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

Abstract

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 Bacillusvelezensis strain GB1 with GenBank accession No. OM836750, was carried out in the stirred tank bioreactor using a batch fermentation process. For the first time, B. velezensis strain GB1 was tested as a biocontrol agent with soil drench application (109 cfu mL−1) for management of Bemisia tabaci and induction of squash plant systemic resistance under greenhouse conditions. β-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 B. velezensis strain GB1 on population density, fertility, and hatchability of B. tabaci on squash plants was studied. The batch fermentation process of B. velezensis 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 B. velezensis strain GB1 induced squash plants to boost their levels of β-1,3-glucanase, chitinase, polyphenol oxidase, and peroxidase enzymes. On the other hand, B. velezensis strain GB1 could significantly reduce the mean number of the attracted B. tabaci on squash plants. Additionally, whiteflies laid a lower mean number of 2.28 eggs/female/day on squash plants inoculated with B. velezensis strain GB1 compared to control. The percentage of B. tabaci egg hatchability declined by 5.7% in the B. velezensis-inoculated squash plants.