MINNESOTA

Barley Rusts in the United States in 2000

D.L. Long¹, B.J. Steffenson^2, K.J. Leonard¹, M.E. Hughes¹, and L. A. Wanschura¹

¹Cereal Disease Laboratory, USDA-ARS and ²Department of Plant Pathology, University of Minnesota

Stem rust (Puccinia graminis f. sp. tritici). In early April, a barley stem rust collection was made in the Uvalde, Texas plots. This was unusual since stem rust rarely occurs on barley in the southern U.S.

In early July, stem rust severities up to 5% were observed on the two-rowed barley Hypana in west and south central Minnesota plots. No stem rust was found on barleys (e.g. Robust, etc.) carrying the resistance gene Rpg1.

Stem rust developed earlier than normal on wild barley (Hordeum jubatum) because of the early spring weather. In mid-July, stem rust severities up to 10% were reported on this host growing alongside the roadway in eastern South Dakota and west central Minnesota. Over the past two years, stem rust has been prevalent on wild barley throughout the northern Great Plains.

In late July, severities of 70% were observed on two-rowed barleys (e.g. Bowman) in east central South Dakota plots. Traces of stem rust also were found on two- and six-rowed barleys growing in plots from northeastern Montana to west central Minnesota; however, no infection was found on plants in commercial fields. The low prevalence of stem rust on barley this year in the northern Great Plains may be due to reduced inoculum levels of pathotype QCC in the southern U.S. population (Table 1).

Ten races of P. graminis f. sp. tritici were identified on barley from 33 collections in 2000 (Table 1). The most common races were QCMJ and QCMD, comprising 51% and 12% of the isolates, respectively. Race QCCJ comprised only 2% of the isolates compared to 83% in 1999. Race RCRS was identified in only 2% of the total isolates compared to 46% in 1998 and 6% in 1999.

Losses to stem rust were generally light in 2000 (Table 2).

Leaf rust (Puccinia hordei) Barley leaf rust was first found in early April in trace amounts in plots at Uvalde, Texas. The greatest amount of barley leaf rust, however, occurred in North Carolina, where it caused 5% yield loss (Table 2).

In early July, severities of 40% were reported on the lower leaves of plants in spring barley plots in south and east central Minnesota and east central South Dakota. In late July, traces of barley leaf rust were found in plots in central Minnesota.

Twelve differential barley genotypes were used to identify races of P. hordei (Table 3). These races were designated according to a system similar to that of Roelfs and Martens (Phytopathology 78:526-533) as shown in Table 4. Six races of barley leaf rust were identified from nine viable collections (Table 5). The most common race identified was MCD, comprising 44% of the collections. This race was found only in Minnesota and North Dakota. The other five races each comprised 11% of the collections. As in the past, virulence to Rph1, 2, 4, 8, and 11 was common, while virulence to Rph3, 5, 6, 9, and 12 was absent. Virulence for Rph7 was observed in one race (RFD) from Minnesota. Virulence for this gene is rare in Midwestern populations of P. hordei, but is fairly common in the eastern U.S.

With the exception of North Carolina, losses to P. hordei were generally light in the U.S. in 2000 (Table 2).

Stripe rust (Puccinia striiformis f. sp. hordei). In early April, stripe rust was found on winter barley cultivars and experimental lines in plots at Corvallis, Oregon. In mid-April, barley stripe rust was severe on susceptible lines and progeny in a nursery in the Sacramento Valley of California. In mid-April, stripe rust severities of 20% were reported on susceptible winter barley lines in a Skagit Valley nursery in western Washington.

By early May, stripe rust severities of 80-100% were observed on susceptible barley cultivars in nurseries in the Sacramento and San Joaquin Valleys of California. In northwestern Washington, severities of 70% were reported on susceptible winter barley cultivars at the late jointing stage.

By mid-May, barley stripe rust spread throughout the Central Valley of California with 100% severities observed on susceptible cultivars and breeding lines at the soft-medium dough stage.

Increase of stripe rust on winter barley in eastern Washington was slowed by dry weather in early and mid-May, but in late May, the disease resumed its increase. By late June, stripe rust was starting to increase also on spring barley in eastern Washington with severities ranging from 20-50% on susceptible cultivars.

In California and Pacific Northwest, losses to stripe rust ranged from 2-6%. Losses to stripe rust would have been much greater, but many fields planted to susceptible cultivars were sprayed with fungicides.

Barley crown rust (Puccinia coronata var. hordei). In mid-June, traces of crown rust were observed on barley near the buckthorn nurseries at Fargo, North Dakota and St. Paul, Minnesota.

In late June, traces of crown rust were found in plots and fields in eastern South Dakota and in south central and east central Minnesota plots.

No losses were reported for barley due to crown rust infection.

Table 1. Races of Puccinia graminis f. sp. tritici identified from barley in 2000
		No. of ^a
State	Source	Coll	Isol	QCCJ	QCMD	QCMJ	QCMS	QCRS	QKMS	RCMJ	RCMS	RCRS	RMRS
MN	Nursery	11	14		7	71				7	7		7
MT	Nursery	3	2								100
ND	H. jubatum	2	2			100
SD	Nursery	4	3		33	33				33
	H. jubatum	8	9		22	56				22
TX	Field	4	12	8	8	33	33	8	8
	Nursery	1	1									100
U.S.	Field	4	12	8	8	33	33	8	8
	Nursery	19	20		10	55				10	15	5	5
	H. jubatum	10	11		18	64				18
	Total	33	43	2	12	51	9	2	2	9	7	2	2
^a Coll = collections; Isol = isolates.

Table 2. Estimated losses in barley due to rust in 2000
				Losses due to:
	1000	Yield in	Production	Stem rust		Leaf rust		Stripe rust
	acres	bushels	in 1000		1000		1000		1000
State	harvested	per acre	bushels	%	bushels	%	bushels	%	bushels
AZ	36	114.0	4,104	0.0	0.0	0.0	0.0	0.0	0.0
CA	85	68.0	5,780	T*	T	1.0	62.2	6.0	372.9
CO	105	115.0	12,075	0.0	0.0	T	T	0.0	0.0
ID	730	76.0	55,480	0.0	0.0	0.0	0.0	T	T
KS	7	35.0	245	0.0	0.0	0.0	0.0
KY	8	75.0	600	0.0	0.0	0.0	0.0
MI	19	60.0	1,140	0.0	0.0	0.0	0.0
MN	240	64.0	15,360	T	T	T	T	0.0	0.0
MT	950	40.0	38,000	0.0	0.0	0.0	0.0	T	T
NE	6	27.0	162	0.0	0.0	0.0	0.0
NC	18	80.0	1,440	0.0	0.0	5.0	75.8
ND	1,780	56.0	99,680	T	T	T	T
OK	NA**	NA	NA	0.0	0.0	0.0	0.0
OR	140	60.0	8,400	0.0	0.0	0.0	0.0	5.0	442.1
PA	75	71.0	5,325	0.0	0.0	0.0	0.0
SC	NA	NA	NA	0.0	0.0	0.0	0.0
SD	105	55.0	5,775	T	T	0.0	0.0
TX	NA	NA	NA	T	T	T	T	0.0	0.0
UT	78	70.0	5,460	0.0	0.0	0.0	0.0
VA	65	89.0	5,785	0.0	0.0	0.0	0.0
WA	490	70.0	34,300	0.0	0.0	0.1	35.0	2.0	700.7
WI	50	64.0	3,200	0.0	0.0	T	T
WY	95	83.0	7,885	0.0	0.0	0.0	0.0
Total of above	5,082	61.0	310,196		T		173.0		1515.7
U.S. % loss				T		0.06		0.49
U.S. Total	5,211	61.4	320,195
*T = Trace **NA = Not Available, therefore not included in loss totals.

Table 3. Barley genotypes used to differentiate isolates of Puccinia hordei
Genotype	Resistance gene(s)
Sudan	Rph1
Peruvian	Rph2
Estate	Rph3
Gold	Rph4
Magnif	Rph5
Bowman/Bolivia selection	Rph6
Cebada Capa	Rph7
Egypt 4	Rph8
Hor 2596	Rph9
Clip BC8	Rph10
Clip BC67	Rph11
Triumph	Rph12

Table 4. A proposed North American system of pathotype nomenclature for Puccinia hordei based on 12 differential barley hosts^a
		Infection phenotype of pathogen and barley Rph genes
	Set 1	Rph1	Rph2	Rph3	Rph4
	Set 2	Rph5	Rph6	Rph7	Rph8
Ph-code	Set 3	Rph9	Rph10	Rph11	Rph12
	B	Low	Low	Low	Low
	C	Low	Low	Low	High
	D	Low	Low	High	Low
	F	Low	Low	High	High
	G	Low	High	Low	Low
	H	Low	High	Low	High
	J	Low	High	High	Low
	K	Low	High	High	High
	L	High	Low	Low	Low
	M	High	Low	Low	High
	N	High	Low	High	Low
	P	High	Low	High	High
	Q	High	High	Low	Low
	R	High	High	Low	High
	S	High	High	High	Low
	T	High	High	High	High
^aPathotype designations are based on the infection phenotypes of the pathogen isolate on the 12 differential barley hosts. Low = incompatibility (infection phenotypes 0, 0;, 1, or 2) and High = compatibility (infection phenotypes 3 or 4). The infection phenotypes from set 1 determine the first letter of the code, those from set 2 the second, etc.

Table 5. Races of Puccinia hordei identified from the United States in 2000
	Number of
State	collections	Source	Pathotypes and (no. of collections)
Minnesota	4	Nursery	MCD (2), RCD (1), RFD (1)
Minnesota	1	Field	MCD (1)
North Dakota	2	Nursery	MCD (1), MCJ (1)
South Dakota	1	Nursery	RBD (1)
Virginia	1	Nursery	MCB (1)
TOTAL	9