Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2009
Publication Date: 7/27/2009
Citation: Bruckart, W.L., Eskandari, F., Berner, D.K., Aime, M.C. 2009. Life cycle of Puccinia acroptili. Mycologia. 102(1):62-68. Interpretive Summary: The weed, Russian knapweed, is diseased by a fungus called Puccinia acroptili. This pathogen has been studied as a candidate for biological control of this very important weed. Although it is a well-known fungus, the life cycle has not been completely described before this report. Recently, under greenhouse conditions, all stages of the fungus were observed and the life cycle fully documented. Isolates from the U.S., Europe, and Asia were examined and found the same. Results confirm that the fungus has only one host (Russian knapweed), an important consideration in determining if this organism is safe for biological control. In addition to those interested in biological control and weed management, information contained in the paper will be of use to mycologists and taxonomists.
Technical Abstract: Russian knapweed (Acroptilon repens) is a rangeland weed pest in the western United States. A rust disease caused by Puccinia acroptili occurs on Russian knapweed in North America but does not control it. Recently, a rust fungus, tentatively identified as a strain of Puccinia acroptili, was collected in Turkey from severely damaged Russian knapweed; greenhouse tests confirmed its potential as a candidate for biological control. Because knowledge of the complete life cycle is essential for identifying good candidates for biological control, additional greenhouse studies were undertaken to elucidate aspects of P. acroptili development not reported in the literature. Severe disease developed both on stems and leaves, particularly after teliospore inoculations. Both spermogonia and aecia developed following teliospore inoculations, as did sori of a uredinial nature, referred to as “uredinoid” pustules. Uredinoid pustules were, on average, 1.8 times as common as spermogonia. Crosses between spermogonia resulted in development of aecia in approximately 30% of the attempts. This is the first description of spermogonia and the first report and description of aecia, aeciospores, and amphispores from P. acroptili. This also is the first report, to our knowledge, of the development of uredinoid pustules from inoculation with teliospores of P. acroptili. Results confirm that P. acroptili is macrocyclic and likely host specific, two important considerations for candidate biological control agents.