A New Oidiodendron maius Strain Isolated from Rhododendron fortunei and its Effects on Nitrogen Uptake and Plant Growth

Xiangying Wei,Dongming Pan,Jianjun Chen,Chunying Zhang

doi:10.3389/fmicb.2016.01327

Abstract

A new mycorrhizal fungal strain was isolated from hair roots of Rhododendron fortunei Lindl. grown in Huading Forest Park, Zhejiang Province, China. Morphological characterization and internal transcribed spacer rDNA analysis suggested that it belongs to Oidiodendron maius Barron, and we designated it as strain Om19. Methods for culturing Om19 were established, and the ability of Om19 to form mycorrhizae on R. fortunei was evaluated in a peat-based substrate. Microscopic observations showed hyaline hyphae on the surface of hair roots and crowded hyphal complexes (hyphal coils) inside root cortical cells of R. fortunei after inoculation, indicating that the roots were well colonized by Om19. In a second experiment, fresh and dry weight of R. fortunei 2 months after Om19 inoculation were greater than uninoculated plants, and the total nitrogen absorbed by plants inoculated with Om19 was greater than the uninoculated controls. qRT-PCR analysis of five genes related to N uptake and metabolism (two nitrate transporters, an ammonium transporter, glutamine synthetase, and glutamate synthase) showed that these genes were highly upregulated with twofold to ninefold greater expression in plants inoculated with Om19 compared to uninoculated plants. In the third experiment, Om19 was inoculated into the peat-based substrate for growing Formosa azalea (Rhododendron indica ‘Formosa’). ‘Formosa’ azalea plants grown in the inoculated substrate had larger canopies and root systems compared to uninoculated plants. Our results show that Om19 could be an important microbial tool for improving production of Rhododendron plants.

Highlights

About 6,000 recognized species of soil fungi form mutualistic symbioses with roots of more than 90% of land plants, which are collectively known as mycorrhizas (Smith and Read, 2008)
Slower growing fungi were subcultured on 2% malt extract agar (MEA; Thom and Church, 1926), a total of 84 were isolated and maintained in the dark at 25◦C for 2–4 weeks for morphological identification, and subcultures were stored at 4◦C until further use
When R. fortunei seedlings were grown in a peat-based substrate for 2 months, substrate pH ranged from 4.9 to 5.2 across all treatments

Summary

Introduction

About 6,000 recognized species of soil fungi form mutualistic symbioses with roots of more than 90% of land plants, which are collectively known as mycorrhizas (Smith and Read, 2008). Endomycorrhiza includes arbuscular, ericoid, and orchid mycorrhiza (Smith and Read, 2008). Ericoid mycorrhizal (ERM) fungi form symbiotic associations with roots of plants in the family Ericaceae (Perotto et al, 2012). Such ERM fungi include Hymenoscyphus ericae (Read) Korf and Kernan, Oidiodendron spp., Cadophora finlandia (Wang and Wilcox) Harrington and McNew, and Scytalidium vaccinii Dalpe, Litten and Sigler (Read, 1996). O. maius has been recorded as ERM endophytes of several taxa in the Ericaceae (Hambleton and Currah, 1997; Addy et al, 2005) and is especially common in the roots of Rhododendron species (Usuki et al, 2003; Bougoure and Cairney, 2005; Zhang et al, 2009; Tian et al, 2011)

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Results

Conclusion