May 31, 2005
Source: Plant Management Network, 4 Mar 2005 [edited] <http://www.plantmanagementnetwork.org/pub/php/brief/2005/stripe/>

Stripe rust, wheat caused by Puccinia striiformis f. sp. tritici on wheat in Florida
Ann R. Blount, University of Florida, 3925 Highway 71, North Florida Research and Education Center, Marianna 32446; Shabbir A. Rizvi, Florida Department of Agriculture and Consumer Services, Division of Plant Industry, Gainesville 32614-7100; Ronald D. Barnett, 155 Research Road, University of Florida, North Florida Research and Education Center, Quincy 32351; Xianming Chen, USDA-ARS, Washington State University, Pullman 99164-6430; Timothy S. Schubert, Florida Department of Agriculture and Consumer Services, Division of Plant Industry, Gainesville 32614-7100; W. Hank Dankers and Timur M. Momol, 155 Research Road, University of Florida, North Florida Research and Education Center, Quincy 32351; and Wayne N. Dixon, Florida Department of Agriculture and Consumer Services, Division of Plant Industry, Gainesville 32614-7100 Accepted for publication 22 Feb 2005. Plant Health Progress doi:10.1094/PHP-2005-0304-01-HN. Corresponding author: Ann R. Blount.

The wheat stripe rust [WSR] pathogen, _Puccinia striiformis_ Westend. f. sp. _tritici_(Pst), occurred on several experimental wheat (_Triticum aestivum_ L.) lines planted at the North Florida Research and Education Center in Quincy, Gadsden Co., FL in early February 2003. Several experimental lines in the 2003 Advanced Wheat A (AWA), the Advanced Wheat B (AWB), and the Uniform Southern Wheat Nursery (US) yield trials then showed traces of WSR on leaves of plants. Diseased lines included: FL K-R-7-1-G4-B27-C3 (AWA), FL K-R-7-1-G1-B21-C4 (AWA), FL 90192-W14-Y1-A7-C9 (AWB), FL8524-X7-V1-21-A4-B1-C (AWB), and NC98-26143 (US).

Field plots were 55 sq ft (5.11 sq m) and arranged in a randomized complete block design with 2 replications. By April 2003, susceptible lines had developed rust severity ranging from 80 to 100 percent, with infection on leaves and leaf sheaths. WSR was prevalent throughout the plots, indicating a uniform rust distribution.

Pst-infected leaf samples were analyzed for virulence factors and race identification on a known set of wheat lines near-isogenic for single genes for WSR resistance and differential genotypes currently used to differentiate races of Pst in North America. An isolate collected from the wheat line FL8524-X7-V1-21-A4-B1-C was classified as race PST-78 (virulent on Lemhi, Heines VII, Lee, Fielder, Express, Yr8, Yr9, and Clement). The isolate from wheat line FLK-R-7-1-GH-B27-C3 was identified as PST-80 with virulence on the same differential genotypes as PST-78 plus Produra.

These 2 races were 1st isolated in 2000 from samples analyzed from the south central U.S. (Texas, Arkansas, Louisiana, etc.) and California. In 2001, PST-78 and PST-80 dominated rust populations prevalent in south central and central states (i.e., Kansas, Nebraska, and South Dakota). By 2002, these races were prevalent throughout the U.S. (X. M. Chen, unpublished data).

An isolate from wheat line NC98-26143 was identified as race PST-97 with virulence on the same differential genotypes as PST-78 plus Stephens. An isolate from wheat line 90192-W14-Y1-A7-C9 was identified as PST-98, which has virulence on the same differential genotypes as PST-80 plus Stephens. These 2 races were 1st detected in 2002 throughout the United States (X. M. Chen, unpublished data). The 4 races (PST-78, PST-80, PST-97, and PST-98) isolated from wheat lines in Florida also were commonly detected throughout the U.S., especially in Texas, Louisiana, Arkansas, Oklahoma, and Georgia in 2003 (X. M. Chen, unpublished data).

Pst only infects members of the _Poaceae_ family, with wheat and triticale (X _Triticosecale_ Wittmack) being the primary hosts. Several wild grasses, including wheatgrass (_Agropyron_ spp.), bromegrass (_Bromus_ spp.), and
Virginia wild rye (_Elymus virginicus_ L.), which are not commonly found in Florida, are less important hosts. WSR is worldwide in distribution in wet areas with cool temperatures, especially in mountainous and upland areas. In the United States, WSR frequently occurs in western states like California, Washington, Idaho, and Oregon.

In Florida, wheat is typically planted in late fall and harvested in late spring. Most wheat grown in the state is used for livestock grazing or wildlife forage plots, although some is milled for use in products requiring soft red winter wheat. Wheat occupies approximately 10 000 acres in the state (2002 Florida Agricultural Statistics).

An unusually cool and wet winter and spring encouraged a scattered outbreak of WSR on susceptible experimental wheat lines.

This report constitutes the 1st documented case of WSR in Florida. Several fungicides are registered by EPA for control of WSR, however, these products may not be legal if wheat is grazed by livestock. If a fungicide application is warranted, it should begin at the 1st sign of disease.

Literature cited:

1. CAB International. 2002. Crop Protection Compendium, 2002 edition. _Puccinia striiformis_. CAB International, Wallingford, Oxan, UK. CD version.

2. Chen, X. M., and Moore, M. K. 2002. Epidemics and races of _Puccinia striiformis_ in North America in 2001. Phytopathology 92:S14.

3. Chen, X. M., Moore, M., Milus, E. A., Long, D. L., Line, R. F., Marshall, D., and Jackson, L. 2002. Wheat stripe rust epidemics and races of _Puccinia striiformis_ f. sp. _tritici_ in the United States in 2000. Plant Dis. 86:39-46.

4. Florida Automated Weather Network. 2004. FAWN archived weather data. Online. Inst. Food Agric. Sci., Univ. of Florida.

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[Common bread wheat/spring wheat, _Triticum aestivum_ is typically planted in Florida in late November to early December and harvested in late April to May, predominantly in the panhandle counties. Wheat occupied ca. 10 000 acres in the 2003 growing season. Unusually cool and wet spring weather encouraged a scattered outbreak of WSR on susceptible varieties. WSR was 1st noticed on experimental wheat lines planted by the Institute of Food
and Agricultural Sciences (IFAS) spring wheat breeder at North Florida Research and Educational Center (NFREC) in Quincy, Florida in early February 2003. Florida wheat breeders and growers have had little reason to be concerned about this rust in the wheat cultivars grown in Florida. In 2004, WSR infections in the southern US were less severe and extensive than last year and therefore will provide less inoculum for the northern wheat growing area.

Yield losses can be severe if the rust appears at flag leaf (boot) or anthesis stage, since the flag leaf is known to contribute 30-40 percent of the grain filling (yield). Management of WSR in Florida is likely to be minimal, but only time will tell. Disease management will depend upon use of resistant varieties with multiple genes for both seedling and adult plant resistance, applications of EPA-approved foliar systemic and contact fungicides registered for WSR on wheat. If fungicides are warranted, application should begin at the 1st sign of disease. A last resort would be to remove wild hosts to reduce inoculum, especially that which over-winters.

Links:
<http://www.doacs.state.fl.us/pi/enpp/pathology/striperust.html>
<http://www.plantmanagementnetwork.org/pub/php/brief/2005/stripe/>
- Mod.DH]