The assessment of the seedling, recruited, and second generation microbiome of Lolium perenne cv. Alto.

• Lolium perenne (perennial ryegrass) is a common temperate pasture grass species and is favoured by dairy farmers for its high yield, feed quality, and persistence. Commercially, the known association with the mutualistic endophytic fungus Epichloë festucae subsp. lolii is used to enhance insect resistance of host plants, but the broader microbiome is largely unknown.• Tag sequencing of the 16S gene was used to examine the bacterial microbiome of perennial ryegrass (cv. Alto) seeds (generation 1) germinated on filter paper, subsequent mature plants grown in two different media (potting mix and sand), and seed (generation 2) from crosses of these mature plants germinated on filter paper.• The bacterial microbiome of perennial ryegrass seed was dominated by the families, Pseudomonadaceae, Enterobacteriaceae, and Burkholderiaceae. The resident fungal endophyte only affected the diversity of bacterial OTUs within the seed microbiome. There was evidence that certain OTUs were seed transmissible, including members from initial seedlings. Large supplementation occurred during the growing season with >85% OTUs persistent from seed being maintained at much lower levels in the mature plants. Clustering of the microbiome profiles, reflected the growth media, indicating microbial recruitment played a key role in the mature plant.• This study sheds new light on perennial ryegrass microbiomes and has identified some OTUs of potential commercial significance due to their seed transmissibility and likely importance in seed germination, early seedling vigour, and protection of the host against pests and disease.