ITEMS FROM THE UNITED STATES

MINNESOTA

CEREAL DISEASE LABORATORY
(formerly CEREAL RUST LABORATORY)

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

D.L. Long, K.J. Leonard, D.V. McVey, M.E. Hughes, and D.H. Casper.

The rusts of wheat in the United States in 1998.

Stem rust. In 1998, wheat stem rust severities were generally light in varietal plots throughout the southern U.S., and traces of stem rust were observed in a few commercial fields. Stem rust was severe in a few cultivars like CK 9835 in northwestern Florida plots, but no stem rust was found on the majority of cultivars. These southern locations normally provide wheat stem rust inoculum for susceptible wheats further north.

During the third week in May, traces of wheat stem rust were found in a nursery in southcentral Kansas. Stem rust and stripe rust pustules were found on the same leaf, which correlated to a deposition of spores 7 to 10 days earlier from a rain storm that originated in the southern Mississippi Valley area. The exact source of the deposited spores is unknown.

In late June, traces of wheat stem rust were found in a plot of the cultivar 2137 in a central South Dakota winter wheat nursery. Stem rust foci in the plot had severities as high as 30 %. The first rust spores probably arrived in early June, indicating that southern Kansas was the likely inoculum source.

By early July, traces of wheat stem rust were found in check plots of highly susceptible spring wheat cultivars such as Baart in eastern South Dakota. Trace to 20 % severities were observed in winter wheat plots in east central Minnesota and southeastern North Dakota. By mid-July, traces of wheat stem rust were found in plots of the spring wheat cultivar Max in southeastern North Dakota. Trace to 20 % severities were reported in susceptible spring (Marquis) and durum (Mindum) wheat plots in east central North Dakota at the soft dough stage by late July.

Two factors delayed stem rust development in the northern plains: first, little stem rust overwintered in the southern U.S., and second, stem rust resistance in the spring wheats remains highly effective in the northern Great Plains.

By mid-July, scattered plants in eastern Washington winter wheat plots had severities of 90 %. In late July, stem rust was severe in winter wheats and a few of the susceptible spring wheat cultivars in eastern Washington and caused lower grain weights in some fields.

Since 1993, race Pgt-TPMK has been the most common wheat stem rust race found in the U.S. However, race TPMK was much less common (Table 1) in 1998, and the most commonly identified races were RCRS and QFCS. Race QFCS has been found at low frequencies for many years, but until 1997, RCRS had not been found at more than 1 % frequency since 1988.

Wheat leaf rust. Southern Plains. Leaf rust was lighter than last year in much of the southern Great Plains. During the last week in March, wheat leaf rust severities ranged from traces to 60 % on the lower leaves of cultivars in nursery plots throughout southern Texas. For example, plots of TAM 300 had traces of leaf rust, but TAM 107 had 60 % severities. In southern Texas commercial fields, rust severities ranged from a trace to 20 % on the lower leaves. In these fields, rust increased on the lower leaves when moisture was abundant, but rust increase farther up the plant was limited, either because of dry weather or because earlier heavy rains washed the rust spores onto the ground. In early February in central Oklahoma, leaf rust was severe on the lower leaves of some of the commonly grown cultivars. However, by early March, leaf rust was less severe, although most of those rusted leaves died without the rust spreading to the younger leaves because of the dry weather in late February.

During the second week in April, leaf rust was much more widely distributed than normal within wheat fields in southern Texas and the Gulf Coast states, but the average severity of leaf rust was low (Fig. 1). In this area, Stagonospora (Septoria) was severe on the lower leaves, destroying much of the leaf area where rust normally increases. Cool, moist conditions in central Texas during the first 2 weeks in April created good conditions for increases in rust and powdery mildew. In mid-April, leaf rust severities of 80 % were observed in central Texas plots of TAM 107 at Temple, although only traces were found in the same plots 3 weeks earlier.

In mid-April, leaf rust was light throughout Oklahoma. During mid-May, leaf rust was increasing in plots in southern and central Oklahoma but was light in fields in these areas. During the third week of May, wheat leaf rust severities of 60 % were observed on the flag leaves of susceptible cultivars growing in commercial fields in central Oklahoma. In northcentral Oklahoma varietal plots, cultivars such as Karl 92, TAM 107, and Chisholm had 60 % severity readings, although rust severities on Custer, Jagger, and 2137 were less than 3 %. In late May, traces of leaf rust were observed on Ae. cylindrica in southwestern Oklahoma. Much less wheat leaf rust occurred in Oklahoma than in 1997 because of the reduced amounts of rust that overwintered, the dry conditions in late February, and cooler than normal temperatures in April and early May.

Central Plains. In late March, leaf rust severities were light throughout most southern Kansas fields and plots. Very little leaf rust overwintered this year in Kansas. During late April, leaf rust was found in the mid- canopy leaves of wheat growing in southcentral Kansas. In mid-May, in southcentral Kansas, 5% leaf rust severities were reported on the flag leaves of susceptible cultivars, whereas 20 % severities were found on flag leaves in southeastern Kansas fields (Fig. 1). In mid-May in central Kansas, the flag leaves were clean, but the flag1 and flag2 had leaf rust severities of trace to 10 %. By late May in central Kansas varietal plots and fields, severities of 10 % were common on susceptible cultivars, but rust severities were less than 1 % on the more resistant cultivars. Leaf rust development was slow during May throughout northern Kansas. By the second week inJune, the last of the green leaves dried up in northern Kansas. Hot, dry winds at the end of May caused premature ripening of wheat in central Kansas. Leaf rust developed late but still managed to kill the flag leaves of susceptible cultivars during the soft-dough stage throughout eastern and central Kansas. Some of the commonly grown varieties like Jagger had significant amounts of rust (50 % severity at early dough). During the fourth week in June, leaf rust severities ranged from 10 to 60 % on flag leaves of susceptible winter wheat cultivars in southcentral Nebraska and southeastern South Dakota fields. Flag leaves dried up quickly because of the leaf rust. Leaf rust severities in late June ranged from a trace to 80 % on cultivars in south and westcentral Nebraska varietal plots. The rust infections in Nebraska and South Dakota probably originated from inoculum sources in Oklahoma and northern Texas.

Northern Plains. During the third week in May, 2 % severities were reported on the flag-1 leaf in a winter wheat nursery in east central South Dakota. Traces of leaf rust were found in winter wheat plots in east central North Dakota and in spring wheat fields in southeastern North Dakota in late May.

On 29 May, severities of 5 % were observed on the flag-1 leaves in the Roughrider winter wheat plot at the Rosemount Experiment Station in east central Minnesota. Traces of rust were observed on other winter wheat cultivars. This rust development originated from rust spores that were deposited with rain, 1216 days earlier. Except in the years when rust overwintered in the plots, this is the earliest that leaf rust has been observed in these plots. The likely source of these infections was from spores that originated in southern Kansas.

During the second week in June, trace to 5 % leaf rust severities were reported on flag leaves of winter wheat in a nursery in southeastern South Dakota. On the lower leaves, leaf rust severities ranged as high as 40 %. In spring wheat plots, traces of leaf rust were observed on early-planted lines at Brookings, South Dakota. During the second week in June, trace to 20 % severities were found in winter wheat varietal plots in east central Minnesota. Leaf rust severities of trace to 1 % were observed on winter wheat in south central Wisconsin in early June.

By the fourth week in June, leaf rust severities ranged from 10 to 60 % on flag leaves of susceptible winter wheat cultivars in southeastern and central South Dakota fields. In both North Dakota and South Dakota, leaf rust caused yield losses in winter wheat.

During the fourth week in June, leaf rust severities of 10 to 40 % were reported on the lower leaves of susceptible spring wheat cultivars in plots in southwestern and west central Minnesota. In fields, severities ranged from 0 to 10 % on the lower leaves of spring wheats in western Minnesota and northeastern South Dakota. In plots of susceptible spring wheats in westcentral Minnesota, eastcentral South Dakota, and eastcentral North Dakota, 20-100 % leaf rust severities were reported on flag leaves by mid-July.

Although many of the spring wheat cultivars in the northern plains are resistant to leaf rust, some cases of higher than usual leaf rust severities were reported. In mid-July in eastcentral North Dakota, trace to 30 % leaf rust severities were observed on flag leaves of commercial spring wheat cultivars (2375, Grandin, and AC Barrie) at the anthesis stage. In late July in northcentral North Dakota spring wheat fields, trace to 40 % severities were observed at soft-dough stage. Losses occurred, especially in late-planted fields.

Southeast. Leaf rust was light in wheat plots and fields in late March along the U.S. Gulf Coast, because of heavy rains in February and early March that limited rust spread by washing the spores off the leaves.

In early April, wheat leaf rust severities were light in plots of southern SRRW cultivars in central Louisiana and southern Arkansas. During mid-April, leaf rust was light in plots of susceptible southern SRRW cultivars throughout the southeastern U.S. In early April, moisture and overcast conditions created ideal conditions for rust development, but the cool nights slowed the rust increase. In mid-April, light amounts of leaf rust were reported in wheat fields in eastcentral and northeastern Arkansas.

During the last week in April in the southeastern U.S., severities of 60 % were observed in plots of susceptible SRWW cultivars, whereas in fields, trace to 1 % severities were more common on the flag1 leaves (Fig. 1). Wheat leaf rust was lighter than normal in both plots and fields due to the cooler than normal early spring and the heavy rainfall in early April, which tended to keep the spores inside the wheat canopy. During mid to late April in the southeastern U.S., relative humidities were low and there was little dew formation, which is needed for rust infection to occur.

In mid-May, in most of the southeastern U.S., leaf rust was severe on susceptible cultivars in plots, but light in commercial fields. Moisture was a limiting factor in rust development in early May, and the crop was mature by mid-May, so losses to leaf rust were limited.

By the third week in May, leaf rust severities of 30 % were reported in rapidly maturing wheat fields of susceptible cultivars in northeastern Arkansas and extreme southeastern Missouri. Losses were light except in a few fields of susceptible cultivars.

Midwest. By 1 June, traces of wheat leaf rust were found as far north as Lafayette, IN. During the second week in June, leaf rust severities of trace to 5 % were reported in wheat fields from northeastern Missouri to northwestern Ohio and southern Michigan (Fig. 1). On 10 June on flag leaves, leaf rust severity ratings of trace to 5 % were recorded on most of the wheat varieties in northeastern Indiana plots, although 60 % severities were recorded on a few susceptible lines. Throughout the northeastern Indiana and northwestern Ohio area, leaf rust was more severe than 1997 because the May weather was wetter and warmer than normal. Losses were light except in a few fields of susceptible cultivars.

East. In mid-April, traces of leaf rust were found on the lower leaves of wheat in North Carolina plots. During late April, leaf rust severities of 510 % were observed on the flag leaves of SRWW in eastcentral North Carolina and central South Carolina. In early May, severities of 20 % were reported on wheat in Clarendon County plots in northeastern South Carolina. Leaf rust was light in plots in eastern Virginia in late April and losses were light in a few fields.

In early May, low levels of leaf rust that overwintered were reported in the snowbelt region east of Lake Ontario. In early June, traces of leaf rust were observed in the winter wheat varietal plots at Ithaca, NY. In late June, leaf rust was common in winter wheat fields in New York, where the flag leaf severities were greater than 30%. Wheat leaf rust losses were light in these fields.

California. During the third week in April, leaf rust was light in wheat plots and fields in the San Joaquin and Sacramento valleys of California. By late April, leaf rust severities ranged from 10-40 % in plots throughout the Central Valley of California, but because of the advanced crop development, losses were not significant. By mid- May, leaf rust was severe in fields of susceptible cultivars in the San Joaquin and Sacramento valleys, where losses to leaf rust occurred.

Northwest. In early May, leaf rust was light in winter wheat fields in northeastern Oregon (Fig. 1). In mid-June, leaf rust was present and increasing in the Willamette Valley of western Oregon. In early July, leaf rust was severe in the spring wheats in northeastern Oregon, but losses were light except for a few fields of susceptible cultivars.

By the second week in June, wheat leaf rust was increasing throughout the state of Washington. Rust severities were high in winter wheat plots at Walla Walla and starting to increase in plots at Pullman in eastern Washington and Mt. Vernon in western Washington. By the fourth week in June, wheat leaf rust was increasing throughout the state of Washington and was severe in winter wheat plots at Pullman in eastern Washington and Mt. Vernon in western Washington.

By mid-July, 90 % severities were observed on susceptible spring wheats growing in eastern Washington plots. Most of the spring wheat cultivars have adequate leaf rust resistance to combat the rust, and rust losses were light except in a few fields of susceptible cultivars.

Canada. During the last week in June, leaf rust was found in winter wheat plots 85 km southwest of Winnipeg, Canada. Infections ranged from 520 % on lower leaves, and traces were found on the flag leaves. This was the normal stage of rust development for the last week of June.

Leaf Rust Races. Virulence formulas for the leaf rust races collected in 1998 are shown in Table 2. The three most common leaf rust races found in the U.S. in 1998 were MDRL, MCDL, and MBRL (Table 3). All three races have been common in recent years.

Wheat stripe rust. In early April, wheat stripe rust foci rated at 40 % severity were observed in a plot of the SRWW CK 9835 at the Uvalde Texas Experiment Station. In other SRWW plots, rust severities ranged from traces to 5 %. Most of the rust was found on the flag-1 leaves, indicating the rust did not overwinter in these plots.

In late March, light stripe rust was reported in southern Arkansas plots. In mid-April, a hot-spot of wheat stripe rust was found in an east central Arkansas field. Traces of wheat stripe rust were found in southern Louisiana plots. During late April in Arkansas, temperatures were cooler than normal (highs in the 60s and lows in the 40s), which allowed for continued development of stripe rust throughout the state in plots and fields.

During the last part of April, stripe rust was severe in westcentral Mississippi plots and light in northwestern and central Louisiana and northcentral Texas varietal plots as well as northeastern Louisiana fields. In early May, wheat stripe rust was severe in plots in northwestern Arkansas and light in commercial fields in the Delta region of eastern Arkansas. Wheat stripe rust was more widespread and heavier than normal this year in the south central U.S. Warm temperatures in late May retarded further development of stripe rust in the south central U.S.

In early May, wheat stripe rust was reported in plots in central Oklahoma. In late April and early May, weather conditions were ideal for stripe rust development in many parts of Oklahoma. A 3-m^2^ wheat stripe rust center was found in a commercial field in Anderson County, KS, on 18 May. The rust ceased developing with the onset of warm weather.

By the third week in May, 10 % severities were observed on 5 % of the plants at the early berry stage in a field of wheat in southcentral Kansas. This rust developed from spores that were deposited in the early part of May from storms that originated in the Mississippi Valley area. The hot temperatures during the last 2 weeks of May disrupted the development of stripe rust in this area.

During the second week in June, stripe rust severities of 60 % were found in a winter wheat plot in eastcentral Minnesota. Hot weather in mid-June slowed the stripe rust development. During the fourth week in June, wheat stripe rust was light on the HRWW 2137 in a central South Dakota nursery.

This year, stripe rust was reported from the TexasLouisiana area northward throughout the central U.S. into the MinnesotaSouth Dakota area. This stripe rust development is the most extensive in the Great Plains in the last 20 years. Generally, when temperatures warm up in an area, stripe rust development ceases.

By late March, wheat stripe rust was increasing in nurseries in the San Joaquin Valley in California, in the Walla Walla area in southeastern Washington, and in the Skagit Valley of northwestern Washington. During mid- April, wheat stripe rust was increasing in the central and Walla Walla areas of Washington. The cool and moist conditions were ideal for the development of wheat stripe rust.

During the second week in April, wheat stripe rust was present in light to severe amounts in varietal plots in the San Joaquin and Sacramento valleys of California. By late April, wheat stripe rust was severe in regional test plots from Butte County (northern Sacramento Valley) south to Kings County (San Joaquin Valley). Rust hot- spots were found in fields of the fall-sown HRSW cultivar Express, the predominantcultivar grown in the Sacramento Valley. In late July, extensive wheat stripe rust was reported in the Tulelake region of California. Losses to wheat stripe rust occurred throughout California this year on many of the susceptible cultivars.

In late April, wheat stripe rust was present in fields as far north as Pullman in eastern Washington and 40 % severities were found on susceptible cultivars in plots at Walla Walla. In southeastern Washington, in fields of hard red winter wheat, severities of 40 % were found, and farmers sprayed for rust control. Also by late April, stripe rust was found on wheat in northeastern Oregon plots but was not as heavy as in the Walla Walla plots. By early May, 50 % stripe rust severities were reported in winter wheat plots in northwestern Washington.

In early May, stripe rust was increasing in the Mount Vernon plots in western Washington, but rust development was slowed by dry weather in central Washington. In mid-May, in the Skagit Valley of western Washington, stripe rust was severe on winter wheat, but BYDV infection impeded further development. Stripe rust was present and increased on spring wheat in the area. In late May, east of the Cascade Mountains in Washington and Oregon and in the Palouse region of northern Idaho, stripe rust was increasing. Severities of 50 % were found on susceptible cultivars in Pullman, WA, with much higher severities at Walla Walla, WA, and Hermiston and south of Pendelton, OR. Frequent rains in the Pacific Northwest during the last 2 weeks of May set the stage for further rust increase. An emergency label for Folicur was obtained for use on wheat and barley in Washington, and Tilt was labeled for use on wheat up to the heading stage. Stripe rust losses in the soft white winter and spring wheats was limited by their adult plant resistance to stripe rust.

During the second week in June, wheat stripe rust was widespread in the Pacific Northwest. In susceptible winter wheat cultivars in plots near Pullman, WA, 100 % severities were observed at heading to anthesis. Severities of 90 % were reported in eastern Washington fields of Westbred 470 near Walla Walla. Farmers growing Westbred 470 sprayed for stripe rust, although cultivars with high-temperature, adult-plant resistance continued to provide durable resistance. By late June, stripe rust was increasing on spring wheats in the Pacific Northwest, but rust losses were minimal, because most of the cultivars have high temperature, adult plant resistance.

During mid-July, wheat stripe rust was increasing in spring wheat fields in the Palouse region of Washington, but the adult plant resistance of commercial cultivars minimized losses. The most severe stripe rust in the Palouse region was on the cultivar Vanna. This increased rust severity may be due to a new race in the area.

UNIVERSITY OF MINNESOTA AND USDAARS PLANT SCIENCE RESEARCH UNIT

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

R. Busch, J.A. Anderson, G. Linkert, L. Mattiesen, A. Procopiuk, and H. Mickelson.


Personnel changes.

Dr. James Anderson joined the Department of Agronomy and Plant Genetics as an assistant professor in August, 1998. He has assumed responsibilities for the wheat-breeding project at the University of Minnesota. Dr. Busch will continue as a research geneticist and coordinator of the spring wheat regional nurseries.


Wheat production, breeding, and scab screening.

Minnesota produced an estimated 78.7 million bushels (2.65 million metric tons) from 1.92 million acres (0.76 million hectares) in 1998. An average yield of spring wheat in 1996 was 41 bu/acre compared to 33 bu/acre in 1997. FHB was very severe in the 1990s, with severe attacks beginning in 1990 and 1991 and devastating attacks in 1993 and 1994. Severe FHB epidemics continued in 1995, but finally in 1996, a much smaller area was attacked. Many of the more popular and newer varieties were susceptible to FHB. Pioneer 2375 was the most tolerant variety to FHB and has remained our most popular variety. Most newly released varieties now have FHB tolerance, and several are higher yielding than 2375 with more competitive canopy for better weed control, but 2375 remains the most-grown variety in the more southern part of the growing area.

Two varieties have been released from Minnesota, both semidwarf with very high yield. HJ98 was released in 1998, with high yield, medium protein, and moderate resistance to FHB spread in the head. This variety was named after the initials of a former department head, Herbert Johnson. HJ98 has consistently ranked 1 or 2 for yield over locations in Minnesota for the past 4 years and has performed similarly in the Uniform Regional Nursery. McVey is a new variety released in 1999 for the northern part of the growing area. McVey is late maturing and has lower than desired protein and test weight, but has been very high yield and has high resistance to FHB spread in the head. This FHB resistance is derived from the Chinese wheat (Ning 8331), which is Sumai 3 based. McVey also has tolerance to foliar fungi and provides high ground cover for weed control. The cultivar was named after long time close collaborator Don McVey, USDA-ARS, Cereal Disease Laboratory.

FHB research continues to be the major focus of a collaborative effort at Minnesota and the region. With the formation of the National Scab Initiative, this has now become a national effort. The type of FHB resistance is important, because there is no known immunity in wheat. Type 1 resistance measures the ability of the fungus to infect the floret and is referred to as incidence (% of spikes infected). If infected, all genotypes of wheat show the infection site. Plants with high resistance to spread, Type 2 resistance, will restrict the spread to no more than thatfloret or spikelet. This type of resistance has received major effort. Type 3 is resistance of the ke