Strong elicitation of plant defense pathways by foliar and collar inoculations of wheat with the Bacillus pumilus strain JM79

Abstract

The ability of the Bacillus pumilus JM79 strain to induce systemic resistance in wheat against Fusarium graminearum (Fg), a major wheat pathogen, was investigated using the Fusarium crown rot (FCR) pathosystem. The B. pumilus strain JM79 exhibited the ability to colonize both root and leaf surfaces while secreting surfactin-like pumilacidin in the root zone of wheat plantlets. Experiments involving foliar inoculation with JM79 revealed its ability to induce a strong local defense response in wheat, characterized by the selective overexpression of genes associated with phenylpropanoid metabolism and cell wall reinforcement pathways. Moreover, pre-inoculation of the wheat collar, at the soil surface interface, with the JM79 strain prior to Fg inoculation led to the overexpression of wheat genes linked to both jasmonic acid/ethylene (JA/ET) and salicylic acid (SA)-dependent defense pathways. This direct induction occurred during the asymptomatic phase of Fg infection, compensating for the lack or absence of an early immune response triggered by Fg infection. Collectively, these findings reveal for the first time that the B. pumilus strain JM79 produces a higher proportion of long-chain pumilacidins under in planta conditions than under in vitro conditions, and is capable of activating both local and systemic resistance in wheat plants, underscoring its potential as a biocontrol agent against major wheat fungal diseases.