J.M. MANNERS^1,2 and C. HE²

¹CSIRO, Tropical Agriculture, St Lucia, Queensland, Australia
²Co-operative Research Centre for Tropical Plant Pathology, University of Queensland, Australia

Abstract

Two biotypes (A and B) of Colletotrichum gloeosporioides that cause anthracnose diseases on Stylosanthes spp. have been recognised in Australia. In this paper, aspects of the molecular genetic relations of these biotypes are reviewed. The biotypes are genetically distinct and are distinguished by many DNA polymorphisms. In contrast, isolates within each biotype exhibit near-monomorphy at the molecular level. These observations indicate that a probable origin for each biotype was by separate clonal descent from 2 introductions into Australia. Mechanisms that may generate genetic variation have been studied recently. A retrotransposon specific to Biotype B has been described and represents the first transposable element described in the genus, Colletotrichum. Evidence from both the field and the laboratory indicates that the selective transfer of at least one specific chromosome from Biotype A to Biotype B has occurred. Transient, slow-growing heterokaryons formed between the biotypes may be an intermediate stage in this chromosome transfer. At present, the limited genetic recombination between biotypes that has been observed does not appear to have affected virulence patterns greatly. Current research, therefore, indicates that, although the biotypes appear to be mainly genetically isolated from each other, the potential for genetic recombination between them does exist. Recombination with other newly introduced biotypes would present a considerable threat to the Australian pasture industry.