GrainGenes

ITEMS FROM THE UNITED STATES

MINNESOTA

CEREAL DISEASE LABORATORY
(formerly CEREAL RUST LABORATORY)

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

D.L. Long, J.A. Kolmer, Y. Jin, M.E. Hughes, and L.A. Wanschura.

The rusts of wheat in the United States in 2006. [p.130-141]

Wheat stem rust (Puccinia graminis f. sp. tritici). The first reports of wheat stem rust were in mid-April in soft red winter wheat plots at Crowley, in south-central Louisiana, with severities of up to 40%. Stem rust was found in 28 of the 102 plots, which were located near rice paddies. The regular dew formation in these plots provided a suitable environment for stem rust infections. On 18 April, wheat stem rust was at low levels in plots at Baton Rouge, Louisiana. By late May, severe stem rust was observed on late-planted wheat nurseries at this same location.

The first report of wheat stem rust in Texas was in late April, where traces were found in a field in Ellis County in north-central Texas.

In mid-May, low levels of wheat stem rust were found in southwestern Georgia plots at Plains.

In late May, traces of stem rust were observed on late-maturing lines of wheat at Kinston, North Carolina.

In mid-July, the susceptible spring wheat cultivar Baart in southern and west-central Minnesota and east-central North Dakota plots had trace to 10% severities of stem rust infection. In late July, 5 to 10% stem rust severities were reported in plots of Baart in east-central South Dakota and trace levels in northwestern Minnesota. All of the currently grown spring wheat cultivars are resistant to the prevalent U.S. races.

In late July, low levels of wheat stem rust were found in plots at Colfax in Whitman County, Washington.

In early August, light to moderate levels of stem rust were observed in spring wheat plots in Aberdeen, Idaho. The rust appeared to come in late as most infection was on late tillers or late maturing lines.

Virulence of wheat stem rust. From collections made from the above locations, race QFCS was identified as the predominant race (Table 1). This is a common race that has been found in the U.S. in the past several years. This race is relatively avirulent; the majority of the U.S. cultivars are resistant to QFCS. Races MCCD and TTTT, one isolate each, were identified from collections in Louisiana.

Stem rust on barberry. In mid-May, aecial development was light on infected susceptible barberry bushes (alternate host for stem rust) growing in south-central Wisconsin. In early June, aecial infections were light on susceptible common barberry in southeastern Minnesota. In 2006, aecial infections on susceptible barberries were much lighter than during the years from 2003 to 2005 in southeastern Minnesota. Aecial infections from Minnesota and Wisconsin were mostly due to P. graminis f. sp. secalis (the form attaching rye) as P. graminis f. sp. tritici (the form attacking wheat) or P. graminis f. sp. avenae (attacking oats) was not identified from the barberry samples.

Wheat leaf rust (Puccinia triticina). Southern Plains ­ Texas. The 2005 autumn and 2006 winter were the driest on record in the state of Texas. In late January, low levels of leaf rust were reported in irrigated central Texas wheat plots. In early March, leaf rust was found in varietal plots at College Station, TX. In a few of the susceptible cultivars, e.g. Jagger, leaf rust severities of 5% were observed on the flag leaves and in a few others, e.g. Cutter in an early planted test, 70% severities were observed on the lower leaves. In mid-March, only traces of leaf rust were found in the irrigated nursery at Castroville, TX. The wheat crop throughout south Texas was under severe drought stress. By the second week of April, the susceptible cultivars Jagelene and Jagger had 80% leaf rust severities in nurseries at Castroville and College Station, TX. In the highly resistant cultivars Fannin and Endurance, no infections were found. Only low levels of rust were reported in grower's fields in southern and central Texas because of the dry conditions (Figure 1).

Oklahoma. In mid-January, leaf rust was found in southern Oklahoma, but conditions were not conducive for infection, spread, and development of leaf rust. By the first week in March, a few pustules of leaf rust were observed on lower leaves in the wheat varietal plot at Stillwater, Oklahoma. In late March, low levels of leaf rust were reported in grower's fields in Oklahoma. On 1 May, traces of leaf rust were found in plots at Stillwater in northeastern Oklahoma. In 2006, leaf rust development was less than normal in Oklahoma because of drought conditions throughout the state.

Central Plains ­ Kansas. In mid-March, no rust pustules were found on wheat that previously had infections in late fall in Kansas. In late April, traces of leaf rust were found in south-central Kansas where wheat was under extreme drought stress. In mid-May, low levels of leaf rust were found in fields and plots in central Kansas. During the third week in May, 1% severities were observed on flag leaves of susceptible cultivars in northeastern Kansas plots. This year leaf rust losses were less than normal in Kansas because of the persistent drought throughout much of the state (Table 4).

Nebraska. In early March, traces of leaf rust were found on the lower leaves of wheat in plots and fields in central Nebraska. In mid-May, low levels of leaf rust were found on lower leaves of wheat plants in research plots in central Nebraska. By early June, leaf rust developed to 15 to 25% severity levels on flag leaves in central and eastern Nebraska, and in irrigated wheat in southwestern Nebraska. As in the southern Great Plains, continued hot dry weather slowed leaf rust development in the central Great Plains.

Northern Plains - Minnesota, South Dakota, North Dakota. On 8 May, leaf rust infections that had apparently overwintered were found on the lower leaves of the susceptible winter wheat Cheyenne at the Rosemount Experiment Station in east-central Minnesota. On 26 May, 5% severities were found on flag-2 leaves in susceptible winter wheat plots at Rosemount. In early June, traces of leaf rust were found on the spring wheat Alsen in Bottineau County in north-central North Dakota, which is near the Canadian border. Drier than normal conditions in May and June slowed leaf rust development in most areas of the northern plains. In late June, plots of susceptible winter wheat cultivars in east-central Minnesota and east-central South Dakota had 60% rust severities, whereas resistant cultivars had only trace levels of infection on the flag leaves. By late June, spring wheat had leaf rust severities of trace to 1% on lower leaves in southern Minnesota and North Dakota fields (Figure 1). Susceptible spring wheat cultivars in southern Minnesota plots had 20% rust severities on the lower leaves.

In early July, high levels of leaf rust were found in susceptible winter wheat in plots in southeastern North Dakota and in mid-July high levels of infection were found in spring wheat fields in north-central North Dakota. By mid-July, trace to 60% leaf rust severities were observed on flag leaves of spring wheat cultivars in fields and plots from north-central South Dakota to west-central Minnesota (Figure 1). In late July, wheat leaf rust was at trace to moderate severity levels in spring wheat fields in northern Minnesota and North Dakota. Plots of susceptible cultivars in the same area had moderate to high leaf rust severities.

Leaf rust was widespread in 2006, but at lower levels than normal in the upper Midwest on both spring and winter wheat. Lower amounts of rust inoculum than in previous years arrived from the winter wheat region because of the persistent drought-like conditions in the southern plains, which reduced rust infections in the winter wheat. Hot and dry conditions in the northern plains in June and July also reduced the incidence and severity of leaf rust. Many spring wheat fields were sprayed with fungicide; further reducing leaf rust infections and also the incidence of leaf spot diseases.

Southeast ­ Louisiana. In mid-February, leaf rust was found on susceptible winter wheat cultivars throughout Louisiana in plots and fields. By early March, cultivars growing in plots in southeast Louisiana had up to 70% leaf rust severity. In late March in wheat plots at Alexandria, Louisiana, susceptible winter wheat cultivars had 20% leaf rust severities on the lower leaves. Some of the fields infected with rust were sprayed for rust control in the southern U.S. During the second week in April, plots in southern Louisiana had leaf rust severities up to 70%. By late April, plots of susceptible wheat cultivars in northeastern Louisiana had leaf rust severities up to 80% on flag leaves.

Arkansas. In early February, leaf rust had survived as far north as northeast Arkansas, however, a mid-February cold snap combined with freezing rain and snow appeared to kill the rust. In mid-March, leaf rust was light in the southern part of the state. By mid-April, leaf rust was found in areas of Arkansas that had sufficient moisture. In late April, plots in east-central Arkansas had 0­50% leaf rust severities. In Arkansas, leaf rust was more widespread than in the last few years, but the high severities occurred too late to cause much yield loss.

Mississippi, Georgia, Alabama, South Carolina. In mid-March, leaf rust was at low levels in southern Georgia plots. In early April, leaf rust was found on the lower leaves of the most susceptible cultivars in southwestern and south-central Georgia. In late April, in the area from central Mississippi to central Georgia, plots of susceptible wheat cultivars had leaf rust severities up to 80%. Fields in the same area had severities from 0 to 10% (Figure 1). In mid-May, susceptible soft red winter wheat cultivars in northern Alabama plots had 60% severities. In early May, flag leaves of soft red winter wheat in central South Carolina plots had 5% leaf rust severity.

Leaf rust was widespread in the southeast U.S. in 2006.

Mid-Atlantic ­ North Carolina. In late March, the cultivar McCormick in southeastern North Carolina plots had low levels of leaf rust on lower leaves. In the second week in May, severe leaf rust infections were reported in plots at the Kinston station in east-central North Carolina. By late May, wheat leaf rust was widespread in the central Coastal Plain and particularly severe in the Neuse River basin; only traces of wheat leaf rust were observed in the Piedmont.

Virginia. In the first week in May, severe leaf rust infections were reported in the wheat-breeding nursery at Warsaw in northeast Virginia. By mid-May, wheat leaf rust was widespread and severities up to 65% were reported on susceptible cultivars McCormick (Lr24) and USG3209 (Lr26), in plots on the eastern shore of Virginia. Leaf rust was earlier and more severe than normal across the state of Virginia. There appeared to be little virulence to the Lr9 gene in the rust population, as Tribute, Coker 9835, and Coker 9663 were virtually clean. In contrast, there seemed to be significant virulence to genes Lr24 and Lr26 and to a lesser extent, Lr18.

Wheat leaf rust development was greater in 2006 than normal in the Mid-Atlantic States and losses occurred in a few areas.

Pennsylvania. In early June, leaf rust that over wintered was limited to the lower canopy of wheat in Pennsylvania.

New York. In early July, low levels of leaf rust were found in winter wheat plots at Ithaca, New York.

Midwest ­ In early June, wheat leaf rust was found in fields from east-central Missouri to southern Illinois at 20% severity on flag leaves. The first report of leaf rust in Ohio was during the second week in May in south-central Ohio, where the rust may have overwintered. By early June, trace levels of leaf rust were found on flag leaves of wheat in fields from northwestern Ohio to south-central Wisconsin. In mid-June, plots in west-central and northwestern Indiana had 40% severities on lower leaves. By mid-June, leaf rust was severe on the upper leaves of susceptible cultivars throughout the northern Ohio. More leaf rust was found in Ohio than in 2005, as moisture conditions throughout this area were conducive for rust development and some losses occurred in susceptible cultivars.

California ­ In mid-May, leaf rust severities up to 80% were observed in susceptible cultivar plots in Kern County and Madera County late in the growing season.

Washington ­ In mid-July, leaf rust was very light in experimental plots at Pullman and Mt. Vernon, WA. No leaf rust was found in farm fields.

Idaho ­ In early August, light to moderate levels of leaf rust were observed in spring wheat and triticale plots in Aberdeen, ID. The rust appeared to come in late as most infection was on late maturing lines.

Wheat leaf rust virulence. In 2006, 60 races of wheat leaf rust were found in the U.S. (Table 2). Races with virulence to Lr24 increased in frequency throughout all wheat growing regions of the U.S. (Table 3). Virulence to Lr24 was highest throughout the Great Plains region, where a number of winter wheat cultivars have Lr24. Races with virulence to Lr9 were found in all regions except for Washington State. Virulence to Lr9 was highest in Texas and Oklahoma. Virulence to Lr26 occurred in all regions of the U.S., and was highest in the Northeast region. Virulence to Lr16 occurred in only two regions, and was highest in the spring wheat region of Minnesota and North and South Dakota. Virulence to Lr17 was found in all regions of the U.S., with the highest frequency in Kansas and Nebraska. Virulence to Lr18 occurred in the southeast, northeast and Ohio valley, and was highest in the Ohio valley region where a number of soft red winter wheats have this gene. Virulence to Lr21 was not found in any region, while virulence to Lr41 was found in all regions except the central plains (Kansas and Oklahoma), California and Washington. Virulence to Lr42 was found in all regions except California and Washington.

In the Southeast, the most common race, TDBJG (23.1%), had virulence to Lr2a and Lr24. In the Northeast, the most common race, MCBJG (20.0%) had virulence to Lr26. In the Ohio Valley, TDBJG (18.6%) was the most common race, which also was the most common race identified in the Southeast U.S. In Texas and Oklahoma, the most common race MLDSB (16.0%) had virulence to Lr9 and Lr17. In Kansas and Nebraska, MLDSB (20.0%) was also the most common race. In Minnesota, South Dakota, and North Dakota, the most common races MFPSC (7.8%) had virulence to Lr24, Lr26, Lr17, and Lr42 and TDBJH (7.8%) had virulence to Lr2a, Lr24, and Lr42.

Wheat stripe rust (Puccinia striiformis f. sp. tritici). Southern Plains ­ In early March, wheat stripe rust was present at low levels on the upper leaves of a cultivar growing in a plot at College Station, TX. In mid-March, traces of stripe rust were found in the nursery at Giddings in central Texas. In late March, wheat fields and plots in southern and central Texas had low levels of wheat stripe rust (Figure 2). Conditions were not favorable for rust development (limited moisture and few cool nights). In early April, only traces of stripe rust were found in southern and central Texas. By mid-April, stripe rust had not been found in Oklahoma or states to the north. In late April, hot and dry conditions slowed stripe rust development in plots and fields throughout the southern U.S. (Figure 2). Stripe rust development in the southern plains in 2006 was much less than 2005 because of the limited moisture and high daytime temperatures. The southern states provided a reduced amount of inoculum for the northern regions of the U.S.

Central Plains - On 22 May, traces of wheat stripe rust were found on the flag leaves of susceptible cultivars in plots at Manhattan, Kansas, but hot dry weather slowed further rust development. In early June, traces of stripe rust were found in a winter wheat nursery at Mead in east-central Nebraska and in winter wheat plots in northeast South Dakota. Stripe rust was very light in 2006 in the central and northern plains because inoculum from the southern plains was light and drought conditions persisted in much of the area.

Northern Plains - On 26 April, light amounts of stripe rust were reported on winter wheat in plots at St. Paul, Minnesota. This may have been an over-wintering site. In early May, stripe rust infections that had apparently over-wintered were observed on susceptible winter wheat cultivars in the Gallatin Valley in southwestern Montana. On 26 May, flag leaves of susceptible winter wheat in east-central Minnesota plots had 10% stripe rust severities.

By the third week in June, traces of stripe rust were found on a few winter wheat cultivars in east-central South Dakota and east-central Minnesota plots (Figure 2). Hot weather slowed rust development in these plots. Many wheat fields were sprayed with fungicide to prevent losses due to rust and scab. By mid-July, hot dry weather had stopped most development of stripe rust on spring wheat in the northern Great Plains. Cool and wet weather the first half of June were favorable to stripe rust development in Montana winter wheat. In central and east-central Montana 15,000­20,000 acres of winter wheat were sprayed with fungicides. There were sporadic reports of stripe rust on spring wheat, but the severity was low. Dry and warm weather in early July slowed stripe rust development.

In mid-June, wheat stripe rust foci of 60­80% severity where observed in winter wheat nursery plots at Winnipeg, Manitoba, Canada. Infections were noted on lower leaves thus indicating that over wintering may have occurred. Very mild winter conditions with adequate snow cover occurred in 2005­06, and near normal spring temperatures were favorable for stripe rust infection.

Louisiana ­ In mid-February, stripe rust was increasing in wheat plots at Winnsboro in north-central Louisiana and by mid-March was severe throughout the plots. In mid-March, stripe rust was severe on a few susceptible cultivars in the nursery at Baton Rouge, LA. In late March, some fields were sprayed for rust control. In south-central Louisiana wheat plots, susceptible cultivars had 60% stripe rust severities. Higher day and night temperatures during the last week of March slowed stripe rust development. In early April, high levels of stripe rust were observed in northeast Louisiana plots, but infections in fields were light.

Arkansas - In early February, wheat stripe rust was found throughout Arkansas. However, a mid-February cold snap slowed rust development in the state. By mid-March, only low levels of stripe rust in east-central Arkansas had been found. In late March, stripe rust was at low levels in fields in southern Arkansas. By early April, stripe rust was increasing throughout Arkansas, but conditions did not favor development of high rust severities.

Southeast - In early April, stripe rust was found in southern Georgia. In late April, high severities of stripe rust were observed in late maturing susceptible cultivars in the nursery at Plains in southwestern Georgia. In the nursery, most of the stripe rust infections had occurred earlier in March and April when temperatures were cooler. By late April, leaf rust was the most prevalent rust on wheat at Plains. In mid-May, light levels of wheat stripe rust were found in Limestone county plots in north-central Alabama.

Midwest - In early May, plots in Urbana, IL, had low levels of stripe rust incidence and severity. The drier and warmer than normal weather in April and May slowed the increase and spread of stripe rust. In early June, traces of stripe rust were found in east-central Missouri fields. In early June, 40% wheat stripe rust severities were observed on flag leaves in plots in northwestern Indiana and trace severities were found in fields. The only report of stripe rust in 2006 in Ohio was in a wheat breeding line in northwestern Ohio. Stripe rust was found at a number of locations in Ohio in 2005.

North Carolina - Heavy stripe rust was reported in fields in the Albermarle/Pamlico Sounds region in east-central North Carolina in early May. Trace levels of wheat stripe rust were present throughout the Coastal Plain of North Carolina in 2006.

Virginia and Maryland ­ In mid-May, hotspots of stripe rust were found in wheat plots in the eastern shore of Virginia and Maryland.

California ­ In mid-March, low levels of stripe rust were found in plots in the southern San Joaquin Valley. In March, California had cool and very wet conditions, which were favorable for stripe rust development. In early April, the susceptible forage wheat cultivar Dirkwin had a stripe rust severity of 30% in the Imperial Valley. Infections also were noted in fields of Orita durum wheat in the Imperial Valley. Light infections of wheat stripe rust were reported in the southern portion of the San Joaquin Valley and more severe infections were reported from scattered areas further north in the San Joaquin Valley and throughout the Sacramento Valley. In some Sacramento Valley fields, 80% severities were recorded in hot spots. By late May, wheat stripe rust was severe throughout the Central Valley of California. The two most widely grown cultivars, Summit and Blanca Grande, are now both fully susceptible to the races of stripe rust that occur in California. Statewide, yield losses to wheat stripe rust were 15% in 2006 (Table 4).

Pacific Northwest ­ By the second week in April, nursery plots at Mt. Vernon (northwestern Washington) had 40% stripe rust severity. Rust also was found in some surrounding fields. During the second week in April wheat stripe rust was not found from central to eastern Washington. By the third week in April, susceptible entries in winter wheat nurseries at Mount Vernon in northwestern Washington had 60% levels of stripe rust infection. In south-central and southeastern Washington, early planted winter wheat fields had 5% stripe rust severity. In this area, the initial stripe development was much later than 2005, but about normal for this area.

In late May, stripe rust was starting to increase on susceptible winter wheat entries in nurseries in the Palouse region of eastern Washington. Severities ranged from 1 to 10% with less than 1% of the plants infected. The stripe rust appeared one month later that 2005 in the Palouse region.

On May 22, stripe rust was found in a field in Franklin County, in southeastern Idaho, which is about 6 miles north of the Idaho-Utah border. Pustules were just beginning to show on the flag leaves.

By mid-June, stripe rust was widespread in eastern Pacific Northwest fields and plots. On 16 June, 30% severities were reported on susceptible winter wheat entries and 10% on susceptible spring wheat entries in disease monitoring nurseries at the Pendleton Experiment Station in Oregon. In nurseries near Walla Walla, WA, stripe rust severities reached 100% on susceptible entries in both winter wheat and spring wheat nurseries. Stripe rust was found in commercial spring wheat fields in the Palouse area, where 10% of the plants were infected with severities less than 5% on lower leaves. The wet and cool conditions the first three weeks in June were conducive for rust production.

By mid-July, stripe rust development had slowed in Pacific Northwest fields because of the hot dry weather. In early-July, 70-100% severities were reported on susceptible entries in plots where moisture was not limiting. Compared to 2005, wheat stripe rust was lighter in the Pacific Northwest (Table 4).

Utah ­ In early June, light stripe rust was found on Garland wheat under irrigation in Logan, UT. Stripe rust was not found in the dry land area in northwestern Utah. This is typical, since rust is rarely seen in Utah. Last year (2005) was an anomaly with quite severe stripe rust in Logan which started much earlier in the growing season. Prior to last year, the previous year that had significant stripe rust (or any rust) was 1993 (which was similar in temperature and moisture to 2005).