L. C. Romero-Rivas, Universidad Nacional Daniel Alcides Carrión, Oxapampa, Pasco, Peru;
L. A. Álvarez,
D. Gramaje, and
J. Armengol, Instituto Agroforestal Mediterráneo, Universidad Politécnica de Valencia, Camino de Vera s/n, 46022 Valencia, Spain; and
C. Cadenas-Giraldo, Departamento de Fitopatología, Universidad Nacional Agraria La Molina, Av. La Universidad s/n, Lima, Peru
Since 2005, symptoms of grapevine decline have been observed on 4- to 8-month-old grapevines (cvs. Red globe and Crimson) grafted onto 1103 P rootstock in Ica and Pisco valleys in southern Peru. Affected plants exhibited weak growth, interveinal chlorosis, necrosis and wilting of leaves, and death. Dark brown-to-black streaking of the xylem was seen when transverse or longitudinal cuts were made in the trunk and shoots. Symptomatic plants were collected and sections (5 cm long) were cut from the zone between the rootstock and the scion, surface sterilized 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 placed onto potato dextrose agar (PDA) supplemented with oxytetracycline (500 mg liter--1). Plates were incubated at 25°C in the dark for 15 days. A Phaeoacremonium sp. was consistently isolated from necrotic tissues. Single conidial isolates were obtained and grown on PDA and malt extract agar (MEA) in the dark at 25°C for 3 weeks until colonies produced spores (3). Colonies were brown on PDA and olive brown on MEA. Conidiophores were branched, 27.5 to 67.5 (42.5) μm long, and often consisting of a single phialide. Conidia were hyaline, oblong ellipsoidal, 2.5 to 4.5 (3.6) μm long, and 1.2 to 1.9 (1.6) μm wide. On the basis of these characteristics, the isolates were identified as Phaeoacremonium parasiticum (Ajello, Georg & C.J.K Wang) W. Gams, Crous & M.J. Wingf. (teleomorph Togninia parasitica L. Mostert, W. Gams & Crous) (2,3). Identity of isolate Ppa-1 was confirmed by PCR-restriction fragment length polymorphism of the internal transcribed spacer region (Phaeoacremonium-specific primers Pm1-Pm2) with the restriction enzymes BssKI, EcoO109I, and HhaI (1). Additionally, the beta-tubulin gene fragment (primers T1 and Bt2b) of this isolate was sequenced (GenBank Accession No. FJ151015). The sequence was identical to the sequence of P. parasiticum (GenBank Accession No. AY328379). Pathogenicity tests were conducted using the isolate Ppa-1. Approximately 20 μl of a suspension containing 103 conidia ml--1 was injected into the pith of four nodes on each of 10 dormant, unrooted, 15 cm long cuttings of cv. Red Globe. Four nodes on each of 10 cuttings were used as controls and injected with an equal volume of sterile distilled water. Inoculation points were covered with Parafilm. The cuttings were planted in plastic pots and maintained at 24 ± 3°C in diffuse light, watering as needed. Within 2 months of inoculation, all P. parasicitum-inoculated cuttings exhibited shoots with very poor growth with small leaves and short internodes. In the xylem vessels, black streaks identical to symptoms observed in declining vines in the vineyard were observed. Control plants did not show any of these symptoms. The fungus was reisolated from internal tissues of symptomatic shoots of all inoculated cuttings but not from the control shoots. To our knowledge, this is the first report of P. parasiticum causing young grapevine decline in Peru.
References: (1) A. Aroca and R. Raposo. Appl. Environ. Microbiol. 73:2911, 2007. (2) P. W. Crous et al. Mycology 88:786, 2006. (3) L. Mostert et al. Stud. Mycol. 54:1, 2006.