應用Bacillus spp.菌株強化西瓜內源之免疫反應防治西瓜果斑病

Intensification of PAMP-triggered immunity in watermelon by Bacillus spp. strains as a strategy for controlling bacterial fruit blotch disease

由Acidovorax citrulli引起的細菌性果斑病（BFB）是在西瓜生產上的重要限制因素。由於受感染的種子可能是引起田間流行病的初級接種源，因此減少種子上所帶病原在幼苗上的病害發展為防治BFB的主要策略。在防治策略中，應用植物根際細菌為一種對環境友善的防治策略。在本研究中首先針對由土壤所分離之270個Bacillus屬的菌株進行對西瓜果斑病菌之拮抗分析，其中PMB04、PMB05和DR81三個菌株具有較強的拮抗活性。進一步將此三個菌株應用於處理帶有A. citrulli的種子，溫室試驗結果顯示其罹病率和罹病度均顯著降低。其中，又以PMB04和PMB05菌株對BFB有良好的防治效果。此外，利用葉片滲透法共同接種A. citrulli與前述拮抗菌株，結果顯示PMB04和PMB05明顯抑制BFB的病徵。為了瞭解拮抗菌株是否於西瓜上強化了內在的植物免疫反應，在植物葉片中將Bacillus spp.菌株與A. citrulli菌株或flg22Pst共同處理，結果顯示PMB04、PMB05均可增強A. citrulli菌株或flg22Pst所誘導的ROS快速產生和癒傷葡聚糖的累積，但DR81菌株則無此現象。此外，在西瓜葉片中以NADPH氧化酶抑制劑共同處理PMB05，可抑制該菌株對BFB的防治能力。依據此研究成果，我們得知應用強化植物免疫的Bacillus屬細菌菌株於西瓜果斑病的防治實為一種新型且有效的策略。

"Bacterial fruit blotch (BFB) caused by Acidovorax citrulli is a devastating disease on watermelon production. The primary inoculum of this disease in fields comes from infested seeds. Thus, reducing pathogen growth on or association with seedlings through seed treatments becomes a feasible strategy to control BFB. In this study, three Bacillus spp. strains with antagonistic activity to A. citrulli were isolated from rhizosphere as an eco-friendly strategy for disease management. The antagonistic strains PMB04, PMB05 and DR81 applied on A. citrulli-infested seeds significantly reduced the disease incidence and disease severity of BFB. Among them, strains PMB04 and PMB05 exhibited better control efficacy against BFB than the strong antagonistic strain DR81. Moreover, leaf infiltration revealed the symptoms and populations of BFB were strongly reduced by co-inoculation of A. citrulli with PMB04 or PMB05. Replacing A. citrulli with flg22Pst, in watermelon leaves strongly induced the innate immune response, which was indicated by the rapid generation of reactive oxygen species (ROS) and callose deposition. However, strain DR81 does not have this effect. Moreover, B. amyloliquefaciens PMB05-induced disease resistance against BFB in watermelon was abolished by the treatment of NADPH oxidase inhibitor. Therefore, we concluded that the application of plant immunity-intensifying B. amyloliquefaciens strains would be a novel and efficient strategy to control BFB of watermelon."