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, M.E. Hughes, and L.A. Wanschura.

 

The rusts of wheat in the United States in 2002. [p.199-208]

Stem rust. In 2002, the only reports of wheat stem rust in the southern Great Plains were in late April, when light amounts were found in plots in south Texas and southwestern Louisiana. In late May, traces of stem rust were found on wheat in a field and plot of the cultivar 2137 in central Kansas.

In the last week in June, traces of stem rust were observed on susceptible winter wheat cultivars in central and eastcentral South Dakota and southeastern North Dakota plots. In much of the northern Great Plains, high temperatures and dry conditions limited stem rust development.

In the third week in July, the susceptible spring wheat cultivars Baart and Max had trace-20 % stem rust severities in southern Minnesota, eastcentral South Dakota, and southeastern North Dakota plots. At the end of July HRWW fields had traces of stem rust in westcentral Wisconsin and northeastern South Dakota. In late July, susceptible spring wheat plots and fields in central North Dakota had 30 % severities.

Much of the early stem rust development in the northern plains was due to spores deposited with rains in mid-June. The stem rust infections can be attributed to inoculum produced on winter wheat cultivars in the southern Great Plains and to the warm temperatures and high moisture conditions, which were ideal for stem rust infection in some areas of the northern plains. If current spring wheat cultivars were susceptible to stem rust, a serious epidemic with substantial yield losses would have occurred.

In late July, traces of wheat stem rust were found in fields and disease nurseries in western Washington.

Stem rust race virulence. Race QCCJ (Table 1) is the most common stem rust race identified from collections made in the U.S. in 2002. This race is virulent on barley cultivars with the Rpg1 (T) gene for resistance. QCCJ and most of the other stem rust races identified in 2002 are avirulent to most wheat cultivars. However, a single isolate of TPMK and two isolates of TTTT were collected from susceptible wheat plots in Minnesota. These races have more virulence to rust resistance genes in wheat. TPMK and TTTT races have survived at low levels in the U.S.

Table 1. Races of Puccinia graminis f. sp. tritici identified from wheat in 2002. Pgt race code after Roelfs and Martens (Phytopathology 78:526-533). Set four consists of Sr9a, 9d, 10, and Tmp.

State	Source	Number of *		Percentage of isolates of Pgt- race
		Coll	Isol	QCCJ	QCCQ	QCCS	QCMJ	QCMS	QFCS	QKCJ	QKCS	RCCJ	RCCS	RCMJ	RCMS	TPMK	TTTT
KS	Nursery	1	3	100
LA	Nursery	1	3		100
MN	Nursery	6	17	59		18			6							6	12
ND	Field	2	1												100
	Nursery	23	61	69		3	10		2	2		3	2	7	3
NE	Nursery	2	6	67				17			17
SD	Nursery	3	9	67			33
TX	Nursery	3	8				25	38	38
WA	Nursery	1	3						100
WI	Nursery	1	3	100
USA	Field	2	1												100
	Nursery	40	110	62	3	5	10	4	5	1	1	2	1	4	2	1	2
	Total	42	111	61	3	5	10	4	5	1	1	2	1	4	3	1	2
* Number of collections (Coll) and isolates (Isol).

Wheat leaf rust. Southern Plains. In early January, traces of leaf rust were found in a nursery in central Texas and by the second week in February 80-100 % severities were on lower leaves and 30 % severities on upper leaves. Freezing temperatures in early March damaged leaves and destroyed rust infected leaf tissue. Drier and cooler weather in March slowed leaf rust development throughout the southern U.S.

In early April, leaf rust was light in fields but severe on susceptible cultivars in nursery plots from central Texas to Georgia. In early April, sufficient moisture in central and southern Texas allowed leaf rust to increase to 70 % severity on flag leaves in plots at College Station and McGregor. At both locations in Texas, cultivars that have Lr9 (Lockett) or Lr41 (Thunderbolt) had 70 % leaf rust severities. In drier areas of west Texas, only 5-10 % severities were on lower leaves.

In mid-April, leaf rust was found in fields in trace to light amounts and was severe on susceptible cultivars in plots from central Texas to South Carolina. In early May fields in central Texas, had 60 % rust severities, but the crop rapidly matured, which limited any additional infections. In early May, leaf rust was light in north Texas fields.

In the second week in March, light amounts of leaf rust were in fields in central Oklahoma. In late March, only traces of leaf rust were found in fields throughout Oklahoma. In early May, leaf rust was light in fields and severe on susceptible cultivars in plots from north central Oklahoma to central Alabama (Figure 1). In mid-May, leaf rust was severe in plots and fields in central Oklahoma, but the crop was near maturity, which reduced losses.

Central Plains. In mid-May, leaf rust in Kansas was common on the flag leaves of susceptible cultivars in the south central area and light in the northern part of the state.

In the last week in May, leaf rust was severe in plots and fields of susceptible cultivars from central Kansas to westcentral Missouri. In fields of Jagger wheat, at the late berry stage in south central Kansas, there were 60 % severities, whereas Jagger in northeast Kansas had 5 % severities. In central Kansas plots, rust severities ranged from trace to 60 %. In late May, plots at Lincoln, Nebraska, had light leaf rust infections.

In late May, leaf rust severities were 40 % on Ae. cylindrica (goatgrass) growing in the roadsides in north central Oklahoma and southcentral Kansas. In 2001 in the same areas, high levels of stripe rust were found on goatgrass.

Leaf rust was severe in the southern part of Kansas in late May. In the second week of June in southeastern Nebraska fields, leaf rust incidence ranged from 30 to 100 %. Drought-like conditions in much of Nebraska slowed leaf rust development for the remainder of the season.

Northern Plains. In mid-June, light infections of leaf rust were on flag leaves of HRWW in eastcentral South Dakota.

In the third week in June, 10 % leaf rust severities were on susceptible winter wheats at anthesis in eastcentral Minnesota plots. Traces of leaf rust were found in two fields in northwestern Minnesota in the third week of June. Weather conditions were ideal for rust infection throughout Minnesota in June.

In the last week in June, rust severities were 60 % on susceptible winter wheat cultivars in east central and southcentral Minnesota plots. During the last week in June, leaf rust on winter wheat was light in central and eastern areas of South Dakota. On a few susceptible cultivars like Jagger and Alliance, leaf rust severities reached 30 %.

The majority of cultivars had only trace levels of infections on the flag leaves. In early June, leaf rust was more severe in Minnesota than in South Dakota since moisture conditions were more favorable for rust in Minnesota. In the last week of June, lower leaves (flag-2) of susceptible spring wheat cultivars had severities of 40 % in southern Minnesota plots. In most of the spring wheat cultivars only traces of rust were observed at this time.

During the fourth week of June, winter wheat plots in eastcentral North Dakota had trace to 20 % rust severities. In the same area, traces of leaf rust were common in fields of spring wheats. In the Fargo, North Dakota nursery, the susceptible cultivar Thatcher had 30 % rust severity. In mid-July, durum lines at the Carrington research center in central North Dakota had 30 % leaf rust severities.

In the third week in July, spring wheat fields had trace-40 % leaf severities in plots in southeastern North Dakota and westcentral and southern Minnesota. In early August, leaf rust was present at high severity in the Red River Valley of Minnesota and North Dakota. In many wheat fields the leaves dried prematurely due to the heavy leaf rust infections combined with high temperatures. Many wheat fields were sprayed with fungicide to reduce leaf rust severities. In the Red River Valley the commonly grown wheat cultivars had 40 % severity levels of leaf rust. High levels of leaf rust were in fields in central and southeastern North Dakota. In the northern tier of counties of North Dakota leaf rust was at reduced levels due to very dry conditions. The wheat in this area was in poor condition due to drought stress.

Most of the spring wheat cultivars currently grown are moderately susceptible to leaf rust. Significant economic losses due to leaf rust occurred in northwestern Minnesota and eastern North Dakota (Table 5).

Southeast. In mid-December 2001, light infections of leaf rust development were uniform on lower leaves in a northeastern Arkansas wheat field. In mid-January, light leaf rust infections were observed on entries in a nursery in southwestern Arkansas. In mid-February, light infections of leaf rust were found throughout Arkansas in plots and fields. In the third week in February, infections that overwintered were observed in northwestern Arkansas and in plots of wheat in southwestern Arkansas. Because of the cold weather in mid-March, there were no signs of leaf rust in northwestern Arkansas wheat plots. In the last week in April, northeastern Arkansas wheat plots had 10 % leaf rust severities and fields had trace levels of infection. In late January, leaf rust was reported in northeastern Louisiana plots. In mid-February, susceptible cultivars in southern Louisiana had 20 % leaf rust severities.

During the second week in February, light amounts of leaf rust were found on the cultivar Coker 9835 in a southcentral Georgia nursery. In late February, rust levels were severe in the vicinity of the initial focus indicating this was a likely overwintering site.

In mid-April, from northeastern Louisiana through Alabama and Georgia to North Carolina, trace to light amounts of leaf rust were observed in wheat plots. Leaf rust was widely present in at least trace amounts throughout the winter wheat area of the southern plains and the southeastern states.

In early May, from central Louisiana to central Alabama, susceptible cultivars had 60 % leaf rust severities and resistant cultivars had trace levels of infection in nursery plots. In some locations, like eastcentral Alabama, where conditions were drier, susceptible cultivars had leaf rust severities of 10-20 %. In 2002, leaf rust was scattered and more severe than 2001 throughout the southeastern winter wheat area of the U.S.

East. In mid-December, leaf rust was easily found on the cultivar Saluda at Kinston, North Carolina. In mid-May, moderately severe leaf rust was reported in eastern Virginia plots. In late May, light leaf rust was reported in Blacksburg (western Virginia) plots. In early June, susceptible cultivars in a nursery in western Virginia and east central Maryland had 50-75 % leaf rust severities. Traces of leaf rust were found in central New York fields in mid-June. In mid-June, light leaf rust was observed in southwestern Ontario. In 2002, leaf rust was observed throughout the eastern SRWW area.

Ohio Valley. In the second week in June, plots of SRWW had trace-40 % leaf rust severities and traces in fields from northeastern Missouri to northwestern Ohio (Figure 1) at the early to late berry maturity stage. One field of susceptible wheat in northwestern Ohio had 60 % severities.

California. In early May, wheat fields in the Sacramento Valley of California had 75 % leaf rust severities. Rust development was reduced in California this year because of the dry conditions in March and April.

In mid-May, leaf rust of wheat had spread throughout the Central Valley of California. In the southern San Joaquin Valley, lines and cultivars in nurseries had 40 % severities. Leaf rust was also found on a few durum wheat cultivars and lines and moderate severity was reported on one triticale cultivar. During the third week in May, leaf rust was severe on flag leaves in most commercial wheat fields throughout the Sacramento Valley, obscuring the stripe rust that occurred earlier in the season on some of the same cultivars in the region.

Washington. In mid-July, wheat leaf rust was increasing on spring wheats in eastern Washington fields and susceptible wheats in nurseries had 10-20 % severities. In late July, traces of leaf rust were found in commercial fields. Yield losses due to leaf rust were minimal in the PNW this year.

Wheat leaf rust virulence. The 2002 leaf rust race identifications from the most common races identified are presented in Table 2 and Table 3. A total of 52 races were found in the U.S. in 2002. From the central and southern Plains the most common races were M-B- (virulent to Lr1, Lr3, Lr10, Lr17, +) (Table 3). Many of the MBDS and MCDS races were identified from collections made from Jagger, which is widely grown in the southern and central Plains states. There has been an increase in T- races with virulence to Lr9 and Lr10 in the southern SRWW area. There also has been an increase in the number of T- races (TNRS, TNRJ, TNGS and TNGJ) with virulence to Lr9, Lr10, and Lr24 in Texas. Many of the T-races with virulence to Lr9 and Lr24 were identified from collections made from the cultivars Lockett (Lr9 resistance) and Thunderbolt (Lr41 resistance). Race MBBJ was the predominant race found in California as it has been for the past 10 years.

Table 2. Wheat leaf rust code and corresponding virulence formula for collections made in 2002.

Race code [1]	Virulence formula [2]	Race code [1]	Virulence formula [2]
MBDS	1, 3, 10, 14a, 17, B	TBRJ	1, 2a, 2c, 3, 3ka, 9, 10, 11, 14a, 30
MBRJ	1, 3, 3ka, 10, 11, 14a, 30	TCTD	1, 2a, 2c, 3, 3ka, 11, 14a, 17, 26, 30
MBRK	1, 3, 3ka, 10, 11, 14a, 18, 30	THBJ	1, 2a, 2c, 3, 10, 14a, 16, 26
MCDS	1, 3, 10, 14a, 17, 26, B	TLGJ	1, 2a, 2c, 3, 9, 10, 11, 14a
MCRK	1, 3, 3ka, 10, 11, 14a, 18, 26, 30	TLGS	1, 2a, 2c, 3, 9, 10, 11, 14a, B
MCRT	1, 3, 3ka, 10, 11, 14a, 18, 26, 30, B	TNRJ	1, 2a, 2c, 3, 3ka, 9, 10, 11, 14a, 24, 30
TBBJ	1, 2a, 2c, 3, 10, 14a
[1] Race code plus Lr10 and 18 near-isogenic supplementals, after Long and Kolmer, Phytopathology 79:525-529. [2] Resistances evaluated for formula: Lr1, 2a, 2c, 3, 9, 16, 24, 26, 3ka, 11, 17, 30, 10, 18, 14a, and B.

Yield loss estimates due to leaf rust are in Table 4 (winter wheats) and Table 5 (spring and durum wheats).

Table 4. Estimated losses in winter wheat due to rust in 2002.

Table 5. Estimated losses in spring and durum wheat due to rust in 2002.

 

Wheat stripe rust. Great Plains. In mid-January 2002, hot spots (70-80 % severities) of stripe rust infection were found in central Texas wheat plots. This indicated that stripe rust may have overwintered in this region. In early February, stripe rust was light in plots in southern Texas. In early March, stripe rust was slowed by cold temperatures in southern Texas plots, but was at 50-70 % severity on lower leaves. The cold temperatures in early March damaged leaves and destroyed much of the rust infected leaf tissue. In the third week in March, rain improved conditions for rust development in much of central and southern Texas. Stripe rust requires cool temperatures (generally less than 70°F) and moist conditions for infection and development. In 2002, stripe rust was widespread and survived the cold temperatures in early March in greater amounts than leaf rust.

In early April, light stripe rust was found in wheat fields in southern and central Texas and from trace amounts to approximately 40 % severity in southern Texas nurseries. Stripe rust severities on SRWW cultivars generally were higher than those on the HRWW cultivars in the southern and central Texas nurseries. Jagger and Cutter were two cultivars that had the best stripe rust resistance in the Uvalde nursery in southern Texas.

By mid-April, wheat stripe rust development in central Texas had slowed in some areas, but was still active despite the warm weather in southcentral Texas. From initial collections made in central Texas race PST-79 was identified. This race was very prevalent in Texas and Great Plains in 2001. By late April, the warmer temperatures slowed stripe rust development in central Texas and eastern Oklahoma.

In the first week in May, wheat stripe rust was still active on some cultivars in northern Texas plots. In early May, severe wheat stripe rust was reported in north central Oklahoma plots; in fields in the same area rust was light or not found. In early May, stripe rust was observed in southcentral Kansas. In mid-May, a 2-meter foci of stripe rust was found in a plot of the highly susceptible cultivar Lakin in northeastern Kansas. In late May, traces of stripe rust were found in central and southern Kansas plots and fields (Figure 2). In late May, traces of stripe rust were found in wheat plots in eastcentral Nebraska.

Much less stripe rust was found in Oklahoma and Kansas in 2002 than in 2001. In both years, cool spring and night temperatures in the 40s and 50s, plus humid weather were conducive for stripe rust development throughout the Great Plains.

Louisiana, Arkansas and Missouri. In mid-March, stripe rust was severe in plots in a southern Louisiana. In mid-April, northeastern Louisiana fields had stripe rust infections of 40 % severity. Across all of Louisiana, stripe rust was at moderate levels, and a number of fields were sprayed with fungicides to reduce yield losses. Significant amounts of stripe rust have occurred in three of the last 5 years in Louisiana. Wheat lines Coker 9663 and AGS 2000 were resistant to stripe rust in Louisiana.

By the third week in February, foci of rust infection were in northwestern Arkansas fields and in plots in southwestern Arkansas. In late March, stripe rust was found in fields and cultivar demonstration plots in eastcentral Arkansas. In mid-April, warm weather slowed the development of stripe rust in Arkansas. In the first week in May, stripe rust development had slowed in southern Arkansas but in the northern part of the state, rust infections were still viable.

In 2002, stripe rust developed in the lower Mississippi Valley area. Stripe rust caused significant yield losses in Arkansas in 2002 (Table 4). Infection levels of up to 95 % severity at flowering stage were seen in fields and research plots. The fungicide Tilt was widely used to reduce stripe rust infections and yield losses. Stripe rust was not as severe in Arkansas as in 2000, because the cultivar CK 9663 (which comprises half of the acreage) was more resistant in 2002.

In the third week in May, soft red cultivars at the late-berry stage in westcentral Missouri had 40 % stripe rust severities. Weather conditions were conducive for the stripe rust inoculum coming from infection sites in Louisiana leading to increased stripe rust in Arkansas and Missouri. In 2002 more stripe rust overwintering sites occurred further east in the U.S. These focal points of stripe rust originated from infections that were established in the autumn of 2001. A general relationship exists between rust severity and the amount of rust that has overwintered.

Southeast. In mid-April, light amounts of stripe rust were found in southern Alabama wheat plots. In early May, stripe rust was found in plots in northcentral Alabama. Severities ranged from traces to 40 %.

Virginia and Maryland. In mid-May, traces of stripe rust were found scattered throughout the state of Virginia. In late May, wheat stripe rust was higher than normal in the plots at the Blacksburg, Virginia. In mid-June, stripe rust was found in eastcentral Maryland plots.

Ohio Valley. During the third week in May, stripe rust foci were found in plots in southwest Indiana. The wheat was in the early milk stage. In mid-June, fields of SRWW cultivars in northeastern Missouri to northwestern Ohio had trace to 10 % stripe rust severities (Figure 2). In mid-June, traces of stripe rust were found in winter wheat plots in southcentral Wisconsin.

California. By late April, moderate to severe wheat stripe rust was reported on susceptible cultivars in the Sacramento/San Joaquin Valley Delta and the Sacramento Valley. In mid-May, stripe rust of wheat had spread throughout the Central Valley of California. In the San Joaquin Valley, some durum wheat cultivars also had stripe rust infections, but at lower levels than hard red wheat. In 2002, stripe rust development in California was less than normal because of the drought-like conditions in late winter.

Pacific Northwest. The 2002 wheat stripe rust epidemic was the most severe in the last 5 years in the PNW. Stripe rust severity of 100 % occurred on susceptible entries in wheat nurseries in western Oregon, western Washington, eastern Washington, and northern Idaho. Although some susceptible winter wheat cultivars had severe rust, the stripe rust epidemic mainly affected spring wheat crops in eastern Washington and northern Idaho. The recently released cultivar Zak, which was grown on over 93,000 acres in Washington and ranked the No. 2 spring wheat cultivar in 2002, was susceptible. Most of the susceptible spring wheat fields were sprayed with fungicides. Stripe rust caused multimillion-dollar losses including fungicide cost and application (Table 5).

Race PST-78 (virulent on Lemhi, Heines VII, Lee, Fielder, Express, Yr8, Yr9, Clement, and Compair) and similar races, which were predominant in California, southcentral states, and the Great Plains in 2000, 2001, and/or 2002, became prevalent in the PNW in 2002. The relatively warm winter and cool weather in spring and summer were favorable to survival and development of the rust. The relatively large acreage of susceptible cultivars like Zak made the severe and large-scale epidemics possible. Fortunately, the No. 1 spring wheat cultivar Alpowa (about 280,000 acres in Washington) and most of winter wheat cultivars (over 70 % of total wheat acreage in Washington) still showed good high-temperature, adult-plant resistance.