Seed or soil: tracing back the plant mycobiota primary sources

Abstract Plants host diverse communities of fungi (collectively called the mycobiota) which play crucial roles in their development. The assembly processes of the mycobiota, however, remain poorly understood, in particular, whether it is transmitted by parents through the seeds (vertical transmission) or recruited in the environment (horizontal transmission). Here we attempt to quantify the relative contributions of horizontal and vertical transmission in the mycobiota assembly of a desert shrub, Haloxylon salicornicum, by comparing the mycobiota of in situ bulk soil and seeds to that of (i) in situ adult individuals and (ii) in vitro -germinated seedlings in soil collected in situ , either autoclaved or not. We show that the mycobiota is partially transmitted through the seeds to seedlings. In contrast, root mycobiota of adults are highly similar to that of bulk soil, whereas adult leaf mycobiota remain similar to that of seeds. Thus, the mycobiota is transmitted both horizontally and vertically depending on the plant tissue. Despite discrepancies between in situ and in vitro approaches, our result may also suggest a compositional turnover in plant mycobiota during plant development. Understanding the respective contribution of these transmission paths to the plant mycobiota is fundamental to deciphering potential coevolutionary processes between plants and fungi.