Puccinia jaceae is established on Yellow Starthistle (Centaurea solstitialis) in Oregon

Authors: Bruckart, William; Thomas, Jami; COOMBS, ERIC - Oregon Department Of Agriculture; PIROSKO, CARRIE - Oregon Department Of Agriculture

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/13/2015
Publication Date: 11/13/2015
Citation: Bruckart, W.L., Michael, J.L., Coombs, E.M., Pirosko, C.B. 2015. Puccinia jaceae is established on Yellow Starthistle (Centaurea solstitialis) in Oregon. Plant Disease. doi: 10.1094/PDIS-09-15-1042-PDN.

Interpretive Summary: Yellow starthistle (YST) is an important weed of pastures and causes a reduction in productivity of grazing lands in many parts of the United States, including Oregon. A disease that only infects yellow starthiste was tested and deliberately released in California with the expectation that it would control YST. A few years later, between 2009 and 2011, the disease was also released on YST in Oregon using the pathogen that occurred in California. In 2014, scientists from the Oregon Department of Agriculture and the USDA, ARS, FDWSRU at Ft. Detrick, MD, found diseased plants near Myrtle Creek, OR, one of the seven locations were the pathogen was released in Oregon. The disease was seen there twice more in 2014 and again in 2015. Search for more symptomatic plants was made in 2015 near the release site at Myrtle Creek, and some were found 1 km and 5.5 km away from the spot of first release, probably because the small spores were spread by wind. Microscopic study of pathogen samples showed it was the same as the one that was first released in California, and DNA analysis of the pathogen provided evidence that it was also the same. It is certain from this that the disease is now established on YST in Oregon and that it is spreading. YST at other locations in Oregon where the pathogen was released are also being examined to see if symptoms of the disease can be found. Once it is known that a beneficial plant pathogen, that is, one intended to control a weed, is established in the United States, studies are possible on how far the pathogen spreads and how much damage the disease causes to such important weed pests.

Technical Abstract: Puccinia jaceae Otth var. solstitialis isolate FDWSRU 84-71 from the California Department of Food and Agriculture was released under APHIS permit at seven sites in Oregon for biological control of yellow starthistle (Centaurea solstitialis) between May, 2008, and April, 2011. Sites were inspected annually for diseased plants. In June, 2014, symptomatic plants were discovered at the site on NE Dole Rd, 2.6 km north of the intersection with North Main St. in Myrtle Creek, OR (Lat, Long: 43.0326, -123.3185), i.e., 115 m south of the original release site. Presence of the rust disease in 2014 was independently confirmed twice, in July, 320 m North of the first 2014 sighting (Lat, Long: 43.03427, -123.3224), and also in September. Diseased plants were present again in July, 2015, at both of the 2014 locations. The accession (FDWSRU 14-004) was moderately-diseased, with >10 dark-brown uredinia per leaf. Telia were not present. Urediniospores were golden-brown, elliptical or obovate, measured (mean [c.i.], P = 0.05; n = 50) 24.9 [0.6] x 23.8 [0.5] um in length and width, respectively, and had two supraequatorial germpores each, characteristic of P. jaceae var. solstitialis. Genomic DNA was extracted from germinated urediniospores and used for amplification of the ITS1, 5.8S, and ITS2 regions using ITS4 and ITS5 primers. The sequence of FDWSRU 14-004 was identical to that of P. jaceae isolate 84-71 as reported by Yourman and Luster. A survey of the Myrtle Creek area was made in 2015 by randomly examining YST infestations every 1 km for 14 km. This resulted in discovery of diseased plants at locations 0.9 km and 5.5 km southeast and southwest of the original site, respectively. Not all plants within the 14 km radius were diseased. These findings are evidence for the establishment and spread of P. jaceae in Oregon, which was not apparent for at least 3 years after release. Disease on YST is a likely result of the original release made at the Myrtle Creek site, although absolute proof of this is not possible; P. jaceae did not establish in Northern California. Careful examination and monitoring of this and the other Oregon release sites is planned. This is first confirmation of permanent establishment and spread of P. jaceae on YST in Oregon, i.e., outside of California where it has become established Sonoma Co.; near San Pablo Bay.