Phylogenetic relationships and genome organisation of Colletotrichum acutatum causing anthracnose in strawberry

Colletotrichum acutatum is a major plant pathogen which infects a broad range of host plants. Extensive research has been carried out on C. acutatum populations affecting various hosts in different geographical locations, showing a considerable genotypic and phenotypic diversity. Anthracnose, caused by Colletotrichum spp., is the major disease of cultivated strawberry, Fragaria x ananassa. In the present study, the phylogenetic relationships within a worldwide sample of fifty-two C. acutatum isolates collected from different strawberry cultivars have been established, by using ITS sequence analyses. Twenty-nine isolates clustered in the molecular group A2, in which seventeen out of eighteen Spanish isolates were included; this may indicate that the group A2 is the key group in Spain. The molecular polymorphism among C. acutatum isolates was determined by southern-blot hybridisation using a telomeric DNA probe. Results indicated that the minimum number of estimated chromosomes ranges between six and nine. The molecular characterisation of C. acutatum isolates was completed using the Pulsed-Field Gel Electrophoresis (PFGE) technique that resolved from six to nine chromosomal bands, this number being coincident with the number of chromosomes obtained by telomeric fingerprinting. The minimum total genome size was estimated to range from 29 to 36 Mb. Comparison of karyotypes patterns and southern-blot analysis demonstrated a high level of molecular polymorphism among C. acutatum isolates from different origins.