Characterization of seed germination and protocorm development of Cyrtopodium glutiniferum (Orchidaceae) promoted by mycorrhizal fungi Epulorhiza spp.

Marlon Corrêa Pereira,Diego Ismael Rocha,Olinto Liparini Pereira,Maria Catarina Megumi Kasuya,Tomás Gomes Reis Veloso,Renata Maria Strozi Alves Meira,Dayana Maria Teodoro Francino

doi:10.1590/0102-33062015abb0078

Abstract

Cyrtopodium glutiniferum is an endemic orchid of Brazil with potential medicinal and ornamental applications. As mycorrhizal fungi are essential for the initiation of the orchid life cycle, the aim of this study was to determine the strains of mycorrhizal fungi suitable for seed germination and protocorm development of C. glutiniferum and to characterize the symbiotic development of protocorms. Seeds of C. glutiniferum were inoculated with nine mycorrhizal fungi, Epulorhiza spp., Ceratorhiza spp., Rhizoctonia sp., originally isolated from Brazilian neotropical orchids. Only Epulorhiza isolates promoted seed germination and protocorm development. Three Epulorhiza isolates (M1, M6 = E. epiphytica, M20 = Epulorhiza sp.) promoted protocorm development until leaf production at 63 days. The protocorms are comprised of parenchyma cells delimited by a unistratified epidermis; the parenchyma cells of the upper part of the protocorms are smaller than those located more towards the base. Intact and digested pelotons were observed inside of protocorms implying that the seedlings were capable of mycotrophy. Additionally, the development of a bud primordium only occurred after colonization by fungus. This study suggests that C. glutiniferum has a preference for strains of Epulorhiza and that fungus digestion is essential to protocorm development.

Highlights

In nature, orchids consume mycorrhizal fungi as an energy source to prompt seed germination (Arditti 1992; Rasmussen 1995)
As mycorrhizal fungi are essential for the initiation of the orchid life cycle, the aim of this study was to determine the strains of mycorrhizal fungi suitable for seed germination and protocorm development of C. glutiniferum and to characterize the symbiotic development of protocorms
This study suggests that C. glutiniferum has a preference for strains of Epulorhiza and that fungus digestion is essential to protocorm development

Summary

Introduction

Orchids consume mycorrhizal fungi as an energy source to prompt seed germination (Arditti 1992; Rasmussen 1995). Inoculation with mycorrhizal fungi has been applied to in vitro symbiotic seed germination and orchid cultivation (Pereira et al 2011; Guimarães et al 2013), with promising applications in the propagation of ornamental (Pereira et al 2003a; 2005a), endangered (Zettler & McInnis 1992; Zettler et al 2007), and medicinal orchids (Chang & Chou 2001; Tan et al 2014). Cyrtopodium glutiniferum is a species of neotropical orchid found in mountainous regions of the states of Minas Gerais and Rio de Janeiro in Brazil (Barros et al 2015). It is terrestrial and sometimes litophytic, with an appealing flower suitable for horticulture (Caramaschi 2001). Given the ongoing threats to the natural habitats of C. glutiniferum, the ability to efficiently propagate this orchid would greatly enhance its conservation

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