Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2005
Publication Date: 4/1/2006
Citation: Widmer, T.L., Guermache, F. 2006. Factors affecting infection of yellow starthistle (centaurea solstitialis) by synchytrium solstitiale, causal agent of false rust disease. Plant Disease. 90:425-428 Interpretive Summary: Yellow starthistle is a noxious weed that has invaded the United States from the Mediterranean region. It is a serious pest of pastures, rangelands, croplands, natural areas, and recreational areas. Chemicals can manage YST but because of economic and environmental issues other control methods are sought. A new fungus, causing orange to red galls, was isolated from leaves of yellow starthistle in France. The disease caused by this fungus on yellow starthistle is described and environmental conditions for best infection are described. In addition, other plants that are infected by this fungus are mentioned. The impact is a new biological agent that can reduce the growth and spread of yellow starthistle, thus allowing areas to restore to their native vegetation.
Technical Abstract: Yellow starthistle (Centaurea solstitialis) is an annual invasive weed in the United States with Mediterranean origins. Expense of chemical control and the vast area of invasion make this weed an appropriate target for classical biological control. Observations of a field site in southern France revealed small orange galls on the leaves of young yellow starthistle seedlings identified as the fungus Synchytrium solstitiale. Inoculation of yellow starthistle seedlings with a suspension of zoospores released from infected tissue resulted in infection. Ten days after inoculation, symptomatic orange galls appeared on the exposed tissue. Preliminary host range testing showed up to 100% infection of C. solstitialis seedlings from either France or the U.S. and limited infection of C. squarrosa, C. diffusa, C. americana, C. rothrockii, Helianthus annuus, and Carthamus tinctorius seedlings. No symptoms were observed on Taraxicum officinale, Cynera cardunculus, Cirsium californica, Cirsium occidentale, Centaurea calcitrapa, C. maculosa, and C. sulfurea seedlings. Zoospores were released in a pH range between 4.45 and 8.25 and optimally at a temperature between 5o and 15oC. Infection of yellow starthistle seedlings occurred after a minimum 1 h exposure to a zoospore suspension at 20oC.