Mycorrhizal Fungi of Phalaenopsis japonica (Orchidaceae) and Their Role in Seed Germination and Seedling Development

Abstract

Epiphytic orchids comprise 68% of vascular epiphytes globally; nevertheless, many are endangered. One such epiphytic orchid is Phalaenopsis japonica, which is widely used in the floricultural industry. This study aimed to identify the mycorrhizal fungi of adult P. japonica and their roles in seed germination and seedling development. Root samples were collected from 32 adults across 4 sites in southern Japan, and mycorrhizal fungi were identified using Sanger and high-throughput sequencing (HTS). The results show phylogenetically diverse mycobionts, mainly Ceratobasidiaceae (CE) and Tulasnellaceae (TU), with dominant OTUs designated CE6 and CE22. Sanger sequencing found 9 OTUs, 4 CE, and 5 TU; HTS detected 22 OTUs, 4 CE, 16 TU, and 2 Serendipitaceae. Seeds inoculated with CE6 improved germination and protocorm development compared with other strains. In addition, asymbiotic seedlings inoculated with CE6, CE22, and TU18 displayed varying effects in growth, with CE6 being the most notable. While TU18 did not promote seed germination, it effectively promoted leaf development in seedlings. Overall, Ceratobasidiaceae was predominantly associated with seed germination, seedling growth, and the adult stages, with CE6 and CE22 becoming the primary partners throughout the life history of P. japonica. Our findings illuminate mycorrhizal symbiosis in epiphytic habitats, offering conservation and commercial production insights.

Orchid Mycorrhizal Association of Cultivated Dendrobium Hybrid and Their Role in Seed Germination and Seedling Growth

“…Additionally, because of the difficulty in amplifying the ITS region of the common OMF Tulasnellaceae using universal fungal primers [ 23 ], we used the Tulasnellaceae-specific primers ITS5/ITS4-Tul2 [ 21 , 24 ] and 5.8S-Tulngs/ITS4-Tul2 [ 24 , 25 ]. PCR amplification was conducted using Mighty Amp DNA polymerase v. 3 (TaKaRa, Shiga, Japan), following the protocol described by Chamara et al [ 15 ].…”

“…PCR was performed in triplicate using 2× KAPA HiFi HotStart ReadyMix (Kapa Biosystems, Wilmington, DE, USA), following the manufacturer’s instructions. Purified PCR products underwent quantification using a Qubit dsDNA HS Assay Kit, and library preparation and sequencing were carried out according to the method presented by Chamara et al [ 15 ].…”

“…In addition, the functions of OMF infecting horticultural cultivars are unknown. OMF can have diverse functions; some fungal species promote seed germination and subsequent growth, while others do not affect seed germination but support leafy seedling growth [ 15 , 16 ]. Conducting symbiotic culture experiments using orchid seeds and asymbiotic seedlings would provide insights into these functions.…”