In September 2009, symptoms of grapevine (Vitis vinifera L.) decline were observed on 3-year-old grapevines in a vineyard in Roquetas de Mar (Almeria Province, southern Spain). Affected vines were weak with reduced foliage and chlorotic leaves. Black spots and dark streaking of the xylem vessels could be seen in cross- or longitudinal sections of the rootstock trunk. Symptomatic plants were collected and sections (10 cm long) were cut from the basal end of the rootstocks, washed under running tap water, surface disinfested for 1 min in a 1.5% sodium hypochlorite solution, and washed twice with sterile distilled water. The sections were split longitudinally and small pieces of discolored tissues were plated onto malt extract agar (MEA) supplemented with 0.5 g liter–1 of streptomycin sulfate. Dishes were incubated at 25 to 26°C in the dark for 14 to 21 days, and all colonies were transferred to potato dextrose agar (PDA). A Phaeoacremonium sp. was consistently isolated from necrotic tissues. Single conidial isolates were obtained and grown on PDA and MEA in the dark at 25°C for 2 to 3 weeks until colonies produced spores (2). Colonies were grayish brown on PDA and dark brown on MEA. Conidiophores were short and unbranched and 11.5 to 46 (25.5) μm long. Phialides were often polyphialidic. Conidia were hyaline, oblong-ellipsoidal or allantoid, 2.5 to 5 (4.2) μm long, and 1 to 1.7 (1.2) μm wide. On the basis of these characters, the isolates were identified as Phaeoacremonium krajdenii L. Mostert, Summerb. & Crous (1,2). DNA sequencing of a fragment of the beta-tubulin gene of the isolate (Pkr-1) using primers T1 and Bt2b (GenBank Accession No. HM637892) matched P. krajdenii GenBank Accession No. AY579330. Pathogenicity tests were conducted using isolate Pkr-1. Ten 1-year-old callused and rooted cuttings of 110 R rootstock grown in pots with sterile peat were wounded at the uppermost internode with an 8-mm cork borer. A 5-mm mycelium PDA plug from a 2-week-old culture was placed in the wound before being wrapped with Parafilm. Ten control plants were inoculated with 5-mm noncolonized PDA plugs. Plants were maintained in a greenhouse at 25 to 30°C. Within 3 months, shoots on all Phaeoacremonium-inoculated cuttings had weak growth with small leaves and short internodes and there were black streaks in the xylem vessels. The vascular necroses that developed on the inoculated plants were 5.5 ± 1.2 cm long, significantly greater than those on the control plants (P < 0.01). Control plants did not show any symptoms. The fungus was reisolated from discolored tissue of all inoculated cuttings, completing Koch's postulates. P. krajdenii has a worldwide distribution, although these reports are from human infections (1). P. krajdenii was first reported as a pathogen of grapevines in South Africa (1). To our knowledge, this is the first report of P. krajdenii causing young grapevine decline in Spain or any country in Europe.
References: (1) L. Mostert et al. J. Clin. Microbiol. 43:1752, 2005. (2) L. Mostert et al. Stud. Mycol. 54:1, 2006.
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