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Grapevine Trunk Diseases in British Columbia: Incidence and Characterization of the Fungal Pathogens Associated with Black Foot Disease of Grapevine

Black foot disease of grapevines, caused by several fungal species in the genera Campylocarpon, Cylindrocarpon, Cylindrocladiella, and Ilyonectria, causes significant economic losses to the grapevine industry worldwide. This study represents the first attempt to identify and characterize the fungal pathogens associated with black foot disease of grapevines in British Columbia (BC). Field surveys conducted throughout all grape-growing regions in BC that included assessment of foliar symptomatology and isolations from symptomatic vines showed Cylindrocarpon/Ilyonectria spp. occurred in 32 of 90 (35.5%) young vineyards surveyed (≤8 year old) and in 41 of 215 (19%) samples collected. In 20 of the 41 (48.8%) samples, Cylindrocarpon/Ilyonectria spp. were the sole fungi isolated from symptomatic tissue. In the rest of the samples, black foot fungi were found to primarily coexist with fungal taxa associated with Petri disease of grapevines. Colony and conidia phenotypical characterization, along with DNA analyses of the internal transcribed spacer region (ITS1-5.8S-ITS2) of the rDNA, and part of the β-tubulin and translation elongation factor 1-α genes, revealed five different black foot fungi occurring in declining young vines in BC, namely Cylindrocarpon pauciseptatum, Ilyonectria liriodendri, Ilyonectria macrodidyma, Ilyonectria robusta, and Ilyonectria torresensis. Pathogenicity studies showed all five species to be highly virulent in the grapevine rootstock cultivar 3309C. Overall, I. liriodendri and I. macrodidyma were the most virulent species when inoculated in Vitis vinifera ‘Chardonnay’ and rootstock 3309C.