Method and timing of rhizobacteria inoculation to plant roots alters success and strength of aphid suppression

Insect pests cause substantial yield losses globally, necessitating novel pest control approaches beyond chemical pesticides. Rhizobacteria, beneficial root-associated bacteria, present a promising alternative by enhancing plant growth and defences against pests. This study explores the use of sodium alginate encapsulation for precise inoculation of two rhizobacteria, Acidovorax radicis and Bacillus subtilis , to suppress aphid populations on barley ( Hordeum vulgare ). We optimized a method using 4mm diameter wet-matrix alginate beads for controlled bacterial delivery directly to plant roots. Two experiments evaluated the impact of inoculation methods and timing on aphid suppression. Results indicated that rhizobacteria inoculation via alginate beads at root emergence significantly reduced aphid reproductive output, outperforming seed soaking methods. This suggests that more consistent bacterial establishment and prolonged release from alginate beads enhances plant defence priming. Additionally, alginate bead inoculation demonstrated effective long-term bacterial viability following storage at 4° C for eight months, supporting potential field application. Our findings highlight the potential of alginate bead-encapsulated rhizobacteria for aphid suppression on barley, but emphasizing the need for precise inoculation timing and placement. This approach offers a robust method for empirical research and practical agricultural application, paving the way for sustainable pest management strategies. Future work should focus on optimizing formulations and understanding plant-microbe interactions to enhance field efficacy.