Genetic diversity and systematics of Colletotrichum species on cranberry (Vaccinium macrocarpon)

Cranberry fruit rot is a major problem for cranberry production in North America. One common causal agent, Colletotrichum gloeosporioides, is poorly understood from both a taxonomic and epidemiological viewpoint. In this project, a repetitive DNA element was cloned and characterized from a cranberry isolate of C. gloeosporioides. This element, designated Cgret (C&barbelow;. g&barbelow;loeosporioides retrotransposon), represents the first member of the gypsy group of long terminal repeat retrotransposons in this fungal species. Cgret was present in all of the cranberry isolates of C. gloeosporioides tested from New Jersey and Massachusetts, but was not in the isolates tested from Wisconsin or Chile. Polymorphic banding patterns were detected among C. gloeosporioides isolates from various hosts and geographic locations using hybridization probes derived from Cgret.;To determine if the retrotransposon was active, a C. gloeosporioides isolate containing Cgret sequence was grown on the toxic chemical potassium chlorate and spontaneous nitrate reductase-deficient (nit) mutants were generated. Molecular analysis of these mutants and the parental isolate demonstrated appearance of novel bands with homology to Cgret sequences as well as loss of some bands. In a collection of 16 C. gloeosporioides field isolates, a deletion in the Cgret sequence was detected among 11 of the isolates. These data suggest the retrotransposon is active in the genome of C. gloeosporioides. Northern blot analysis indicated that the Cgret is transcribed. However, no difference in the levels of transcription were detected in isolates grown on toxin containing media versus those grown without. Cgret may contribute to the generation of genetic diversity observed in the C. gloeosporioides fungal populations on cranberry.;The genetic relatedness of Colletotrichum fungal isolates from 5 different cranberry-growing regions, and the phylogenetic positions of these cranberry pathogens in the genus Colletotrichum were analyzed. The internal transcribed spacers (ITS) sequence of the rDNA repeat units, sensitivity to the fungicide benomyl, and the distribution of Cgret retrotransposon in their genomes demonstrated the presence of two species. Isolates from Washington and Wisconsin were classified as C. acutatum, and the isolates from Massachusetts and Chile were C. gloeosporioides. Both species were present on cranberry from New Jersey.