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Research Project: DISCOVERY AND CHARACTERIZATION OF PLANT PATHOGENS FOR BIOLOGICAL CONTROL OF INVASIVE WEEDS FROM THEIR NATIVE RANGE

Location: Foreign Disease-weed Science Research

Title: Risk assessment and implications of common crupina rust disease for biological control

Author
item Bruckart, William - Bill
item Eskandari, Farivar
item Berner, Dana

Submitted to: Journal of Invasive Plant Science Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/31/2015
Publication Date: 1/15/2016
Citation: Bruckart, W.L., Eskandari, F., Berner, D.K. 2016. Risk assessment and implications of common crupina rust disease for biological control. Journal of Invasive Plant Science Management. 9:33-40.

Interpretive Summary: Common crupina is an invasive plant in the United States (USA) that is very difficult to control and continues to spread within the states of California, Idaho, Oregon, and Washington. Differences within crupina are also known in the USA, there are two varieties, and each variety has great potential to infest very large parts of the region. There are no diseases that damage crupina in the USA, but there is a fungus disease where it occurs in Europe. It is a candidate for classical biological control in the USA, but before this disease can be used in the USA, it must be tested and found capable of damaging crupina and not any other important plant. Results of this evaluation show that the fungus damages crupina from California (Santa Rosa), Idaho, and Washington, but not from the location at Modoc, California. After multiple inoculations, the number of seeds was 40 percent less than in the controls, except for plants from Modoc, California, which were infected but not damaged in this study. Reduction in seed yield is an important objective of classical biological control, because seeds are the only way that crupina survives. Other yield effects were noted, as well, also with the exception of crupina from Modoc, California. The fungus did not infect any plants related to crupina, including some that are commercially-important and others valued as natives, so it is considered safe for classical biological control. For these reasons, the fungus is considered potentially useful for classical biological control of crupina in the USA, with the possible exception of plants from Modoc, California. The conclusion is that continued evaluation of the fungus is justified, and proposal to regulators for its use in biological control should be considered. Results of this study substantiate earlier findings that the crupina at Modoc, California, is different from the others, requiring additional planning and research, particularly for a better pathogen, if classical biological control of plants from Modoc, California, is pursued. Release of the fungus, if permitted, may result in control of crupina that is taking away food for grazing animals and where land managers and farmers don’t want it.

Technical Abstract: Common crupina is listed as a Federal noxious weed infesting rangelands and pastures in the states of Idaho, Washington, Oregon, and California. Because there is no practical control measure for this plant, and considering its potential to spread extensively at least within the region, an evaluation was made of Puccinia crupinae, a candidate rust fungus, for biological control. Tests were made on susceptibility of four accessions of C. vulgaris representing the two varieties of the target present in the USA. Based upon pustule counts, the number and weight of seeds per plant, and shoot dry weight, after multiple inoculations, three accessions (var. brachypappa from Lake Chelan, WA, var. vulgaris from Salmon River, ID and Santa Rosa, CA) were similarly diseased and damaged. In comparison, an accession of var. brachypappa from Modoc, CA was not damaged by the disease. Signs of the fungus and symptoms on inoculated plants also differed for the two varieties. Host specificity of P. crupinae was indicated by the lack of symptoms on any of 26 taxa of related species in the Tribes Cardueae and Cichoriae, including commercially-important safflower and artichoke as well as natives in the genera Cirsium and Plectocephalus. The lack of disease on the accession from Modoc, CA, confounds the potential for effectiveness of P. crupinae as a biological control candidate, although populations occupying the greatest part of the crupina distribution were damaged in these tests.