spring and winter members in six of 16 comparisons. In every instance, the winter sib out yielded its spring counterpart. Most of the time, the winter sib had better winter survival or spring recovery than its spring sib. The winter Vrn1 sibs had less winter injury than their spring Vrn1 sibs in all cultivar sets, whereas no differences occurred between the winter and spring Vrn2 sibs of any cultivar set.
Vrn1, Vrn2, and Vrn3 are believed to be an orthologous set of genes. Hence the numerous agronomic differences that occurred among NILs of the four genes was unexpected. Apparently, Vrn genes behave differently when placed in different genetic backgrounds. Adaptative differences between winter and spring wheats must not be completely due to their allelic makeup for vernalization response. All spring habit NILs of the four Vrn genes had delayed heading, suggesting that spring and winter wheats probably differ for other genes affecting heading such as those mediated by photoperiod or temperature. Testing of these genetic stocks is continuing; once evaluation is complete they will be released as USDA-ARS germ plasm and made available to others.
Xianming Chen, David A. Wood, Mary K. Moore, Guiping Yan, and Roland F. Line.
Wheat stripe rust, leaf rust, and stem rust were monitored throughout the PNW using trap plots and field survey in 2001. 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 cooperators in many other states, wheat stripe rust was monitored throughout the United States. Similar to the year 2000, wheat stripe rust occurred from California and the PNW to Georgia and Virginia and from Louisiana and Texas to North Dakota and Minnesota. Severe yield losses caused by stripe rust occurred in fields of susceptible wheat in the PNW, California, Colorado, Texas, and especially Kansas. The severe epidemics in the Great Plains were due to the weather conditions, new races of the stripe rust pathogen, and widely grown susceptible cultivars. The spring weather was cooler than normal, favoring stripe rust development. The most severe yield losses caused by stripe rust occurred in Kansas (7.3 %) and Colorado (8 %). Wheat yield losses caused by stripe rust were estimated over 39.5 million bushels in the United States, which may be the biggest losses in 20 years.
In the PNW, wheat stripe rust widely occurred, but yield losses were the minimum in 2001 because the most wheat fields were grown with resistant cultivars. The winter of 2000-01 was mild, favoring stripe rust overwintering. Severities of over 90 % were observed on susceptible varieties in the stripe rust nurseries and on susceptible cultivars such as Westbred 470 in commercial fields. Resistant cultivars that were widely grown in the PNW provided effective control of wheat stripe rust. The durable, high-temperature, adult-plant resistance that is in most SWWW, HRWW, and spring wheats and the multiline cultivar Rely of club wheat with many seedling-resistance genes prevented stripe rust epidemics.
In 2001, wheat leaf rust occurred in some locations in the PNW but generally in lower levels because of unfavorable conditions. Yield losses due to leaf rust were negligible. Only race MDBJ (virulence on Lr1, Lr3a, Lr10, Lr14a, and Lr24) was detected in Washington. Wheat stem rust occurred in the later growing season in the PNW and caused significant losses in some fields. Madsen, the number one SWWW cultivar grown in the state of Washington, had moderate level of stem rust.
Hundreds of stripe rust collections from 19 states were evaluated to determine their virulence. These samples were increased on susceptible cultivars and tested on a set of 20 wheat genotypes that are used to differentiate races of P. striiformis f. sp. tritici in the United States. In 2001, the most prevalent races in the PNW were those attacking Lemhi, Fielder, Produra, Moro, Paha, and seedlings of Druchamp and Stephens. The most prevalent races in California were Express-attacking races and races attacking Express, Lee, Fielder, and varieties with stripe rust resistance genes Yr8 and Yr9. The predominant races east of the Rocky Mountains were those attacking varieties with Yr8, Yr9, plus Express, Lee, Fielder, and Produra. The Express-attacking races, which were first detected in California in 1998, were in all regions. The races attacking Yr8 and Yr9, which were first detected in the United States in 2000, were widely distributed in 2001. Races with new combinations of virulences were identified in 2001.
In 2001, more than 5,700 entries of wheat germ plasm and breeding lines from the National Germplasm Collection Center and wheat breeders in the western U.S. were evaluated for stripe rust resistance in fields under natural infections and in the greenhouse with selected races to cover all possible virulences. Germ plasm and breeding lines with stripe rust resistance were identified. High-temperature, adult-plant (HTAP) resistance continues to be the most effective and durable type of stripe rust resistance. More than 95 % of the wheat cultivars in Washington state have stripe rust resistance, and all newly released cultivars have HTAP resistance.
To develop molecular markers for Yr5, a wheat gene conferring resistance to all races of P. striiformis f. sp. tritici in the U.S., a BC7F3 population was developed by backcrossing the Yr5 donor T. spelta album (TSA) with the recurrent parent Avocet Susceptible (AVS). Seedlings of the Yr5 NIL (AVS/6*Yr5, developed in the Plant Breeding Institute, University of Sydney, Australia), AVS, TSA, and the BC7F3 lines were tested separately with two races PST-29 and PST-43 of P. striiformis f. sp. tritici under controlled greenhouse conditions. The single gene was confirmed by a 1:2:1 segregation ratio for homozygous resistant, heterozygous, and homozygous susceptible BC7F3 lines. Genomic DNA was extracted from the parents and 202 BC7F3 lines. The resistance gene analog polymorphism (RGAP) technique was used to identify molecular markers. The parents (the Yr5 NIL and AVS) and the homozygous resistant and homozygous susceptible BC7F3 bulks were used to identify putative RGAP markers for Yr5. Association of the markers with Yr5 was determined using cosegregating analysis with DNA from the individual BC7F3 lines. Of 16 RGAP markers confirmed by cosegregating analysis with 109 BC7F3 progenies, five positive and four negative markers were coincident with the Yr5 locus, and the other seven markers were closely linked to Yr5 with a genetic distance between 0.5 and 7.3 cM. Of nine markers verified further with additional 93 BC7F3 lines, two positive markers and three negative markers still cosegregated with the Yr5 locus and the other four markers were tightly linked to the locus with a genetic distance from 0.2 to 1.2 cM. Analysis of a set of Chinese Spring nulli-tetrasomic lines with three negative markers (Xwgp-18, Xwgp-20, and Xwgp-23) confirmed that the Yr5 locus is on chromosome 2B. Five RGAP markers that were cloned and sequenced, the codominant markers Xwgp-17 (546 bp) and Xwgp-18 (540 bp) had 98 % homology in both DNA and translated amino-acid sequences. The two markers had as high as 97 % homology with a resistance gene like sequence from Ae. ventricosa and had significant homology with many known plant resistance genes such as Mi, I2C, RPM1, RPP8, and RPP13, as well as ESTs from wheat and other plant species. The markers also have high homology with the NB-ARC domain that is in several plant resistance genes, nematode cell death genes, and human genes involving apoptosis. To develop user-friendly STS markers for Yr5, specific primers were designed based on the sequences of Xwgp-17 and Xwgp-18, the codominant markers completely co-segregating with Yr5. The primers were used to amplify genomic DNA of the resistant (the Yr5 NIL) and susceptible (AVS) parents, TSA, and the resistant and susceptible bulks of BC7F3 lines. Almost all STS primer pairs produced expected polymorphic bands in the bulk segregant analysis. The cosegregation of the STS markers with Yr5 was analyzed using 114 BC7F3 lines. Among the three primer pairs that were analyzed with 114 BC7F3 lines, one produced a dominant marker and two produced codominant markers that were completely associated with the Yr5 locus. The codominant markers were more specific and easier to score than the original RGAP markers. RGAP markers either tightly linked or coincident with Yr15, another wheat gene conferring resistance to all races of P. striiformis f. sp. tritici, also were identified. These markers should be useful for transferring the resistance genes into commercial cultivars and for combining them with other genes for durable and superior resistance.
Foliar fungicides were evaluated for control of the rusts in
winter and spring wheat plots near Mount Vernon and Pullman, WA.
Foliar applications of Folicur, Stratego, Tilt, Quadris, or combinations
of Tilt and Quadris at boot to heading stages either completely
or almost completely controlled stripe rust. Applications of the
fungicides increased wheat yield by 9-69 % compared to untreated
checks depending upon cultivar and location.