根部內生細菌對青蔥捲葉型炭疽病生物防治潛力之評估

Abstract

青蔥 (Allium fistulosum L.) 為臺灣重要之香辛蔬菜，近年受 Colletotrichum siamense 所引起的新興病害青蔥捲葉型炭疽病 (anthracnose-twister disease of green onion) 危害，造成嚴重經濟損失。由於該病原具潛伏感染特性且現行化學防治效果有限，需發展替代性防治策略。本研究首先建立一穩定的病原性試驗系統，並分別篩選具促進植物生長與病原拮抗潛力之有益根部內生細菌 (beneficial root endophytes, BREs)，評估其合成菌群 (synthetic microbial community, SynCom) 於青蔥捲葉型炭疽病管理上之應用潛力。研究結果顯示，C. siamense Col-413 具穩定且較強之致病力，因此選定為標準病原菌株。透過比較不同接種濃度、接種方式及植株週齡，成功確立可穩定誘發中度病徵之接種條件。另外，不同青蔥品種 (系) 對青蔥捲葉型炭疽病之感病性不同，其中「北蔥」於實生苗與分蘗株苗階段皆展現較佳抗病性，而「吉品蔥」與「乙品小蔥」等四季蔥品種則表現更為感病。本研究成功分離出四株具顯著促進植物生長效果且非人體伺機病原之菌株，分別為Fictibacillus enclensis (S3R3)、Pseudomonas atacamensis (V3R2)、P. nitroreducens (V3K2) 及 Comamonas terrigena (O3N3)。於盆栽試驗中，上述菌株所組成之 SynComs (如 All 與 All-S3R3 組合) 於多數生長指標上皆顯著優於單一菌株與未處理對照組，顯示其具備促進青蔥生長之潛力；然而這些 SynComs 組合於試驗條件下未能顯著抑制病害發展。病原拮抗潛力與內生性菌株篩選中鑑定出 Bacillus velezensis 與 B. subtilis，其中 B. velezensis (C-KBM-453) 於實生苗防治試驗中可顯著降低罹病度，但在分蘗苗試驗中，所有處理組 (包含SynComs) 皆無顯著防治效果。綜言之，本研究確立穩定的感病系統與評估基礎，並證實 SynComs 在促進青蔥生長方面具應用潛力。未來透過優化內生菌接種濃度與施用策略，應可提升有益根部內生菌於青蔥整合性管理中之生物防治潛力。

Green onion (Allium fistulosum L.) is an important culinary herb in Taiwan. Recently, its production has been severely threatened by an emerging disease, anthracnose-twister disease caused by Colletotrichum siamense, resulting in substantial economic losses. Because this pathogen frequently establishes latent infections and current chemical control measures are often ineffective, the development of alternative management strategies is urgently needed. In this study, a stable pathogenicity assay system was first established, and beneficial root endophytes (BREs) with plant growth-promoting or antagonistic activities were subsequently screened to evaluate their application potential as synthetic microbial communities (SynComs) for managing anthracnose-twister disease of green onion. The results showed that C. siamense Col-413 exhibited stable and relatively high virulence and was therefore selected as the standard pathogen strain. By comparing various inoculum concentrations, inoculation methods, and plant ages, conditions that consistently resulted in moderate disease severity were successfully established. In addition, green onion cultivars (land variety) differed in their susceptibility to anthracnose-twister disease: both the seed-propagated seedlings and tiller-propagated plants of the “Beicong” cultivar exhibited comparatively higher resistance, whereas several “Sijicong” cultivars, including “Jipincong” and “Yipincong” were more susceptible. Four plant growth-promoting bacteria, showing no potential as human pathogens, were successfully isolated and identified as Fictibacillus enclensis (S3R3), Pseudomonas atacamensis (V3R2), P. nitroreducens (V3K2), and Comamonas terrigena (O3N3). In pot experiments, SynComs composed of these strains (e.g., the All and All-S3R3) performed significantly better than single-strain treatments and the untreated control in most growth-related parameters, indicating strong growth-promoting potential in green onion. However, under the experimental conditions tested, these SynComs did not significantly suppress disease development. During the screening of antagonistic and endophytic strains, Bacillus velezensis and B. subtilis were identified. Among them, B. velezensis (C-KBM-453) significantly reduced disease severity in seed-propagated seedlings, whereas no significant disease control effects were observed in tiller-propagated plants across all treatment, including the SynComs. Overall, this study establishes a stable and reproducible pathogenicity assay system and demonstrates the potential of the SynComs for promoting green onion growth. Further optimization of endophyte inoculum concentrations and application strategies may enhance the biocontrol potential of the beneficial root endophytes within integrated disease management programs for green onion.