Annals of Botany 82 : 189–194, 1998

Nuclear DNA Content of 26 Orchid (Orchidaceae) Genera

with Emphasis on Dendrobium
W. E. J O N E S*, A. R. K U E H N LE*† and K. A R U M U G A N A T H AN‡
* Department of Horticulture, UniŠersity of Hawaii at Manoa, 3190 Maile Way, Honolulu HI 96822–2279 and
‡ Center for Biotechnology, UniŠersity of Nebraska, N322 The Beadle Center, Lincoln, NE 68588–0665, USA

Received : 18 March 1997 Returned for revision : 24 September 1997 Accepted : 17 April 1998

2C DNA content values for 70 orchid species from 26 genera, including 37 Dendrobium species from eight taxonomic
sections, were analysed using flow cytometry. The resulting nuclear DNA content values for species other than
Dendrobium ranged from 1±91 pg 2C−" to 15±19 pg 2C−" nuclei for Cadetia taylori and Vanilla phaeantha, respectively.
Dendrobium nuclear DNA content values ranged from 1±53 pg 2C−" to 4±23 pg 2C−" nuclei for D. cruentum and D.
spectabile, respectively. DNA content measurements varied greatly within Dendrobium sections Latouria and
Spatulata. Nuclear DNA content values for the six species analysed within Latouria ranged from 1±88 pg 2C−" nuclei
for D. macrophyllum to 4±23 pg 2C−" nuclei for D. spectabile. Nuclear DNA content values for the 16 species analysed
within Spatulata ranged from 1±69 pg 2C−" nuclei for D. discolor to 4±05 pg 2C−" nuclei for D. samoense. The least
variation in DNA content was found within the section Phalaenanthe, with nuclear DNA content values of 1±79 pg
2C−", 1±86 pg 2C−" and 1±98 pg 2C−" for D. bigibbum, D. affine and D. phalaenopsis, respectively.
# 1998 Annals of Botany Company

Key words : Orchidaceae, Dendrobium, flow cytometry, propidium iodide, nuclear DNA, genome size, 2C values.

Dendrobium is of considerable interest due to its broad

I N T R O D U C T I ON
geographic distribution, tremendous diversity in growth
Demand for comparative studies of angiosperm genome habits and form, and high value of hybrids as a floricultural
size has increased steadily since the discovery of methods to commodity. However, classification of species using a
measure DNA content during the 1950s (Bennett and morphology-based system is frequently dynamic (e.g. Cribb,
Smith, 1976, 1991 ; Bennett and Leitch, 1995). Knowledge 1983, 1986) and also disputed based on chromosome pairing
of genome size has application in fields of diverse interest behaviour of hybrids (Wilfret, Takeshita and Kamemoto,
such as cell and molecular biology, ecology, phytogeography 1979 ; Kamemoto, 1987). Currently, the DNA content is
and systematics. For example, genome size has been used to known for only five Dendrobium species, with values ranging
study the effect of gain (De Azkue and Martinez, 1988) or from 5±1 pg 2C−" to 11±7 pg DNA 2C−" nuclei (Narayan et
loss (Srivastava and Lavania, 1991) of DNA on speciation, al., 1989). Determination of genome sizes of additional
confirm taxonomic assignments (Maxted, Callimassia and species may aid taxonomists, systematists and plant
Bennett, 1991), or separate taxa into different species breeders.
(Raina, Srivastav and Rama Rao, 1986). In molecular In this study, nuclear DNA contents of 70 species from
studies, knowing the genome size of a test organism is useful the orchid subfamily Epidendroideae were determined using
for estimating the number of clones required to create a flow cytometry. This included 37 species of Dendrobium
genomic library containing the genes of interest. from eight taxonomic sections and 33 representative species
To date there are only about 2500 angiosperm species for from 25 additional orchid genera from seven tribes. Only
which nuclear DNA content values have been published five of these species have been previously analysed using
(Bennett and Leitch, 1995). For the Orchidaceae, considered other methods. The data presented here are intended to fill
the largest plant family with an estimated 17 000 to 35 000 a gap that exists in the current orchid genetic knowledge
species, DNA content is reported for only 41 species (Nagl base. Variation in genome size for orchid species is discussed.
and Capesius, 1977 ; Narayan, Parida and Vij, 1989 ; Differences in the amount of DNA between each
Arumuganathan and Earle, 1991 a ; Cox et al., 1993 ; Bennett Dendrobium species, as well as among species within each
and Leitch, 1995). Nuclear DNA content values are notably section, are also discussed.
lacking for several of the commercially valuable genera
including Cattleya, Cypripedium, Encyclia, Epidendrum,
Vanda and Dendrobium. The latter is the largest orchid MATERIALS AND METHODS
genus, comprising approximately 1000 identified species
Plant material
(Dressler, 1993).
Leaf samples of 37 Dendrobium species and 33 species from
† For correspondence. Fax ­1 808 9563894. 25 other genera were obtained from the University of
0305-7364}98}080189­06 $30.00}0 bo980664 # 1998 Annals of Botany Company
190 Jones et al.—Orchid DNA Content
T     1. Mean DNA content for species of 25 orchid genera, excluding Dendrobium

Chrm. g Mean DNA

per 2n content³s.e.
Species Tribe* Subtribe* nuclei† (pg 2C−") Mbp‡

Ansellia africana Lindl.s Cymbidieae Cyrtopododiinae 42 3±70³0±16 1785

Barkeria lindleyana Batem. ex Lindl.s Epidendreae Laeliinae unk 3±29³0±22 1587
Brassia maculata R.Br.s Maxillarieae Oncidiinae 60 3±74³0±31 1804
Broughtonia sanguinea (Sw.) R.Br.s Epidendreae Laeliinae 40 2±12³0±09 1023
Bulbophyllum cocoinum Batem. ex Lindl.s Dendrobieae Bulbophyllinae 38 5±35³0±28 2581
Cadetia taylori (F.Muell.) Schltr.s Dendrobieae Dendrobiinae unk 1±91³0±08 922
Cattleya bowringiana f. alba O’Briens Epidendreae Laeliinae 40, 42 4±98³0±23 2403
Cattleya bowringiana var. coerulea O’Briens Epidendreae Laeliinae unk 4±99³0±26 2408
Cattleya forbesii Lindl.s Epidendreae Laeliinae 54–60 3±29³0±16 1587
Cattleya walkeriana Gardn.s Epidendreae Laeliinae 40 5±97³0±24 2880
Cattleya walkeriana var. coerulea Hort.§ Epidendreae Laeliinae 40 5±31³0±26 2562
Cattleya walkeriana f. alba Hort. ‘ Pendentive ’§ Epidendreae Laeliinae ca. 80 8±55³0±20 4005
Cattleya walkeriana f. alba Hort. ‘ Limerick ’§ Epidendreae Laeliinae ca. 60 8±13³0±22 3923
Cattleya walkeriana var. coerulea Hort. ‘ Chouju ’§ Epidendreae Laeliinae unk 9±29³0±60 4482
Cattleya walkeriana f. semi-alba Hort. ‘ Puanani ’§ Epidendreae Laeliinae unk 7±30³0±15 3522
Cleisostoma subulatum Bl.s Vandeae Aeridinae 38 6±40³0±27 3088
Coelogyne pastulata Pfitz.s Coelogyneae Coelogyninae unk 5±48³0±22 2644
Cymbidium sinense (Jacks.) Willd.§ Cymbidieae Cyrtopododiinae 40 6±31³0±21 3045
Doritis pulcherrima Lindl.s Vandeae Aeridinae 38 9±25³0±28 4463
Epidendrum steinbachii Amess Epidendreae Laeliinae unk 2±87³0±11 1385
Grammatophyllum scriptum (L.) Bl.s Cymbidieae Cyrtopododiinae 38, 40 3±44³0±11 1660
Laelia rubescens Rolfes Epidendreae Laeliinae 40 2±45³0±07 1182
Laelia tenebrosa Rolfes Epidendreae Laeliinae unk 3±51³0±20 1694
Neofinetia falcata (Thunb.) H.H.Hu.s Vandeae Aeridinae 38 4±73³0±35 2282
Oncidium ampliatum Lindl.s Maxillarieae Oncidiinae 44 4±78³0±20 2306
Oncidium sphacelatum Lindl.s Maxillarieae Oncidiinae 56 4±74³0±20 2287
Oncidium Šaruelum Moirs Maxillarieae Oncidiinae 63 3±85³0±19 1858
Peristeria elata Hook.s Maxillarieae Stanhopeinae 40 9±34³0±16 4507
Phaius tankerŠilleae (Banks) Bl.s Arethuseae Arethusinae 46 11±38³0±49 5491
Phalaenopsis equestris (Shauer) Rchb.f.s Vandeae Aeridinae 38 5±53³0±28 2668
Phalaenopsis luedemanniana Rchb.f.s Vandeae Aeridinae 38 8±65³0±41 4174
Rhynchostylis gigantia (Lindl.) Ridl.s Vandeae Aeridinae 38 6±02³0±26 2905
Rhynchostylis retusa (L.) Bl.s Vandeae Aeridinae 38 9±65³0±48 4656
Schomburgkia lyonsii Lindl.s Epidendreae Laeliinae unk 3±89³0±14 1877
Smitinandia micrantha (Lindl.) Holtt.s Vandeae Aeridinae 38 4±19³0±32 2022
Trichopilia maculata Rchb.f.s Maxillarieae Oncidiinae unk 4±67³0±09 2253
Vanda lamellata Lindl.§ Vandeae Aeridinae 38 4±10³0±22 1978
Vanilla phaeantha Rchb.f.s Triphoreae Vanillinae 32 15±19³0±96 7329
Vanilla pompona Schiedes Triphoreae Vanillinae 32 14±45³0±71 6972

* Classification according to Dressler (1993).

† Chromosome numbers are taken from Tanaka and Kamemoto (1974, 1984) and came from different specimen plants than those analysed
in this study ; unk, unknown count.
‡ Megabase pairs per haploid genome (Mbp 1C−" nuclei) calculated based on the equivalent of 1 pg DNA ¯ 965 Mbp (Strauss, 1971).
s Source of plant material : University of Hawaii, Honolulu, HI.
§ Source of plant material : R. Tokunaga, H & R Nurseries, Waimanalo, HI.

Hawaii at Manoa orchid collection, or were donated by

Nuclei extraction methods
R. Tokunaga (H & R Nurseries, Inc. Waimanalo, Hawaii).
For many non-Dendrobium species only two separate Nuclei for DNA content analysis were extracted from
specimens existed in the collections. The source of each fully expanded young leaves or from healthy mature leaves
sample is indicated by footnote in Tables 1 and 2. Table 1 on new season pseudobulbs. Extraction of nuclei and DNA
lists nuclear DNA content values for all non-Dendrobium staining were performed according to Arumuganathan and
species examined along with the available 2n chromosome Earle (1991 b). Approximately 100 mg of tissue, excluding
counts and taxonomic designations according to Dressler midrib, were sliced into 0±5 mm or less strips in 1 ml chilled
(1993). All Dendrobium species analysed were previously MgSO extraction buffer containing 1 mg ml−" dithio-
%
determined to have 2n ¯ 2N ¯ 38 chromosomes, except for threitol, 100 µg ml−" propidium iodide and 2±5 µg ml−"
D. formosum with 2n ¯ 2N ¯ 40 chromosomes (Tanaka Triton X-100. After filtration through a 33 µm nylon mesh
and Kamemoto, 1984). Table 2 lists the examined (Fisher Scientific) and precipitation at 15 000 rpm, nuclei
Dendrobium species and their sectional designations ac- pellets were resuspended in 400 µl of extraction buffer plus
cording to Schelpe and Stewart (1990). 2±5 µl ml−" DNase-free RNase and incubated at 37 °C for
 Jones et al.—Orchid DNA Content 191
T     2. Mean nuclear DNA content for Dendrobium species from eight taxonomic sections

Mean DNA
Species content³s.e.
[Synonym] Subgenus* Section* (pg 2C−") Mbp†

D. affine (Deane) Steud.‡ Dendrobium Phalaenanthe 1±86³0±10 897

[D. dicuphum F.Muell.]
D. antennatum Lindl.‡ Dendrobium Spatulata 2±77³0±10 1336
[D. d ’albertsii Rchb.f.]
D. atroŠiolaceum Rolfes Athecebium Latouria 2±57³0±07 1240
D. bellatulum Rolfes Dendrobium Formosae 2±67³0±09 1288
D. bicaudatum Reinw.‡ Dendrobium Spatulata 2±41³0±03 1163
[D. rumphianum Teijsm.]
D. bigibbum Lindl.‡ Dendrobium Phalaenanthe 1±79³0±05 864
D. bracteosum Rchb.f.s Dendrobium Pedilonum 3±53³0±09 1703
D. bullenianum Rchb.f.‡ Dendrobium Pedilonum 3±60³0±16 1737
[D. topaziacum Ames]
D. canaliculatum R.Br.‡ Dendrobium Spatulata 2±71³0±00 1308
D. conanthum Schltr.‡ Dendrobium Spatulata 2±25³0±11 1086
D. cruentum Rchb.f.s Dendrobium Formosae 1±53³0±09 738
D. crumenatum Sw.‡ Rhopalobium Rhopalanthe 2±61³0±17 1259
D. discolor Lindl.‡ Dendrobium Spatulata 1±69³0±13 815
[D. undulatum R.Br.]
D. forbesii Ridl.s Athecebium Latouria 1±91³0±11 922
D. formosum Roxb. ex Lindl.s Dendrobium Formosae 1±73³0±11 835
[D. infundibulum Rchb.f.]
D. gouldii Rchb.f.‡ Dendrobium Spatulata 2±09³0±06 1008
D. helix Cribb‡ Dendrobium Spatulata 2±32³0±08 1119
D. lasianthera J.J.Sm.‡ Dendrobium Spatulata 2±12³0±14 1023
[D. ostrinoglossum Rupp]
D. lindleyi Steud.‡ Athecebium Callista 2±40³0±06 1158
[D. aggregatum Roxb.]
D. macrophyllum A.Rich.‡ Athecebium Latouria 1±88³0±06 907
D. moschatum (Buch.-Ham.) Sw.‡ Dendrobium Dendrobium 3±48³0±14 1679
D. parishii Rchb.f.‡ Dendrobium Dendrobium 2±41³0±13 1163
D. phalaenopsis Fitzg.‡ Dendrobium Phalaenanthe 1±98³0±05 955
[D. bigibbum var. superbum Hort. ex Rchb.f.]
[D. bigibbum var. phalaenopsis (Fritz.) Bail.]
D. polysema Schltr.s Athecebium Latouria 3±03³0±06 1462
D. pulchellum Roxb. ex Lindl.‡ Dendrobium Dendrobium 3±18³0±01 1534
D. rhodostictum F.Muell. & Kranzl.s Athecebium Latouria 2±94³0±10 1418
D. samoense Cribb‡ Dendrobium Spatulata 4±05³0±15 1954
D. schulleri J.J.Sm.‡ Dendrobium Spatulata 1±96³0±09 946
D. signatum Rchb.f.‡ Dendrobium Dendrobium 2±92³0±01 1408
[D. hildebrandii Rolfe]
D. smillieae F.Muell.‡ Dendrobium Pedilonum 3±15³0±13 1520
D. spectabile (Bl.) Miq.‡ Athecebium Latouria 4±23³0±23 2041
D. stratiotes Rchb.f.‡ Dendrobium Spatulata 3±35³0±05 1616
D. streblocerus Rchb.f.‡ Dendrobium Spatulata 3±73³0±36 1800
D. strepsiceros J.J.Sm.‡ Dendrobium Spatulata 2±92³0±14 1409
D. tangerinum Cribb‡ Dendrobium Spatulata 2±19³0±17 1057
D. taurinum J.J.Sm.‡ Dendrobium Spatulata 1±92³0±06 926
D. ŠiolaceoflaŠens Thomson‡ Dendrobium Spatulata 2±69³0±24 1298

* Classification according to Baker and Baker (1995).

† Megabase pairs per haploid genome (Mbp 1C−" nuclei) calculated based on the equivalent of 1 pg DNA ¯ 965 Mbp (Strauss, 1971).
‡ Source of plant material : University of Hawaii, Honolulu, HI.
s Source of plant material : R. Tokunaga, H & R Nurseries, Waimanalo, HI.

15 min. Samples were placed on ice following incubation 610 nm. Preliminary samples were run at the University of
until flow cytometry analysis. Nebraska, Biotechnology Laboratory using an EPICS V
flow cytometer. Data collected by FCM were analysed
simultaneously using CYCLOPS software (Cytomation,
Flow cytometry (FCM ) analysis
Inc., Fort Collins, CO, USA). No less than two different
A minimum of 10 000 nuclei per sample were analysed on specimens per species were analysed twice per FCM run on
a Coulter EPICS 753 argon laser flow cytometer (Marine at least two separate occasions each to confirm results.
Sciences Department, University of Hawaii at Manoa) Chicken erythrocyte nuclei (2±33 pg 2C−" ; BioSure, Inc.,
exciting at 488 nm and recording emissions no longer than San Jose, CA, USA) were used as an internal or external
192 Jones et al.—Orchid DNA Content
DNA content standard depending on the proximity of the T     3. Range of DNA content Šalues found within each
2C populations, as well as for instrument calibration. When Dendrobium section
an external standard was used, the sample run was
immediately preceded and followed by the standard to DNA content range
control for instrument shift. The presence of endopolyploidy Section [Synonym]* g Species† (pg)
made selection of another internal standard problematical
(Jones and Kuehnle, 1998). Nuclear DNA content values Callista 1 2±40
Dendrobium [Eugenanthe] 4 2±41–3±48
were calculated using the mean values (in channel number) Formosae [Nigrohirsutae] 3 1±53–2±67
for the 2C nuclear peak of the sample divided by that of the Latouria 6 1±88–4±23
standard multiplied by the nuclear DNA content of the Pedilonum 3 3±15–3±60
standard. Nuclear DNA content values listed in Tables 1 Phalaenanthe 3 1±79–1±98
Spatulata [Ceratobium] 16 1±69–4±05
and 2 represent the mean 2C genome size for each species. Rhopalanthe 1 2±61

RESULTS * Classification according to Baker and Baker (1995).

† Number of Dendrobium species sampled for each taxonomic
The mean DNA content per 2C nuclei measured for 33
section.
orchid species from genera other than Dendrobium ranged
from 1±91 pg 2C−" for Cadetia taylori (F.Muell.) Schltr. to
microdensitometry to determine a genome size of 5±0 pg
15±19 pg 2C−" for Vanilla phaeantha Rchb.f. (Table 1). Two
2C−" for Oncidium ampliatum Lindl. The present study
varieties of Cattleya bowringiana O’Brien were analysed and
resulted in genome sizes of 3±48, 3±74, 11±38, 9±65 and 4±78 pg
gave nearly identical results. Six speciemens of C. walkeriana
2C−" for B. maculata, P. tankerŠilleae, R. retusa and O.
Gardn., including four cultivated forms, were analysed and
ampliatum, respectively. The causes of the differences or
resulted in a DNA content range of 5±31 pg 2C−" to 9±29 pg
similarities in DNA content of the five species previously
2C−".
analysed by other methods are currently unknown. Further
The mean DNA content per 2C nuclei measured for 37
studies are needed to clarify whether the apparent differences
Dendrobium species ranged from 1±53 pg 2C−" for D.
are real or artifact. The nuclei analysed by FCM in this
cruentum Rchb.f. to 4±23 pg 2C−" for D. spectabile (Bl.) Miq.
study were from leaves at the same stage of development
(Table 2). Values for DNA content were also variable for
and only 2C nuclei at the G }G phase were used to measure
species within each taxonomic section. DNA content values ! "
DNA content. Thus, while the values presented here may
for the four species within the section Dendrobium ranged
not be considered as absolute, a few general comparisons
from 2±41 pg 2C−" for D. parishii Rchb.f. to 3±48 pg 2C−" for
between genus and family members can be made.
D. moschatum (Buch.-Ham.) Sw. Three species within the
This study shows that genome size can vary widely within
section Formosae ranged from 1±53 pg 2C−" for D. cruentum
a taxonomic assignment. For example, among 15 species
to 2±67 pg 2C−" for D. bellatulum Rolfe. Within the section
examined from six genera within the subtribe Laeliinae
Latouria, values for six species ranged from 1±88 pg 2C−" for
there was a three-fold difference in genome size between the
D. macrophyllum A.Rich. to 4±23 pg 2C−" for D. spectabile.
smallest (Broughtonia sanguinea (Sw.) R.Br.) and largest
Three Pedilonum species ranged from 3±15 pg 2C−" for D.
species (Cattleya walkeriana). Moreover, the size variation
smillieae F.Muell. to 3±60 pg 2C−" for D. bullenianum Rchb.f.
was not limited to the intergeneric level. An examination of
Three species within Phalaenanthe ranged from 1±79 pg
Cattleya species showed a two-fold difference between C.
2C−" for D. bigibbum Lindl. to 1±98 pg 2C−" for D.
forbesii Lindl. and both C. walkeriana and C. bowringiana.
phalaenopsis Fitzg. Sixteen species within Spatulata ranged
Intraspecific variation also existed between the wild-
from 1±69 pg 2C−" for D. discolor Lindl. to 4±05 pg 2C−" for
collected specimens of C. walkeriana (2n ¯ 2x ¯ 40) and the
D. samoense Cribb. Only a single species was analysed for
four micropropagated, cultivated specimens, with a positive
each of the sections Callista (D. lindleyi Steud.) and
correlation between chromosome number and genome size.
Rhopalanthe (D. crumenatum Sw.), yielding values of 2±40 pg
Differences in DNA content were also found for the eight
2C−" and 2±61 pg 2C−", respectively. Results for the eight
species sampled from the tribe Cymbidieae. The genome
Dendrobium sections are summarized in Table 3.
sizes ranged from 3±44 pg 2C−" (Grammatophyllum scriptum
(L.) Bl.) to 6±31 pg 2C−" (Cymbidium sinense (Jacks.) Willd.).
D I S C U S S I ON
Similarly large tribal genome size variation was previously
This study presents 2C genome values, as determined by reported for other plant tribes (reviewed by Bennett and
FCM, for 70 orchid species including 33 species outside the Leitch, 1995). A ninth Cymbidioid type species, Peristera
genus Dendrobium. Of these species, DNA contents of five elata Hook., from the subtribe Maxillarieae, was nearly
species were previously analysed using other methods. Nagl three times larger than G. scriptum. Dressler (1981) suggested
and Capesius (1977) used reassociation kinetics to determine that Maxillarieae is a primitive group of Cymbidieae type
the genome size for Brassia maculata R.Br. to be 7±1 pg species. He also suggested that a comparatively larger
2C−" ; Narayan et al. (1989) used Feulgen microdensitometry genome size, not accredited to ploidy changes, may be
to determine genomes sizes of 9±32 pg 2C−", 17±0 pg 2C−" primitive in nature. The large genome size found for P.
and 5±2 pg 2C−" for Dendrobium moschatum, Phaius tanker- elata, along with its more primitive morphological charac-
Šilleae (Banks) Bl. and Rhynchostylis retusa (L.) Bl., teristics, may lend support to this assertion. The largest
respectively ; and Bennett and Leitch (1995) used fluorescent genome sizes found in this study belonged to the two Vanilla
 Jones et al.—Orchid DNA Content 193
species. These large values are comparable to a previously improve recovery of isolated nuclei. Another option is to
reported value for V. planifolia by Arumuganathan and extract nuclei from other tissues, such as pollen or root tips,
Earle (1991 a). The entire tribe Triphoreae is considered to or from protoplasts. Other analytical methodologies, such
be distinctly primitive based on morphology and habit, and as microfluorimetry, are additional options to be explored.
only superficially similar to other groups within Epiden- This study was successful in providing the nuclear DNA
droideae. Dressler (1981) left this group in ‘ systematic content values for 70 orchid species, 65 of which had not
limbo ’, but replaced it in this subfamily in his revised previously been analysed by any quantitative method. 2C
classification (Dressler, 1993). values were found to be effective estimates of ploidy level in
The family Dendrobineae contains the genus Dendrobium cultivated C. walkeriana specimens as was confirmed by
as well as Cadetia and Bulbophyllum. However, the latter chromosome counts. A continued survey of orchid species
genus was recently removed to a separate subfamily by flow cytometric analysis should provide researchers with
(Dressler, 1993). A survey of the genus Dendrobium resulted an additional quantitative trait for future molecular sys-
in a three-fold range in genome size. The genome size for tematic studies.
Cadetia taylori fell towards the lower end of that size range.
Bulbophyllum cocoinum Batem. ex Lindl. was over twice the
A C K N O W L E D G E M E N TS
size of C. taylori and was beyond the upper size range for
Dendrobium. We thank Hector Nolla (Oceanography Dept., Univ. of
Five species of Dendrobium, D. aphyllum (Roxb.) C.Fisch. Hawaii) for technical assistance. This research was
(6±7 pg 2C−"), D. densiflorum Schltr. (5±1 pg 2C−"), D. supported by A. Kuehnle’s USDA Hatch Project No. 842
fimbriatum (6±3 pg 2C−"), D. hookeriana Lindl. (11±7 pg and the W. Tenney Foundation. W. Jones’ graduate
2C−"), and D. moschatum (9±3 pg 2C−"), were previously assistantship was funded by the W. Tenney Foundation.
analysed using Feulgen microdensitometry (Narayan et al.,
1989). Of these, D. moschatum (3±48 pg 2C−") is the only one
L I T E R A T U R E C I T ED
reanalysed in the present study. The previous DNA content
value reported is nearly three times larger. The reason for Arumuganathan K, Earle ED. 1991 a. Nuclear DNA content of some
this is unknown but could arise from differences between important plant species. Plant Molecular Biology Reporter 9 :
208–218.
varieties or between methods of DNA content analysis. Arumuganathan K, Earle ED. 1991 b. Estimation of nuclear DNA
Results from this study show both differences and content of plants by flow cytometry. Plant Molecular Biology
similarities among Dendrobium species, despite uniform Reporter 9 : 229–233.
chromosome numbers of 2n ¯ 2x ¯ 38. Previous work by Baker ML, Baker CO. 1995. Orchid species culture. Dendrobium.
Portland : Timber Press.
Wilfret and Kamemoto (1971) showed that karyotype could
Bennett MD, Leitch IJ. 1995. Nuclear DNA amounts in angiosperms.
be used to differentiate species that were morphologically Annals of Botany 76 : 113–176.
very similar. Their study also found that D. bigibbum was Bennett MD, Smith JB. 1976. Nuclear DNA amounts in angiosperms.
distinct from D. phalaenopsis, with the latter having three Philosophical Transactions of the Royal Society of London, Series
more pairs of large subterminal chromosomes and three less B 274 : 227–274.
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a PCR-generated synthetic probe. Annals of Botany 72 : 239–247.
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Cribb P. 1983. A revision of Dendrobium section Latouria. Kew Bulletin
help distinguish species, or at least varieties nearly identical 38 : 229–306.
in morphological appearance but with different karyotype Cribb P. 1986. The Antelope Dendrobiums. Kew Bulletin 41 : 615–692.
profiles. De Azkue D, Martinez A. 1988. DNA content and chromosome
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Dressler RL. 1981. The orchids : natural history and classification.
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