Characterization of Cylindrocarpon Species, the Cause of Black Foot Disease of Grapevine in California.

This study investigated phylogenetic divergence, morphological difference, and pathogenic variation among Cylindrocarpon species isolates associated with black foot disease of grapevine (Vitis sp.) in California. To assess phylogenetic divergence, we sequenced the internal transcribed spacer (ITS) of the nuclear ribosomal DNA (rDNA), partial beta-tubulin (BT) gene introns and exons, and the small subunit mitochondrial rDNA. Isolates associated with black foot disease belonged to two paraphyletic species, Cylindrocarpon destructans and C. macrodidymum. The morphology of these isolates was in agreement with published descriptions of both species. We found that C. macrodidymum isolates were reliably distinguishable from C. destructans isolates in culture by a unique orange-dark brown colony color on 2% malt extract agar and genetically by a species-specific 52-bp DNA insertion in the BT region. Selected isolates of each species inoculated onto grapevine rootstock 5C caused typical black foot disease symptoms. This is the first report of C. macrodidymum in California.