First Report of Canker Disease Caused by Neofusicoccum australe on Eucalyptus and Pistachio in Spain

Abstract

In 2005 and 2006, dieback and branch cankers were observed in 12-year-old Eucalyptus globulus Labill. plantations in Gijón (northern Spain) and a 20-year-old pistachio (Pistacia vera L.) plantation in Constantí (northeastern Spain). Isolations were made from symptomatic branches. Small pieces of necrotic tissues were surface sterilized for 1 min in 1.5% NaOCl and plated onto malt extract agar amended with 0.5 g L^-1 streptomycin sulfate. Plates were incubated at 25°C in the dark and all growing colonies were transferred to potato dextrose agar (PDA). A Neofusicoccum sp. was consistently isolated from necrotic tissues of both host species. On PDA at 25°C, isolates developed a moderately dense mycelium, initially with a pale yellow pigment diffusing into the medium but becoming olivaceous gray after 5 to 6 days. Pycnidia were produced on sterile eucalyptus and pistachio twigs placed on the surface of water agar after 1 month. Conidia were hyaline, fusiform, aseptate, with granular contents. Conidia from eucalyptus isolates measured (22.5-) 25.4 (-28.1) × (5-) 6.2 (-7.5) μm, (n = 40) and (20.0-) 23.6 (-28.0) × (6.5-) 7.1 (-8.0) μm, (n = 40) from pistachio isolates. Isolates were identified as Neofusicoccum australe (Slippers, Crous & M.J. Wingf.) Crous, Slippers & A.J.L. Phillips (1,2). DNA sequences of the rDNA internal transcribed spacer region (ITS), part of the beta-tubulin (BT2), and part of the translation elongation factor 1-alpha (EF1-α) genes from isolates CBS 122027 (pistachio) and CBS 122026 and CBS 122025 (eucalyptus) were used to confirm the identifications through BLAST searches in GenBank. Representative sequences of all studied regions were deposited in GenBank (ITS: EU375516 and EU375517; BT2: EU375520; EF1-α: EU375518 and EU375519). Pathogenicity tests were conducted on 8-month-old eucalyptus seedlings and 2-year-old pistachio plants with the three N. australe strains mentioned above. A mycelial plug taken from the margin of an actively growing colony of each isolate was put in a shallow wound (0.4 cm²) made with a scalpel on the stem of each plant. Inoculation wounds were wrapped with Parafilm. Controls were inoculated with sterile PDA plugs. Ten replicates for each isolate and plant species were used, with an equal number of control plants. Plants were maintained in a greenhouse at 25°C. After 3 weeks, all eucalyptus seedlings showed leaf wilting, stem canker, and pycnidia formation around the inoculation site. No foliar symptoms were observed in pistachio plants after 3 months, but depressed cankers variable in size and pycnidia formation developed around the inoculation site. Vascular necroses that developed on the inoculated plants were 10.2 ± 1.2 cm long in eucalyptus and 6.4 ± 1.6 cm long in pistachio, significantly greater than their respective controls (P < 0.01). There were no significant differences in necrosis lengths among the three N. australe isolate inoculations, irrespective of the inoculated host. These results point to a high susceptibility of eucalyptus to N. australe. No symptoms were visible in the control seedlings and no fungus was isolated from them. The pathogen was reisolated from all inoculated plants. To our knowledge, this is the first report of N. australe causing canker disease on eucalyptus and pistachio trees in Spain. References: (1) P. Crous et al. Stud. Mycol. 55:235, 2006. (2) B. Slippers et al. Mycologia 96:1030, 2004.