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Update on Wheat Stripe Rust from the University of California

The following was reported by U.C. Extension Agronomist Lee Jackson on 4/12/04:

Disease observations of California statewide wheat nurseries in the Sacramento Valley (during week of March 29-April 2, wheat in boot to flowering stage) and in the San Joaquin Valley (during the week of April 5-9, wheat headed to anthesis) are as follows:

 Sacramento Valley

Septoria tritici blotch is severe on Cavalier, Yecora Rojo, and several advanced lines in Colusa County and at UC Davis; stripe rust is severe on varieties Yecora Rojo and Cavalier and several advanced lines at UC Davis and in Colusa County and at low severity at Butte and Glenn counties.  Stripe rust is very severe on several varieties (Yecora Rojo, Anza, Cavalier, Serra) and advanced lines and moderately severe on other varieties (Stander, Express) and advanced lines in the Sacramento/San Joaquin Delta (Victoria Island, 12 mi w. of Stockton).

 San Joaquin Valley (Madera, Kings, and Kern counties),

Stripe rust is very severe on Yecora Rojo, Cavalier, and advanced lines WWW CHBR1933 and BZ 998-247W; severe on Anza; and moderately severe on Express, Stander and advanced lines YU900-62W, APB W01-106-2, and APB W01-374-4.  Stripe rust is at low to moderate severity on durum varieties Kofa, Mohawk, Orita, Bravadur, Ria, YU 895-130, and advanced lines WWW D5384-2, BZ898-63, and WWW D9737.  Wheat stripe rust pressure is high throughout the Central Valley judging by natural infection of the border plots of the susceptible check variety D6301 (100% severity/100% incidence).

With regard to commercially grown resistant varieties (Summit, Plata, Blanca Grande), they currently show good resistance in the statewide nurseries. However, very small stripe rust infection foci have been observed in a few commercial fields of Summit in the Sacramento Valley (a field south of Esparto and one on Sutter Island in Yolo County, and a field east of Dixon in Solano County as reported by farm advisor Kent Brittan) and in the Sacramento-San Joaquin Delta in the field where the statewide nursery is planted. In these limited areas, some plants of Summit support pustules showing high sporulation, although most affected plants show necrotic stripes with little sporulation. It appears that at least one new strain virulent to Summit is developing in California.  Collections have been sent to Xianming Chen at USDA-ARS, Washington State University, Pullman WA for race identification.

 The wheat stripe rust screening nursery at UC Davis has high stripe rust severity and good uniformity of infection (natural infection of the border plots of the susceptible check variety D6301 is nearly 100% severity and 100% incidence). The barley stripe rust screening nursery at UC Davis is showing very high stripe rust severity (100%) on a relatively few entries, but the disease has yet to spread uniformly through the nursery.

Final note: Aphid populations have been very high throughout the Central Valley. Aphid-feeding damage, exclusive of damage from a low to moderate level of BYD virus, has been severe enough to reduce yields to some extent.

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