SPECIES IDENTIFICATION AND VARIATION IN THE NORTH AMERICAN CRANBERRY FRUIT ROT COMPLEX

Abstract

Many different species of pathogenic fungi cause cranberry fruit rot. The contribution of any given species can be quite variable depending on a host of cultural and environmental factors. Control of fruit rot can be problematic in the Northeast and in other growing regions since losses due to fruit rot can be episodic. One possible cause for inadequate control is that pathogenic fungi typically have differential sensitivity to fungicides. Thus, variation in the species or populations of the fungi present can affect the success and quality of control. Our primary objective in this project was to determine the variation within five species of cranberry fruit rot pathogens (Phyllosticta vaccinii, Coleophoma empetri, Colletotrichum acutatum, Colletotrichum gloeosporioides, and Physalospora vaccinii) across geographic regions [NJ, MA, WI and British Columbia (BC)] using morphologic and molecular characters. Our secondary objective was to reexamine the taxonomy of these pathogens at the molecular level, particularly those that are cranberry- or Vaccinium species-specific. Our results suggest that morphologically, within-species variation was low. We did however collect atypical non-pigmented C. acutatum from BC and Physalospora vaccinii isolates from all regions varied from dark gray to pure white on V8 juice agar medium. Molecular analysis of ribosomal ITS sequences showed a low level of variability for most pathogen species, with the exception of the morphologically distinct isolates. Phylogenetic analysis showed that the atypical, non-chromogenic C. acutatum formed a distinct, but closely related clade, to the normal pink-pigmented isolates. In contrast, the pure white isolates of Physalospora vaccinii possessed an ITS sequence distinct from those of the gray strains, suggesting they may represent a different species.