Clonal plant networks and the potential for horizontal transmission of endophytic fungi in the field

Clonal plants form networks of ramets connected by rhizomes, which may enable not only the transport of water and assimilates but also the transport of microorganisms, including fungi that form the plant mycobiota. In this study, the following questions were asked: (1) whether the mycobiota is present in rhizomes in naturally functioning linear networks of Maianthemum bifolium in the field, , and (2) whether horizontal transfer of mycobiota occurs between neighbouring ramets. The presence of mycobiota was examined in ramets and rhizome internodes in 30 network fragments occurring in a pine forest. Endophytes were cultured in vitro on PDA medium and subcultured to obtain single colonies. A total of 256 pure isolates were obtained and molecularly identified by ITS rDNA sequence analysis (≥ 98% similarity). Altogether, 48 fungal taxa representing 32 genera were identified, mainly from Ascomycota and Basidiomycota . Some taxa were specific to ramets or internodes, while four taxa were shared, such as the biocontrol species Meyerozyma guilliermondii . The frequency of lateral transmission of fungi along the clone was inferred on the basis of the match in species composition between pairs of consecutive segments. Only 9 pairs (out of 31) of adjacent rhizome segments and only 1 pair (out of 9) of adjacent leaf segments supported the hypothesis of lateral fungal transmission. These results show that the horizontal transfer of the mycobiota in the network under natural conditions, in which plants are constantly exposed to microbial infections, is more limited than it is in networks developed under sterile and controlled laboratory conditions.