Table Of ContentTHE SPIKELET CALLUS OF ERIOCHLOA VILLOSA (POACEAE)
Stephen Darbyshire Marie-Josee Simard
J.
and Canada and Canada
Agriculture Agri-Food Agriculture Agri-Food
960 Carling Ave., Saunders Building #49 2560 Hochelaga
CANADA CANADA
Ottawa, Ontario, K1A 0C6, Quebec, Quebec, GIV2J3,
[email protected]
and Canada
Agri-Food
Agriculture
2585 County RR#1
Rd. 20,
NOR CANADA
Harrow, Ontario, 1G0,
ABSTRACT
The and which
panicoid grass genus Eriochloa contains about 30-35, primarily tropical subtropical, species are
&
characterized by an unusual swelling and cup-like callus structure at the base of the spikelets (Clayton Ren-
intemode
voise 1986). This unusual structure has been interpreted as a swelling of the lowest rachilla sur-
&
Shaw
mounted by the lower (proximal) glume which reduced to a short flange of tissue (Hsu 1965; Smeins
is
Thompson
1979, 1983). However, in their anatomical examination of the callus of three Eriochloa species, et al.
(1990) found that the in the spikelet rachis remained unbranched until the upper glume traces, and inter-
stele
an no
preted the lack of stelar nodes within the callus region as indication that part of the callus is likely to
number
represent a lower glume. Although the callus structure has been investigated in a of Eriochloa
vestigial
species, has not been studied in E. villosa (Thunb.) Kunth. This species is native to eastern Asia from the Rus-
it
sian Far East to northern Viet Nam, but has been introduced to other areas including North America where it
has been spreading as an agricultural weed (Darbyshire et al, 2003).
Shaw and Smeins examined epidermal characteristics of the spikelet callus in 20 species of
1983)
(1979,
was two both with
Eriochloa. They observed that the structure divided into parts, characteristics of the epider-
mis consistent with the interpretation that the callus is formed from an expansion of the lowest rachilla inter-
node and surmounted by remnants of the glume. Three types of calluses were described (Table The
the first 1).
common examined
Type 1 callus was by far the most in the genus, being seen in 16 of the species (E. aristata
Vasey, E. boxiana Hitchc., E. contracta Hitchc., E. eggersii Hitchc., E. ekmanii Hitchc., E. acuminata Presl)
(J-
&
Kunth (= E. lemmonii var. gracilis (E. Foum.) Gould), E. lemmonii Vasey Scribn., E. meyeriana (Nees) Pilger,
E. michauxii montevidensis Griseb., E. pacifica Mez, E. peruviana Mez, E. punctata (L.) Ham.,
(Poir.) Hitchc., E.
E. sericea (Scheele) Vasey, E. setosa (A. Rich.) Hitchc., and E. weberbaueri Mez). Distinctive features of the Type
1 callus included a basal portion with a smooth epidermis beset with silica bodies and an apical portion of
plicate epidermal The Type 2 seen in 3 species (E. distachya Kunth, E. grandiflora (Trin.) Benth.
callus,
tissue.
;
Callus Type 1 Callus Type2 Callus Type J
bead macrohairs
&
and
was
E. nelsonii Scribn. J.G. Sm.), similar to Type 1 but larger in size and lacking silica bodies. The Type 3
New
callus, seen in only one World species (E. polystachya Kunth), had the basal portion without a smooth and
indurate epidermis and was membranous
the apical portion a “reduced glume”
encircling the base of the spike-
The Old World
let. species E. rovumensis (Pilg.) Clayton (= E. biglumis Clayton) somewhat anomalous in the
is
genus, possessing a swollen spikelet base and well-developed lower glume, although Shaw and Smeins
(1983)
state that the lower glume is similar to that seen in E. polystachya.
The
purpose of this study was to examine the characteristics of the spikelet callus in the Asian
E. villosa
and compare
with
it the previously published observations on other species which are primarily from North
and South America and
Africa.
AND
MATERIALS METHODS
Spikelets originating from populations occurring in southern Quebec
(Darbyshire were
et 2003) used.
al.
Thirty randomly
selected spikelets from one population were measured under
lOx magnification
for spikelet
and
and
callus size the measurements were compared with those given by Shaw and Smeins
Selected
(1979).
were
spikelets air-dried, coated with gold and examined with XL30 ESEM
a Philips microscope 5kV
at accel-
eration 70%
voltage. Spikelets stored in ethanol were hand
re-hydrated, sectioned and stained with methylene
blue or toluidine blue O. Air-dried were hand
spikelets re-hydrated, and
sectioned stained with Sudan
IV.
Spikelets are broadly and
elliptical dorsiventrally compressed The
(Fig. 1 A). size is reported as 3.9-5.5(-6.5)
mm
mm
long, 2.0-2.8(-3.0) wide (Darbyshire Shaw
et al. 2003; et al. 2003). Spikelets from the Quebec popula-
mm
mm
measured
tion 5.3 (SD = 0.18) long and (SD = mm
2.7 0.09) wide, with the callus 0.8 (SD = long
0.09)
mm
and (SD =
1.5 0.12) wide. The observed
was
E. villosa callus size larger than in any of the 19 species exam-
ined by Shaw and Smeins The
(1979). callus length and width averaged 15% and 55%
of the spikelet length and
width, Shaw
respectively. and Smeins
(1979) reported
variation in callus sizes between species they measured,
with Type
2
calluses tending to be larger than Type but no
correlation between
1, callus size (length/width)
and was
type
detected in this study (data not shown). Epidermal
characteristics of the
callus of E. villosa are
most
similar to those described as Type by Shaw and
Smeins
1
(1979).
Apart from
the central bundles, no branching
of vascular was
tissue observed anywhere
in the callus
Thompson
structure
(cf. et al. 1990). The callus was divided into two mart
or equal and
less strongly demar-
cated parts The
(Fig. basal part (bead) formed
1). ™is of hardened tissues and the
apical portion (cup) above
is
the caltas usuall f°nn
a complete
°‘ >' ring thereby incompletely
clasping the spikelet
(Fig. 1 although sometimes the cup was
B), almost
completely
encircling with only a small notch
the junction
at
699
fa- view
1. Spikelets of Eriochloa A, adaxial view, right abaxial
villosa. left <
callus (SEM).
of the lateral edges (Fig. 1 A, left). The callus cup was directly opposite the upper glume or only slightly off
An from
centre not quite bilaterally symmetrical). additional flap of tissue arising the adaxial surface of
(i.e.,
Shaw
and was an by and Smeins
the callus cup present in some species of Eriochloa referred to as “extension”
is
(1979) and as a “ventral projection” by Thompson et al. (1990). The ventral projection in the callus of E. villosa
was observed to arise from the adaxial side of the cup at its base, where it formed a second inner, but incomplete
membranous
cup 2 A, Sometimes
(Fig. B). the ve
tion extended beyond
the fleshy portion of the
cu]
A
(Fig. 1 (right), 2 A), but usually
this flange of
visible without
ti )t dissection 2 The
(Fig. B, posi
4).
tion of the ventral
projection
is consistent with the position
of the first glume, although no
there
is other evi
dence
of homology.
No
stomata
or prickle hairs were observed on
either part of the E. The
villosa callus. bead epidermis wa<
hardened and smooth
or minutely
roughened
3 A,
(Fig. B). Bicellular microhaiis were common
apically
(Fig. 2
W, but macrohairs were
rarely seen. Rounded
broadly
to
eliptic or shallowly lobed commor
were
silica cells
basally 3 The
(Fig. A). abaxial epidermis of the cup was
heavily
plicate (Fig. 3 C) bodies were
Silica not
ob-
served on
the cup. Bicellular microhairs were common
throughout
cup and
the
macrohairs were
occasional!.
Darbyshire et al., Spikelet callus of Eriochloa villosa
seen (Fig. 3 C). Long cells with interlocking cell walls were seen in the epidermis of the cup and the ventral
projection.
Unlike the callus descriptions of most other Eriochloa species, occasional macrohairs were detected on
both the lower and apical portions of the E. villosa callus (Table Fig. 3 C), but see also Shaw and Smeins
1;
common
on
(1983). This not unexpected as macrohairs are a epidermal feature other structures of E. villosa
is
(cf., Thompson et 1990) and their occasional detection simply a function of the large numbers of E. villosa
al.
The callus of untreated spikelets has an oily or waxy appearance (Fig 1A). Parenchyma cells of the cup
whose
portion and the ventral projection of the callus contained large vacuoles contents stained red with Su-
A
dan amount
IV, indicating that this tissue is rich in lipids (Fig. 4). lesser of staining occurred in the upper
portion of the harder bead tissues of the callus. The large amount of lipids present in the fleshy callus cup sug-
No
gests that this tissue may act as an elaiosome (myrmecochory) or animal attractant (Davidse 1987). evi-
dence was observed of secretion or accumulation in concave cavity formed by the cup (or ventral projec-
oil
tion), as was suggested by Arriaga (2000). It is uncertain what types of vectors might serve as effective dispersal
agents, but and (including birds and rodents) seed predators might be
various types of insect vertebrate at-
tracted to the food Optimal seedling emergence was observed from soil depths up to about 5 cm,
lipid source.
&
but occurred from depths > 9 cm (Liu Owen 2003). This would suggest that diaspores can tolerate burial by
seed
caching
animals.
The range from 0.91 to 0.97 at 15°C (Lide 1990). Large quantities of
specific gravity of plant oils typically
may
oils buoyancy, movement and orientation (when unevenly distributed) of E. villosa diaspores under
affect
aqueous While cup unlikely to have a major impact on hydrochory, the increased
conditions. the callus is
buoyancy may provide some secondary functionality in diaspore transport
at the basal portion of the spikelet
and
placement when
water present.
free is
nsistent with those of Shaw and Smeins (1979, 1983) and
species in the genus, but provide no further evidence of the ontogeny of the
most similar to the Type 1 callus of Shaw and Smeins (1979), the most com-
and most
observed in the distribution of micro- macrohairs. In species of
e
Eriochloa the lower glume described as absent or greatly reduced and fused with the callus bead,
tally
i:
ribed to the genus are said to have well-developed lower glumes and resemble
&
species of Brachiaria (Clayton 1975; Gibbs Russell 1981; Shaw Smeins 1983). Detailed anatomical study of
b
these species (primarily African) is necessary for a
and
the generic relationships of Eriochloa, Urochloa Brachiaria.
ACKNOWLEDGMENTS
New Kew
Clayton, W.D. 975. species of Eriochloa from 07-1
Africa. Bull. 30:1 09.
1
SA
W.D. and Genera Graminum, Kew
Clayton, Renvoize. 1986. grasses of the world. Addit. -389.
Bull. Ser. 3:1
1
Darbyshire, SJ., C.E. Wilson, and K. Alison. 2003. The biology of invasive alien plants in Canada. Eriochloa villosa (Thunb.)
1
.
Kunth. Can. Plant 83:987-999.
J. Sci.
Davidse, G. 1987. Fruit dispersal in the Poaceae. ln:T.R. Soderstrom, K.W. Hilu, C.S. Campbell and M.E. Barkworth, eds.
Grass systematics and evolution. Smithsonian Institution Press, Washington, D.C. Pp. 43-1 55.
1
A new
Gibbs Russell, G.E. 981 combination in Eriochloa. Bothalia 3:457.
1
. 1
The
Hsu, C-C. 1965. classification of Panicum (Gramineae) and
it
and lemma.
cule, style-base J. Fac. Sci. Univ. Tokyo Sect. Bot. 9:43-150.
Ill
Ude, D.R., ed. 1 990. CRC handbook of chemistry and physics. CRC Press, Boca Raton,
L<
M-C. and M.D.K. Owen. 2003. of seed
Liu, Effect
ri
Weed
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Sci.
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Iselya
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University Press, York and Oxford. 25:507-51
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RA,
Thompson, RJ. Tyrl, and J.R. Estes. 1 990. Comparative anatomy of the spikelet callus of Eriochloa, Brachiaria, and Uro-
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