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Title: Population structure of the North American cranberry fruit rot complex

item Polashock, James

Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/27/2009
Publication Date: 11/9/2009
Citation: Polashock, J.J., Oudemans, P.V., Caruso, F.L., Mcmanus, P., Crouch, J. 2009. Population structure of the North American cranberry fruit rot complex. Plant Pathology. 58:1116-1127.

Interpretive Summary: Cranberry fruit rot (CFR) is a very difficult disease to control because it is caused by many different fungi. In order to improve disease management strategies, it is important to know which fungi are present and how the species composition differs among growing areas. To do this, we collected and characterized CFR- causing fungi from three states and British Columbia. We found that within most species there was little variation among regions. However, some exceptions were found and this could be of concern since new variants are likely to respond differently to control measures. This information will be used by scientists and extension agents testing new control strategies for CFR.

Technical Abstract: Cranberry fruit rot (CFR) is caused by any one of thirty species of pathogenic fungi, with the contribution of any given species varying from bed to bed, year to year, and region to region. Because cranberry vines are shipped between growing regions for propagation, we hypothesized that a concurrent movement of the associated fungi might result in a convergence of CFR pathogen genotypes. To begin to examine this theory, we assessed the morphological and genetic variation of five of the most common CFR pathogens (Phyllosticta vaccinii, Coleophoma empetri, Colletotrichum acutatum, Colletotrichum gloeosporioides, and Physalospora vaccinii) and further attempted to verify taxonomic placement of these pathogens. Representative samples of each species were isolated from rotted fruit collected from NJ, MA, WI, and British Columbia (BC). All isolates were identified using morphological criteria. Some isolates were atypical. For example, non-chromogenic isolates of C. acutatum were found in BC and atypical white isolates of Physa. vaccinii were found in NJ and WI. The white isolates of Physa. vaccinii also possessed spore morphology distinct from the dark isolates. ITS sequence data showed that variation was generally narrow (98-100% nucleotide similarity) between individuals in each of the five CFR species. However, the sequence analysis also showed that the non-pigmented C. acutatum form a distinct, but closely related clade, relative to the pigmented isolates. In contrast, the white isolates of Physalospora show a unique ITS sequence, suggesting these isolates represent either a different species or highly divergent population. On the basis of ITS sequence analysis, it appears that Physa. vaccinii, Phyllo. vaccinii, C. empetri, C. gloeosporioides and C. acutatum are genetically uniform on the cranberry host in North America