Monotropoid Mycorrhizal Characteristics of Monotropa uniflora (Ericaceae) Collected from a Forest in Korea

Abstract

The roots of Monotropa uniflora were collected from a forest in Korea. Morphological characteristics of monotropid mycorrhizas of the plants were determined. Thick mantles covered the roots and fungal pegs inside the epidermal cells of the roots were observed. Fungal symbionts were identified by sequence analysis of internal transcribed spacer region. Phylogenetic analysis based on the sequences demonstrated that the fungus was the most closely related to Russula heterophylla. The result support the strong specificity between M. uniflora and Russula species. Monotropoideae is a subfamily of the Ericaceae, and most of the species in this subfamily are achlorophyllous, and thus, heterotrophic plants [1]. These plants are not able to fix carbon by themselves because they have very low amounts of chlorophyll-related pigments [2]. They obtain fixed carbon from photosynthetic plants through mycorrhizal hyphae; plants exhibiting this relationship are referred to as mycoheterotrophic plants [3, 4]. The mycorrhizal relationship between Monotropoideae plants and fungi is referred to as monotropoid mycorrhiza. Such relationships are associated only with certain genera of fungi, including Lactarius, Rhizopogon, Russula, and Tricholoma, which also form ectomycorrhizas with surrounding photosynthetic plants [5-8]. In particular, Lac-tarius and Russula are well known as relatively dominant ectomycorrhizal fungi in forest ecosystems [9, 10]. Structures of monotropoid mycorrhizas have been studied in species of several Monotropoideae plants [11-13]. The mycorrhizal structure has typical ectomycorrhizal characteristics, including a hyphal mantle covering the roots and Hartig nets between cortex cells of the roots. In addition, fungal hyphae penetrate and produce fungal pegs inside the epidermal cells of plant roots, which is the characteristic structure of monotropoid mycorrhizas. Fungal pegs have been known as structures that trans-locate photosynthetic carbon compounds from the fungi to photosynthetic plants. Monotropoideae consists of 15 species belonging to 10 genera [1], and many species of Monotropoideae are endangered because of habitat destruction. It is important to conduct studies on Monotropoideae to protect the declining populations of these plants, as well as to provide important clues regarding translocation of nutrients through the hyphal networks [14-16]. Monotropa spp. are distributed in the northern hemisphere. In particular, M. uniflora are often found in shaded and wet areas of old forests in Korea. The mycor-rhizal status and fungal symbionts of M. uniflora have not yet been determined in Korea. The purpose of this study was to investigate the symbiotic fungi in the roots of M. uniflora collected from a forest in Korea. A total of seven individual M. uniflora were collected from a mixed forest in Gangwon-do, Korea (37 o 43'29" N, 128 o 35'53" W). The roots along with the soil were collected and taken to the laboratory. These were then washed under running tap water to remove the attached soil particles. The root balls were observed under a stereomicro-scope (Olympus SZX9, Olympus, Japan). Root tips were This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http:// creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.