# Barley Genetics Newsletter (2005) 35:23-26

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**Races of *Puccinia striiformis* f. sp. *hordei*, the pathogen of**

**barley stripe rust in the United States in 2004**

Xianming Chen^1,2^ and Laura Penman^2^

^1^ USDA-ARS Wheat Genetics, Quality, Physiology, and Disease Research
Unit and

^2^ Department of Plant Pathology, Washington State University, Pullman,
WA 99164-6430.

**Abstract**

Stripe rust of barley, caused by *Puccinia striiformis* f. sp. *hordei*
(PSH), occurred mainly in California, Idaho, Oregon, and Washington and
caused localized damage to barley crops. Growing cultivars with
high-temperature, adult-plant resistance and the cropping system
contributed to the low level of stripe rust. Stripe rust samples were
collected from the four states and tested under controlled greenhouse
conditions on seedlings of a set of 12 barley genotypes used to
differentiate races of the fungal pathogen. A total of 15 races were
detected, of which three were new. PSH-72, a new race, was virulent on
all 12 differential genotypes. The most predominant race was PSH-71 that
was virulent on differential genotypes Topper, Emir, Hiproly, Varunda,
Abed Binder 12, Trumpf, Mazurk, Bigo, and Bancroft.

**Introduction**

*Puccinia striiformis* Westend. f. sp. *hordei* Eriks., the causal agent
of barley stripe rust, has established in the United States since it was
first reported in southern Texas in 1991 (Marshall and Sutton, 1995;
Roelfs et al., 1992). In the early 1990s, the disease occurred in the
south central states and later spread to the states west of the Rocky
Mountains (Chen et al., 1995). The disease has caused major damage to
barley crops in the U.S., mainly in California and the Pacific Northwest
(Brown et al., 2001; Chen, 2004).

Chen et al. (1995) selected 11 barley genotypes for differentiating
races of *P. striiformis* f. sp. *hordei*. Later, the barley cultivar
'Bancroft' was added to the differential set (Chen and Line, 2001).
Using the differential genotypes, 69 races were identified from the
early 1990s to 2003 (Chen et al., 1995; Chen and Line, 2001; Chen,
2004). The objectives of this study were to 1) monitor the occurrence
and distribution of barley stripe rust and 2) identify races and
determine their frequencies and distributions in the United States in
2004.

**Materials and Methods**

*Monitoring barley stripe rust.* Stripe rust was monitored by surveying
commercial fields during the growing season. Trap plots consisting of
the set of differential genotypes (Table 1) and other cultivars either
susceptible or resistant to *P. striiformis* f. sp. *hordei* were
planted at various locations. For commercial field survey, infection
type, severity (percentage of leaf areas infected), prevalence
(percentage of plants infected), and information on cultivar, location,
and growth stage were recorded. For the trap plots, infection type and
severity were recorded one to three times during the growing season.
Stripe rust infected leaf samples were collected for race
identification.

*Race identification.* Races of stripe rust samples were determined
using a set of differential genotypes following the methods described by
Chen et al. (1995). In this study, 12 barley genotypes (Table 1) were
used to differentiate races of *P. striiformis* f. sp. *hordei*. Samples
of infected leaves that were usually shipped in glassine envelops were
used to inoculate seedlings of 'Steptoe' or 'Topper', which are
susceptible to all races of *P. striiformis* f. sp. *hordei*, for
increasing urediniospores. For samples of poor quality (received more
than 7 days after collection or with limited uredia), leaf pieces were
placed on moist filter paper in a Petri dish that was kept at
temperatures of 4-12^o^C overnight. Fresh spores produced on the leaves
were used in inoculation for spore increase.

Inoculated plants were kept in a dew chamber at 10^o^C for 18 to 24
hours for infection and then grown in a greenhouse growth chamber at a
diurnal temperature cycle gradually changing from 4^o^C at 2:00 am to
20^o^C at 2:00 pm. The light period consisted of day light supplemented
with metal halide lights to extend the photoperiod to 16 hours.
Urediniospores that were collected 16 to 30 days after inoculation were
used to inoculate seedlings of the set of differential genotypes.
Inoculated plants were kept in the dew chamber for infection and then
grown in a growth chamber for symptom development under the same
conditions as described for the spore increase. Infection type (IT) data
were recorded 18-22 days after inoculation according to the 0-9 scale
described by Line and Qayoum (1991). Isolates that produced ITs 0 - 5
were considered avirulent and 6 - 9 were considered virulent on
individual barley differential genotypes. New races that had virulence
patterns different from previously identified races were confirmed at
least in one more test with the differential genotypes. Frequency of
each race was determined as percentage of the isolates that were
identified as that race from the total of isolates in the study.

Table 1. Barley genotypes used to differentiate races of *Puccinia
striiformis* f. sp. *hordei*

  -------------- --------------------- -------------------- ------------------
  Differential                                              Resistance
  genotype                                                  

  Number         Name                  ID number            gene^a^

  1              Topper                \-                   \-

  2              Heils Franken         PI 290183            *Rps4*, *rpsHF*

  3              Emir                  CIho 13541           *rpsEm1*, *rpsEm2*

  4              Astrix                CIho 13862           *Rps4*, *rpsAst*

  5              Hiproly               CIho 03947           *rpsHi1*, *rpsHi2*

  6              Varunda               PI 410865            *rpsVa1*, *rpsVa2*

  7              Abed Binder 12        PI 327961            *rps2*

  8              Trumpf                PI 548762            *rpsTr1*, *rpsTr2*

  9              Mazurka               PI 399501            *Rps1.c*

  10             Bigo                  CIho 11795           *Rps1.b*

  11             I 5                   PI 288187            *Rps3*, *rpsI5*

  12             Bancroft              PI 605474            Not determined
  -------------- --------------------- -------------------- ------------------

^a^ Chen and Line (2003).

**Results and Discussion**

In 2004, stripe rust occurred in California, Oregon, Washington, and
Idaho. Of a total of 39 viable isolates of *P. striiformis* f. sp.
*hordei*, 18 were obtained from California, 3 from Oregon, 13 from
Washington, and 5 from Idaho. All isolates were from barley (*Hordeum
vulgare*) cultivars, except for one isolate that was collected from wild
barley (*H. spontaneum*) in California. The isolate from wild barley was
identified as race PSH-33 that was virulent only on two (Topper and Abed
Binder 12) of the differential genotypes. As shown in Table 2, a total
of 15 PSH races were identified, of which three were new and designated
as PSH-70, PSH-71, and PSH-72 (Table 3). PSH-70 was virulent on four
(Topper, Abed Binder 12, Bigo, and Bancroft) of the 12 differential
genotypes. PSH-71 was virulent on nine (Topper, Emir, Hiproly, Varunda,
Abed Binder 12, Trumpf, Mazurk, Bigo, and Bancroft). PST-72 was virulent
on all 12 differential genotypes. Of the 15 races, nine were presented
by only one isolate, one by two isolates, three by four isolates, one by
five isolates, and one by 14 isolates. Although PSH-71 was new, it was
the most predominant race. Nearly 85% of the isolates were collected
from disease monitoring and germplasm screening nurseries. Only 15% of
the isolates were obtained from commercial fields, indicating that the
severity levels of stripe rust in commercial field were generally low.

The barley stripe rust incidence was relatively low compared to wheat
stripe rust in 2004. The barley yield losses due to stripe rust were
estimated as 63,000 bushels in the four states
(<http://www.cdl.umn.edu/loss/loss.html>). In contrast, wheat stripe
rust had a much wider spread and severer epidemic, which caused yield
losses of about 6.6 million bushels
(<http://www.cdl.umn.edu/loss/loss.html>), plus millions of dollars
spent on fungicide application in the four states. The relatively light
stripe rust epidemic on barley compared to wheat stripe rust epidemic in
the Pacific Northwest were attributed to 1) the smaller barley acreage,
2) the lack of winter barley, which reduces rust inoculum from previous
crops, and 3) the use of high-temperature, adult-plant resistant
cultivars such as Baronesse (Chen, 2004). In California, the reduced
barley acreage compared to that in early 1990s and growing resistant
cultivars have contributed the low level of stripe rust in the recent
years.

Even though stripe rust was generally light in commercial fields,
susceptible cultivars in various nurseries had up to 100% of severity in
California and western Washington. The disease monitoring data suggest
that stripe rust is still a threat to barley production in the western
United States. For this region, stripe rust resistance should remain as
one of the top priorities for barley breeding programs.

Table 2. Races of *Puccinia striiformis* f. sp. *hordei* (PSH) and their
frequencies and distributions in 2004

  ------ ---------------------------- ---------- ---------- ----------- -----------------
  PSH                                 1st year   No. of     Frequency   Distribution

  race   Virulence^a^                 detected   isolates   (%)         state (No.)

  19     1,3,5,6,7,8                  1995       1          2.4         WA(1)

  22     1,4,7,8,9,10                 1995       1          2.4         WA(1)

  33     1,7                          1996       1          2.4         CA(1)

  35     1,4,7                        1996       2          4.8         CA(2)

  45     1,3,4,6,7,8                  1996       1          2.4         CA(1)

  46     1,7,8                        1996       1          2.4         WA(1)

  52     1,5,7,8                      1998       1          2.4         CA(1)

  56     1,5,7,8,12                   2001       4          9.5         CA(1), WA(3)

  60     1,5,7,8,9,10,12              2001       4          9.5         CA(2), WA(2)

  64     1,5,7,8,10,12                2002       5          11.9        CA(3), ID(1),
                                                                        WA(1)

  65     1,2,3,4,7,8,12               2002       1          2.4         CA(1)

  69     1,5,6,7,8,9,10,11,12         2003       1          2.4         ID(1)

  70     1,7,10,12                    2004       1          2.4         CA(1)

  71     1,3,5,6,7,8,9,10,12          2004       14         33.3        CA(6), ID(2),
                                                                        WA(5)

  72     1,2,3,4,5,6,7,8,9,10,11,12   2004       4          9.5         CA(1), ID(1),
                                                                        OR(2)
  ------ ---------------------------- ---------- ---------- ----------- -----------------

^a^ See Table 1 for the barley genotypes used to differentiate races of
*P. striiformis* f. sp. *hordei*.

Table 3. New races of *Puccinia striiformis* f. sp. *hordei* (PSH)
detected in 2004, type isolates, and dates, locations, and cultivars
collected

  --------- -------------- ------------ ------------ ------------ -----------
  PSH       Type           Date         Collected                 
                                        from                      

  race      Isolate        Collected    State        Location     Cultivar

  70        04-304         7/14/2004    California   Tulelake     Steptoe

  71        04-023         3/29/2004    California   Davis        APB b-12

  72        04-51-12       4/9/2004     Oregon       Corvallis    88Ab536
  --------- -------------- ------------ ------------ ------------ -----------

**Acknowledgement**

We would like to thank Drs. Lee Jackson, Patrick Hayes, and Don Obert
for sending samples of barley stripe rust. We also like to thank David
Long and Mark Hughes for compiling yield loss data from various states.
The financial support from USDA-ARS and Washington Barley Commission is
highly appreciated.

**References**

Brown, W. M. Jr, Hill J. P., Velasco V. R. 2001. Barley yellow rust in
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Chen, X. M. 2004. Epidemiology of barley stripe rust and races of
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States. Cereal Rusts and Powdery Mildews Bulletin 32:
\[www.crpmb.org/\]2004/1029chen.

Chen, X. M., and Line, R. F. 2001. Races of barley stripe rust in the
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Chen, X. M., Line, R. F., 2003. Identification of genes for resistance
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Marshall, D., Sutton, R. L., 1995. Epidemiology of stripe rust,
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