First Report of Cylindrocarpon liriodendri Causing Black Foot Disease of Grapevine in California.

Black foot disease is a recently identified but worsening problem in vineyards worldwide (2). Roots of symptomatic grapevines show black, sunken, necrotic lesions (2). In cross section, the base of the trunk appears necrotic and xylem vessels are plugged with black inclusions and tyloses (2). Aboveground, leaves of infected vines appear to be scorched, and the entire vine becomes stunted and frequently dies (2). In California, we previously identified two Cylindrocarpon species as causal agents of this disease: C. macrodidymum and C. destructans (2). In earlier molecular phylogenetic studies, tremendous variation in C. destructans from diverse hosts was found, indicating that this species might encompass more than one species (2). On the basis of analysis of sequences of three independent DNA regions, we concluded that the group of C. destructans isolated from grapevines in France, South Africa, and California have nearly identical sequences and form a well-supported sister clade divergent from the clade containing C. destructans found in numerous hosts (2). Further studies compared DNA sequences of C. destructans causing black foot in France, Portugal, and South Africa with an ex-type strain of C. liriodendri isolated from tulip poplar (Liriodendron tulipifera) (1). Because these species had identical sequences, C. destructans causing black foot in France, Portugal, and South Africa was renamed C. liriodendri (1). The objective of the current study was to clarify the taxonomy of C. destructans causing black foot in California. We compared C. liriodendri isolate CBS112602 from South Africa (1) with three C. destructans isolates (USME116, USST148, and USSO150) from California (2). We analyzed four sequences on three genomic regions: the internal transcribed spacer of ribosomal DNA, partial sequences of the beta tubulin gene, and the mitochondrial small subunit ribosomal DNA. We used sequences from the South African C. liriodendri isolate CBS112602 (AY997566, AY997586, AY997581, and AY997532) and sequences from Californian isolates of C. destructans (AY997568, AY997588, AY997534, AY997583, AY997569, AY997601, AY997547, AY997584, AY997570, AY997598, AY997544, and AY997585) previously deposited in GenBank (2). Sequences were aligned using Clustal X 1.8 (3). On the basis of visual inspection of each DNA region alignment, the South African C. liriodendri isolate was identical to Californian isolates of C. destructans. Thus, Californian isolates of C. destructans causing black foot (2) are renamed C. liriodendri. To our knowledge, this is the first report of C. liriodendri causing black foot disease of grapevine in California. References: (1) F. Halleen et al. Stud. Mycol. 55:227, 2006. (2) E. Petit and W. D. Gubler. Plant Dis. 89:1051, 2005. (3) J. D. Thompson et al. Nucleic Acids Res. 25:4876, 1997.