Races of Puccinia striiformis f. sp. hordei in the United States from 2004 to 2007

 

Xianming Chen

 

USDA-ARS and Department of Plant Pathology, Washington State University, Pullman, WA 99164-6430

 

Virulences of Puccinia striiformis Westend. f. sp. hordei (PSH) Eriks., the causal agent of stripe rust of barley, have been studied since the pathogen was first detected in southern Texas in 1991.  Races of the pathogen are determined based on virulence and avirulence patterns of stripe rust samples on a set of barley differential genotypes (Chen et al. 1995; Chen 2004, 2007).  Chen (2007) reported a total of 74 races that was identified from 1992 to 2005.  Data on frequency and distribution of PSH races were reported up to 2004 (Chen et al. 1995; Line and Chen 1996, 1999; Chen 2004).  This newsletter reports PSH races and their frequencies and distributions from 2004 to 2007 (Table 1).

 

The standard procedures were used to identify races of P. striiformis f. sp. hordei (Chen et al.  1995).  Stripe rust samples from barley and grasses were used to inoculate Steptoe, susceptible to all P. striiformis f. sp. hordei isolates, for increasing urediniospores.  Fresh urediniospores were used to inoculate 2-leaf stage seedlings of the 12 barley genotypes used to differentiate races of P. striiformis f. sp. hordei in a mixture with talc powdery at about 1:20 ratio.  Inoculated plants were kept in a dew chamber without light at 10oC for 24 h and then placed in a growth chamber with 16/8 h (light/dark) at a diurnal temperature cycle gradually changing from 4oC at 2:00 am to 20oC at 2:00 pm.  Infection types based on a 0-9 scale were recorded 18 to 22 days after inoculation.  Infection types 0-5 (mostly 0-3) were considered avirulent for the isolate (resistant for the barley differential genotype) and 6-9 (mostly 8-9) were considered virulent for the isolate (susceptible for the differential genotype).    

 

In 2004, 42 isolates were obtained, of which 20 were from California, 5 from Idaho, 2 from Oregon, and 15 from Washington.  From these isolates, 15 PSH races were identified and 3 of them (PSH-70, PSH-71, and PSH-72) were first identified in 2004.  Race PSH-71 was the most popular.  Other popular races included PSH-56, PSH-60, PSH-64, and PSH-72.  PSH-72 was the most virulent race with virulences on all of the 12 barley differential genotypes.

 

In 2005, 32 isolates were obtained from California (8), Idaho (12), Montana (6), Oregon (1), and Washington (5).  A total of 15 races were detected, of which 2 (PSH-73 and PSH-74) were new. PSH-56 was still the most popular race, accounting for 26.7% of the isolates. 

 

In 2006, 44 isolates were obtained, of which 12 were from Arizona, 17 from California, 10 from Washington, 4 from Oregon, and 1 from Minnesota.  A total of 17 races were detected and 7 (PSH-75, PSH-76, PSH-77, PSH-78, PSH-79, PSH-80, and PSH-81) of them were first identified.  Races PSH-71 and PSH-75 were predominant.  The stripe rust sample from a breeding line in an experimental plot near Crookston, Minnesota was identified as a new race, PSH-81, with virulences on Topper, Abed Binder 12, and Bigo. 

 

In 2007, only 9 isolates were successfully obtained, 3 from California, 4 from Colorado, and 2 from Washington. Five races were detected, of which PSH-33 were identified from 5 samples of California and Colorado. The other four races (PSH-46, PSH-52, PSH-64, and PSH-71) were each identified from one sample.

 

So far, a total of 81 races have been identified for the P. striiformis f. sp. hordei. Over the four years, a total of 128 isolates were tested and 30 races were detected. The results indicate a great diversity of races in the stripe rust population.  The most predominant race was PSH-71, accounting for 22% of the isolates.  The race is virulent on 9 of the 12 differential genotypes.  The predominance of the relatively high virulent race was in contrast to the situation before 2004 when relatively low virulent races were predominant (Chen 2004). 

 

During the four years of this study, stripe rust was relatively light in the states where the disease occurred compared to the epidemics in the middle to late 1990s.  The less severe stripe rust of barley was in contrast to the severe epidemics of wheat stripe rust caused by P. striiformis f. sp. tritici, especially in 2005 (Chen 2007).  The less severe stripe rust damage during this period was due to growing resistant cultivars, use of fungicides, and reduced barley acreage in many states.  The most popular barley cultivar, Baronesse, which has a moderate level of non-race specific high-temperature, adult-plant (HTAP) resistance, has contributed significantly to the reduced rust inoculum pressure, especially in the Pacific Northwest. 

 

The isolate from a barley breeding line in Minnesota is interesting.  The rust was not severe on the barley line (Steffenson, personal communication) with infection type 3 (necrotic stripe with light sporulation).  The phenotype indicated that the rust was more likely P. striiformis f. sp. tritici, as we know that the wheat stripe rust pathogen can infect some barley genotypes (Chen et al. 2005).  In fact, this isolate was also identified as wheat stripe rust race PST-123 that has the same virulences as the predominant race PST-100 plus virulence on wheat differential Druchamp (Chen 2007).  However, the isolate was virulent on 3 (Topper, Abed Binder 12, and Bigo) of the 12 barley differentials, indicating that the isolate also is P. striiformis f. sp. hordei.  Even though the isolate will be unlikely a big problem to barley production in the Midwest region and other regions, it may indicate that the wheat stripe rust pathogen may be able to evolve into new races that are able to infect more barley cultivars.  Molecular studies are undertaken to determine if the isolate is more of the barley form, wheat form, or a combination of both. 

 

References:

 

Chen, X. M. 2004.  Epidemiology of barley stripe rust and races of Puccinia striiformis f.

    sp. hordei: the first decade in the United States.  Cereal Rusts and Powdery Mildews

    Bulletin 32: online: [www.crpmb.org/]2004/1029chen.

Chen, X. M.  2007.  Challenges and solutions for stripe rust control in the United States.

     Australian J. of Agric. Res. 58:648-655.

Chen, X. M., Line, R. F., and Leung, H. 1995. Virulence and polymorphic DNA

     relationships of Puccinia striiformis f. sp. hordei to other rusts.  Phytopathology

     85:1335-1342.

Line, R. F., and Chen, X. M.  1996. Wheat and barley stripe rust in North America. Pages 101-104 in “Proc. of the 9th Eur. and Mediter. Cereal Rusts & Powdery Mildews Conf.” 2-6 Sep., 1996. Lunteren, The Netherlands,

Line, R. F., and Chen, X. M. 1999. Control and epidemiology of barley stripe rust in

     North America. Page 24 in "Proc. of 16th American Barley Researchers Workshop".

     July 11-15, 1999. Idaho Falls. Idaho.

 

Table 1.  Races of Puccinia striiformis f. sp. hordei and their frequencies and distributions in the United States from 2004 to 2007

 

PSH

 

First year

No of

Frequency

Distribution

Year

race

Virulence formulaa

detected

isolates

(%)

Stateb (No)

2004

PSH-19

1,3,5,6,7,8

1995

1

2.4

WA(1)

 

PSH-22

1,4,7,8,9,10

1995

1

2.4

WA(1)

 

PSH-33

1,7

1996

1

2.4

CA(1)

 

PSH-35

1,4,7

1996

2

4.8

CA(2)

 

PSH-45

1,3,4,6,7,8

1996

1

2.4

CA(1)

 

PSH-46

1,7,8

1996

1

2.4

WA(1)

 

PSH-52

1,5,7,8

1998

1

2.4

CA(1)

 

PSH-56

1,5,7,8,12

2001

4

9.5

CA(1), WA(3)

 

PSH-60

1,5,7,8,9,10,12

2001

4

9.5

CA(2), WA(2)

 

PSH-64

1,5,7,8,10,12

2002

5

11.9

CA(3), ID(1), WA(1)

 

PSH-65

1,2,3,4,7,8,12

2002

1

2.4

CA(1)

 

PSH-69

1,5,6,7,8,9,10,11,12

2003

1

2.4

ID(1)

 

PSH-70

1,7,10,12

2004

1

2.4

CA(1)

 

PSH-71

1,3,5,6,7,8,9,10,12

2004

14

33.3

CA(6), ID(2), WA(6)

 

PSH-72

1,2,3,4,5,6,7,8,9,10,11,12

2004

4

9.5

CA(1), ID(1), OR(2)

 

Total

 

 

42

 

 

2005

PSH-33

1,7

1984

3

10.0

CA(2), ID(1)

 

PSH-46

1,7,8

1991

1

3.3

CA(1)

 

PSH-48

1

1992

1

3.3

ID(1)

 

PSH-51

1,5,7

1998

1

3.3

OR(1)

 

PSH-52

1,5,7,8

1998

1

3.3

ID(1)

 

PSH-56

1,5,7,8,12

2001

8

26.7

CA(1), ID(2), MT(5)

 

PSH-59

1,7,8,11,12

2001

1

3.3

ID(1)

 

PSH-60

1,5,7,8,9,10,12

2001

3

10.0

ID(1), WA(2)

 

PSH-63

1,3,5,7,8,12

2002

2

6.7

ID(1), MT(1)

 

PSH-64

1,5,7,8,10,12

2002

1

3.3

WA(1)

 

PSH-65

1,2,3,4,7,8,12

2002

1

3.3

ID(1)

 

PSH-69

1,5,6,7,8,9,10,11,12

2003

2

6.7

ID(2)

 

PSH-71

1,3,5,6,7,8,9,10,12

2004

3

10.0

CA(1), WA(2)

 

PSH-73

1,5,7,8,9

2005

2

6.7

CA(1), ID(1)

 

PSH-74

1,5,7,12

2005

2

6.7

CA(2)

 

Total

 

 

32

 

 

2006

PSH-1

1,2

1993

1

2.3

CA(1)

 

PSH-33

1,7

1996

1

2.3

CA(1)

 

PSH-36

1,4

1996

1

2.3

CA(1)

 

PSH-48

1

1997

2

4.5

CA(2)

 

PSH-52

1,5,7,8

1998

1

2.3

CA(1)

 

PSH-56

1,5,7,8,12

2001

2

4.5

WA(2)

 

PSH-60

1,5,7,8,9,10,12

2001

3

6.8

CA(1), OR(1), WA(1)

 

PSH-63

1,3,5,7,8,12

2002

1

2.3

WA(1)

 

PSH-71

1,3,5,6,7,8,9,10,12

2004

10

22.7

CA(4), OR(3), WA(3)

 

PSH-72

1,2,3,4,5,6,7,8,9,10,11,12

2004

1

2.3

AZ(1)

 

PSH-75

1,2,3,4,5,6,7,8,9,10,12

2006

10

22.7

AZ(8), WA(2)

 

PSH-76

1,5,6,7,8,9,10,12

2006

4

9.1

CA(4)

 

PSH-77

1,3,5,7,8,9,10,12

2006

1

2.3

CA(1)

 

PSH-78

1,2,4,5,6,7,8,12

2006

3

6.8

AZ(3)

 

PSH-79

1,2,4,5,7,8,9,10,12

2006

1

2.3

WA(1)

 

PSH-80

1,5,7,10

2006

1

2.3

CA(1)

 

PSH-81

1,7,10

2006

1

2.3

MN(1)

 

 

Total

 

44

 

 

2007

PSH-33

1,7

1996

5

55.6%

CA(2), CO(3)

 

PSH-46

1,7,8

1996

1

11.1%

CO(1)

 

PSH-52

1,5,7,8

1998

1

11.1%

CA(1)

 

PSH-64

1,5,7,8,10,12

2002

1

11.1%

WA(1)

 

PSH-71

1,3,5,6,7,8,9,10,12

2004

1

11.1%

WA(1)

 

 

Total

 

9

 

 

a Differentials:  1 = Topper, 2 = Heils Franken, 3 = Emir, 4 = Astrix, 5 = Hiproly, 6 = Varunda,   7 = Abed

  Binder 12, 8 = Trumpf, 9 = Mazurk, 10 = Bigo, 11 = I 5, and 12 = Bancroft.

b  AZ = Arizona, CA = California, CO = Colorado, ID = Idaho, MN = Minnesota, MT = Montana, OR =

  Oregon, and WA = Washington.