Races of
Barley Stripe Rust in the United States
Xianming
Chen1,2 and Roland F. Line2
1 USDA-ARS, the Wheat Genetics Unit, Pullman, WA 99164-6430
2 Dept. of Plant Pathology, WSU, Pullman, WA 99164-6430
Barley stripe rust, caused by Puccinia striiformis f. sp. hordei, is a
relatively new disease in the United States.
It was first observed in Texas in 1991.
Within five years, the disease spread north and west to the states of
Oklahoma, New Mexico, Arizona, Colorado, Utah, California, Idaho, Montana,
Oregon, and Washington. The disease,
which is now well established in the western United States, has caused severe
yield losses in many regions of the West and has a high potential for causing
major yield losses in the future.
The barley stripe rust pathogen in the
United States was initially considered to be Race 24, which was first reported
in Europe and subsequently reported in South America and North America. However, the pathogen is extremely variable,
and the population originally identified as Race 24 in the United States
consisted of many races (Chen et al. 1995; Line and Chen, 1996). Table 1 lists 52 races based on virulence
and avirulence on the 11 barley cultivars that are used to differentiate races
of P. striiformis f. sp. Hordei that we have named by 2000.
In 2000, P. striiformis f. sp. hordei continued to survive and increase in the West. The disease was especially prevalent in California, Oregon, Idaho, and Washington. It was most severe in the Central Valley of California and northwestern Washington, where 100% severity was observed on susceptible cultivars in trap plots, disease nurseries, and commercial fields. About 6% (372,900 bushels), 5% (442,100 bushels), and 2% (700,700 bushels) of yield losses caused by barley stripe rust were estimated for the states of California, Oregon, and Washington, respectively.
Pathogenic races were monitored in 2000 by using trap plots in different regions in the
western United States. Also, stripe
rust samples were collected from the trap plots, disease nurseries, and
commercial fields and tested on the set of barley cultivars that are used to
differentiate races of P. striiformis
f. sp. hordei in North America. Seven races (shown in bold type in Table 1)
were identified from the samples collected in 2000. The number of races that were identified was relatively small
compared to those identified from 1993 to 1999. From the samples collected in 1993 and 1994, we identified 14
races (Chen et al. 1995). From samples
collected in 1995, we identified 17 additional races (Line and Chen,
1996). Previously identified races were also detected in 1995. In 1996, 26 races were identified and 16 of
them were new. In 1997, 24 races were
identified and two of them were new. In
1998, 17 races were identified and three of them were new. The three new races did not have more than
four virulence factors (they did not attack more than four of the differential
cultivars). About 40% of the isolates
had one to four virulence factors. In
1999, 12 races were detected and 52% of the isolates had 1 to 4 virulence
factors. In 2000, only seven races were
detected and none of the races or isolates had more than 4 virulence factors. These results indicate that the barley
stripe rust population in the United States has become less complex. Races with fewer virulence factors have
become more prevalent. The changes
from a population with numerous races to a population with few races and from a
population with many virulence factors to a population with few virulence
factors may have resulted from selection pressure. It is not clear what kinds of selection have changed the
population structure. When we detected
large variations in the U.S. population of P.
striiformis f. sp. hordei a few
years ago, we speculated that the population would become less heterogeneous in
virulence after resistant cultivars are widely grown. Several resistant cultivars have been released, but they have not
been widely used in commercial production.
Therefore, resistant cultivars may not have provided enough selection
pressure for the changes in the rust population. One hypothesis is that races with more virulence factors may have
less fitness or aggressiveness. The
environment may favor selection of races that have fewer virulence factors but
better ability to survive.
The major barley cultivars grown in the
western United States are generally susceptible to barley stripe rust, but they
vary in their level of susceptibility.
For example, the cultivar ‘Baronesse’, which is widely grown in the
western United States, is less susceptible to barley stripe rust than
‘Steptoe’. In the disease nurseries,
Baronesse had 40 to 60% rust while Steptoe had 90 to 100% rust. The cultivar ‘Orca’ also has a moderate level of resistance. Among the newly released cultivars and
breeding lines, ‘Bancraft’, ‘Tango’, ‘Kold’, and ‘Strider‘ are resistant. The durability of their resistances is unknown. Because the barley stripe rust population changes very rapidly,
non-race-specific, durable resistance should be identified, characterized, and
used in breeding programs.
References:
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.
Proc. Of the 9th Eur. and Mediter. Cereal Rusts & Powdery Mildews
Conf.,
Lunteren, The Netherlands, 2-6 Sept. pp. 101-104.
Table 1. Races of Puccinia
striiformis f. sp. hordei
detected in the United States before and in 2000.
|
PSH |
Virulence |
First year |
In 2000 |
|
|
race |
descriptiona |
detected |
(%) |
Distributionb |
|
1 |
1,2 |
1993 |
ndc |
nd |
|
2 |
1,2,3 |
1994 |
nd |
nd |
|
3 |
1,2,4 |
1993 |
nd |
nd |
|
4 |
1,2,5 |
1993 |
nd |
nd |
|
5 |
1,6,7 |
1994 |
nd |
nd |
|
6 |
1,2,3,4 |
1993 |
nd |
nd |
|
7 |
1,2,4,5 |
1993 |
nd |
nd |
|
8 |
1,2,3,7 |
1994 |
nd |
nd |
|
9 |
1,2,3,4,6 |
1993 |
nd |
nd |
|
10 |
1,3,5,6,7 |
1994 |
nd |
nd |
|
11 |
1,3,6,7,8 |
1993 |
nd |
nd |
|
12 |
1,2,3,4,5,8 |
1993 |
nd |
nd |
|
13 |
1,2,3,6,8,9,10 |
1994 |
nd |
nd |
|
14 |
1,2,3,4,5,6,7,8 |
1993 |
nd |
nd |
|
15 |
1,3,4,7,8 |
1995 |
nd |
nd |
|
16 |
1,3,5,7,8 |
1995 |
5.3 |
CA |
|
17 |
1,2,4,5,7,8 |
1995 |
nd |
nd |
|
18 |
1,3,4,5,7,8 |
1995 |
nd |
nd |
|
19 |
1,3,5,6,7,8 |
1995 |
nd |
nd |
|
20 |
1,3,6,7,8,9 |
1995 |
nd |
nd |
|
21 |
1,3,4,7,8,9,10 |
1995 |
nd |
nd |
|
22 |
1,4,7,8,9,10 |
1995 |
nd |
nd |
|
23 |
1,2,3,4,7,8,9 |
1995 |
nd |
nd |
|
24 |
1,3,4,5,6,7,8 |
1995 |
nd |
nd |
|
25 |
1,3,4,5,7,8,9 |
1995 |
nd |
nd |
|
26 |
1,2,3,4,5,7,8,9 |
1995 |
nd |
nd |
|
27 |
1,3,5,6,7,8,9,10 |
1995 |
nd |
nd |
|
28 |
1,2,3,4,5,6,7,8,9 |
1995 |
nd |
nd |
|
29 |
1,2,3,4,5,6,7,8,10 |
1995 |
nd |
nd |
|
30 |
1,3,4,5,6,7,8,9,10 |
1995 |
nd |
nd |
|
31 |
1,2,3,4,5,6,7,8,9,10 |
1995 |
nd |
nd |
|
32 |
1,3,5 |
1996 |
nd |
nd |
|
33 |
1,7 |
1996 |
18.4 |
CA, WA |
|
34 |
1,7,8,9 |
1996 |
nd |
nd |
|
35 |
1,4,7 |
1996 |
nd |
nd |
|
36 |
1,4 |
1996 |
nd |
nd |
|
37 |
1,2,4,7 |
1996 |
nd |
nd |
|
38 |
1,2,3,4,5,7,8 |
1996 |
nd |
nd |
|
39 |
1,3,7,8 |
1996 |
nd |
nd |
|
40 |
1,2,3,4,7,9 |
1996 |
nd |
nd |
|
41 |
1,3,4,6,7,9 |
1996 |
nd |
nd |
|
42 |
1,4,5,7,9 |
1996 |
nd |
nd |
|
43 |
1,4,8 |
1996 |
nd |
nd |
|
44 |
1,3,7 |
1996 |
nd |
nd |
|
45 |
1,3,4,6,7,8 |
1996 |
nd |
nd |
|
46 |
1,7,8 |
1996 |
26.3 |
CA, ID, WA |
|
47 |
1,3,4,5,7 |
1996 |
nd |
nd |
|
48 |
1 |
1997 |
13.2 |
ID, WA |
|
49 |
1,2,3,4,5,6,7,8,9,10,11 |
1997 |
nd |
nd |
|
50 |
1,5 |
1998 |
7.9 |
CA, ID |
|
51 |
1,5,7 |
1998 |
7.9 |
WA |
|
52 |
1,5,7,8 |
1998 |
21.1 |
CA, OR, WA |
a Virulence on barley differential cultivars: 1 = Topper, 2 =
Heils Franken, 3 =
Emir, 4 = Astrix, 5 = Hiproly, 6 =Varunda,
7 = Abed Binder 12, 8 = Trumpf,
9 = Mazurka, 10 = Bigo, and 11 =I 5.
b CA = California, ID = Idaho, OR = Oregon, and WA =
Washington.
c nd = not detected.