Submitted to: Australian Journal of Agricultural Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2004
Publication Date: 1/1/2004
Citation: Mackie, J.M., Musial, J.M., Oneill, N.R., Irwin, J.A. 2004. Pathogenic specialisation with colletotrichum trifolii in australia, and lucerne cultivar reactions to all known australian pathotypes. Australian Journal of Agricultural Research. 54:829-836. Interpretive Summary: Foliar, crown, and stem fungal pathogens cause serious diseases and significant yield losses in alfalfa. Anthracnose disease, caused by the fungus Colletotrichum trifolii, occurs world wide and is one of the most destructive of these diseases. The fungus formerly was known to occur mainly in two forms, or races, that differ in their ability to attack various cultivars of alfalfa. In this study, we discovered that race 2 of the pathogen is no longer confined to the United States but is now present and causing disease damage to alfalfa grown in Australia. In addition, a new race was discovered in Australia that can overcome the race 1 and 2 resistance that is present in U.S. and Australian cultivars. The specific identity of these races was determined by inoculating cultivars of alfalfa with known genetic backgrounds, and by molecular genotype comparisons. This report highlights the need to find new sources of resistance to anthracnose in alfalfa. The research will be used by breeders, seed companies, and research scientists.
Technical Abstract: Anthracnose and crown rot, caused by Colletotrichum trifolii are serious diseases of lucerne (Medicago sativa L.) in humid regions of the world. A race survey was conducted by inoculating individual lucerne clones (genotypes) with C. trifolii isolates collected from a range of Medicago hosts, locations and years in Southeast Queensland. This survey revealed for the first time in Australia the presence of race 2 (virulence on anthracnose resistance gene An1) and the first world report of race 4 (virulence on An2). A collection of North American race 1 and race 2 C. trifolii isolates, when inoculated on to the Australian differential clones, gave responses that were in agreement with their North American reactions. A RAPD analysis was conducted on 10 Australian C. trifolii isolates including races 1, 2 and 4; two C. destructivum and one C. gloeosporioides isolate were included as known outliers. For the C. trifolii isolates, 94.6% similarity was found regardless of host origin or race, compared to 2.1% similarity between this group and the C. gloeosporioides and C. destructivum isolates, confirming that the new races belong to C. trifolii. Currently, it is hypothesised that only plants carrying genes An1 and An2 are resistant to the three races. Of 22 cultivars screened against the three races, only UQL-1, Hallmark and Pioneer 54Q53 had >30% of plants resistant to the three races in separate screenings. The research highlights the need to find new sources of resistance to C. trifolii in lucerne.