Rust Update in California, Oregon, and Washington

April 14, 2006

Xianming Chen

Dr. McIntosh (from the Plant Breeding Institute, University of Sydney, Australia) and I were checking rusts on wheat, barley, and grasses in California, Oregon and Washington from April 8 to 13, with helps from Drs. Cal Qualset, Lee Jackson, Jorge Dubcovsky, Patrick Hayes, Jim Peterson, and several others.

California

As Lee Jackson reported, stripe rust was reported in the Imperial Valley on March 23 and increased on durum and forage wheat crops. Wheat stripe rust is increasing in the San Joaquin Valley and the Sacramento Valley. When we check the experimental nurseries near Davis on April 9, stripe rust developed up to 60% severity on susceptible wheat lines. Barley stripe rust was up to 30% on susceptible barley lines. A “Blanca Grande” wheat field between Davis and Woodland was quite uniformly infected, with severities up to 80%. We found wild barley grasses heavily infected (100% incidence and 100% severity) in orchards near Winter City. The stripe rust on wild barley grasses could be the wheat stripe rust or barley stripe rust pathogen as we experienced in the past, or another form specific on wild barley grass as reported in Australia.

On April 10, we found stripe rust in every wheat fields as we checked from Davis to Ciha, California along High Way 99. Some fields had stripe rust of 80% severity in hot spots. We also found stripe rust on wild barley grasses in orchards and along roadsides near towns. We found crown rust on wild oats in this region.

Regarding stripe rust on Blanca Grande, a hard white spring wheat, we got first stripe rust samples from this cultivar in 2004 from Madena and Winter, CA in 2004. The sample from the Winter field had 70% severity and susceptible reaction, and was identified as race PST-101 (virulent on differentials 1 (Lemhi), 2 (Chinese 166), 3 (Heines VII), 8 (Produra), 9 (Yamhill), 10 (Stephens), 11 (Lee), 12 (Fielder), 16 (Express), 17 (Yr8), 18 (Yr9), 19 (Clement), and 20 (Compare). The sample from Madena, CA had less stripe rust (10% severity, 10% incidence, and resistant reaction with some rust pustules) , and was identified as race PST-112 (with the same virulences as PST-101 but avirulent on Heines VII and Yamhill). In 2005, two samples of Blanca Grande were from Straford, CA, and both had low rust infection (10-20% severity and < 1% incidence) and identified as race PST-113 (with the same virulences as PST-101 plus virulence on differential 14 (Tres). In 2005, PST-113 was identified from 8 samples in California and only one sample outside California (from Winnesboro, Louisiana). The sample from Louisiana was made from the Yr1 line (Chinese 166 has Yr1) by myself. The rust data indicate Blanca Grande has Yr1 and probably another Yr gene. Yr1 was probably in wheat cultivars RSI 5, Bonus, and Summit, which became susceptible earlier than Blanca Grande. The Yr1 gene should not be used even though the Yr1-virulent races have been mainly in California.

Oregon

I have not found stripe rust in central Oregon when I was checking wheat fields on April 8 along HW 97. Dr. Patrick Hayes reported stripe rust on barley in nurseries near Corvallis on April 5. When we looked the nurseries on April 11, stripe rust developed up to 30% on susceptible barley lines. Stripe rust was not found on wheat in the experiment farm and not in wheat fields as we checked along HW 99.

Washington

Stripe rust occurred on both wheat and barley in our nurseries at Mt Vernon (northwestern Washington), up to 40% severity on April 12. The rust also occurred in some surrounding fields. When I was checking stripe rust in south central Washington (mainly the Horse Heaven Hills) on April 8, I could not find any rust. The same was true when I was checking from the central Washington (the Connell area) to eastern Washington on April 13. Today (April 13), I got a report of stripe rust found in a early-planted irrigated winter wheat field in south-central Washington. This will be confirmed early next week. Stripe rust will be later this year than last year in the most wheat and barley producing areas in the eastern Pacific Northwest as I forecasted early this year. For wheat and barley growers in eastern Washington and Northern Idaho, if you were happy with your Blanca Grande crop last year, you should be careful about planting that cultivar this year. For spring wheat, the cultivars such as Hank, WPB 926, Tara, IDO377s, and some others that were resistant to stripe rust before 2005 will be more vulnerable to stripe rust this year because these cultivars became susceptible last year and we predict that the races infecting these cultivars last year will predominant this year. Cultivars like Alpowa and Louis should be fine this year because they have durable high-temperature adult-plant resistance and the rust will be later than last year. If you have not decided to plant spring wheat or spring barley, you may consider spring barley because barley is in generally under less stripe rust pressure than spring wheat. Barley varieties Baronesse and Bob have durable high-temperature adult-plant resistance to stripe rust. We predict barley stripe rust should not be severer than last year unless you grown highly susceptible varieties. Check stripe rust ratings in the Seed Buyer’s Guide for resistant and moderately resistant varieties of both spring and winter wheat.