The noxious weed Allium triquetrum (Alliaceae) has invaded widespread areas in southern Australia, forming dense monocultures that threaten indigenous ground flora. Two soilborne biocontrol agents, the fungus Stromatinia cepivora and the bacterium Pectobacterium carotovorum subsp. carotovorum (Pcc) have previously been reported as killing A. triquetrum in gnotobiotic controlled conditions. This study aimed to find why glasshouse pot trials in complex potting media and field trials showed no effect of inoculation with either agent. Bacteria were consistently isolated from inside surface-sterilised bases and bulbs of A. triquetrum. Most bacteria from actively growing plants were closely related to Bacillus but one from dormant bulbs (RPTAtOch1) belonged to Ochrobactrum. Most bacteria reduced soft rot caused by Pcc in vitro by up to 100% when inoculated the day before Pcc. Co-cultivation with Pcc reduced its extracellular pectin lyase and polygalacturonase, which target plant cell walls. RPTAtOch1 was identified as O. quorumnocens by traditional physiological, biochemical and molecular tests, whole genome sequencing and Average Nucleotide Identity comparisons. Its draft genome consisted of 76 contigs, 70% of which were closest to isolate A44 of O. quorumnocens, which antagonises soft rotting of potato by Pcc by destroying its quorum-sensing lactones but, like RPTAtOch1, does not inhibit growth of Pcc. Also, endophytic bacteria inhibited germination of S. cepivora sclerotia and so prevented white rot. Thus, the failure in biocontrol of A. triquetrum by both S. cepivora and Pcc may be due, ironically, to biocontrol of the intended pathogens by endophytic bacteria inside the target weed.

中文翻译：

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澳大利亚维多利亚州内生细菌对有害杂草角洋葱（Allium triquetrum）的生物防治

有害杂草葱属（Alliaceae）已侵入澳大利亚南部的广泛地区，形成密集的单一栽培，威胁着当地的地面植物群。两种土传生物防治剂，真菌 Stromatinia cepivora 和细菌 Pectobacterium carotovorum subsp。carotovorum (Pcc) 以前曾被报道在无菌控制条件下杀死三角锥虫。本研究旨在找出为什么在复杂的盆栽培养基和田间试验中的温室盆栽试验显示接种任何一种药剂都没有影响。细菌始终从 A. triquetrum 的表面消毒的基部和球茎中分离出来。大多数来自活跃生长植物的细菌与芽孢杆菌密切相关，但来自休眠球茎 (RPTAtOch1) 的细菌属于 Ochrobactrum。在 Pcc 前一天接种时，大多数细菌在体外将 Pcc 引起的软腐病减少了 100%。与 Pcc 共培养减少了其细胞外果胶裂解酶和多聚半乳糖醛酸酶，它们靶向植物细胞壁。通过传统的生理、生化和分子测试、全基因组测序和平均核苷酸同一性比较，RPTAtOch1 被鉴定为 O. quorumnocens。它的基因组草图由 76 个重叠群组成，其中 70% 最接近 O. quorumnocens 的 A44 分离群，通过破坏其群体感应内酯来拮抗 Pcc 对马铃薯的软腐烂，但与 RPTAtOch1 一样，不抑制 Pcc 的​​生长。此外，内生细菌抑制 S. cepivora 菌核的萌发，从而防止白腐病。因此，具有讽刺意味的是，S.cepivora 和 Pcc 对 A. triquetrum 的生物防治失败可能是由于，