The rhizosphere microbiome is critical for plant growth and protection against plant pathogens. However, rhizosphere microbial communities are likely to be restructured upon plant infection by fungal pathogens. Our objective was to determine the shifts in rhizosphere bacterial communities of avocado trees (Persea americana Mill.) after Fusarium dieback (FD), a disease triggered by the symbiotic fungi of invasive ambrosia beetles (Euwallacea kuroshio and Euwallacea sp. nr. fornicatus), using 16S rDNA gene amplicon sequencing and a culture-dependent approach. Rhizosphere soil samples were collected from five asymptomatic and five FD-symptomatic avocado trees in a Californian orchard. Sequence analysis showed that diversity metrics of the rhizosphere bacterial communities associated with asymptomatic avocado trees were larger than those of communities from FD-symptomatic trees. Moreover, FD produced significant shifts in rhizobacterial community structure, which were mainly caused by rare OTUs. Bacterial taxa such as Armatimonadetes, Sporocytophaga or Cellvibrio were exclusively associated with the rhizosphere of asymptomatic trees and may act as an insurance mechanism against fungal invasions. Conversely, genera such as Myxococcus or Lysobacter, which have been described as effective biocontrol agents against Fusarium oxysporum, Colletotrichum gloeosporioides or Rhizoctonia spp., among other phytopathogens, were only found in the rhizosphere of FD-symptomatic trees. The culturable bacterial communities in the rhizosphere of both FD-symptomatic and asymptomatic trees were dominated by isolates from the Bacillus and Pseudomonas genera, indicating that potential biocontrol agents against FD may be isolated from healthy and diseased avocado trees. Altogether, our results showed that FD elicited shifts in the avocado rhizosphere microbiome, which could potentially affect soil microbial processes, and provide a basis for the selection of biocontrol agents that could be used for FD prevention.

根际微生物组对于植物生长和抵抗植物病原体至关重要。但是，根际微生物群落很可能在真菌病原体感染植物后发生重组。我们的目标是确定鳄梨树的根际细菌群落的转变（鳄梨美洲枯萎枯死后磨。）（FD），侵入豚草甲虫（共生真菌引发的疾病Euwallacea黑潮和Euwallacea属NR。fornicatus），使用16S rDNA基因扩增子测序和依赖培养物的方法。从加利福尼亚果园的五棵无症状和五棵有FD症状的鳄梨树中收集了根际土壤样品。序列分析表明，与无症状鳄梨树相关的根际细菌群落的多样性指标大于FD无症状鳄梨树的群落。此外，FD导致根瘤菌群落结构发生重大变化，这主要是由罕见的OTU引起的。细菌类群（如Armatimonadetes，Sporocytophaga或Cellvibrio）仅与无症状树的根际相关，并且可以作为防止真菌入侵的保险机制。相反，诸如粘球菌或溶杆菌，其已经被描述为针对有效生物防治剂尖孢镰刀菌，胶孢炭疽菌或丝核菌属，其它植物病原体中，只在FD-对症树木根际找到。FD症状树和无症状树的根际可培养细菌群落以芽孢杆菌和假单胞菌的分离株为主属，表明可能从健康和患病的鳄梨树中分离出针对FD的潜在生物防治剂。总之，我们的结果表明，FD导致鳄梨根际微生物组发生变化，这可能会影响土壤微生物过程，并为选择可用于FD预防的生物防治剂提供基础。