During a survey for grapevine decline, 10 young grapevines (cvs. Tempranillo and Verdejo) with low vigor and little foliage were collected between June 2008 and August 2009. Small pieces of vascular and brown wood were placed onto malt extract agar supplemented with 0.25 g/liter of chloramphenicol and incubated at 25°C. Fifteen resulting colonies were transferred to potato dextrose agar in petri dishes (90 mm). Colonies with white mycelium covered the dishes after 10 days of incubation at 25°C in darkness; mycelium gradually became yellowish with some brownish aspect. Macroconida were predominantly three septate (40 to 45 to 50 × 8.6 to 9 to 9.5 μm with a length and width ratio of 4.7 to 5 to 5.4), straight, and cylindrical with both ends broadly rounded. Chlamydospora and ovoidal microconidia were observed on synthetic nutrient-poor agar (1). Cylindrocarpon pauciseptatum was not easy to distinguish from other Cylindrocarpon species based on morphological characteristics. Ribosomal internal transcribed spacer region sequences of single-spore cultures confirmed the morphological identification and revealed 100% genetic identity with other isolates of C. pauciceptatum present in GenBank (EF607090), a sequence of the fragment was deposited with Accession No. EU983277. Pathogenicity tests were conducted with two isolates. The inoculations were done on 110R rootstock wood of four different young plants and 15 detached canes of current-season growth (cv. Tempranillo). Plants were inoculated with an agar plug containing C. pauciceptatum; controls were treated with agar only. Grapevines were maintained in a greenhouse at 20 to 25°C. After 3 to 4 months, C. pauciceptatum was reisolated from brown tissues and internal vascular lesions in 45% of inoculated samples, fulfilling Koch's postulates. Control plants were asymptomatic and C. pauciceptatum was not recovered. To our knowledge, this is the first report implicating C. pauciceptatum as a cause of grapevine black foot disease in Spain with potentially significant impact on grapevine nurseries.
Reference: (1) H. J. Schroers et al. Mycol. Res. 112:82, 2008.
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