Biocontrol of grapevine aerial and root pathogens by Paenibacillus sp. strain B2 and paenimyxin in vitro and in planta

Paenibacillus sp. strain B2, isolated from the mycorrhizosphere of Sorghum bicolor, was previously shown to possess antagonistic activity against fungi and bacteria due to the secretion of the peptide paenimyxin. The effects of strain B2 and paenimyxin were assessed against grapevine pathogens as they potentially represent a non-polluting complement or an alternative biocontrol agent to existing disease management strategies. In this study, the effects of Paenibacillus sp. strain B2 and paenimyxin were analyzed in vitro or in planta on the aerial or root pathogens of grapevine Botrytis cinerea, Plasmopara viticola and Xiphinema index. The bacterium significantly reduced B. cinerea development in vitro, and substantially decreased X. index numbers in soil and gall formation in the root system of grapevine plants. In vitro, paenimyxin inhibited the mycelial growth of B. cinerea, the mobility of the zoospores of P. viticola and X. index activity. Supplying paenimyxin at the time of inoculation of leaf tissue with P. viticola decreased infection sites, compared to application prior to fungal inoculation. Using the P. viticola/grapevine pathosystem, we showed that paenimyxin acts as a biopesticide against the oomycete but does not trigger plant defense. Conversely, Paenibacillus sp. strain B2 can induce the expression of the defense genes CHI (chitinase), PR-3 (proteinase inhibitor) and LOX (lipoxygenase). Altogether, the results obtained highlight the interest of Paenibacillus sp. strain B2 and paenimyxin for the biocontrol of different grapevine diseases.