Verticillium dahliae is one of the most destructive pathogens in many cotton-growing countries around the globe. There is still the lack of high-resistant upland cotton cultivars against this pathogen, and the usage of fungicides is threatening the environment. Biocontrol is an environment-friendly and a green technique in plant protection. In this regard, the present work was aimed to investigate antagonistic bacterial strains and to introduce them as new bioinoculants against V. dahliae in cotton. Numerous bacteria were isolated from cotton roots, and their antagonism was examined against V. dahliae. Strain SZAD2 which was identified as Bacillus velezensis on the bases of 16S rRNA gene analysis had significantly high biocontrol potential both in plate assay and under greenhouse conditions. The biocontrol efficacy in seed treatment was 60.31%, while in the soil drench method, it was 79.19%. Transmission electron microscopy (TEM) analysis revealed that the strain systemically colonized the roots and lived within the intercellular space. Hydrogen peroxide staining exposed that the strain increased plant basal defense response by the accumulation of hydrogen peroxide (H2O2) in both roots and leaves. Furthermore, the bacterization of cotton roots triggered induced systemic resistance (ISR) in the roots and caused the activation of the antioxidant enzymes such as phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), peroxidase (POD), and phenol contents. Moreover, the antifungal extract produced by the strain contained the activity of both cellulase and chitinase, which were able to suppress fungal mycelia both in the presence and absence of cotton. Strain SZAD2 systemically colonized the plant, showed multiple modes of action against the pathogen which played a vital role in V. dahliae control, and is recommended for commercial exploration as a safe alternative bioinoculant instead of hazardous chemical fungicides.

中文翻译：

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韦氏芽孢杆菌新菌株作为棉花黄萎病菌的生物制剂：分离和分子鉴定

在全球许多棉花种植国，大黄萎病菌是最具破坏性的病原体之一。仍然缺乏针对这种病原体的高抗旱性棉花品种，杀真菌剂的使用正在威胁环境。生物防治是一种绿色环保的植物保护技术。在这方面，目前的工作旨在研究拮抗细菌菌株，并将其作为抗棉铃虫的新生物抑制剂。从棉花根中分离出许多细菌，并检查了它们对大丽花弧菌的拮抗作用。在16S rRNA基因分析的基础上被鉴定为velacensis velacensis的菌株SZAD2在平板测定和温室条件下均具有显着高的生物防治潜力。种子处理的生防效果为60.31％，而在土壤淋湿法中为79.19％。透射电子显微镜（TEM）分析显示该菌株系统地定植在根部并生活在细胞间空间内。过氧化氢染色表明该菌株通过在根和叶中积累过氧化氢（H2O2）来增强植物的基础防御反应。此外，棉花根部的细菌化在根部引发了诱导的系统抗性（ISR），并导致了抗氧化酶的活化，例如苯丙氨酸氨解酶（PAL），多酚氧化酶（PPO），过氧化物酶（POD）和苯酚含量。此外，由该菌株产生的抗真菌提取物同时具有纤维素酶和几丁质酶的活性，在存在和不存在棉花的情况下，它们都能够抑制真菌菌丝体。