Identification of Species from
the Genus Ganoderma Using the Internal Transcribed
Spacer 2 Region of the Mushroom DNA
Reviewed: Liao
B, Chen X, Han J, et al. Identification of
commercial Ganoderma (lingzhi)
species by ITS2 sequences. Chin Med.
2015;10:22. doi: 10.1186/s13020-015-0056-7.
A number of Ganoderma
species are sold as dietary supplements and herbal medicines worldwide. Ling zhi* (Ganoderma lucidum,
Ganodermataceae) and zi zhi (G. japonicum syn. G. sinense; zi zhi means black reishi) are both listed in the Chinese Pharmacopoeia to supplement qi,
calm the spirit, relieve cough, and to calm panting.1 In the United
States, dietary supplements made from G. lucidum, G. sinense, or G. tsugae are
sold using the common name “reishi”; other commercial Ganoderma
species in the United States include Oregon ganoderma (G.
oregonense) and artist’s conk (G. applanatum).
The main use of reishi is for its immunomodulatory benefits, but it is also
consumed as a tonic, sedative, and antidepressive agent.2
The authors of this paper analyzed 63
specimens belonging to 11 Ganoderma
species. The samples included 33 commercial samples (G. lucidum
[26], G. resinaceum [2], G. sinense
[5]). The remainder of the sequences included in the analysis was obtained from
GenBank accessions. The use of the nuclear ribosomal Internal Transcribed
Spacer 2 (ITS2) as the single locus to distinguish
the species was based on recommendations by the International Barcode of Life Conference
and by Chinese researchers who suggested using ITS2
as a universal DNA barcode for identification of medicinal plants.3,4
The authors were able to authenticate all
the samples using the ITS2 sequence,
and concluded that this was an appropriate approach for authentication of ling zhi materials. Based on their observed difference in
the ITS2 sequences of G. lucidum
samples collected in Southeast Asia and those from Europe, they suggest that
the European G. lucidum is actually an
entirely different species and should be re-classified.
Comment: The
various species of Ganoderma are
readily distinguishable in their whole form. However, correct identification of
Ganoderma is rather challenging when the
morphological features of the fruiting body portion of the mushroom are no
longer recognizable, e.g., with powdered material or with extracts. High-performance
thin-layer chromatography (HPTLC) fingerprints for three Ganoderma
species have been published by the American Herbal Pharmacopoeia,2
but G. lucidum and G. sinense
are difficult to distinguish by chemical means. Since some of the species can
be used interchangeably, a determination down to the species level may not be necessary,
but the DNA-based approach detailed in this paper will allow doing so. This may
be a uniquely applicable approach in identifying Ganoderma mycelia
biomass products, which are prevalent on the North American market.
There is a risk associated with using
genetic sequences data deposited in GenBank, although it is widespread practice.
Since there is no verification of the data, the deposition of erroneous
sequences is known to occur and, therefore, relying solely on GenBank data for
certain species may introduce errors in species identification. It is also unclear
if fungi can be generally differentiated using only one genetic locus (ITS2 in this case), or if the choice of the region to be
sequenced is as controversial as with plant ingredients, where often two or
three loci are amplified to enable a clear distinction among related species,
in particular since the Consortium for the Barcode of Life proposed the use of matK and rbcL as
universal barcodes for land plants.5
*Note: There are a number of different
color variations observed with G. lucidum; chi zhi specifically relates to red reishi, but generically
they are all called ling zhi or lingzhi.
References
1.
Zhao Z, Chen H. Ling zhi – Ganoderma. In: Chinese Medicinal
Identification: An Illustrated Approach. Taos, NM: Paradigm Publications;
2014: 466-467.
2.
Upton
R, ed. American Herbal Pharmacopoeia and
Therapeutic Compendium: Reishi Mushroom: Ganoderma lucidum: Standards of
Analysis, Quality Control, and Therapeutics. Scotts Valley,
CA: American Herbal Pharmacopoeia; 2000.
3.
Zhang
Y, Guo L-D. Progress of fungal DNA barcode. Mycosystema.
2012;31(6):809-820.
4.
Chen
S, Yao H, Han J, et al. Validation of the ITS2 region as
a novel DNA barcode for identifying medicinal plant species. PLoS One. 2010;5(1):e8613. doi:
10.1371/journal.pone.0008613.
5.
CBOL
Plant Working Group. A DNA barcode for land plants. Proc Natl
Acad Sci U S A. 2009;106(31):12794-12797.
