Peanut preinoculation with a root endophyte induces plant resistance to soil-borne pathogen Fusarium oxysporum via activation of salicylic acid-dependent signaling

Abstract

The root endophyte Phomopsis liquidambaris B3 effectively protected peanut against root rot caused by Fusarium oxysporum. We investigated (i) the effects of preinoculation (before F. oxysporum inoculation) and postinoculation (post F. oxysporum inoculation) with B3 on pathogenic infection and (ii) the potential mechanisms underlying the suppression of root rot by B3 colonization. Peanut seedlings preinoculated, postinoculated or noninoculated with B3 and challenged or not challenged with F. oxysporum were cultivated in pots with sterilized vermiculite. The root rot severity, plant growth, defense-related enzyme activity and signaling compounds in plant tissues were investigated. Chemical manipulation experiments were performed to verify the signals involved in the suppression of root rot by B3. B3 preinoculation efficiently suppressed root rot, as evidenced by decreased cell death, pathogenic colonization and disease severity; however, these effects were absent in the B3 posttreated roots. B3 preinoculation locally and systemically enhanced resistance against pathogenic infection, which coincided with increased activities of pathogenesis-related proteins. These increased activities positively correlated with increased salicylic acid (SA) and hydrogen peroxide (H2O2) levels, in which SA played a dominant role. Preinoculation with B3 effectively suppressed F. oxysporum infection in peanut roots by activating the SA-dependent defense pathway.