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Environment has a Stronger Effect than Host Plant Genotype in Shaping Spring Brassica napus Seed Microbiomes

Seed are reproductive units that transfer genetic information to the next generation and harbor microbial communities that may interact with a host plant at all stages of its development. Here, we assessed the effect of the environment and plant genotype on the seed microbiome of eight spring Brassica napus lines harvested from four site years in Saskatchewan, Canada: one location each in 2016 and 2017 and two additional locations in 2017. Seed microbiomes were characterized using high-throughput amplicon sequencing of the bacterial 16S ribosomal RNA and fungal internal transcribed spacer regions. Our results revealed that microbial communities were predominantly shaped by the environment, with location explaining 34% of bacterial and 43% of fungal total variance. Meanwhile, genotype had a smaller effect, accounting for only 9% of bacterial and 13% of fungal variance. The seed microbiome of B. napus predominantly contained members of Enterobacteriales and Pseudomonadales bacterial orders as well as Pleosporales and Capnodiales fungal orders. Additionally, common taxa, including Enterobacteriales, Pseudomonadales, Micrococcales, Sphingomonadales, Pleosporales, Capnodiales, Tremellales, Filobasidiales, and Sporidiobolales, were detected across all site years. Our results demonstrate that the environment plays a dominant role in shaping spring B. napus seed microbiomes, with more subtle contributions related to host plant genotype. Information collected in this study may contribute to the development of novel and sustainable breeding and agricultural strategies that consider microorganisms carried by seed.