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

The rusts of wheat in the United States in 2001. [p.234-244]

Stem rust. In 2001, except for light infections in Texas, there were few reports of stem rust in wheat in the southern U.S. The first wheat stem rust report was in early May in central Texas, where light rust was reported in fields of Wintex and traces were reported in plots of McNair 701. In mid May, stem rust severities ranged from trace to 40 % in plots from northwestern Arkansas to northwestern Oklahoma. In wheat plots in north central Oklahoma, 20 % severities were observed on 10 % of the plants in plots of Chisholm, Lockett and Thunderbolt. Wheat stem rust developed later than normal and was light this year throughout the southern plains area of the U.S.

In late May, traces of stem rust were found in wheat fields in west central Missouri and east central Kansas. By the last week in June, stem rust was found in fields and plots in north central Kansas and southern Nebraska. Trace amounts of stem rust were observed in commercial fields, whereas 20 % severities were observed on susceptible lines in plots. The rusted wheat in these fields and plots provided inoculum for susceptible wheat further north.

In early June, severe wheat stem rust was found in a southern Louisiana nursery in plots, which were planted, much later than the normal, in late January.

In early July, traces of stem rust were observed on the winter wheat cultivar Norstar in east central North Dakota plots. In mid July, trace to 40 % stem rust severities were observed on the cultivar 2137 in plots throughout South Dakota. Stem rust also was observed on winter wheat cultivars Rose and Scout 66. Stem rust developed late in the season so losses were minimal.

In late June, traces of stem rust were found on the susceptible spring wheat Baart in southern and westcentral Minnesota rust detection plots. During mid July, 10-40 % wheat stem rust severities at 100 % prevalence were observed on Baart (at the full berry stage) in southern Minnesota disease detection plots. In west central Minnesota and east central South Dakota plots, trace-20 % stem rust severities were found on Baart at the one-quarter berry stage. No stem rust was found in the commonly grown spring wheat cultivars at these locations.

Stem rust infections were found in moderate amounts on susceptible spring wheat trap plots throughout North Dakota and northwestern Minnesota during the last week of July. No stem rust infections were observed on released wheat cultivars in either farm fields, or breeding plots.

In 2001, the number of stem rust samples received at the Cereal Disease Lab was twice the number in recent years, which continues the trends of increased sample numbers in 1999 and 2000. The increased severity of stem rust can be attributed to the increased amount of inoculum produced on susceptible winter wheat cultivars, e.g., 2137, in the Central Plains and to the temperatures and early 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 may have occurred.

Stem rust race virulence. The preliminary results from the 2001 national wheat stem rust survey indicate the most commonly identified races in 2001 were QCCJ, QCMJ, QCMS, QFCS, QCCS, and QCMD (Table 1). In 2000, these also were the most commonly identified races. 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 and 2001 TPMK was not identified from samples received at the Cereal Disease Laboratory. Race QCCJ is virulent on barley cultivars with the Rpg1 (T) resistance gene.

Wheat leaf rust. Southern Plains. By the third week in March, light amounts of wheat leaf rust were found on some wheat cultivars and lines in the Beeville nursery in southern Texas. Rust infections were noted on the lower leaves of the wheat plants, which indicates the rust may have overwintered in the nursery. In early April, in southern Texas wheat fields, traces of leaf rust were observed. By late April, rust was severe on susceptible lines and cultivars in southern Texas. In mid April, light leaf rust was found in central Texas plots. Throughout Texas, wheat was planted late and conditions were cooler than normal in late winter, which accounted for the slow development of leaf rust. By mid May, 40% severities were reported on flag leaves of susceptible cultivars in winter wheat plots in north central Texas and southern Oklahoma nurseries. During the last week in May, in plots of Jagger wheat in north central Oklahoma, 20 % severities were found whereas in fields of Jagger in south central Kansas, 5 % severities were observed on 1 % of the plants (Fig. 1). In late May, 20 % severities were observed on Ae. cylindrica growing in the roadside in north central Oklahoma.

Central Plains. In early May, traces of wheat leaf rust were found in southern Kansas. During the last week in May, leaf rust was light in plots and only traces were found in fields from west central Kansas to west central Missouri. In south central Kansas wheat plots, 20 % severities were found on Jagger at the late berry stage compared to 80 % severities reported in 2000 on Jagger in the same nursery at the same plant growth stage. The cooler than normal temperatures and excessive moisture during the last part of May actually slowed leaf rust development in Kansas. During late June, leaf rust was found in fields and plots in north central Kansas and southern Nebraska. The loss to leaf rust in Kansas this year was 0.4 % (Table 4), which was significantly less than the 2.9 % loss in 2000 and the 10-year average loss of 4.8 %. Twenty percent leaf rust severities were observed on lower leaves in wheat fields (at soft dough stage) in east central and southern Nebraska. This was a poor year for leaf rust development in the southern and central plains.

Northern Plains. In mid June, light leaf rust was observed on the flag leaves of hard red winter wheats in an east central South Dakota nursery. By late June, 20 % severities were common on lower leaves of winter wheats and traces on susceptible spring cultivars in southern Minnesota and east central South Dakota plots. In late June, trace-40 % severities were observed on winter wheats growing in east central North Dakota plots. By late June, leaf rust in the northern plains had developed slower and to a lesser extent than normal. This is due to the small amount of leaf rust inoculum arriving from the southern grain growing areas, cool wet spring weather, and the hot dry conditions in late June that were not favorable for rust development. Also, many of the flag leaves of the winter wheats that previously were free of rust were infected with wheat stripe rust, which normally was not found in this area. During mid July, 10 % severities were found on leaves of winter wheat growing in northeastern South Dakota and southeastern North Dakota fields at the late berry maturity stage.

In late June, traces of leaf rust were found in a spring wheat field in south central North Dakota and in plots in east central North Dakota. In mid July, 40 % wheat leaf rust severities were noted on susceptible spring wheat in southern Minnesota and east central South Dakota plots. Trace to 10 % severities were noted on a few of the commonly grown spring wheat cultivars. The hot, dry weather in late June slowed rust development, but July rains stimulated further rust increase. By the last week in July, leaf rust infections were found on spring wheat throughout North Dakota and Minnesota. Leaf rust was found on wheat in nearly every field and breeding plot that was surveyed in North Dakota and Minnesota. Heavy leaf rust infections were observed in plots and fields in central North Dakota near Carrington and Minot. Many wheat fields in this area had leaf rust severities of over 50 % at the late milk to soft dough stage, and flag leaves were starting senescence due to leaf rust. Most wheat cultivars in the demonstration plots at Carrington and Minot had leaf rust severities of over 20 %. A significant yield loss due to leaf rust would normally be expected with this level of rust severity, however the extreme temperatures of over 90°F in the last week of July and first week of August increased leaf senescence, reducing the effects due to leaf rust (Table 5). The high rust severities of the cultivars in the nursery plots indicates that many spring wheat cultivars do not have good levels of resistance to leaf rust. Leaf rust infections were generally lighter in the Red River Valley area of North Dakota and Minnesota. Leaf rust severity ratings of spring wheat cultivars in Minnesota and North Dakota in 2001 is available on the Cereal Disease Laboratory website (http://www.cdl.umn.edu/germplasm/survey/MN_ND2001.html).

In early July, leaf rust was present on susceptible winter wheat cultivars across much of southern Wisconsin. By mid-July, light levels of leaf rust were observed in winter wheat plots and fields in northeastern Wisconsin.

Southeast and east. In mid April, light leaf rust was found in plots in southern Georgia, southern Alabama, and southern Louisiana. This was the lightest and latest in the year leaf rust that has been observed in this southern region in many years. In late April, leaf rust was light in plots in southern and central Georgia and Alabama and central Louisiana. In plots at Tallassee in central Alabama a 40 % severity was reported on 20 % of the plants of the cultivar Jackson and in a few of the other entries only 1-2 % severities were observed. In early May, traces of wheat leaf rust were found in eastern Arkansas and southern South Carolina fields. By the second week of May, light leaf rust was found in fields in eastern Arkansas. In late May, 20-40 % severities were observed on plots of Thatcher wheat at Plymouth, North Carolina. Leaf rust incidence and severity on winter wheats in North Carolina was very light in 2001 compared to previous years. Some rust was observed on Coker 9663 and Foster in plots. Late planting of the crop in the fall, colder than normal winter in January and February and dry conditions in April all contributed to the light rust development in the southern U.S.

By the last week in May, 10-70 % leaf rust severities were observed on susceptible cultivars in a nursery in east central Virginia.

During the second week in June, trace-10 % leaf rust severities were reported in plots and traces in fields of soft red winter wheat cultivars from northeastern Missouri to northwestern Ohio (Fig. 1). The cooler than normal temperatures during the last part of May and first part of June actually slowed leaf rust development.

By the last week in June, 5-20 % severities were reported on winter wheat fields in northwestern New York at the late milk growth stage.

California. During the second week of May, light leaf rust was found in fields in the San Joaquin and Sacramento Valleys of California. During the fourth week of May, 60 % wheat leaf rust severities were common in plots of susceptible varieties and in commercial fields throughout the Central Valley of California.

Washington. During the second week in June, 10 % leaf rust severities were found on susceptible winter wheat cultivars at the milk growth stage in southeastern Washington. By early July, only light amounts of leaf rust were found on wheat throughout Washington.

Leaf rust development was abnormally light throughout most of the U.S. and losses to leaf rust were minimal (Table 4 and Table 5).

Canada. In late June, high levels of leaf rust were observed on susceptible winter wheat varieties in southwestern Ontario, Canada. In early July in winter wheat fields (anthesis stage) in southern Manitoba, 1 % severities and 10 % prevalences of leaf rust were observed. Light losses were expected on winter wheats because of the low rust levels and the advanced growth stage.

Leaf rust on durum. Leaf rust resistance in some commercial durum cultivars in northwestern Mexico broke down this year. In some fields farmers applied fungicides.

Wheat leaf rust virulence. The 2001 leaf rust race identifications from collections made in the U.S. are presented in Table 2. From the central and southern plains rust collections the most common races were M-races (virulent to Lr1, Lr3, Lr10, Lr17, +) (Table 3). 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. Race MBRK was the race most commonly identified from collections from North Carolina and also was the most widely found race from that area of the country in 2000. Race MBGJ was the predominant race found in California and has been for the past 10 years. There also has been an increase in the number of T-races (virulent to Lr1, Lr2a, Lr2c, Lr3, +), particularly, an increase in T-races with virulence to Lr9 and Lr10 in the southern SRWW area. The Lr9 and 10 combination was found in significant amounts in the race survey for the first time in 2001. Virulence to Lr16 was found in over 50 % of the isolates from the northern plains. Since Lr16 is present in some spring wheats this helps to account for the increased leaf rust severity on spring wheats in 2001.

Wheat stripe rust. Southern Plains. In mid March, wheat stripe rust was severe in the Beeville, Texas nursery and in a few southern Texas fields. Commercial wheat in this area was at the heading stage. This is the most stripe rust observed in this nursery in the past 20 years. Prevalences were rated at 15-20 % with 20 % severities within the foci. Primary infections were noted on the upper leaves and were 3-4 weeks old. This indicates the initial stripe rust spore shower may have come from infected areas further south, i.e., Mexico, in early to mid February. During the third week in March in a SRWW field near College Station in central Texas light stripe rust was observed on the middle and lower leaves of wheat plants. By the third week in March, farmers were spraying wheat fields for stripe rust in the San Angelo area in westcentral Texas. Throughout Texas in 2001, the winter crops were planted later than normal and moisture conditions were above normal. The cool temperatures in late winter were especially favorable for stripe rust development throughout southern Texas. In early April, wheat stripe rust was found in wheat fields in southern Texas and in south central Texas. Disease severities ranged from trace amounts to 80 % infection. At high severities, stripe rust significantly reduces yields and test weight. In early April, stripe rust caused complete losses in many of the entries in nurseries in south Texas. Jagger and TAM 201 were the two cultivars that showed the best stripe rust resistance in the Uvalde, southern Texas nursery. In 2000, no stripe rust was observed in southern Texas, but was found farther north and east in Texas. In 2001, south Texas provided inoculum for susceptible wheat in the northern wheat growing area.

By mid-April, stripe rust was reported in central and north Texas. Rust was severe in a few central Texas fields that were planted early and in McCulloch county plots rust was light on the lower and middle leaves. Cool spring temperatures and unusually cool nights allowed for more stripe rust development in early April. In Texas by mid April, wheat stripe rust had slowed with the onset of hot dry weather. In central Texas rust was severe in a few fields. In late April, in north central Texas, stripe rust was severe on highly susceptible lines but undetectable in fields. In northeast Texas, stripe rust was not detected in either fields or nurseries. In early May, in west central Texas, stripe rust was moderate on susceptible cultivars, but because of the drought conditions and hot weather further rust development was limited. During the second week in May, severe stripe rust was found in fields of 2137, 2174, and Custer in southwestern Oklahoma (Fig. 2).

Central Plains. During the first week in May, wheat stripe rust was found on susceptible cultivars in a south central Kansas nursery and in fields of susceptible cultivars in southern Kansas. The plants were in the late boot maturity stage. By the second week in May, stripe rust had nearly defoliated susceptible varieties at the late milk stage across southern Kansas. In late May, severe stripe rust was reported in northern Kansas. Despite expectations that the epidemic would be halted by warm weather in mid-May, unusually cool conditions prevailed and allowed it to stay active through the first week of June. Three main factors apparently came together to generate the stripe rust problem in Kansas. First, unusually cool, wet weather in Texas in March and April were favorable for rust development. Second, very strong southerly winds transported a heavy spore shower to Kansas in mid April. Third, unusually cool wet weather in Kansas in May allowed the epidemic to prosper. Economic losses were significant in many fields of susceptible varieties across a large portion of the state. The loss to stripe rust this year in Kansas was 7.3 %, which is the most stripe rust loss on record for the state.

During the last week in June, stripe rust was the most common rust found on wheat throughout southern and eastern Nebraska. Stripe rust on susceptible winter wheat cultivars ranged from 20-80 % on the flag leaves at late anthesis to soft dough.

In early June, stripe rust was severe in irrigated wheat, but light in dryland wheat in northeastern Colorado. In late June, stripe rust was severe on the flag leaves of irrigated white wheat (e.g., Platte) in the Front Range of the Rocky Mountains in Colorado.

Northern Plains. On 8 and 9 June, light infections of wheat stripe rust were found in SRWW plots at Rosemount, and St. Paul, Minnesota, respectively. In contrast to last year, stripe rust and leaf rust were not found together on the same leaves, which probably indicates they did not develop from the same spore shower. By mid June, wheat stripe rust development was extensive in east central and northern South Dakota and severities ranged from trace-80 % on flag leaves of winter wheats. Much of the stripe rust development originated from spores produced farther south in Texas, Oklahoma, Kansas or adjacent states. During late June, stripe rust was found in winter wheat plots in east central North Dakota. Hot temperatures that followed the initial rust sighting in the Minnesota and the Dakotas set back the rust development, but cool and moist weather in mid-June resulted in further development. In mid July, stripe rust was still evident on some winter wheat cultivars, (especially the cv. Foster which has Yr9 resistance) despite hot, dry weather in northeastern North Dakota.

In late June, traces of stripe rust were observed on lower leaves of susceptible spring wheat in the disease observation nurseries in east central South Dakota and in a field in south central North Dakota. Stripe rust in spring wheats was limited because most spring wheats have Yr18/Lr34 resistance and there are no reports of stripe rust isolates that have virulence to the resistance conditioned by Yr18. Also, with the onset of the hot dry temperatures in late June and early July, stripe rust development essentially ceased in spring wheats.

The past 2 years have seen the most widely dispersed stripe rust development observed throughout the northern winter wheat area in at least 40 years. Louisiana and Arkansas. During the second week in March, wheat stripe rust was found in fields in the Evangeline parish of southern Louisiana. By this date in 2000, stripe rust was already found in northeastern Louisiana. By early April, wheat stripe rust was severe in a few fields at the one-quarter berry- maturity stage in southern Louisiana. The fields in this area had centers (foci) with 40-50 % severities, whereas throughout the rest of the field there was light infection. The rust infection centers probably developed from rust spores that arrived in early March. Stripe rust losses were significant in a few southern Louisiana fields. The hot, dry weather in April slowed stripe rust development in Louisiana. By late April, only light amounts of stripe rust were found in central Louisiana wheat plots at the one-half berry stage and none had been reported in fields. In late April, the only report of stripe rust in Arkansas was in an infection center 2 feet in diameter in the east central part of the state. In 2000, stripe rust was severe by this date throughout the state of Arkansas. By mid May, reports of stripe rust in Arkansas were limited to only a few areas in the east central and west central parts of the state. Losses to stripe rust were light in Louisiana and Arkansas in 2001.

Mideast. By mid-June, wheat stripe rust was found in northeastern Indiana plots and severities ranged from traces to 80 % on flag leaves. Light stripe rust was observed in fields in northern Indiana and northeastern Ohio. Losses to stripe rust were light.

California. In early April, wheat stripe rust was found in Central Valley, California plots. In the Davis, California nursery susceptible entries had 5-40 % severities. In mid-April, the moist cool conditions were ideal for increase of rust in the Davis nursery. By mid April, wheat stripe rust had reached 70-100 % severities in plots of susceptible entries in the Davis, California nursery. By early May, wheat stripe rust was found on susceptible cultivars growing in fields in the Sacramento Valley of California. The cool moist conditions were ideal for rust development.

Washington. In late April, as usual, stripe rust was severe in the cereal disease nurseries at Mt. Vernon in the Skagit Valley in northwestern Washington. Severities of 40-60 % were reported on susceptible wheat entries, whereas in commercial fields traces of rust were observed. In late April, in a few eastern Washington fields, traces of stripe rust were found. In mid May, wheat stripe rust was increasing in western Washington and traces were found on winter wheat in eastern Washington. The rains and cool temperatures provided ideal conditions for stripe rust increase in most of the Pacific Northwest. By late May, wheat stripe rust was increasing on susceptible winter wheat cultivars in the Pacific Northwest. In mid June, 100 % severities of wheat stripe rust were reported on susceptible winter wheat cultivars in plots in western Washington. In eastern Washington 40 % severities were observed in some fields of susceptible varieties. In early July, wheat stripe rust was present in eastern Washington but severity levels generally were low because most cultivars are resistant except for a few fields of susceptible cultivars such as WestBred 470. Stripe rust did not cause much damage on winter wheats in the Pacific Northwest this year. Because most spring wheats have good resistance to stripe rust, losses were minimal.

Canada. By late June, stripe rust was found in several locations across southwestern Ontario in plots of several cultivars of winter wheat. Infections were generally localized, but spreading rapidly. Grain filling was in the early stages, so yields were affected in some plots. In southern Manitoba, in early July, in winter wheat fields (anthesis stage), 1 % severities and 10 % prevalences of stripe rust were observed. Light losses are expected because of the low rust levels and the advanced growth stage. In late July, wheat stripe rust was widespread in southwestern Ontario, Canada, but severity was low and it was very spotty in many commercial fields and in plots no cultivar was more susceptible or resistant than the rest.

Results of stripe rust race identification show that the group of new races virulent on Yr8, Yr9, and Express, that were identified in 2000 were prevalent again in 2001 in California and Texas.