The Role of Non-Mycorrhizal Fungi in Germination of the Mycoheterotrophic Orchid Pogoniopsis schenckii Cogn.

Abstract

Endophytic fungi are those that inhabit within organs and tissues without causing damage, while mycorrhizal fungi develop hyphal complexes called pelotons within cortical cells of orchid roots. Although abundant and frequent in all plant organs, the role of endophytic fungi has been neglected in relation to orchid’s early development. Pogoniopsis schenckii Cogn. is an aclorophyllated and mycoheterotrophic (MH) orchid. This study aimed at i) investigating the endophytic fungal community in organs of P. schenckii and its mycorrhizal fungi associated; ii) evaluating the ability of isolated fungus in the in vitro germination of the seeds of the species, and iii) describing the development of P. schenckii protocorm, analyzing the ultrastructure of the infected cells. Six genera of fungi were isolated and identified through the partial sequencing of the internal transcribed spacer region, all belonging to the phylum Ascomycota. Also, Tulasnellaceae was identified through uncultured technique as potentially mycorrhizal in this MH orchid. Some isolates of the genera Trichoderma, Fusarium, and especially Clonostachys presented germinative potential on P. schenckii seeds, causing rupture of the external tegument. The protocorms showed complete absence of peloton formation, but fungal hyphae were clearly observed within living cells. This is the first report of germination of a MH and aclorophyllated orchid species stimulated by the presence of non-mycorrhizal endophytic fungi isolated from fruits and roots of the same species.

The Diversity Analysis and Functional Prediction of Endophytic Fungi Community of Gymnadenia Conopsea from Different Altitudes in Tibet

“…A total of 14,800 OTUs belonging to 4 phyla, 73 families, and 99 genera obtained from tissues and rhizosphere soils were analyzed. It was previously reported that mycorrhizal fungi associated with orchids were mainly Basidiomycota and Ascomycota (Sisti et al 2019). In our study, Ascomycota (33.71%-86.38%)…”

“…Endophytes can not only promote plant growth but also produce bioactive components (Sisti et al 2019 Ng et al (2013) declared that the genome of UM238, a dematiaceous fungus belonging to Herpotrichiellaceae, contained a variety of protective genes that helped the fungus survive in adverse environments. We also found that the abundance of Herpotrichiellaceae in roots was high, with the highest at the LD collection site; this family may aid G. conopsea adaptation to the environment of the Qinghai-Tibet Plateau, which is characterized by low temperature, strong UV ultraviolet light and low oxygen.…”

In Vitro Symbiotic Germination: A Revitalized Heuristic Approach for Orchid Species Conservation

“…In nature, this is achieved by mycorrhizal symbiosis, which is discussed later in this review. Germination usually takes several months to a year [ 20 ] since germinating orchid seeds do not directly produce leaf and root primordia. Instead, a protocorm develops during the germination process.…”

“…Most recognized OMF genera are basidiomycetous fungi with an anamorphic stage resembling the well-known plant pathogen, Rhizoctonia , and are named “ Rhizoctonia -like fungi” [ 26 , 29 ]. Though uncommon, studies showing non- Rhizoctonia -like fungi forming OM have increased since the early 2000s [ 20 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 ]. Those genera include strong pathogen [ 6 , 30 , 33 , 38 ], saprobes [ 39 , 40 ], ectomycorrhizal fungi [ 41 , 42 ], and ascomycetous fungi [ 20 , 43 ].…”

“…In a study on Cyrtosia septentrionalis , a small box chamber was used for inoculation with no direct contact between the fungus and seeds [ 33 ]. Depending on the species, seed viability, OMF compatibility, or medium components, seeds can germinate in a month ( Figure 1 d) or less [ 48 ] or even up to a year [ 20 , 55 ].…”