Inoculation of indigenous plant growth-promoting bacteria increases resistance and the growth of lettuce in the hydroponic system

Cultivating vegetables in the hydroponic system is often exposed to biotic and abiotic stresses. The use of suitable plant growth-promoting bacteria (PGPB) that can alleviate the impact of biotic stress is urgently needed. This study aims to evaluate the role of Universitas Brawijaya educational forest (UB Forest) indigenous PGPB strains on the induction of plant resistance against plant pests or diseases and the promotion of lettuce growth in a Nutrient Film Technique (NFT) hydroponic system. This study used a randomized block design with 7 treatments and 3 replications. The results showed that the PGPB strain inoculation reduced plant damage caused by thrips, induced phenylalanine ammonia-lyase (PAL), peroxidase (PO), and polyphenol oxidase (PPO) enzyme accumulation in planta, and increased the growth and photosynthetic pigments of lettuce. However, the treatments had no effect on increasing total phenolic compounds. Pseudomonas lundensis UB-53 and Pseudomonas migulae UB-54 inoculations exhibited higher activity in suppressing plant damage caused by thrips, inducing enzymes related to plant defense, and increasing lettuce growth. Two PGPB strains, i.e. P. migulae UB-54 and P. lundensis UB-53, have a high potential to be developed as eco-friendly biocontrol agents to overcome biotic stress and boost lettuce crop growth in NFT hydroponic systems.