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Etiology and Population Genetics of Colletotrichum spp. Causing Crown and Fruit Rot of Strawberry

Isolates of Colletotrichum spp. from diseased strawberry fruit and crowns were evaluated to determine their genetic diversity and the etiology of the diseases. Isolates were identified to species using polymerase chain reaction primers for a ribosomal internal transcribed spacer region and their pathogenicity was evaluated in bioassays. Isolates were scored for variation at 40 putative genetic loci with random amplified polymorphic DNA and microsatellite markers. Only C. acutatum was recovered from diseased fruit. Nearly all isolates from crowns were C. gloeosporioides. In crown bioassays, only isolates of C. gloeosporioides from strawberry caused collapse and death of plants. A dendrogram generated from the genetic analysis identified several primary lineages. One lineage included isolates of C. acutatum from fruit and was characterized by low diversity. Another lineage included isolates of C. gloeosporioides from crowns and was highly polymorphic. The isolates from strawberry formed distinctive clusters separate from citrus isolates. Evaluation of linkage disequilibrium among polymorphic loci in isolates of C. gloeosporioides from crowns revealed a low level of disequilibrium as would be expected in sexually recombining populations. These results suggest that epidemics of crown rot are caused by Glomerella cingulata (anamorph C. gloeosporioides) and that epidemics of fruit rot are caused by C. acutatum.