GrainGenes

ITEMS FROM THE UNITED STATES

 

MINNESOTA

UNIVERSITY OF MINNESOTA AND USDA-ARS PLANT SCIENCE RESEARCH UNIT

Department of Agronomy and Plant Genetics, University of Minnesota and USDAARS, St. Paul, MN 55108, USA.

J. Anderson, R. Busch, G. Linkert, L. Matthiesen, E. Wennerlind, A. Procopiuk, H. Mickelson, S. Liu, K. McGowan, J. Gonzalez, D. Bowen, G. Hareland, M. Pumphrey, R. Dill-Macky, C. Evans, W. Thompson, J. Wiersma, K. McGowan, and D. Bowen.

 

Personnel changes. [p. 263]

Dr. Robert Busch retired June, 2000. J. Gonzalez joined our project as a postdoctoral research associate in April. D. Bowen and M. Pumphrey are new M.S. students. Dr. Ana Maria Procopiuk accepted a position as a postdoctoral research associate at the University of Illinois.

 

Wheat production, breeding, and scab screening. [p. 264]

Minnesota produced an estimated 79.2 million bushels (2.67 million metric tons) from 1.99 million acres (0.81 million hectares) in 1999. Losses from leaf rust were estimated at 4 %. During the 1998-99 crossing cycle, 317 crosses were made. Most of these crosses involved elite germ plasm from the University of Minnesota HRSW breeding program and sources of FHB resistance. A total of 1,980 lines were under small-scale increase (8 ft. rows) in the 1998-99 winter nursery in California. A total of 17,000 F3 seeds were planted in New Zealand in the autumn of 1998 for generation advance by SSD. During the 1999 growing season, 439 and 140 experimental lines were evaluated in replicated preliminary and advanced yield trials, respectively. The preliminary yield and advanced yield trials were grown at two and three locations, respectively. The Variety Trial, which contained 31 released varieties and two University of Minnesota experimental lines, was grown at seven locations. FHB-inoculated, misted, replicated nurseries were established at three locations. Approximately 2,500 lines were tested for FHB resistance in the greenhouse during the past year. Most of these materials were experimental lines, but also included potential new resistance sources from China and elsewhere and materials for genetic studies. McVey (MN93413) was released in 1999. Developed under the project leadership of Dr. Robert Busch, McVey has shown high yield levels, even in the presence of FHB.

 

Fusarium head blight resistance gene mapping. [p. 264]

J.A. Anderson, S. Liu, and E. Wennerlind.

We continued research to identify and map DNA markers linked to genes controlling FHB resistance in two spring wheat RILs. Both populations are segregating for genes from the widely used resistance source Sumai 3. The first population is from the cross 'Sumai 3/Stoa', in which we previously identified five resistance QTLs. The second population is from the cross 'ND2603 (Sumai 3/Wheaton) (resistant)/ Butte 86 (moderately susceptible)'. Both populations were evaluated for reaction to inoculation with F. graminearum in two greenhouse experiments by R. Stack, North Dakota State University. A combination of 521 RFLP, AFLP, and SSR markers were mapped in the 'Sumai 3/Stoa' population and all DNA markers associated with resistance were screened on the 'ND2603/Butte 86' population. Two new QTL on chromosomes 3AL and 6AS were found in the 'ND2603/Butte 86' population, and AFLP and SSR markers were identified that explained a greater portion of the phenotypic variation compared to the previous RFLP markers. Both of the Sumai 3-derived QTL regions (on chromosomes 3BS, and 6BS) from the 'Sumai 3/Stoa' population were associated with FHB resistance in the 'ND2603/Butte 86' population. Markers in the 3BS QTL region (Qfhs.ndsu-3BS) alone explain 41.6 and 24.8 % of the resistance to FHB in the 'Sumai 3/Stoa' and 'ND2603/Butte 86' populations, respectively. This region contains a major QTL for resistance to FHB and should be useful in marker-assisted selection.

 

Marker-assisted selection for Fusarium head blight resistance. [p. 264-265]

M.O. Pumphrey, J. Gonzalez, E. Wennerlind, and J. Anderson.

Eight hundred seventy lines from our 2000 F4 headrow nursery were screened with SSRs for the presence of the 3BS FHB QTL (Qfhs.ndsu-3BS). Three hundred and 157 were homozygous and heterozygous, respectively, for the QTL. Four hundred thirteen lines did not contain the QTL and were discarded based on our marker analysis. The resistance level associated with the Qfhs.ndsu-3BS QTL is expected to be observed in a high proportion of the 457 lines containing this QTL. Using a LiCor DNA analyzer, we estimate our costs for this marker screening at approximately $0.90 for the first SSR run on a genotype, including all consumables and labor. This is reduced to about $0.50 per data point for additional SSRs on the same genotype. We are experimenting with various DNA extraction protocols with the goal that one person can prepare PCR-ready DNA from leaf tissue from at least 400 lines in one day.

We plan to test the effectiveness of this FHB screening procedure by examining the FHB reaction of near-isogenic lines with and without the QTL in a wide variety of genetic backgrounds. Approximately 50 F4 and/or F5 derived lines, near-isogenic for the chromosome 3BS QTL, have been isolated from the heterozgous F4 lines identified from the 2000 F4-headrow nursery. These lines (50 homozygous with the QTL and 50 sib-lines without the QTL) plus checks will be evaluated under greenhouse conditions and in field FHB nurseries. We also are backcrossing this QTL into advanced lines.

 

HMW-glutenin subunit screening. [p. 265]

A. Procopiuk, G. Hareland, and J. Anderson.

The introgression of genes for FHB resistance from Chinese resistance sources has also resulted in the incorporation of HMW-glutenin subunits that are not favorable for the production of yeast-leavened products. We surveyed all Minnesota experimental HRSWs that were entered in our 2000 advanced yield trials to assess the degree of introgression of the unfavorable alleles (Table 1). Based on the literature, we expect that the null allele (n) at the Glu-A1 locus and the 2+12 allele at the Glu-D1 locus would be particularly detrimental for yeast-leavened products. Our preliminary analysis of this data confirms those findings, though there were several interesting cases in which lines with undesirable HMW-glutenin patterns produced strong mixing doughs with high loaf volume. We are using this information to guide parental selection for crossing.

 

 

Assessment of Fusarium head blight reaction in spring wheat: breeding-nursery requirements. [p. 265]

H. Mickelson, R. Busch, R. Dill-Macky, C. Evans, W. Thompson, J. Wiersma, and J.A. Anderson.

Our objective was to predict optimum resource allocation for line discard during early-generation evaluations, and for accurately determining Fusarium head blight (FHB) reaction during advanced-generation line evaluations. Replicates of 14 cultivars were evaluated in 10 inoculated Minnesota FHB screening nurseries from 1997-2000. FHB reaction was determined on spikes in the field (disease index), and on harvested grain as percent visually scabby kernels (VSK) and deoxynivalenol (DON) concentration. Consistent and strong correlation was observed between VSK and DON across all environments, even though several fold differences in trait expression were observed. The pooled r-value was 0.87 (n = 14). Disease index, VSK, and DON concentration likely represent different aspects of FHB resistance, and did not always rank the cultivars the same. McVey ranked second for disease index, sixth for VSK, and eleventh for DON, suggesting that each trait needs to be evaluated. Based on predicted LSD0.05, evaluations of disease index on 20 spikes plot-1, with two replicated row plots in three environments, along with determination of percent VSK, appears ample for early-generation evaluations. Although less advisable, a single environment could be used. Stability analysis was used to determine the number of environments needed to identify 'stable' FHB resistance in advanced lines. Disease index and VSK should be evaluated in 5 to 7 environments to thoroughly characterize FHB reaction, and DON evaluated in 3 to 5 environments.

 

Mapping FHB-resistance genes in the Chinese lines Wuhan 3 and Fujian 5114. [p. 265]

K. McGowan, D. Bowen, and J. Anderson.

We are examining the inheritance of FHB resistance and trying to find DNA markers from two additional sources, Wuhan 3 and Fujian 5114. Wuhan 3 is a Chinese Spring wheat from an early generation population collected by CIMMYT personnel at a Chinese Experiment Station near the city of Wuhan in the province of Hubei. The pedigree is unknown. Fujian 5114 is from the Fujian province of China where FHB epidemics occur on an annual basis. The pedigree is 'Longxi18/Ning8017'. RIL populations from each resistance source crossed with the susceptible cultivar Norm have been evaluated in the field and greenhouse for FHB reaction. Preliminary data with these populations and crosses between the two resistance sources and Sumai 3 indicates that they possess novel resistance genes.

Our goal for each of these populations is to explain at least 60 % of the phenotypic variation in FHB resistance. At this level, we can be confident that all major (and breeding relevant) QTL were discovered. We will continue to build a skeleton map covering all chromosomes at approximately 20 cM density until the goal is reached.

 

Publications.

• Anderson JA, Waldron BL, Moreno-Sevilla B, Stack RW, and Frohberg RC. 2000. DNA markers for Fusarium head blight resistance QTLs in two wheat populations. In: Proc Internat Symp Wheat Improvement for Scab Resistance (Raupp WJ, Ma Z, Chen PD, and Liu DJ eds). Kan Agric Exp Sta, Manhattan, KS. pp. 105-110.
• Anderson JA. 2000. Marker-assisted selection of disease resistance genes in wheat. In: Application of Biotechnologies to Wheat Breeding, Proc Conf (Kohli MM and Francis M eds). CIMMYT, Montevideo, Uruguay. pp. 71-84.
• Anderson JA, Liu S, Pumphrey MO, Gonzalez-Hernandez JL, and Wennerlind EJ. 2000. A protocol for marker-assisted selection of a Fusarium head blight resistance gene derived from Sumai 3. In: Proc 2000 Natl Fusarium Head Blight Forum (Ward RW, Canty SM, Lewis J, and Siler L eds.). Kinko's, Okemos, MI. pp. 239-243
• Anderson JA. 2000. Marker-assisted breeding of wheat. In: Agron Abstr:114.
• Busch RH, McVey DV, Linkert GL, Wiersma JV, Dill-Macky R, Hareland GA, Edwards I, and Schmidt JJ. 2000. Registration of 'HJ98' wheat. Crop Sci 40:296-297.
• Hu CC, Dill-Macky R, Anderson JA, and Busch RH. 2000. Screening for scab resistance of wheat in the greenhouse. In: Proc Internat Symp Wheat Improvement for Scab Resistance (Raupp WJ, Ma Z, Chen PD, and Liu DJ eds). Kan Agric Exp Sta, Manhattan, KS. pp. 180-183.
• Liu S, Anderson JA, Stack RW, and Frohberg RC. 2000. Microsatellite markers for a major Fusarium head blight resistance QLT in two wheat populations. Agron Abstr:186

 

 

CEREAL DISEASE LABORATORY - USDA-ARS

University of Minnesota, 1551 Lindig, St. Paul, MN 55108, USA.

D.L. Long, K.J. Leonard, D.V. McVey, J.A. Kolmer, M.E. Hughes, and L.A. Wanschura.

 

The rusts of wheat in the United States in 2000. [p. 266-277]

Stem rust. In 2000, except for light infections in Texas, there were few reports of stem rust in wheat fields in the southern U.S. The first wheat stem rust report was in mid-March, when traces were found in plots of soft red winter wheats at the Uvalde experiment station in southern Texas.

By mid-April, wheat stem rust was severe in south Texas plots and light in central Texas plots and light amounts of stem rust were found on several entries in central Louisiana wheat plots. During late April, wheat stem rust was severe on a few susceptible cultivars in central Texas plots and light in north central Texas plots. In southern Texas at Uvalde, stem rust was severe on susceptible entries throughout the plots. By the end of April, traces of wheat stem rust were observed in southern Louisiana plots.

In mid-May, traces of wheat stem rust were found on the cultivar 2137 at the south-central Kansas experiment station at Hutchinson. During late May, foci of 20 % severity were observed scattered throughout a SRWW field in west central Missouri and traces were found in a south central Kansas HRWW nursery. Light stem rust was observed on susceptible wheats during harvest in northern Texas wheat plots in late May.

In mid-June, foci of stem rust were found in soft red winter wheat fields in northeastern Missouri, east-central Illinois, westcentral Indiana, and southcentral Wisconsin. Rust severities ranged from 1 to 20 % in the center of the foci to trace level (< 1 %) at about 1 foot from the center. In eastern Nebraska, leaves of HRWW were heavily infected, but stems were only slightly infected. On 18 June, traces of stem rust were found on the HRWW cultivar 2137 in southeastern North Dakota. Rust pustules were found on both the leaf blades and leaf sheaths, which is unusual for stem rust except when the spores are rain deposited, as most likely occurred in the infections found in North Dakota and those seen in Nebraska.

By late June, 20 % stem rust severities were reported in plots of susceptible winter wheat cultivars, e.g., 2174, in eastcentral South Dakota and eastcentral Minnesota. In winter wheat fields in northern Kansas and southern Nebraska, wheat stem rust developed late and since most of the wheat cultivars were early maturing they escaped the stem rust. The southern and central Great Plains, where the winters were mild this year, provided spores for susceptible wheats farther north. In much of the northern Great Plains the temperatures in early June were near normal and moisture levels were ideal for the spore infection process to occur.

By the first week in July, trace-20 % stem rust severities were observed on the susceptible spring wheat varieties Baart and Morocco in southcentral Minnesota and eastern South Dakota plots. In the southcentral Minnesota plots on 22 June, only traces were observed on Baart wheat. The rust development was due to spores that were deposited with rains in early to mid-June. During the third week in June, most of the stem rust development was found on the leaves and by the first week in July, stem rust was found on both leaves and stems.

In the third week of July, 10-40 % stem rust severity ratings were recorded on susceptible winter wheat cultivars like Norstar, Seward, and Windstar in eastcentral North Dakota plots. On the susceptible spring wheat cultivar, Max, 40 % severities were reported at the soft-dough plant growth stage in late July at the eastcentral North Dakota nursery. During the fourth week in July, trace-5 % severities were reported on older susceptible varieties like Baart, throughout plots in northwestern and central Minnesota and 5-40 % severities in the rust nursery in central North Dakota. No wheat stem rust was observed by Cereal Disease Lab staff when conducting surveys in spring wheat fields in the upper Midwest this year.

As in 1999, the number of stem rust samples received at the Cereal Disease Lab this year was twice the number in recent years. The increased severity of stem rust can be attributed to the large amount of inoculum produced on susceptible winter wheat cultivars, e.g., 2137, farther south in the central plains and to the temperature and moisture, which were ideal for stem rust infection in the northern plains this year. If current spring wheat cultivars were susceptible to stem rust, a serious epidemic with substantial yield losses would have occurred.

Stem rust races. The preliminary results from the 2000 national stem rust survey indicate the most commonly identified races in 2000 are QCMS, QCMJ, RCMS, RCRS, QCCS, QCCJ, and QFCS. Further testing is underway and the final results will be published in Plant Disease. From 1993 to 1997, race Pgt-TPMK was the most common wheat stem rust found in the U.S. and in 1999 it had dropped to the third most common. In 2000, TPMK was not identified from samples received at the Cereal Disease Laboratory. The QCCJ race is virulent on barley cultivars with the Rpg1 (T) resistance gene. Race RCRS was the most commonly identified race in 1998 and 1999. In 1999, races QCCS and QCMS were only found in North Dakota and in 2000 were identified from Texas rust collections.

Wheat leaf rust. Southern Plains. In early February, light amounts of leaf rust were found on the susceptible cultivar TAM 107 in central Texas plots, but near drought conditions throughout much of Texas kept rust development to a minimum. In early March, leaf rust increased rapidly in south and north central Texas wherever moisture was present for rust infection to occur. By the third week in March, 10-40 % severity rust readings were observed on the lower leaves of susceptible cultivars in southern Texas at the experiment stations in Uvalde and Beeville.

During the third week in April, leaf rust was severe in plots from south to north Texas on susceptible cultivars, but rust development was light in Texas farm fields (Fig. 1). The mild winter and rainfall in late March and early April contributed to the rust development in much of this area. In mid-April, leaf rust severities of 60 % were observed in central Texas plots of TAM 107.

In early April, leaf rust was light in fields throughout Oklahoma. In central Oklahoma plots, 10-30 % severities were observed on the lower to mid leaves.

During the last week of April, wheat leaf rust severities in northcentral Texas and southern Oklahoma plots ranged from trace to 80 %. Severities were as high as 70 % in fields where rust overwintered (Fig. 1). By early May, rust increased throughout Oklahoma. The mild winter and rainfall in late March and early April contributed to the rust development in most of this area. This region provided leaf rust inoculum for wheat grown farther north.

Central Plains. Leaf rust was light throughout southcentral Kansas in early April. During the third week in April, in southcentral Kansas plots, 10 % severities were observed on the mid leaves. In Kansas, only light amounts of leaf rust overwintered, which is the same as in 1998 and 1999.

In early May, traces of leaf rust were found on the flag leaves of susceptible wheat cultivars in fields in the southern half of Kansas (Fig. 1). This was similar to leaf rust development last year.

By the third week in May, 100 % severities were observed on susceptible cultivars in south central Kansas plots. Some cultivars, e.g., Jagger, had 30 % severities in fields, but leaf rust was light in fields of 2174. Rust was light in northcentral Kansas because of the dry conditions which prevented rust infections during early May.

During the last week in May, trace-80 % severities were reported on winter wheat cultivars in south central Kansas nurseries. In fields in the same area, 40 % severities were observed on susceptible cultivars like Jagger, but on most of the other cultivars severities were 1 % or less. In north-central Kansas and westcentral Missouri, 20 % severities were observed on susceptible cultivars at the early berry stage. In late May, in southcentral Kansas spring wheat plots (i.e., 2375), trace­20 % severities were observed at the one-forth berry stage. During April and early May, leaf rust development was slowed throughout the central Great Plains because of moisture shortage, but with rain and dew in mid-May conditions for leaf rust infection improved. However, near the end of May, the hot windy conditions made conditions less than ideal for rust development. In 2000, the overall estimated loss due to leaf rust in Kansas was 2.9 % (Table 5), which is below the 10-year average of 4.8 %, but close to last year's estimate of 3.5 %. Yield losses were estimated from fungicide plot data, cultivar surveys, cultivar disease ratings and disease surveys.

Northern Plains. At Rosemount, Minnesota, viable leaf rust pustules that had apparently overwintered were found on April 27 on lower leaves in hard red winter wheat plots.

On May 30, traces of leaf rust were observed on the leaves of winter wheat cultivars in eastcentral North Dakota plots. The rust development in the North Dakota plots probably originated from rust spores that were deposited with rain around the middle of May. The timing of this rust development was the same as last year.

During the first week in June, 10 % leaf rust severities were observed on the flag leaves of susceptible winter wheat cultivars and traces on the lower leaves of susceptible spring wheats in Rosemount, Minnesota plots.

By mid-June, 20 % severities were reported on susceptible winter wheat cultivars at the early boot stage in east central North Dakota. In mid-June, trace-15 % severities were observed on susceptible spring wheat cultivars in central North Dakota.

During the final week in June, leaf rust on winter wheat was moderate in central and western South Dakota and moderate to severe in eastern South Dakota. Susceptible cultivars like Alliance, Jagger, TAM 107 and Rose had 100 % severities at the soft-dough maturity stage in east central South Dakota varietal plots. The rust infections in South Dakota probably originated from inoculum sources in Oklahoma and Kansas. As in previous years winter wheat flag leaves senesced because of leaf rust and hot windy conditions throughout South Dakota.

In late June, susceptible winter wheat cultivars had leaf rust severities ranging from 20-50 % in southeastern North Dakota plots.

During the first week in July, leaf rust severities of 60 % were reported on the flag leaves of susceptible spring wheat cultivars, e.g., 2375 and Oxen, in southcentral Minnesota plots. In fields, severities ranged from trace to 10 % on the lower leaves of spring wheats in western Minnesota and eastern South Dakota.

In late July, trace-10 % severities were found in spring wheat fields and trace-80 % severities in plots throughout northeastern Montana, central and northern North Dakota, and western Minnesota. Throughout northeastern North Dakota more fields were sprayed for fungal diseases than in past years. This year in southern North Dakota, leaf rust severities were normal but less than last year. Some losses occurred in the northern spring wheat growing area, especially in late planted fields and in fields that were not sprayed.

This year, 1-2 % leaf rust losses were reported in the northern plains states (Table 4). This was not as severe and concentrated in the upper Midwest as last year when 3-4 % losses occurred in the Dakotas and Minnesota. This year, less rust inoculum arrived from the south, but spring wheat cultivars currently grown are less resistant to leaf rust than 10 years ago. However, one of the more susceptible spring wheat cultivars, AC Barrie, was generally removed from production in 2000.

Canada. By late July, in fields not sprayed with fungicides, trace-5 % severity was found on wheat in southeastern Manitoba. Leaf rust infections in the southcentral area were lighter with only trace amounts of leaf rust. Some late planted wheat fields seeded with susceptible varieties experienced yield losses.

Southeast and East. In early February, light leaf rust was found in susceptible spreader rows in southern Louisiana. Rust development was slower starting than normal because of the lack of moisture throughout the southern soft red winter wheat area. In early March, wheat leaf rust was increasing throughout the state of Louisiana and by late March severe leaf rust was observed in the plots in southern Louisiana. By late March, leaf rust was severe on susceptible cultivars in nurseries in west central Mississippi, whereas most of the commercial fields in the area were sprayed and did not have rust.During late March, light leaf rust was found in plots of susceptible lines in southwestern Georgia and the Panhandle of Florida. By mid-April, plots of susceptible wheat had moderate leaf rust infection and fields within 75 miles of the Gulf Coast had light infection. Leaf rust development in much of the southeast was inhibited by drought conditions. Wheat plots in central South Carolina had 30-50 % leaf rust severities in mid April. A few plots of susceptible SRWWs in the southeast had 80 % leaf rust severities by early May, but fields generally had trace-20 % severities. Fungicides were applied in a few fields, e.g., Coker 9835, to control leaf rust. Dry weather in the southeast limited rust development, and fewer spores than usual were available for spread to areas further north.

In late April, in Arkansas leaf rust had increased where rust overwintered. Some cultivars that were severely rusted in previous years were resistant while other cultivars, e.g., Shiloh, were susceptible, which indicates a change in the race population in that area.

By the third week in May, in northeastern Arkansas, leaf rust was generally light in plots and fields but was severe on a few cultivars, e.g., Shiloh. Leaf rust also was light in southwestern Kentucky plots during the third week in May.

In most of the southeastern U.S., weather was drier and cooler than normal through March and most of April and was a limiting factor in rust development. In late April, frequent rains occurred which were followed by rapid leaf rust increase on susceptible cultivars. Because the crop matured so fast losses to leaf rust were limited.

In 2000, in North Carolina, wheat leaf rust was first observed in the middle of March in breeding plots at Plymouth and Kinston. The leaf rust infections were widely scattered on plots of susceptible wheat lines, which indicated that infections may not have overwintered in 2000 compared to 1999 when infections were found in the middle of February and tended to be concentrated in smaller areas. The severity of leaf rust infection on susceptible lines increased slowly through the spring, reaching near 100% by the second week of May.

In fields, infection levels were generally light to moderate, because of the cultivation of leaf rust resistant cultivars. Dry weather in the first part of May also reduced rust severity. Infection levels were heaviest in the coastal plain region, where the majority of the wheat is grown in the state. In the Piedmont region near Raleigh, very little rust could be found The cultivar Coker 9663, which was widely grown in 2000, had little if any rust infection in fields or in nursery plots. Coker 9835, which also is widely grown, had moderate to high levels (20-50 %) in nursery plots. Pioneer 2580 had moderate levels of rust infection in both nursery plots and fields.

Wheat lines and cultivars with combinations of adult plant genes Lr12 and Lr34 had a high level of resistance. Adult-plant gene Lr13 did not provide effective resistance, either singly or in lines with other genes. Test lines of wheat with single genes Lr9, Lr16, Lr17, Lr19, Lr21, Lr23, Lr24, Lr25, Lr26, Lr29, Lr33, Lr41, Lr42, and Lr43 at Kinston, NC showed useful resistance to leaf rust.

By late May, 5-80 % leaf rust severities were reported on wheat in nurseries in eastern Virginia.

In mid-June, trace levels of wheat leaf rust were common in wheat fields of central and western New York. Both May and June were characterized by above normal precipitation and below normal temperatures.

Midwest. During late May, in central Indiana, leaf rust was increasing on the upper leaves of plants on which Septoria had destroyed the lower leaves.

By the second week in June, 40 % leaf rust severities were reported in plots of susceptible SRWW cultivars from northeastern Missouri to northwestern Ohio and in fields severities ranged from 0 to 10 % (Fig. 1). In fields in northwestern Ohio, 5 % severities were noted on 20 % of the wheat plants at the 1/2 berry maturity stage.

In mid-June, traces levels of wheat leaf rust were common in wheat fields in southern Wisconsin. Both May and June were characterized by above normal precipitation and below normal temperatures.

California. In early May, 20-80 % leaf rust severities were reported on wheat lines growing in southern California nurseries. In mid-May, leaf rust severities were low in California commercial wheat fields, but 50-100 % severities were reported on a few lines and varieties in nurseries in central and southern San Joaquin Valley.

Pacific Northwest. In early July, wheat leaf rust was increasing on spring wheats in eastern Washington fields and susceptible wheats in nurseries had 60­70 % severities.

Wheat leaf rust virulence. The 2000 leaf rust race identifications from collections made in the U.S. are presented in Tables 1 and 2. From the central and southern Plains rust collections the most common races were M-races (virulent to Lr1, Lr3, Lr10, Lr17, and Lr+). Many of the MBDS and MCDS races were identified from rust collections made from Jagger which is grown on significant acreage in the southern and central Plains states. There also has been an increase in the number of T races (virulent to Lr1, Lr2a, Lr2c, Lr3, and Lr+), particularly, an increase in T races with virulence to Lr9 and Lr10 in the southern SRWW area. This Lr9 and Lr10 combination has rarely been found in past leaf rust surveys.

Wheat stripe rust. Southeast. This year, wheat stripe rust was reported in a southern Georgia nursery for the first time since 1974. On 9 May, a wheat stripe rust focus 1 m in diameter, was found in northwest Georgia (Fig. 2). This is one of the first records of stripe rust ever being found in north Georgia. In late April, stripe rust was light in northern Alabama plots. In westcentral Mississippi plots where it was dry, wheat stripe rust was more scattered and easier to evaluate than wheat leaf rust. Trace losses were reported throughout the southeastern U.S.

In early March, light amounts of stripe rust were found in a wheat field in southern Louisiana. In late March, light stripe rust was found in plots in northeastern Louisiana. By the third week in April, wheat stripe rust was severe in commercial fields throughout northwestern Louisiana. The wheat stripe rust loss in Louisiana was estimated to be 0.5 % (Table 4).

In mid-March, stripe rust was widespread on the lower leaves and upper leaves of several cultivars in northwestern Arkansas where the rust had overwintered. During mid-April, stripe rust was increasing throughout the state of Arkansas. Foci several hundred feet in diameter were found where stripe rust had overwintered. More of the fungicide Tilt was sprayed this year in Arkansas than in any of the last 5 years. As of early May, stripe rust was still increasing in northern Arkansas because there still had not been any prolonged periods of hot weather, which usually stops stripe rust development. During the third week in May in northeastern Arkansas, active stripe rust sporulation was observed in wheat plots and fields. The crop matured fast and with the arrival of hot temperatures stripe rust development stopped. By the third week in May, 50 % of the entries in northwestern Arkansas plots were either destroyed by stripe rust or severely damaged. Estimated losses to stripe rust in Arkansas reached 7.0 % (Table 4), which was the largest loss reported in recent history.

Southern Plains. During late March, infections of stripe rust that had overwintered were found on the lower leaves of SRWW cultivars at the Uvalde, Texas experiment station. By the third week in April, wheat stripe rust was severe in commercial fields throughout northeastern Texas. Entire fields were yellow from top to bottom and many fields were abandoned because of stripe rust. Many fields were sprayed with the fungicide Tilt, which reduced yield loss. Late-maturing, SRWW fields had high stripe rust severities. The high level of stripe rust in March-April was due to the mild winter which allowed wheat to start growing early and more rust to overwinter. In the early spring there was good moisture with cool nighttime temperatures which provided perfect conditions for stripe rust development. There was an estimated 10 % loss to wheat stripe rust in northeastern Texas and overall a 0.5 % estimated loss in the state.

By late April, wheat stripe rust was severe in southern Oklahoma. This year estimated losses to stripe rust totaled 1.0 % (Table 4) of the yield in the state.

Central Plains. In mid-May, stripe rust was found throughout Kansas. The mild winter and cool spring were conducive for stripe rust development. In southcentral Kansas plots, stripe rust was severe on a few of the HRWW cultivars, especially those with the T1B·1R gene translocation, which indicated virulence to Yr9. In late May, stripe rust was observed throughout eastern Kansas, northwestern Missouri and southeastern Nebraska fields. In southcentral Kansas plots, severities ranged from traces to 60 %, whereas in Nebraska fields, 1 % severities were observed. This year in the Great Plains, the cool spring and night time temperatures in the low 50s were favorable for stripe rust development. However, the hot windy conditions the later part of May probably disrupted much of the stripe rust development. Losses to wheat stripe rust in Kansas were estimated to be 0.05 % (Table 4).

Northern Plains. Trace amounts of stripe rust were found in wheat breeding plots at Brookings, South Dakota in mid-May. The wheat plots ranged from late boot to heading stage. On 8 June, light amounts of wheat stripe rust were found in SRWW plots at Rosemount, MN. Hot temperatures that followed the initial rust sighting in the Minnesota plots may have delayed the rust development, but cooler weather in mid-June allowed further increase. In mid-June, traces of wheat stripe rust were found on the cultivar 2137 in southeastern North Dakota.

In late June, wheat stripe rust was widespread in central and eastern South Dakota on winter wheat. In plots at Brookings, some winter wheat entries had a high level of infection, e.g., 80 % on Siouxland, which has the T1B·1R gene translocation and indicates virulence to Yr9. Traces of stripe rust were found easily in spring wheat fields and nursery plots. In rust foci, 30 % severities were observed in some spring varieties and lines. By the later part of the first week in July, stripe rust development had slowed in South Dakota because of the hot temperatures during the day and temperatures at night that were greater than 60°F.

By late July, traces of stripe rust were found in spring wheat fields and 50 % severities were reported in irrigated plots in northeastern Montana. Traces of stripe rust were scattered throughout northern North Dakota spring wheat fields and in plots severities ranged from trace to 20 % (e.g., McNeal and NorPro). There was little yield loss to stripe rust in the northern Great Plains.

During the second week in June, wheat stripe rust was found in a northeastern Colorado field. Normally, stripe rust is found at higher elevations in Colorado, i.e, San Luis Valley (7,500 ft) or in the front range of the Rockies.

Midwest. In central Indiana, light stripe rust was found in late May in fields and in breeding nurseries where it was more severe. By mid-June, wheat stripe rust development was extensive from central Illinois to southwestern Michigan and severities ranged from traces to 20 %. This was the most widely dispersed stripe rust development observed throughout the northern SRWW area in at least 20 years. In the northern-most locations, rust severities ranged from trace to 10 % with large sporulating pustules. At many of these locations, stripe rust was found together with leaf rust on the same leaf, which could mean that they developed from the same spore shower. Much of this stripe rust development originated from spores produced farther south in Texas, Arkansas, or adjacent states.

Northeast. In mid-May, traces of stripe rust were found in plots in Blacksburg, VA, one of the first reports of wheat stripe rust east of the Appalachian mountains.

Wheat stripe rust this year was the most widespread throughout the southern U.S. than has ever been reported (Fig. 2). Last year, no stripe rust was reported in south central U.S., but 2 years ago light amounts of wheat stripe rust were scattered from the lower Mississippi Valley north to eastcentral Minnesota. This year stripe rust was found early, because it overwintered in many areas in the southern U.S. where the winter was milder than normal. Furthermore, the spring weather was cooler than normal, favoring stripe rust development. A large source of inoculum appears to have arrived early in the crop growing year in the southern U.S. from some location like Mexico. Preliminary data from the wheat stripe rust collections indicate a shift in the stripe rust virulences from 1998 to 2000 in the southern U.S.

California. In mid-May, temperatures were cool and several storm systems provided moisture that allowed stripe rust to continue to increase in the Central Valley of California. There were reports of wheat stripe rust at 100 % severity in commercial fields of the widely grown variety RSI 5 throughout the Sacramento Valley and the northern part of the San Joaquin Valley. Cool spring weather also allowed wheat stripe rust to increase in commercial fields of several varieties in the central and southern portion of the San Joaquin Valley. Severities of 100 % were observed on breeding lines and varieties in nurseries in this area. Estimated losses to stripe rust were 3.0 % in California this year (Table 4).

Pacific Northwest. By mid-March, wheat stripe rust was increasing in plots and fields in western Washington. In mid-April, wheat stripe rust severities of 60 % were reported on susceptible winter wheat lines in the Skagit valley nursery in western Washington. By the first week in May, wheat stripe rust was prevalent throughout the state of Washington. Stripe rust exceeded 70 % severity on susceptible winter wheat cultivars in northwestern Washington. By late May, in eastern Washington, stripe rust was starting to increase in winter wheats and development was slower than normal because of the dry conditions in early and mid-May, which were not conducive for rust development.

By late June, wheat stripe rust was starting to increase on spring wheats in the Pacific Northwest, and the susceptible cultivars were sprayed with fungicides. Rust losses were 1.0 % or less, since most of the cultivars have high temperature, adult plant resistance (Table 4).

Canada. In late July, trace-l5 % stripe rust severities were reported in spring wheat fields in southeastern and south central areas of Manitoba. Because of the early planting of most cereal fields this year and cooler than average June temperatures, susceptible wheat varieties that were not sprayed with fungicides experienced low levels of stripe rust infection and associated yield losses. However, later planted fields avoided infection due to higher July temperatures that impeded further development of stripe rust.