Production of <i>Bacillus velezensis</i> Strain GB1 as a Biocontrol Agent and Its Impact on <i>Bemisia tabaci</i> by Inducing Systemic Resistance in a Squash Plant

Pests represent a huge problem in crop production causing significant losses. Currently, biocontrol is utilized as an eco-friendly approach for controlling pests and reducing the shortage in crop production. In the current study, the production of a biocontrol agent, which was identified based on sequencing of the 16S rRNA gene as <i>Bacillus</i><i>velezensis</i> strain GB1 with GenBank accession No. OM836750, was carried out in the stirred tank bioreactor using a batch fermentation process. For the first time, <i>B</i>. <i>velezensis</i> strain GB1 was tested as a biocontrol agent with soil drench application (10⁹ cfu mL⁻¹) for management of <i>Bemisia tabaci</i> and induction of squash plant systemic resistance under greenhouse conditions. <i>β</i>-1,3-glucanase, chitinase, polyphenol oxidase, and peroxidase activity were measured in squash leaves at 24, 48, 72, 96, and 120 h. The influence of <i>B</i>. <i>velezensis</i> strain GB1 on population density, fertility, and hatchability of <i>B</i>. <i>tabaci</i> on squash plants was studied. The batch fermentation process of <i>B</i>. <i>velezensis</i> strain GB1 maximized the production of secondary metabolites and culture biomass, which reached a maximum value of 3.8 g L⁻¹ at 10.5 h with a yield coefficient of 0.65 g cells/g glucose. Treatment with <i>B</i>. <i>velezensis</i> strain GB1 induced squash plants to boost their levels of <i>β</i>-1,3-glucanase, chitinase, polyphenol oxidase, and peroxidase enzymes. On the other hand, <i>B</i>. <i>velezensis</i> strain GB1 could significantly reduce the mean number of the attracted <i>B. tabaci</i> on squash plants. Additionally, whiteflies laid a lower mean number of 2.28 eggs/female/day on squash plants inoculated with <i>B. velezensis</i> strain GB1 compared to control. The percentage of <i>B. tabaci</i> egg hatchability declined by 5.7% in the <i>B. velezensis</i>-inoculated squash plants.