CSIRO PUBLISHING www.publish.csiro.au/journals/app Australasian Plant Pathology, 2004, 33, 559–569 Morphological and molecular discrimination of Colletotrichum truncatum causing anthracnose on lentil in Canada R. Ford A,D , S. Banniza B , W. Photita C andP. W. J. Taylor A A BioMarka, Joint Centre for Crop Innovation, Institute of Land and Food Resources, University of Melbourne, Vic. 3010, Australia. B Crop Development Centre, College of Agriculture, The University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5A8, Canada. C Department of Biology, Faculty of Science, Chiang Mai University, Chiang Mai, 50200, Thailand. D Corresponding author. Email: rebeccaf@unimelb.edu.au Abstract. Colletotrichum truncatum is an important exotic pathogen threat to the Australian lentil industry. Canadian isolates of C. truncatum from lentil were assessed for morphological and molecular differences against Australian and international isolates of C. truncatum from hosts other than lentil and other Colletotrichum species. Although similar in dimension, conidiospores from lentil C. truncatum were ellipsoidal and those from C. truncatum originating from Australian Glycine max, Xanthium occidentale and Arachis hypogaea were falcate in shape. Conidiospores of Australian C. trifolii, C. gloeosporioides and C. destructivum were cylindrical. Molecular analysis, using both RAPD markers and 18–25S rDNA sequences, demonstrated the genetic relatedness of C. truncatum isolates from the same host species and discriminated among isolates from lentil and other host species. The Canadian isolates of C. truncatum from lentil formed a single distinct cluster, separate from that of the C. truncatum isolates originating from other legume host species and other Colletotrichum species from within and outside Australia. Conserved nucleotide sequence was used to develop a sensitive and highly specific diagnostic marker for the Canadian lentil isolates. The marker detected the pathogen in as little as 0.1 ng of DNA from infected plant tissue and represents a major step towards preventing or delaying the introduction and establishment of lentil anthracnose in Australia. Introduction The fungal pathogen Colletotrichum truncatum causes anthracnose on legume crops worldwide (Barbetti 1985; Hartman et al. 1986; Kaiser et al. 1998). In particular, anthracnose is an important disease of lentil and has been detected on lentil in the northern United States (Venette et al. 1994). It causes widespread disease and yield losses throughout the Canadian lentil-growing regions of Manitoba and Saskatchewan (Buchwaldt et al. 1993; Anderson et al. 2000). In Canada, growers are reliant upon fungicides and crop rotations since only partial resistance is available (Chongo and Bernier 1999). A recent screening of 1772 lentil accessions from the World Lentil Collection identified 16 accessions with varying levels of resistance. Using six of these accessions as a differential set, two pathotypes of the fungus were proposed (Ct0 and Ct1). So far, no resistance to Ct0 has been found (L. Buchwaldt, personal communication) and a monogenic resistance mechanism to an isolate of the Ct1 pathotype was recently characterised (Tullu et al. 2003). In Australia, anthracnose of lentil is classified as an exotic disease, which poses a large threat to the expanding lentil industry since all Australian lentil cultivars were highly susceptible when tested in Canada (Lindbeck et al. 2001). Although C. truncatum exists in Australia on other host legume species (Barbetti 1985; Walker et al. 1991), the disease has not yet been detected in any commercial lentil crops or experimental plots (K. Lindbeck, personal communication). This is despite the previous lack of quarantine on importing lentil seed sourced from Canadian and USA breeding programs, and the seed-borne transmission of the pathogen. Therefore, there is great concern that if a lentil-infecting pathotype of C. truncatum is brought into Australia, given the correct environmental conditions, an epidemic may occur. The pathogen is capable of surviving for up to 4 years as microsclerotia in crop residue and may become active again when in contact with fresh host tissue, spreading as conidia with rain splash and on plant debris through wind dispersal between crops (Buchwaldt et al. 1996). Much like the lupin disease caused by related © Australasian Plant Pathology Society 2004 10.1071/AP04058 0815-3191/04/040559