First Report of Wilt of Eucalyptus Caused by Ceratocystis fimbriata in China

Abstract

Eucalyptus spp., most of which are native to Australia, are one of the world's most commonly planted forestry crops, and have been widely planted in the tropics and subtropics. Eucalyptus trees are distributed in more than 600 counties in 19 provinces/regions throughout China, especially in the southern regions of the country (1). From April of 2013 to May of 2014, eucalyptus trees were noted to be wilting and dying rapidly in Kunming, Yunnan Province (25°02′ N, 102°42′ E), southwest China. Symptomatic trees typically have many wilted or dead leaves hanging throughout the tree or on some major branches, sometimes followed by death of the whole tree. Dark brown to black discoloration can be seen in the woody xylem, and elongated cankers were also present on some affected trees. A fungus was consistently isolated from the leaves and cankers when symptomatic tissue was incubated between two slices of fresh carrot root. Spore masses were removed from the apices of perithecia, transferred to malt extract agar medium (MEA), and incubated at 25°C. Perithecia developed on the medium, and were black, globose, 212.5 to 242.4 × 207.5 to 254.2 μm, and possessed a long black neck (952.3 to 1,303.3 μm). Ascospores had the typical “hat” morphology and were 4.3 to 5.2 × 3.0 to 3.8 μm. Cylindrical endoconidia (11.2 to 22.2 × 3.9 to 6.1 μm) were found. Chlamydospores produced on media were ovoid and smooth, and were 7.8 to 9.7 × 9.9 to 12.8 μm. Chains of barrel-shaped conidia were not found. PCR amplification and sequencing of the ITS region of rDNA were carried out for one isolate, E2-2, using the procedures of Thorpe et al. (3). Analysis of ITS sequence data (GenBank Accession No. KJ511481) showed that the isolates were 99% homologous to the isolate of C. fimbriata from diseased Colocasia esculenta in Cuba, China, and Hawaii (AY526304 to 06) by BLAST analysis. Thus, the fungus was identified as C. fimbriata based on morphological and molecular characteristics. Pathogenicity tests were made on 1-year-old E. grandis seedlings as follows. A conidial suspension of each isolate was diluted to 106 conidia/ml, and 0.2 ml was injected into wounds on three petioles on each of five healthy plants of E. grandis, and control seedlings were injected with sterile water that had been placed on MEA plates. The seedlings were incubated at 25°C in moist chambers. After 3 days, all inoculated E. grandis plants showed dark brown to black discoloration in the leaf axils. After 5 days, leaf wilting was present. C. fimbriata was re-isolated from all inoculated symptomatic tissue. No symptoms were visible in the control plants and no fungus was isolated from them. Ceratocystis wilt was first observed in eucalyptus in 1997 in the state of Bahia. This was followed by a report of C. fimbriata causing wilt of E. grandis in the Republic of Congo, Uganda, and Uruguay (2). Chen et al. reported two species of Ceratocystis, C. acaciivora and a previously undescribed species C. chinaeucensis, from eucalyptus plantations in Guangdong Province in China (1). To our knowledge, this is the first report of C. fimbriata causing wilt of eucalyptus in China. References: (1) S. F. Chen et al. Fungal Diversity 58:267, 2011. (2) F. A. Ferreira et al. Fitopatol. Bras. 24:284, 1999. (3) D. J. Thorpe et al. Phytopathology 95:316, 2005.