Whether wheat stripe rust (Puccinia striiformis f. sp. tritici) will cause problems on barley and barley stripe rust (P. striiformis f. sp. hordei) will cause problems on wheat is a very interesting topic. My quick answer is unlikely now but may be likely in the future.
Reasons for “unlikely now” include the following factors:
- Stripe rust of wheat and stripe rust of barley are two different diseases caused by two different formae speciales based on our virulence and molecular tests. Although few barley varieties are susceptible to wheat stripe rust and few wheat varieties are susceptible to barley stripe rust, wheat stripe rust mainly attacks wheat and barley stripe rust mainly attacks barley.
- Wheat stripe rust has been in the US for more than 100 years but barley had never got stripe rust epidemics (stripe rust was occasionally observed on barley) before 1991 in the US. Since 1991 when barley stripe rust was first reported in the US, the pathogen has been identified from Texas, Oklahoma, New Mexico, Arizona, Colorado, Utah, Idaho, Montana, California, Oregon, and Washington and has not been reported in other states. In this year, we have got barley stripe rust samples from Texas, California, Oregon, Washington, and Colorado. Last year, stripe rust samples from the Great Plains were all wheat stripe rust. Most of the isolates were virulent on wheat differential cultivars Lemhi (Yr21), Heines VII (Yr2, YrHVII), Lee (Yr7, Yr22, Yr23), Fielder (Yr6, Yr20), Express (unknown), Yr8 (Yr8), Yr9 (Yr9), Clement (Yr9, YrCle), and Compair (Yr8, Yr19). All the isolates from wheat were avirulent on barley cultivars used to differentiate barley stripe rust.
- Since 1991, all major stripe rust epidemics on barley were caused by barley stripe rust and those on wheat caused by wheat stripe rust.
Reasons for “may be likely in the future” include the following:
- Although barley stripe rust and wheat stripe rust are two different formae speciales, they are more closely related to each other than to other formae speciales of P. striiformis, such as blue grass stripe rust (P. striiformis f. sp. poae).
- The two stripe rust pathogens have some common hosts including some wheat, barley, and grasses.
- There have been some reports that wheat stripe rust races caused problems on barley in China, Europe, and may be in India.
In the US, 80 PST races (formerly called CDL races) of P. striiformis f. sp. tritici and 52 PSH races of P. striiformis f. sp. hordei have been identified. We are going to submit a manuscript on wheat stripe rust epidemics and races in 2000 to Plant Disease and have submitted a short report on barley stripe rust races to Barley Newsletter.
Although there were some earlier attempted studies, it is still need to determine whether barley stripe rust and wheat stripe rust can somatically recombine their virulence factors. If they do, some future isolates of stripe rust may able to cause problems on both wheat and barley. We should watch for such isolates. I wrote a NRI proposal for a project to determine the possibility and to determine the mechanisms of resistance in wheat to barley stripe rust and in barley for resistance to wheat stripe rust. We have started this project.
Any questions, comments, and suggestions are appreciated.
Stripe rusts of wheat and barley continue increasing in western Washington. Susceptible cultivars had 70 to 95% stripe rust. In eastern Washington (east of the Cascades Mountains), stripe rust of wheat became prevalent. In some locations (for example, Central Ferry), 60% of stripe rust was found on susceptible wheat lines in breeders’ nurseries and 20% of stripe rust was found in some commercial fields.
Barley stripe rust starts to show up in eastern Washington.
Wheat leaf rust starts to show up in eastern Washington. I just sent three samples of leaf rust to Dave today.
About a week of dry and hot weather occurred in later May. But since the beginning of June, the weather has been cool again and with scattered showers in the Pacific Northwest, being favorable for stripe rust.