|AIME, MARY - Louisana State University|
Submitted to: Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/2012
Publication Date: 5/31/2012
Citation: Bruckart, W.L., Eskandari, F., Berner, D.K., Aime, M.C. 2012. Comparison of Puccinia acroptili from Eurasia and the USA. Botany. 90:465-471.
Interpretive Summary: Russian knapweed is a rangeland weed pest in the United States (U.S). It is diseased by a fungus called Puccinia acroptili. This fungus occurs on Russian knapweed in North America, but it does not control it. For this reason, new isolates from Europe and Asia were studied for biological control. Comparisons of the foreign isolates with those from the U.S. included how the different isolates looked morphologically and how the DNA compared. Isolates from Europe, Asia, and the U.S. were studied to learn if other isolates of this fungus might be useful to control the weed. It was found that U.S. isolates have shorter overwintering spores, but they were also significantly wider than the isolates from Eurasia. The DNA was very similar; only small differences were found between isolates. The isolates also caused the same amount of disease on inoculated plants that came from Colorado. For these reasons, the U.S. and Eurasian isolates can be considered a single species, i.e., P. acroptili. Also, study of new isolates for biological control of Russian knapweed is not recommended.
Technical Abstract: Russian knapweed (Rhaponticum [= Acroptilon] repens) is a rangeland weed pest in the western United States (U.S). A rust disease caused by Puccinia acroptili occurs on Russian knapweed in North America but does not control it. Evaluations of new, Eurasian isolates of P. acroptili for biological control included comparisons, i.e., morphological and molecular, and crosses, with U.S. isolates to determine similarity. In an earlier limited comparison by Savile (Can. J. Bot. 48:1567-1584), a U.S. specimen was reported to have shorter teliospores than one from Turkey, thus suggesting potential differences exist among isolates of this fungus. Detailed comparisons with additional isolates were made when considering evaluation of new, Eurasian isolates of P. acroptili for biological control of R. repens. Morphologically, U.S. isolates were found to have shorter teliospores, as suggested by Savile, but they also are significantly wider in diameter than isolates from Eurasia. DNA sequence analyses of the nuclear rDNA large subunit and internal transcribed spacer regions also revealed small levels of variation between isolates from Turkey, Russia, Kazakhstan, and the U.S. Biologically, the isolates were the same; all were equally aggressive on the single accession of R. repens from Colorado used in inoculations, and fertile crosses occurred between isolates regardless of source. For these reasons, it has been concluded that U.S. and Eurasian accessions can be considered a single species, i.e., P. acroptili, and that additional collecting for candidate biological control isolates is not justified for this organism.