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

Abstract

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 defence against pests. This study explored the use of sodium alginate encapsulation for precise inoculation of two rhizobacteria, Acidovorax radicis and Bacillus subtilis, to suppress aphid (Sitobion avenae) populations on barley (Hordeum vulgare). We optimised a method using 4 mm diameter wet-matrix alginate beads for controlled bacterial delivery directly to plant roots. Rhizobacteria inoculation via alginate beads at root emergence significantly reduced aphid reproductive output, outperforming seed soaking methods, with increased effects when plants were infested with a high initial density of aphids. This suggests the prolonged release from alginate beads led to more consistent bacterial establishment to enhance plant defence responses triggered by aphid feeding. Alginate bead encapsulation demonstrated effective long-term bacterial viability following storage at 4°C for 8 months. Our findings highlight the potential of alginate bead-encapsulated rhizobacteria for reducing aphid populations on barley but emphasise 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 optimising formulations and understanding plant-microbe interactions to enhance field efficacy.