Colonization and antagonistic activity of endophytic fungi in seagrasses: Understanding endophyte interaction

Abstract

Endophytic fungal colonization in plants is governed by complex interactions with the defense mechanism of the host and antagonistic effects of other endophytes. In this study, endophytic fungal interaction was assessed by histological examination and co-culture methods. Results showed fungal colonization in the intercellular space of the epidermis and both intercellular and intracellular spaces of the cortical cells suggesting close interaction with their seagrass hosts. Dense colonization, hyphal branching, coiling and formation of networks were observed in the cortical cells. Less competition for space and reliable source of nutrition in the cortex may favor fungal growth. No fungal hyphae were detected in the vascular tissues of seagrasses. All the endophytic fungi isolated from seagrasses showed antagonistic activity. Aspergillus tamarii, A. ochraceopetaliformis, Penicillium citrinum, Beauveria bassiana, Eutypella sp. and Xylaria sp were the most active antagonists. Antagonistic interaction involved deadlock and replacement. Deadlock was associated with physical blocking of the antagonist’s colony by hyphal aggregation and production of inhibitory metabolites. Demarcation line and colony pigmentation in Xylaria sp. during co-culture assay indicated the production of high quantities of inhibitory molecules. Endophytic fungi in seagrasses also produced volatile organic compounds (VOC) which resulted to deadlock at mycelial distance. Thus, endophyte colonization and distribution in seagrass tissues are in�uenced by their interaction with the hosts and other endophytes. But interestingly, cyclical intransitivity of multispecies interaction manifested by these fungal species suggested possible co-existence in seagrass tissues.