Larvicidal activity against Phenolia (Lasiodites) picta (Coleoptera: Nitidulidae) on jujube (Zizyphus jujuba Miller var. inermis Rehder) and the improvement of high-quality fruit production using Bacillus licheniformis PR2

The increasing consumption and demand of jujube fruits has accelerated production over the recent past. However, the aspects of eco-friendly strategies for pest control and high-quality fruit production are becoming more important to combat the impending dangers of repeated chemicals use in orchard management. This study identified for the first time, the sap beetle (Phenolia (Lasiodites) picta) larvae (based on mitochondrial DNA barcode sequencing), as the major insect pest causing damage in jujube fruits in Korea. The study investigated the insecticidal potential of cuticle-degrading enzymes from Bacillus licheniformis PR2 against P. picta larvae, and the enhancement of fruit quality and yield, through phytohormone production, ammonia production and phosphate solubilizing properties of the bacterium. Bacillus licheniformis PR2 produced chitinase and protease and caused larval mortalities of 55.56 % and 68.89 % when treated with the bacterial broth culture and crude enzyme fraction, respectively. The insecticidal activity in both treatments were characterized by deep cuticle fissures with swollen/depressed surfaces and loss of sensilla. Field application of B. licheniformis PR2 effectively controlled P. picta larvae in jujube orchard during active feeding period as they moved from fruit-to-fruit which reduced the damage and premature fruit-drop. Moreover, B. licheniformis PR2 produced indole-3-acetic acid (IAA) and gibberellic acid (GA) phytohormones, and increased the soil concentration of nitrogen and phosphorus concentration in the soil. The application of B. licheniformis PR2 in jujube orchard increased the chlorophyll content/photosynthetic activity, fruit yield, fruit characteristics (such as length, diameter and fruit weight) and the organoleptic properties (such as the Ca content, firmness and sugar concentration) of jujube fruits, compared to the control and conventional treatment. Thus, we demonstrate that B. licheniformis PR2 can be a viable alternative to chemical pesticides and fertilizers and could enhance the eco-friendly and sustainable production of high-quality jujube fruits to meet the increasing demands.