Abstract: As one of the largest and most diverse flowering families on Earth, orchids are represented across every continent, with the exception of Antarctica. Though highly diverse in growth strategy and floral morphology, all orchids are unified by an obligate dependence on symbiotic fungi known as orchid mycorrhizal fungi (OMF) for basic nutrition. This is especially apparent in the dust-like seeds of orchids which are devoid of nutrients and are thus reliant on colonization by compatible fungi to initiate germination and growth. Most studied OMF have been identified belonging to Tulasnellaceae, Ceratobasidiaceae, Sebacinaceae, and Serendipitaceae, however such information remains limited in tropical Pacific islands despite the region’s high rates of orchid diversity and endemism. Colonization of these remote oceanic islands by obligate symbiotic organisms would tend to favor generalists over specialists, but this has yet to be proven with orchids and their OMF.
Arundina graminifolia is a terrestrial orchid widely distributed across subtropical and tropical Southeast Asia and several islands in the Pacific. Though the orchid has been documented to have a high degree of symbiotic specificity with Tulasnellaceae in continental Asia, it remains unclear whether a similar pattern exists in populations scattered across the Pacific islands. To better understand whether symbiotic specificity precludes colonization of these remote oceanic islands, we investigated the identity of OMF of A. graminifolia in the western Pacific island of Guam. We sampled individuals of A. graminifolia from two distinct populations in Mt. LamLam and Priests Pools located in southern Guam. Mycorrhizal DNA from orchid roots was isolated, extracted, amplified by polymerase chain reaction (PCR), and sequenced by Sanger sequencing. Phylogenetic analyses will be conducted using sample sequences and documented Tulasnellaceae symbionts.
We found that A. graminifolia in Guam were similar to orchids in continental Asia showing predominant mycorrhizal specificity towards Tulasnellaceae across collected samples. Phylogenetic analyses are currently being conducted and results will be published at a later time. The findings of this study suggest that colonization of remote oceanic islands does not limit symbiotic specialization. In the future, we intend on studying the mycorrhizal symbionts of A. graminifolia in other Pacific islands in addition to other areas in continental Asia in a more comprehensive island biogeography study.
