Transmission of <i>Xanthomonas campestris</i> pv. <i>incanae</i> and Associated Microbiome in <i>Matthiola incana</i> Seed

Xanthomonas campestris pv. incanae (Xci) is known to cause systemic infections in the stem of Matthiola incana. Prior research observed that the pathogen can invade the vascular system and extend into the seed peduncles of infected plants, suggesting a likely mean for internal contamination of the seeds. However, this and other potential pathways of seed infection and seed-to-seed transmission, have not been sufficiently investigated. Using both culture-based and metagenomic approaches, we evaluated the potential for and efficiency of seed infection by Xci after vascular and floral inoculation of the mother plants, as well as the possibility for seed-to-seed transmission. We also explored the diversity of the M. incana seed microbiome in response to inoculation with Xci. Results showed that the vascular system was a viable and highly efficient pathway of seed infection by Xci, unlike the floral organs, and that seed infection by the vascular pathway negatively impacted seed germination. We also demonstrated that seed-to-seed transmission of Xci occurred at an epidemiologically significant degree. The primary difference among microbiomes of seeds harvested from inoculated and non-inoculated plants was the presence of Xci, which had extremely high relative and absolute abundance in infested seeds. Additionally, minor effects of inoculation treatment, seed infection pathway, and the interaction between the two were observed for overall seed microbial community composition and diversity. These findings pave the way to future exploration of the seed microbiome in M. incana.