The insecticidal potential of Bacillus velezensis CE 100 against Dasineura jujubifolia Jiao & Bu (Diptera: Cecidomyiidae) larvae infestation and its role in the enhancement of yield and fruit quality of jujube (Zizyphus jujuba Miller var. inermis Rehder)

Abstract

Jujube (Zizyphus jujuba Miller var. inermis Rehder) is highly susceptible to jujube gall midge (Dasineura jujubifolia Jiao & Bu) larvae infestation, which causes rolled leaf damage, leaf galls, discoloration, and a decline in fruit yield. In this study, we demonstrate the larvicidal potential of cuticle-degrading chitinase and protease produced by Bacillus velezensis CE 100 against jujube gall midge larvae and the plant growth-promoting effect on jujube fruit yield. The laboratory insecticidal assay involving bacterial broth culture and crude enzymes of B. velezensis CE 100 revealed that both treatments caused gall midge larvae mortality rates of up to 85.5% and 96.7%, respectively. Both treatments caused severe degradation of the larvae cuticle, such as deformation of the exoskeleton and loss of sensilla. Foliar application of the bacterial broth culture in the jujube field reduced the rate of rolled leaf damage by 3.8-fold more than that in the control group. In addition, B. velezensis CE 100 produced indole-3-acetic acid (IAA) up to 3.5 mg/mL, which improved root development, and exhibited the potential for nitrogen-fixation and phosphate solubilization to improve nutrient availability and uptake. Compared to the control, applying the bacterial treatment in the jujube field increased the leaf chlorophyll content by 1.3-fold and improved the fruit yield by 2.4-fold. For the first time, we demonstrate the dual larvicidal and bio-stimulation potential of entomopathogenic B. velezensis CE 100 in managing gall midge larvae and the improvement of jujube fruit production, respectively.