Oxalis purpurea sclerotium rot caused by Athelia rolfsii
- 806 Downloads
Over a 3-year period (2015–2017), sclerotium rot was observed on purple wood sorrel (Oxalis purpurea) in the exhibition field of Gyeongsangnam-do Agricultural Research and Extension Services, Jinju, South Korea. Infected plants exhibited blight and rot symptoms. White mycelial mats spread over lesions, and numerous sclerotia formed on the petiole near the soil line. Sclerotia were globoid in shape, 1–3 mm in size, and white to brown in color. The optimum temperature for mycelial growth and sclerotium formation on potato dextrose agar (PDA) was 30 °C and the hyphal width was 4–8 μm. Typical clamp connections were observed in the hyphae of fungi grown on PDA. Molecular identification was conducted by sequencing and analysis of the complete internal transcribed spacer (ITS) rDNA sequence of the causal fungus. On the basis of mycological characteristics, molecular identification, and pathogenicity to host plants, this fungus was identified as Athelia rolfsii. This is the first report of sclerotium rot on purple wood sorrel caused by A. rolfsii.
KeywordsAthelia rolfsii Sclerotium rot Oxalis purpurea Purple wood sorrel
Purple wood sorrel (Oxalis purpurea) is cultivated as an ornamental plant for use as a flowering groundcover in gardens, and for natural landscaping projects. It spreads by running roots and bulbs to form colonies (Dreyer and Makwarela 2000; Goldblatt and Manning 2000). All parts of the plant, including the flowers, leaves, stems, and bulbs are edible; however, it should not be eaten in large quantities due to its high concentration of oxalic acid. In Korea, the petals and leaves of purple wood sorrel are used as salad material for bibimbap.
Sclerotium rot is a serious disease affecting many plants. As the disease progresses, petioles of infected inflorescences turn brown, and then became watery, followed by the appearance of abnormal symptoms in the plant. Diseased plants slowly turn brown, wilt, and eventually die. White mycelia and small round sclerotia form in the stems of diseased plants. To date, there has been no report of sclerotium rot in purple wood sorrel (Farr and Rossman 2018).
Over a 3-year period (2015–2017), we observed sclerotium rot on purple wood sorrel that was cultivated at the roadside as landscaping in the exhibition field of Gyeongsangnam-do Agricultural Research and Extension Services, Jinju, South Korea. During this period, rainfall was frequent, temperature and humidity were constant, and the disease was well-developed.
Pathogenicity tests were conducted as follows. We purchased and seeded 30 healthy bulbs in Wagner pots (one bulb per pot). After 4 months, the plants were artificially inoculated with PDA blocks containing fungal mycelia and sclerotia. Five isolated fungi including KACC 48132 were cultivated on PDA medium for 7 days. Mycelial mats (1 cm2) containing mycelia and sclerotia from the five fungal isolates were placed near each purple wood sorrel bulb, and plants were placed in a greenhouse. The plants slowly faded and died within 7 days of inoculation, exhibiting unusual vigorously growing mycelia. On the lesion, white mycelia and brown, round sclerotia formed (Fig. 2c). To fulfil Koch’s postulates, the fungal pathogen was re-isolated from the lesions and its fungal morphological characteristics and ITS DNA sequences were confirmed.
As described above, the mycological characteristics, pathogenicity, and ITS nucleotide sequence analysis of the pathogens were consistent with A. rolfsii (Mordue 1974; Tu and Kimbrough 1978). Two diseases have been reported on purple wood sorrel in the United States Department of Agriculture (USDA) fungal databases (Farr and Rossman 2018): Aecidium oxalidis from South Africa (Doidge 1950) and Puccinia oxalidis from Canary Islands (Gjaerum and Sunding 1986). To our knowledge, the current paper is the first report of sclerotium rot on purple wood sorrel caused by A. rolfsii. This study was presented at the Korean Plant Pathology Conference on April 26, 2018 in Cheongju, South Korea (Kwon et al. 2018).
This work was carried out with the support of the Cooperative Research Program for Agriculture Science & Technology Development (Project No. PJ012826092018), Rural Development Administration, Republic of Korea.
- Doidge EM (1950) The south African fungi and lichens to the end of 1945. Bothalia 5:1–1094Google Scholar
- Dreyer LL, Makwarela AM (2000) Oxalidaceae. In: Leistner OA (ed) Seed plants of southern Africa: families and genera, vol 10. National Botanical Institute, Pretoria, pp 432–433 StrelitziaGoogle Scholar
- Farr DF, Rossman AY (2018) Fungal databases, systematic mycology and microbiology laboratory, ARS, USDA. Internet Resource: http://nt.ars-grin.gov//fungaldatabases/ (verified May 30, 2018)
- Gjaerum HB, Sunding P (1986) Flora of Macaronesia. Checklist of Rust Fungi. Sommerfeltia 4:1–42Google Scholar
- Goldblatt P, Manning J (2000) Cape plants: a conspectus of the cape Flora of South Africa, National Botanical Institute of South Africa, Strelitzia 9. PretoriaGoogle Scholar
- Kwon JH, Lee JT, Son D, Kim J (2018) Sclerotium rot of purple woodsorrel (Oxalis purpurea) caused by Sclerotium rolfsii. Proceedings of the Korean Society of Plant Pathology Conference, Cheongju, South Korea (Poster abstract I-17)Google Scholar
- Mordue JE (1974) Corticium rolfsii. CMI descriptions of pathogenic fungi and bacteria. No. 410. Surrey: Commonwealth Mycological InstituteGoogle Scholar
- White TJ, Bruns T, Lee S, Taylor JW (1990) Amplification and direct sequencing of fungal ribosomal RNA genes for phylogenetics. In: Innis MA, Gelfand DH, Sninsky JJ, White TJ (eds) PCR protocols: a guide to methods and applications. Academic Press, New York, pp 315–322Google Scholar