Leaf spot disease on seedlings of Quercus acutissima caused by Tubakia dryina in Korea
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Severe attack by a leaf spot disease was found on seedlings of Quercus acutissima in Jeungpyeong, Korea in 2017. Based on the morphological characteristics of the fungus, it was identified as a member of Tubakia. Sequence comparisons based on the ITS and 28S rDNA regions confirmed the identity of the fungus as Tubakia dryina. This is the first report of Tubakia leaf spot caused by T. dryina on Q. acutissima.
KeywordsFagaceae Melanconidaceae Oak
Tubakia species have been reported as endophytes or causing leaf spots on Castanea spp., Quercus spp., and some other members of Fagaceae in Asia, Europe and North America (Yun and Rossman 2011; Harrington et al. 2012; Boroń and Grad 2017). Tubakia dryina is a known leaf spotting fungus which has been reported in many countries. Although a wide range of host species have been recorded for T. dryina, the fungus is most frequently found on oaks (Proffer 1990; Kowalski 2006), including at least 40 species according to Farr and Rossman (2017).
During a recent survey of plant diseases carried out to identify the fungal pathogens infecting oaks in 2017, a damaging leaf spot disease was consistently observed on seedlings of Quercus acutissima (sawtooth oak) (Fagaceae), in Jeungpyeong, Korea. Quercus acutissima is a deciduous broad-leaved tree, native to eastern Asia with a wide distribution and is one of the important forest components in hillsides of South Korea.
In addition to the morphological identifications, DNA barcode sequences were compared with sequences deposited in GenBank to assure the correct identity of the fungus. DNA sequence analyses were carried out following the techniques described by Lee et al. (2015) for internal transcribed spacer (ITS) regions including the 5.8S rDNA gene region and large-subunit (LSU) 28S rDNA. A BLASTn search with the isolates obtained in this study further revealed >99% similarity with those of T. dryina isolates from Poland (KR362909 for ITS) and from Italy (JF704187 for LSU). All sequence data obtained in this study were deposited in the NCBI database (accession numbers; MF579755 and MF579756 for ITS; MG798658 and MG793660 for LSU).
Pathogenicity of CFPR-QA1TD and CFPR-QA2TD to Q. acutissima, was tested through inoculations of healthy detached leaves of Q. acutissima. Three weeks-old culture formed on 2% MEA plates at 25 °C were flooded with sterile distilled water and the surface was scraped. The suspension was filtered and adjusted to 105 conidia/mL with a haemocytometer. Ten healthy leaves of Q. acutissima were selected, half being inoculated with the suspension obtained from one strain and five with the other. Inoculated leaves were left in plastic bags to keep humidity levels high and left in an incubator at 25 °C under a 12-h photoperiod. Additionally, five healthy leaves were treated with sterile water and kept under the same conditions to serve as controls. Leaf spot symptoms, identical to those observed in the field, developed on the inoculated leaves 7 days after the inoculation, while no symptoms were observed on the control. Re-isolations of the fungus from the leaf spots developed on the inoculated leaves were successfully made, fulfilling Koch’s postulates.
To our knowledge, this is the first report of T. dryina causing leaf spots on Q. acutissima in Korea. The symptoms developed by T. dryina attack are similar to those caused by anthracnose and other causes and may have been underestimated (Kowalski 2006). Thus, more rigorous identification of the pathogen is needed to better access the relevance of the disease and decide about the need for control measures.
This work was supported by a project for the development of effective control measures for oak wilt diseases (Project No. FE0700-2017-2017, National Institute of Forest Science, Republic of Korea).
- Farr DF, Rossman AY (2017) Fungal databases. Systematic Mycology & Microbiology Laboratory, ARS, USDA. http://nt.ars-grin.gov/fungaldatabases/. Accessed 23 July 2017
- Proffer TJ (1990) Tubakia leaf spot. Florida Department of Agriculture and Consumer Services, division of plant industry, Gainesville. Plant Pathol Circ 337:2Google Scholar