Differences in stability of seed-associated microbial assemblages in response to invasion by phytopathogenic microorganisms

Abstract

Seeds are involved in the vertical transmission of microorganisms from one plant generation to another and consequently act as reservoirs for the plant microbiota. However, little is known about the structure of seed-associated microbial assemblages and the regulators of assemblage structure. In this work, we have assessed the response of seed-associated microbial assemblages ofRaphanus sativusto invading phytopathogenic agents, the bacterial strainXanthomonas campestrispv.campestris(Xcc) 8004 and the fungal strainAlternaria brassicicolaAbra43. According to the indicators of bacterial (16S rRNA gene andgyrBsequences) and fungal (ITS1) diversity employed in this study, seed transmission of the bacterial strainXcc8004 did not change the overall composition of resident microbial assemblages. In contrast seed transmission of Abra43 strongly modified the richness and structure of fungal assemblages without affecting bacterial assemblages. The sensitivity of seed-associated fungal assemblage to Abra43 is mostly related to changes in relative abundance of closely related fungal species that belong to theAlternariagenus. Variation in stability of the seed microbiota in response toXccand Abra43 invasions could be explained by differences in seed transmission pathways employed by these micro-organisms, which ultimately results in divergence in spatio-temporal colonization of the seed habitat.