First Report of Root Rot Caused by Dactylonectria torresensis on Bletilla striata (Baiji) in Yunnan, China
Bletilla striata (Thunb.) Rchb.f. (Orchidaceae family, known as Baiji in Chinese) is an endangered plant species with important medicinal value in China. Bletilla striata plants with symptoms of wilting, leaf yellowing and rotting on underground parts were found in Shizong (24.82822 N; 103.99084 E),...
| Veröffentlicht in: | Plant disease. - 1997. - (2020) vom: 22. Okt. |
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| 1. Verfasser: | |
| Weitere Verfasser: | , , |
| Format: | Online-Aufsatz |
| Sprache: | English |
| Veröffentlicht: |
2020
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| Zugriff auf das übergeordnete Werk: | Plant disease |
| Schlagworte: | Journal Article Bletilla striata Dactylonectria torresensis Root Rot identification |
| Zusammenfassung: | Bletilla striata (Thunb.) Rchb.f. (Orchidaceae family, known as Baiji in Chinese) is an endangered plant species with important medicinal value in China. Bletilla striata plants with symptoms of wilting, leaf yellowing and rotting on underground parts were found in Shizong (24.82822 N; 103.99084 E), Yunnan Province, China in July 2016. In the following years, this disease occurred and became prevalent when high temperature and high humidity prevailed in the fields from May to August. The incidence of the disease varied from 45 to 75%, with yield losses of 40 to 65% in different B. striata fields. To identify the causal agent of the disease, symptomatic vascular tissue fragments were soaked in 2% sodium hypochlorite for 2 min, rinsed twice with sterile distilled water, and then placed on 4% (w/v) potato dextrose agar (PDA) plates. The plates were incubated at 26°C in 12h light/dark for three days. Mycelia grown from the edges of the plant fragments were transferred to PDA plates and incubated at 26°C in 12h light/dark. After three days, hyphal tips were isolated from the edge of the colonies to PDA plates. Three hyphal-tip isolates from different plants were further studied. The colonies of these three isolates were dark red, with cottony mycelia of moderate density. Hyphae were transparent and branched. Numerous hyphae anastomosed frequently and formed hyphal coils. For further morphological analysis, sporulation was induced as described by Cabral et al. (2012) and Lombard et al. (2014). Macroconidia were abundant, 37.2 to 44.0 µm × 5.2 to 8.7 µm based on the measurement of 20 conidia from each isolate. Ascospores divided into two cells of equal size, ellipsoid to oblong-ellipsoid, 12.5 to 14.8 µm × 4.8 to 5.9 µm based on the measurement of 20 spores from each isolate. Conidiophores simple or complex, sporodochial. Simple conidiophores arising laterally or terminally from aerial mycelium, solitary to loosely aggregated, unbranched or sparsely brached, more or less cylindrical. These morphological characteristics were consistent with the description of Dactylonectria spp. by Cabral et al. (2012) and Lombard et al. (2014). From one isolate, the internal transcribed spacer (ITS) region of ribosomal DNA and the beta-tubulin (tub2) gene were amplified by polymerase chain reaction (PCR) using the primer pairs ITS1/ITS4 (White et al. 1990) and T1/Bt-2b (Cabral et al. 2012), respectively. PCR products were sequenced and deposited in GenBank with accession numbers MH458779 (ITS) and MH626485 (tub2). BLAST search revealed that both sequences showed 99 to 100% homology with the corresponding sequences of previously identified D. torresensis isolates. Specially, MH458779 shares 100% identity with the entire 463-base pair (bp) sequence of KP411806, the ITS sequence of a D. torresensis isolate identified from olive trees (Nigro et al. 2019); MH626485 shares 99% identity with the entire 320-bp sequence of KP411801, the tub2 sequence of the same olive tree isolate. In addition, the entire 609-bp sequence of MH626485 shares 99% identity with JF735478, the tub2 sequence of a D. torresensis isolate identified from grapevines (Cabral et al. 2012). To test the pathogenicity of the fungus, plants of B. striata in plastic pots filled with sterilized nursery soil were inoculated with each of the three isolates by placing a fungal-colonized wheat kernel adjacent to each health plant. Plants inoculated with noncolonized wheat kernels were used as controls. Plants in three pots (replicates), with one plant per pot, were inoculated by each isolate. The pots were maintained in a greenhouse with a 12h photoperiod at 25°C. Ten days after inoculation, black necrotic lesions identical to those observed in the field were evident on the roots of all inoculated plants. Using the same methods described above, fungi with identical morphologies as described above were isolated from lesions caused by each of the three isolates. The control plants remained healthy, and no fungus was re-isolated. This completed Koch's postulates. Based on the morphological characteristics and molecular identification, the pathogen was determined to be D. torresensis. To our knowledge, this is the first report of D. torresensis causing root rot of B. striata in Yunnan, China. It is important to further study the impacts of this new disease on B. striata production in China |
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| Beschreibung: | Date Revised 22.02.2024 published: Print-Electronic Citation Status Publisher |
| ISSN: | 0191-2917 |
| DOI: | 10.1094/PDIS-10-20-2166-PDN |