Field damage to yellow starthistle infected by Synchytrium solstitiale, and greenhouse maintenance and host range of the fungus

Authors: Eskandari, Farivar; Bruckart, William; Widmer, Timothy

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2011
Publication Date: 4/6/2011
Citation: Eskandari, F., Bruckart, W.L., Widmer, T.L. 2011. Field damage to yellow starthistle infected by Synchytrium solstitiale, and greenhouse maintenance and host range of the fungus. Plant Disease. DOI: 10.1094/PDis-2-11-0139.

Interpretive Summary: Yellow starthistle is a very important weed in the United States. Recently, very sick plants were found in France. They were damaged by a fungal pathogen that causes False Rust Disease. Infected plants in a French study were much smaller and had half as many flowers then healthy controls. The pathogen was sent from France to the United States (U.S.) for more study in a special greenhouse to see if it would be safe to use for control of this weed in the U.S. Ways to grow the pathogen were tested. Good infections occurred using several different methods of inoculation, and one method was chosen for a study to test if the pathogen would infect other plants. For this method, a piece of leaf with the fungus in it was enclosed in the test plant leaves, which were then wrapped with a plastic wrap. Plants were put into an incubator with cool temperatures for 3 days and then moved into a greenhouse. After 10 days, symptoms of the disease appeared. Using this method, the pathogen was found to infect plants besides yellow starthistle, including safflower and some important plants that are from the U.S. For this reason, a decision has been made not to use this pathogen for biological control in the U.S.

Technical Abstract: Synchytrium solstitiale damaged yellow starthistle (YST) plants in the field in France, causing reductions of 58, 82, 20, and 56 percent in plant height, plant area, stem diameter, and capitula production, respectively, compared to controls. It was therefore evaluated for biological control in the United States (U.S.). Greenhouse evaluation and risk assessment in containment in the U.S. involved rosette inoculations with galled leaf tissue; plants were incubated for 3 days in a growth chamber (10/15oC, night/day, 8 hr photoperiod) before benching in a greenhouse. Exhumed plants (plants washed of soil and put into flasks of water) had twice the ratio of infected leaves than plants growing in soil. Wrapping leaves of potted plants around galled tissue using a plastic wrap also resulted in very good infection and was used during the host range determination. YST was most susceptible to infection by S. solstitiale, but good infection occurred also on safflower (Carthamus tinctorius). To a lesser extent, infections occurred on a few weedy Centaurea species, and three native North American species, i.e., Plectocephalus americanus, P. rothrockii, and Cirsium neomexicana. The non-target infections preclude proposal of S. solstitiale for biological control of YST at this time.