In November 2010, four grapevine plants of cv. Crimson from a vineyard located in Sevilla (south Spain) revealed trunk cankers. Several pathogens were isolated, including Cylindrocarpon liriodendri (2), Phaeoacremonium aleophilum (2), Pleurostomophora richardsiae, Neofusicoccum parvum, and Botryosphaeria dothidea (2). Among Botryosphaeriaceae fungi isolated on potato dextrose agar (PDA) were two types that did not fit the above mentioned species. Isolates of type 1 produced an abundant, gray mycelium with a diurnal zonation that gradually became dark olivaceous. Mycelium growth occurred from 5 to 37°C with an optimum at 28°C. Conidia were hyaline, fusiform, aseptate, thin walled, but gradually became obscured and septate with age, and measured (18.4-) 21.4 (-24.3) × (4.2-) 5.5 (-7.2) μm with a length/width (L/W) ratio of 4.0 ± 0.5 (n = 100). Isolates of type 1 were identified as N. mediterraneum (3). Single-spore cultures of type 2 developed a whitish, dense, aerial mycelium and remained white up to 10 days on PDA and darkened to gray thereafter. Mycelium growth occurred from 3 to 37°C with an optimum at 29 to 30°C. Conidia were hyaline, aseptate, thick walled, oblong to cylindrical, sometimes becoming light brown and one or two septate after discharge, and measured (24.6-) 30.2 (-42.8) × (10.9-) 14.3 (-18.6) μm with a L/W ratio of 2.1 ± 0.2 (n =100). Isolates of type 2 were identified as Diplodia corticola (1). Nucleotide sequences of the ribosomal internal transcribed spacer (ITS) region and the β-tubulin genes were used to confirm the identifications through BLAST searches in GenBank. Comparison of the sequences of types 1 and 2 showed 99 to 100% homology with N. mediterraneum (HM443604 (4) and GU251836) and D. corticola (AY268421 (1) and EU673117), respectively. Representative sequences of N. mediterraneum (JF949757 and JF949756) and D. corticola (JF949758 and JF949759) were deposited in GenBank. The pathogenicity of one representative isolate of each of N. mediterraneum and D. corticola was confirmed by inoculating 10 detached grapevine canes (averaging 12 mm in diameter and 30 cm long) per isolate. A shallow wound was made with a scalpel on the internodes. A colonized 6-mm agar plug, from the margin of an actively growing colony, was inserted in every wound and sealed with Parafilm. Ten grapevine canes controls received only sterile PDA agar plugs. Canes were maintained at 25°C and 70% humidity. After 5 weeks, all inoculated canes developed cankers and pycnidia around the inoculation site. Vascular necroses that developed on the inoculated canes were an average of 28.6 mm for N. mediterraneum and 27.7 mm for D. corticola. One-way analysis of variance and Tukey's test confirmed significant differences in the extent of vascular necroses. The average necroses length in the inoculated canes was significantly greater (P < 0.05) than the average length of discoloration induced by the simulated inoculation process in the control. Both pathogens were reisolated from all inoculated plants but not from controls. To our knowledge, this is the first report of N. mediterraneum and D. corticola as pathogens on grapevine in Spain.
References: (1) A. Alves et al. Mycologia 96:603, 2004. (2) A. Aroca and D. Gramaje et al. Eur. J. Plant. Pathol. 126:165, 2010. (3) P. W. Crous et al. Fungal Planet. No. 19, 2007. (4) F. P. Trouillas et al. Plant. Dis. 94:1267, 2010.
