Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2002
Publication Date: 2/1/2003
Citation: Denoyes-Rothan, B., Guerin, G., Delye, C., Smith, B.J., Minz, D., Maymon, M., Freeman, S. 2003. Genetic diversity and pathogenic variability among isolates of Colletotrichum species from strawberry. Phytopathology. 93:219-228 Interpretive Summary: Strawberry anthracnose has become a major disease of strawberry worldwide often causing millions of dollars of crop loss. Three species of the fungus Colletotrichum are known to cause similar anthracnose symptoms on strawberry. C. acutatum is the most prevalent causal species in Europe. In order to control anthracnose more information is needed about the causal fungi and their movement from crop to crop. Genetic analysis using molecular markers determined that most C. acutatum isolates from strawberry collected in Europe are very similar; however, C. acutatum isolates collected from other hosts in Europe are more variable. Inoculation trials determined that there was not an association between genetic and pathogenicity groupings. Techniques used in this study can be used to study the epidemiology of anthracnose and to develop resistant cultivars. The results of this study will be of greatest importance to plant pathologists and plant breeders trying to develop reliable controls for strawberry anthracnose. The finding that most of the European isolates of C. acutatum from strawberry are genetically identical suggests that anthracnose in Europe may have spread from a single introduction of the pathogen. This emphasizes the importance of strict quarantine laws to prevent the introduction of new pathogens. The development of molecular techniques that quickly and accurately identify the species of the pathogen present will expedite the development of resistant cultivars and serve as a tool for regulatory agencies.
Technical Abstract: Ninety-five isolates of Colletotrichum including 81 isolates of C. acutatum (62 from strawberry) and 14 isolates of C. gloeosporioides (13 from strawberry) were characterized by various molecular methods and by pathogenicity tests. Results based both on RAPD polymorphism and ITS2 sequence data provided clear genetic evidence of two subgroups. The first subgroup was characterized as `CA-clonal' which included only isolates from strawberry, exhibiting identical RAPD patterns and ITS2 sequence analysis, and a larger genetic group `CA-variable' including isolates from various hosts, exhibiting variable RAPD patterns and divergent ITS2 sequence analysis. Within the C. acutatum population characterized from strawberry, the CA-clonal group appeared to be prevalent in Europe (54 of 62 isolates). A subset of European C. acutatum isolates, isolated from strawberry and representing the `CA-clonal' and `CA-variable' groups, were assigned to two pathogenicity groups. No correlation could be drawn between genetic and pathogenicity groups. On the basis of molecular and pathogenicity data, it is proposed that the `CA-clonal' subgroup contains closely related, highly virulent C. acutatum isolates that may have developed host specialization to strawberry. C. gloeosporioides isolates from Europe, which were rarely observed, were either slightly or non pathogenic on strawberry. The absence of correlation between genetic polymorphism and geographical origin in Colletotrichum species suggests a worldwide dissemination of isolates, probably through international plant exchanges.