Pre-inoculation with Arbuscular Mycorrhizal Fungi and Humic Acid Enhances Tomato Growth, Nutrient Uptake, and Induced Resistance Against Ralstonia solanacearum

Bacterial wilt caused by Ralstonia solanacearum race 1 is one of the most destructive diseases of tomato, resulting in severe yield losses worldwide. This study evaluated the individual and combined effects of humic acid (H) and arbuscular mycorrhizal fungi (AMF) with or without NPK supplementation on tomato growth, nutrient uptake, defense activation, and suppression of bacterial wilt. Disease severity was highest in inoculated controls (60.4%), while integrated treatments markedly reduced wilt incidence, with the triple combination (NPKHM+) achieving the lowest severity (23.2%). Growth performance and nutrient uptake of N, P, and K were enhanced, particularly when combined with humic acid and AMF, which improved biomass, chlorophyll content, and nutrient assimilation under both healthy and infected conditions. Biochemical and molecular analyses revealed that phenol accumulation, peroxidase (POX), polyphenol oxidase (PPO), and phenylalanine ammonia-lyase (PAL) enzyme activities, as well as the expression of POX, PPO, PAL, and PR-2 genes, were highly upregulated in treated plants. The NPKHM⁺ treatment produced the highest biochemical and transcriptional responses, which coincided with maximal wilt suppression and improved plant vigor. These findings demonstrate that the integration of mineral nutrition with organic and microbial amendments synergistically enhances tomato resistance to bacterial wilt while promoting growth, providing a sustainable and effective strategy for disease management.