A Trojan horse approach for white mold biocontrol: paraconiothyrium endophytes promotes grass growth and inhibits Sclerotinia sclerotiorum

Abstract

Endophytic Paraconiothyrium strains associated with Brachiaria spp. and Panicum maximum were screened in vitro and in vivo for antagonism against Sclerotinia sclerotiorum and grass growth promotion. Based on multilocus phylogenetic analyses, three Paraconiothyrium estuarinum strains and two Paraconiothyrium cyclothyrioides strains were identified. In vitro, P. estuarinum strain CML 3699 was the most efficient in S. sclerotiorum mycelial growth inhibition. Volatile organic compounds (VOCs) produced by Paraconiothyrium strains reduced the sclerotia number, sclerotia weight and apothecia number in comparison to the control. The VOCs of P. cyclothyrioides strain CML 3698 promoted higher inhibitory effects on apothecium production. Paraconiothyrium estuarinum CML 3695, when inoculated into Brachiaria ruziziensis seeds, promoted increased biomass in comparison to those in non-inoculated seeds. All strains were sensitive to higher glyphosate doses, which reduced their mycelial development. However, when the mycelia of the endophytic fungi were removed and transferred to new PDA medium, the fungi recovered growth. After desiccation of Paraconiothyrium-inoculated B. ruziziensis with glyphosate, Paraconiothyrium strains recovered the ability to colonize the sclerotia of S. sclerotiorum and reduced carpogenic germination via a Trojan-horse-like mode of action. Considering that grass can be deployed by farmers as a physical barrier to S. sclerotiorum ascospore release, the growth promotion and parasitism of sclerotia exerted by Paraconiothyrium strains towards B. ruziziensis reinforce this disease control strategy.