新穎材料農業：農業新穎材料在植物保健開發、應用與機理【植物病理學系/洪爭坊助理教授】
| 論文篇名 | First report of dragon fruit (Hylocereus undatus) stem rot caused by Diaporthe ueckerae in Taiwan |
| 期刊名稱 | PLANT DISEASE |
| 發表年份,卷數,起迄頁數 | 2022; 106(5),1527 |
| 作者 | Wang, Yen-Chieh; Liu, Jan-Hong; Huang, Chieh-Chen(黃介辰); Hong, Cheng-Fang(洪爭坊)* |
| DOI | 10.1094/PDIS-09-21-1902-PDN |
| 英文摘要 | Dragon fruit (Hylocereus polyrhizus and H. undatus) is a rapidly growing commodity in Taiwan. Production acreage has tripled since 2011, with an estimated over 2,800 ha in 2019. During a July 2020 disease survey, reddish-orange to blackish-brown lesions similar to stem canker caused by Neoscytalidium dimidiatum were observed on dragon fruit cladodes in two orchards in Central Taiwan. In the lab, diseased cladodes were surface disinfested with 70% ethanol for 15 to 30 s and blotted dry with a paper towel. Small pieces (∼3 × 3 mm) of necrotic spots were excised, put on 2% water agar (WA) plates, and incubated with 12 h photoperiod at 28 ± 2°C for 3 days. Of the isolates from necrotic spots, 21 were N. dimidiatum, and 3 from other spots were unknown. Single hyphal tips of the three unknown fungal colonies with similar morphology were transferred on potato dextrose agar (PDA). Brownish- to grayish-white colonies with fluffy aerial mycelium were observed on PDA after 8 days of incubation. To induce sporulation, all the isolates were cultivated on autoclaved cowpea pods on 2% WA plates with 12 h photoperiod at 25 ± 2°C for 3 weeks. Black pycnidia embedded in cowpea tissues and creamy yellowish exudates with pycnidiospores extruding from the ostiole were observed. Alpha-conidia were aseptate, hyaline, smooth, ellipsoidal or fusiform, often biguttulate, and ∼6.0 to 6.5 × 2.0 to 2.3 μm (n = 50 per isolate). Beta-conidia were not observed. Morphological characteristics resembled Diaporthe spp. described by Udayanga et al. For further identification, the internal transcribed spacer (ITS), β-tubulin (TUB), and translation elongation factor 1-α (EF1-α) regions were amplified using primer pairs ITS1/ITS4, Bt2a/Bt2b, and EF1-728F/EF1-986R, respectively. BLAST analysis of isolates CH0720-010 (ITS: OK067377; TUB: OK149767; EF1-α: OK149764), CH0720-013 (ITS: OK067378; TUB: OK149768; EF1-α: OK149765), and TC0720-016 (ITS: OK067379; TUB: OK149769; EF1-α: OK149766) showed 99.78 to 100% of ITS identity, 98.8 to 99.2% of TUB identity, and 100% of EF1-α identity with Diaporthe ueckerae (ITS: KY565426; TUB: KY569384; EF1-α: KY569388). Phylogenetic trees were constructed using concatenated ITS, TUB, and EF1-α sequences based on maximum likelihood with the HKY+G model, maximum parsimony, and Bayesian inference method in MEGA X and Geneious Prime 2020.2.4. All isolates were clustered in D. ueckerae with similar topology based on these methods, so the phylogram of maximum likelihood was presented. To confirm pathogenicity, detached dragon fruit (H. polyrhizus and H. undatus) cladodes (20- to 30-cm long) were surface disinfested, wounded with a sterilized syringe (∼2-mm depth), and inoculated with mycelial plugs (6-mm diameter) from 5-day-old colonies on PDA. Each isolate had three mycelial plugs. PDA plugs without mycelium were inoculated as a negative control. Inoculated cladodes were incubated in a moisture chamber at 30 ± 2°C and a 12 h photoperiod. Two days after inoculation (DAI), plugs were removed, and symptom development was photographed every 2 days. The experiment was repeated twice. At 6 DAI, round to irregular, dark-brown, water-soaking lesions were observed on the cladodes of both species inoculated with the three D. ueckerae isolates, and all negative controls were asymptomatic. Morphologically identical fungi were reisolated from inoculated cladodes, fulfilling Koch’s postulates. Several Diaporthe species have been reported infecting dragon fruit in southeastern Asian countries such as Thailand, Bangladesh, and Malaysia. To our knowledge, this is the first report of stem rot caused by D. ueckerae in Taiwan. Since the field symptoms may be easily confused with those caused by N. dimidiatum, the potential threat of Diaporthe species complex on dragon fruit should be raised and may warrant further study. |
| 發表成果與本中心研究主題相關性 | 本研究調查全臺不同地區紅龍果罹病枝條，首次記錄在台灣田間由 Diaporthe ueckerae 造成與 Neoscytalidium dimidiatum 類似的莖腐病徵。根據目前調查結果，N. dimidiatum 仍為紅龍果田間栽培的主要病害，但隨著 D. ueckerae 被記錄，代表紅龍果上，仍可能存在其他造成相似病徵的不同病原菌。這些病原菌的危害程度與風險，目前可能仍不如莖潰瘍病，但在耕作習慣改變與環境變遷的情境下，應留意次要病原菌轉為主要病原菌的風險。 |
