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Hereditas
114: 117-124 (1991)
Meiotic studies
of
the hybrids among
Pseudoroegneria cognata,
Elymus
semicostatus
and
E.
pendulinus
(Poaceae)
BAO-RONG LU, BJORN SALOMON and ROLAND VON BOTHMER
Department
of
Crop Genetics and Breeding, The Swedish University
of
Agricultural Sciences.
Svaliiv,
Sweden
Lu,
B.-R.,
SALOMON,
B.
and
BOTHMER,
R.
VON.
1991. Meiotic studies of the hybrids among
Psuudoroe,y-
neria cognata. Eiymus semicostatus and
E.
penduiinus
(Poaceae).
-
Hereditas
114:
I
17-124.
Lund,
Sweden. ISSN
0018-0661.
Received October 29, 1990. Accepted December 17, 1990
Intergeneric and interspecific crosses were made among Pseudoroegneria cognata (Hackel)
A.
Love
(2n=14,
SS),
Elymus semicostatus (Nees ex Steud.) Melderis (2n=4x=28,
SSYY)
and
E.
pendulinirs
(Nevski) Tzvelev (2n=4x=28,
SSYY),
collected in Pakistan and China. Chromosome pairing and numerical
analysis of meioses were studied
in
the hybrids. Meiotic configurations of all triploid hybrids fit a
2:l
model with X-values ranging from 0.924
to
0.979, and those of tetraploid combinations fall into a
22
model with X-values ranging from 0.883
to
0.939.
It
is concluded
from
the study that (i) the
“S”
genome
in
P.
cognata is more closely related to
E.
semicostatus than to that in
E.
pendulinus;
(ii)
the
“SSYY”
genomes of
E.
semicostatus and
E.
pendulinus are slightly differentiated from one another; and
(iii)
a
certain degree of homoeology exists between
“S”
and
“Y”
genomes of the species studied.
Roland von Bothmer, Department
of
Crop Genetics and
Breeding,
The Swedish
University
of
A,yric.ri/fura/
Sciences,
S-268
00
Svaiov.
Sweden
Interspecific
or
intergeneric hybridization and
meiotic analyses
of
the hybrids are valuable me-
thods to investigate phylogenetic relationships in
the tribe
Triticeae
Dumort. (STEBBINS and SNYDER
1956; JACOBSEN and BOTHMER I98
1
;
DEWEY 1984;
BOTHMER et al. 1986; Lu et al. 1988; WANG 1989).
Studies of chromosome pairing behaviour in the
intergeneric and interspecific hybrids during meio-
sis may facilitate the understanding of relationships
among genomes of their parental species (BOTHMER
et al. 1986), and investigate the origin of different
genomes in order to illustrate the evolution
of
the
tribe. ALONSO and KIMBER (198 1) and
KIMBER
and
ALONSO (1 98
1)
developed methods to determine the
relative affinity between genomes in triploid and
tetraploid hybrids by a numerical analysis of meio-
sis, which should make the assessment of genomic
relationships of different parental species more ob-
jective.
Pseudoroegneria
A. Love, a newly established
genus (LOVE 1980), includes about
15
perennial
species distributed on open hillsides in the northern
hemisphere (DEWEY 1984; LOVE 1984). According
to DEWEY (1984) and LOVE (1984), this genus con-
tains diploids and autotetraploids with the basic
“S”
genome, whereas WANG et al. (1986) found that the
tetraploid species
P. tauri
(Boiss
&
Bal.)
A.
Love
contained the
“SP’
genomes. The
“S”
genome is
one
of
the most important genomic components,
present in more than half of the perennial Triticeae
species. This genome in combination with other
genomes has formed the basis of polyploid genera,
namely,
Elymus
L.
(SH,
SY,
SHY
and
SPY),
Elytri-
gia
L.
(SSX),
and
Pascopyrum
A. Love (SHJN), cf.
DEWEY (1984) and JENSEN (1990a). Several
in-
tergeneric hybrids have been obtained between di-
ploid species of
Pseudoroegneria,
mainly
P. spicuta
(Pursh)
A.
Love, and tetraploid species
of
E/yrnus
with SSHH genomes in order to produce
SSH
tri-
ploids (DEWEY 1982; LOVE and CONNOR 1982).
These were relatively easy to obtain even without
embryo rescue procedures, which suggests a close
affinity and potential for gene introgression be-
tween the two genera (DEWEY 1984). The intergen-
eric crosses between the Asian diploid
Pseudoroeg-
neria
species
(SS)
and tetraploid
Elymus
species
with the
“SY”
genomes have not been reported.
However, DEWEY
(1
981) published the cytogenetic
behaviour of
P. cognata
(he used the name
Agro-
pyronferganensis
Drob.) together with its genomic
relationship to three tetraploid
Elymus
species con-
taining
“SH”
genomes. JENSEN et al. (1986) publ-
Hereditas
114
11991)
Fig.
1
A-F.
Veio\ii in the rriploid h! hid\
(2n=:!
1
1.
Fig.
A-C.
E(yniir.s
.scniic~ostcztrr,s
x
Pseudororynariu
cognnfu
(HH
2-1731
:rith
7
hi\aleni\
(6
rings
and
I
rod)
and
7
uni\alent\
in
A-B;
2
trivaients indicated
by
arrows,
5
bivalents
(3
:~II$\
and
7
rods!
and
5
univalenrs
in
C.
Fig.
0.
P
(.(~:.itti~i
x
E.
pc~dtilitzus
(BB
6853)
with
1
quadrivalem
indicated
4)
'I
:louhle-headed xron.
!
tri\'alent
indicated
by
a
\ingle-headed arrow.
5
bivalents
(1
ring and
4
rods)
and
4
:init
dun\.
Fig.
E.
F
\~~~f~/l,~~.\~tr~ir.\
x
P
r'o,q,itrtci
tHH
2480)
with
3
trivalents
indicated
by
arrows.
Fig.
F.
Anaphase-
I
ot
i.
wrii/('o\/t//ir.\
x
P.
i
oyriufli.
showing lapping chromosonirs
in
addition
to
;I
bridge indicated
by
an
arrow.
-
3ai-
=
10
prn
Herrditas
114
(1991)
HYBRIDS
OF
PSEUDOROEGNERIA
AND
tLYMUS
12
1
Fig.
2A-F.
Meiosis
of
the tetraploid hybrids
(2n=28)
E.
pendulinus
X
E.
semicostatus.
Fig.
A.
One trivalent indicated
by an arrow,
12
bivalents (6 rings and
6
rods) and
1
univalent (BB 6703).
Fig.
B.
One quadrivalent indicated by an
arrow,
8
bivalents (3 rings and
5
rods) and
8
univalents (BB 6703).
Fig.
C.
Two quadrivalents
(1
ring and
1
chain)
indicated by two double-headed arrows,
1
trivalent indicated by a single-headed arrow, 7 bivalents
(5
rings and
2
rods)
and
3
univalents (BB 6703).
Fig.
D.
One quadrivalent indicated by an arrow,
9
bivalents
(5
rings and
4
rods) and
6
univalents (BB 6764).
Fig.
E.
One chain quadrivalent indicated by an arrow,
10
bivalents
(8
rings and
2
rods) and 4
univalents (BB 6764).
Fig. F.
Anaphase-I, showing a laggard and two chromosomal bridges indicated by arrows.
-
Bar
=
10
pn.
age
of
ca
1
1
(maxiniuni
14)
per
cell
and.
hence.
a
relatively
lot\
frequent)
ot
tiniv:ilent formation.
ca
3
(maximum
7)
per
cell.
Tri-
and
quadrivalent\
\&ere
frequently ob\ervctI. nveruging iilmo\t
0.5
(max-
imum
3)
per
cell
(Fig.
2C).
Lagging chromosomes
M
ere
comnionl~~
obserxd
at
antiphase
I
and
I1
in
all
crosw
and
chromosome
bridyes together
with
f'ragments
M
ere
recorded
in
thc
coinbinations
of
E.
\c/uiuisr~/rrrs
x
Y
('o<q/itifu
and
I:
pt>rih/i/iu.\
x
F.
.\c,/~ii(,~~.s~(r/rt.\
(Fig.
1
F
mcl
2F.l.
Micronuclei
\\ere
ob\er\ed
iii
most ofthe quar-
hc bcst
fitting
tnathem~iticiil
genomic
model\
lor
the triploid and tetraploid hybrids are
pre\ented
cspeciall!
in
the triploid hybrid\.
-r:tbic
1.
\\t-\
1968:
Li
et
al.
1990~;
Jtmsi:N
1990b). There-
fore,
the
triploid hybrids presumably have
"SSY"
genotnes.
and chromosome pairing in the hybrids
must
be attributed
to
the synapsis between the
"S"
genomes from the respective parential species,
P.
cogrrtrttr.
E.
.scniit~ostt~tr~.s
and
E.
pcndulinus.
This
allow
a
direct comparison
to
be
made of the
"S"
genome
in
Eljniirs
species with the original
"S"
genotne
in
the supposed ancestral donor,
Pscu-
tlo/.o('g/ic/-itr.
Meiotic pairing of the combination
P.
(vgrrtrttr
x
E.
.scniic.,j.sttrtirs
with
an
average chiasma
frequent\
of
ca
11-13
in
the two crosses
is
dis-
tinctl) higher than that of
P.
c~qriutu
x
E.
pendu-
/itrrr.\,
nhich
has
iin
average
of
cii
9
chiasmata per
cell.
This result
is
similar to that published by
DE-
\\i.\
(1081
1.
in
which
cii
8-14 chiasmata per cell
MC~C
(herved
in
the
hybrids between
P.
cngntrfu
and three
E/ytui/.\
species with the
"SH"
genome.
.It-\\i.\
et
al.
(
1986)
also
reported similar chromo-
sonic
pairing
figtircs
in
the
combination
E.
crlutu-
vic,r/.v
x
P.
co,prrtrtrr
with
ca
5
chiasmata
per
cell. An
explanation
for
the
different chiasma formation in
thij
\ttidy
i4
that
the
3"
genome
in
the two
Elymus
specie\
had
;I
polyphyletic origin, it., that
E.
ximi-
derii
ed
from different dip1
species.
However.
the
most likely explanation
is
that the
5"
genome
has
been modified
to
a
greater
extent in
E.
/w~rdu/i~ii/s
than
in
I:.
semic~ostutus,
in
other
~vords.
the
"S"
genome in
E.
seniicostdus
show
claw
homology
to
the original
"S"
genome
of
P.
cogrirrfrr
than
to
that in
E. priizduli/irr.s.
Geo-
grnphically,
P.
c'ogirtrru
and
E.
semir'ostufus
are dis-
tributed
in
adjacent
areas
in
North
Pakistan,
v.,herea\
E.
/wdu[i/u/.s,
which grows in Eastern
China
and
South Eastern
USSR,
is isolated from
the
former two
5pecies.
Meiotic
configurations
of
the tetraploid hybr
E.
/wrid/rli/iits
x
E.
seniic'ostutus,
fall
into
the
model with X-values
rllnging
from
0.8834.93
different combinations (Table 4). This indicates that
two genomes in the hybrids arc probably more
closely related to each other than they are to
a
simi-
larly
related
another
pair of genomes. which sup-
ports the
previous
conclusion about the genomic
constitution
(SSYY)
for
t
two species
(Df;wex
1968:
Li
et al.
1990~:
JEN
1990b).
The
meiotic
pairing
in
the
hybrids with
an
average
of
ca
11.5
hi\ dent\
and
ca
1
Y
chiasmata
per
cell sugests that
the
two
genomes
of
E.
.smij(,r)strrtir.s
and
E.
pr/rr/rr-
/i/r//.\
have
been
to
some extent differentiated from
cacti
othcr.
At
Icast four chromosomes always
remained
unpaired.
The
occasional
bridge-fragment
formation may
he
it
result of inversion
or
of
a
sub-
"o.sft/rrr.\
and
E.
[lc~'lrdl//i~ll~s
po
Hereditus
114
(1991)
HYBRIDS
OF
PSEliDOKOtGNtKlA
AND
ELYMLS
123
Table
4.
Observed and calculated meiotic configurations in the triploid and tetraploid hybrids according to ALONSO and KIMBLR
(1
98
I).
and KIMBER and ALONSO
(1981)
Combinations Cross
number *Obs/
Model Univ Rod Ring Triv Chain
quad.
E
wni(o~tatu~
x
P
tognata HH
2478
E.
semicostatus
x
P.
cognata
HH
2480
P.
i’ognata
x
E. pendulinus BB
6853
E.
pendulinus
x
E.
semicostatus BB
6713
E. pendulinus
x
E.
semicostatus BB
6764
obs
2:
I
obs
2:
1
obs
2:
1
obs
2:2
obs
2:2
6.45
6.54
6.72
6.56
7.66
8.23
3.98
3.28
3.71
2.90
1.10 5.65 0.35
0.78 5.71 0.47
2.14 3.20 1.20
2.40 3.14 1.12
4.02 1.88 0.44
3.35 1.67
0.91
5.08 6.18 0.22
5.49 5.67 0.32
4.61 6.76 0.28
5.16 6.14 0.32
0.02
0.08
0.12
0.66
0.16
0.38
Ring
quad.
-
0.08
0.02
0.02
0.03
C
x
ss
0.936 0.979 0.129
0.78
1
0.924 0.103
0.607 0.X83 1.038
0.663 0.939 0.979
0.688 0.932 1.647
*
ObdModel
=
Ohaerved or Model;
Univ
=
univalents; Rod
=
rod
bivalents;
Ring
=
ring
bivalents; Triv
=
trivalents; Chain
quad
=
chain
quadrivalents:
Ring
quad
=
ring
quadrivalent5:
c
=
mean arm
pairing
frequency;
x
=
relative
affinity
of
the most closely
related genomes:
SS
=
Sum
of
squares
chromatid (“U”-type) exchange
(
JONSE
and
BRUMP-
Elymus
canadensis
X
Agropyron
caninum, A.
trac~h~cuulim.
and A. striatum.
-
Am.
.I.
But.
55:
1
133-1
139
DEWEY, D. R.
1970.
The origin of Agi-opyron alhicans.
-
An?.
./.
DEWEY, D. R.
1981.
Cytogenetics of ARropyronfer~~orrensis and
TON
1971).
Average frequencies
of
ca
0.5
multivalents per
cell were observed in both SSY- and SSYY-hy-
Bar,
,-,
12-18
brids, with
a
maximum of three per cell in the two
combinations.
It is
possible, therefore, that chromo-
somal structural rearrangements, e.g., transloca-
tions, have arisen between parental chromosomes,
but it is more likely that
a
certain degree of homoe-
ology exists between the
“S”
and
“Y”
genomes in
these
Elymus
species, as suggested previously
(Lu
and
BOTHMER
1989, 1990; Lu et al. 1990a).
Arknowkfgements.
-
We thank Dr T.
Sall
for kindly assisting
with the calculation of a meiotic model for the tetraploids. We are
also grateful to prof.
N.
Jacobsen, Copenhagen for supplying two
of
the hybrids and to Mr.
R.
Pickering for kindly correcting the
English language.
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WA\L
R.
R.-C.,
DENL~. D.
R.
and
HISAO.
C.
1986.
Genome
analy5is of
the
retraploid
PseirtioroeSnrriu
tuuri.
~
Crop
Sri.
26:
773-727
