Recently we demonstrated that the seed microbiome of certain spinach (Spinacia oleracea) seed lots can confer disease suppression against Globisporangium ultimum damping-off (previously known as Pythium ultimum). We hypothesised that differences in the microbial community composition of spinach seed lots correlate with the levels of damping-off suppressiveness of each seed lot. Here, we show that a large proportion of variance in seed-associated bacterial (16S) and fungal (ITS1) amplicon sequences was explained by seed lot identity, while 9.8 % of bacterial and 7.1 % of fungal community variance correlated with disease suppression. More specifically, a higher relative abundance of basidiomycetous dimorphic yeasts such as Vishniacozyma, Filobasidium and Papiliotrema and of the bacterial genus Massilia was a key feature of suppressive seed microbiomes. We suggest that the abundance of these genera is indicative of seed lot suppressive potential. Seed processing and treatment can become more targeted with indicator taxa being used to evaluate the presence of beneficial seed-associated microbial functions. This process in turn could contribute to the sustainable management of seedling diseases. Finally, this study highlights the ubiquity of yeasts in spinach seed microbiota and their potential beneficial roles for seed health.