Background and aim

Consortia-based inoculants, such as the microbiome method, are advocated over individual biocontrol agents (BCAs), owing to partner reinforcement and rapid rhizospheric establishment. Herein, we screened the sole and dual suppressive effects of selected desert spurge (Euphorbia antiquorum) derived Bacillus spp. vis-à-vis Ralstonia solanacearum.

Methods

The conventional agar diffusion method was used to examine the BCAs' capacity to release antibiotics. Thereafter, the compatibility, the ability to form biofilm and the phytotoxicity of the BCAs towards tobacco leaves were screened. The Box-PCR fingerprinting technique was adopted to ascertain the endophytism of the BCAs, and the wilt suppression test followed by the specific activity of defence-related enzymes was performed.

Results

R. solanacearum was completely inhibited by the extracts from Bacillus velezensis CBv_BE1, Bacillus amyloliquefaciens CBa_BFL2, and Bacillus amyloliquefaciens CBa_RA37 at 0.625 mg/mL. The outstanding candidates could form biofilm and colonize into tomato seedlings, with a plateau at log10 CFU = 4.29/g fresh weight. The consortium from CBa_BFL2 and CBa_RA37 (CBa_BFL2/CBa_RA37) yielded vigorous plants (up to a 319% increase in biomass). Likewise, a 90% and 89% reduction in wilt incidence and severity was recorded by the CBa_BFL2-CBa_RA37 combination. The Guaiacol peroxidases (GPX), phenylalanine ammonia lyase (PAL), and superoxide dismutase (SOD) specific activity were significantly and inversely correlated with wilt severity via Pearson's test. This alludes to a greater innate defence system in tomatoes in response to bacterization.

Conclusions

Our data suggest that tomato priming with a consortium of B. amyloliquefaciens CBa_BFL2 and CBa_RA37 resulted in vigorous and healthier tomato seedlings as referred to their sole effects, with altered activities of key plant distressing enzymes. However, further studies are warranted to reveal its full potential as a pioneering alternative to agrochemicals for the control of bacterial wilt.

Graphical Abstract

中文翻译：

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沙漠三角大戟解淀粉芽孢杆菌 CBa_BFL2 和 CBa_RA37 对番茄青枯病的协同作用

 背景和目的

由于伙伴强化和快速根际建立，基于联合体的接种剂（例如微生物组方法）比单独的生物防治剂（BCA）更受提倡。在此，我们筛选了选定的沙漠大戟 ( Euphorbia antiquorum)衍生芽孢杆菌的单一和双重抑制作用。相对于青枯罗尔斯顿菌。

 方法

使用传统的琼脂扩散方法来检查BCAs释放抗生素的能力。此后，对BCAs对烟叶的相容性、形成生物膜的能力和植物毒性进行了筛选。采用Box-PCR指纹技术确定BCA的内生性，并进行枯萎抑制试验和防御相关酶的比活性。

 结果

0.625 mg/mL 的贝莱斯芽孢杆菌CBv_BE1、解淀粉芽孢杆菌CBa_BFL2 和解淀粉芽孢杆菌CBa_RA37 提取物完全抑制青枯菌。优秀的候选者可以形成生物膜并定植到番茄幼苗中，并在 log10 CFU = 4.29/g 鲜重处达到稳定水平。 CBa_BFL2 和 CBa_RA37 (CBa_BFL2/CBa_RA37) 的联合体产生了旺盛的植物（生物量增加了 319%）。同样，CBa_BFL2-CBa_RA37 组合记录枯萎病发病率和严重程度分别降低了 90% 和 89%。根据 Pearson 检验，愈创木酚过氧化物酶 (GPX)、苯丙氨酸解氨酶 (PAL) 和超氧化物歧化酶 (SOD) 比活性与枯萎严重程度显着呈负相关。这暗示西红柿具有更强的针对细菌的先天防御系统。

 结论

我们的数据表明，用解淀粉芽孢杆菌CBa_BFL2 和 CBa_RA37 联合体对番茄进行引发，可以产生充满活力和健康的番茄幼苗（就其单独效果而言），并改变了关键植物苦恼酶的活性。然而，需要进一步的研究来揭示其作为控制青枯病的农用化学品的开创性替代品的全部潜力。

 图解摘要