Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2006
Publication Date: 6/1/2006
Citation: Bruckart, W.L. 2006. Supplemental risk evaluations of puccinia jaceae var. solstitialis. Biological Control 37:359-366 for biological control of yellow starthistle. Biological Control.
Interpretive Summary: A rust fungus called Puccinia jaceae var. solstitialis (PJ) is being tested, because it might be useful to control yellow starthistle (YST), a very important weed in the United States (US). More tests were made with native thistles and a crop plant, safflower, to make sure that this fungus does not infect or damage them. These tests were the last in study on risk of PJ to important US plants. All tests were made in a special containment greenhouse on plants that had not been studied before, new thisles and new safflower varieties. Leaves of 19 different thistles and 11 safflower varieties were inoculated with spores of the fungus and given dew that made infection possible, if the plants were susceptible to infection. None of the new thistles were infected and only a few infections, similar to some noted before, were found on the safflower varieties. It was not possible to keep PJ alive on any of the test plants, even with the best conditions in the greenhouse. Also, it was not possible to get infection of safflower seedlings with another kind of PJ spore (the teliospore). In this test, similar spores of a fungus from safflower, called Puccinia carthami, caused large cankers on seedlings. It is evident that native Cirsium spp. and modern safflower cv will not be damaged by PJ in nature, if it is used for biological control of the weed, YST.
Technical Abstract: Additional tests of native North American Cirsium species and modern safflower cultivars (cv) were requested by regulators and specific interest groups during the risk assessment of foreign isolates of Puccinia jaceae var. solstitialis (PJ) for biological control of yellow starthistle (Centaurea solstitialis) in the United States (US). These results completed a risk assessment of PJ, supplementing data from previous host-range tests. Evaluations were conducted in a containment greenhouse and included new Cirsium species and new safflower cv that were high in oleic or linoleic acid. Foliage of 19 Cirsium spp. and 11 safflower cv was inoculated with urediniospores and given a 16-hr dew period at 18-20oC. None of the Cirsium species became infected and only minor infections, similar to those in earlier studies, occurred on the modern safflower cultivars. PJ could not be maintained under optimal greenhouse conditions on the foliage of any test plants. Also, quantitative PJ teliospore infestation of safflower hypocotyls did not cause infection, even though large cankers were observed on safflower plants inoculated with P. carthami. Clear microscopic evidence of infection was observed also in safflower hypocotyls following inoculation of with P. carthami. Native Cirsium spp. and modern safflower cv are not susceptible to or damaged by PJ from YST.