Cytogenetical Studies in Wheat VI. Chromosome Location and Linkage Studies Involving Sr13 and Sr8 for Reaction to Puccinia Graminis F. Sp. Tritici

Abstract

Sr 13 was located on the fl arm of chromosome 6A and showed a recombination value of 0.54±0.07 with the centromere. Sr8 was localized to the opposite (α) arm and exhibited a recombination value of 0.44 ± 0.05 with the centromere. Genetic independence between Sr13 and Sr8 was confirmed in a genetic study involving a cross between two near.isogenic lines, each carrying one of the genes. The use of rare chimaeric plants in monosomic populations for isolating marked chromosome misdivision products was demonstrated. The β telocentric arm of chromosome 6A, previously unavailable in any stock, was isolated by this means.

Full text

CYTOGENETICAL
STUDIES
IN
WHEAT
VI..
CHROMOSOME
LOCATION
AND
LINKAGE
STUDIES
INVOLVING
Sr13
AND
Sr8
FOR
REACTION
TO
PUCCINIA
GRAMINIS
F.
SP.
TRITICI
By
R.
A.
McINTOSHt
[Manuscript
received
26
January
1972]
Abstract
Sr
13
was
located
on
the
fl
arm
of
chromosome
6A
and
showed
a
recombination
value
of
0·54±0·07
with
the
centromere.
Sr8
was
localized
to
the
opposite
(tt)
arm
and
exhibited
a
recombination
value
of
0·44
±
0·05
with
the
centromere.
Genetic
independence
between
Sr13
and
Sr8
was
confirmed
in
a
genetic
study
involving
a
cross
between
two
near.isogenic
lines,
each
carrying
one
of
the
genes.
The
use
of
rare
chimaeric
plants
in
monosomic
populations
for
isolating
marked
chromosome
misdivision
products
was
demonstrated.
The
fl
telocentric
arm
of
chromosome
6A,
previously
unavailable
in
any
stock,
was
isolated
by
this
means.
I.
INTRODUCTION
Athwal
and
Watson
(1956) found
that
common
wheat
(Triticum aestivum
L.)
cv.
Khapstein
possessed
two
genes, one
dominant
and
one recessive, for resistance
to
certain
cultures
of
Puccinia graminis Pers.
f.
sp. tritici
Eriks.
& E.
Henn.
isolated
in
Australia
prior
to
1954,
and
to
a
culture
of
Indian
origin.
North
American
studies
(Knott
1962)
indicated
that
Khapstein
carried
three
genes for resistance, one
of
which was identified as Sr7a.
The
other
two, previously unidentified, were designated
Sr
13
and
Sr
14.
Following
the
development
of
near-isogenic lines
carrying
genes for resistance
to
P. graminis
in
the
genetic
background
of
cv. Marquis
(Knott
1968)
it
has
been
established
at
this
institution
that
the
genes identified
by
Athwal
and
Watson
were
Sr13
and
Sr14.
Of
the
three
genes
in
Khapstein,
only
Sr13 confers resistance
to
all
Australian
field cultures. Cultures collected since 1954
are
virulent
on
Sr14
and
most
are
virulent
on
Sr7a.
This
paper
reports
on
the
location,
arm
localization,
and
genetic relationship
of
Sr13
and
Sr8.
The
latter
was previously
located
on
chromosome 6A (Sears 1954;
Sears, Loegering,
and
Rodenhiser 1957).
II.
MATERIALS
AND
METHODS
Khapstein
W 1451
(W
numbers
refer
to
the
Sydney
University
Wheat
Accession
Register)
was
crossed
as
the
male
parent
to
the
Chinese
Spring
monosomic
series.
Although
genes
for
resistance,
which
Khapstein
inherited
from
its
tetraploid
parent,
were
expected
to
reside
in
the
A
or
B
genomes,
the
full series
of
crosses
was
made
because
earlier
attempts
to
locate
genes
in
Khapstein
had
proved
unsuccessful.
*
Part
V,
Can.
J.
Genet. Cytol., 1970, 12, 60.
t
Department
of
Agricultural
Botany,
University
of
Sydney, Sydney,
N.S.W.
2006.
Aust.
J.
biol.
Sci.,
1972,25,
765-73

766
R.
A.
McINTOSH
Cytological
tests
for
validity
of
telocentric
rnisdivision
products
obtained
in
Fg
and
Fa
populations
involving
chromosome
6A
were
made
in
crosses
with
Chinese
Spring
plants
ditelo-
centric
for
the
'"
arm.
To
test
for allelism
between
Sr13
and
Sr8,
the
respective
near.isogenic
lines
(W
2401
and
W 2931)
were
crossed. Telocentric
mapping
of
Sr8
was
performed
by
analysing
the
selfed
progeny
of
a monotelodisornic (20" +
It")
plant
from
Chinese
Spring
monotelo-6A
*
4/Mentana
(pedigree
system
of
Purdy
et al. 1968)
and
the
test
cross
progeny
of
a monotelodisornic
plant
from
Chinese
Spring
monotelo-6A
*
5/Mentana.
The
P.
graminiB
cultures
utilized
were chosen for
appropriate
pathogenic
abilities.
These
were:
64726
(strain
designation
116---4,5
on
the
system
of
Watson
and
Luig
1963, 1965).
68-L-4
(34-1,2,3,4,5,6,7)
70-L-5
(34-1,2,3,4,5,6,7)
334 (126-6,7)
70290 (21-5)
University
of
Missouri
culture
59-51A
(59-5,7).
All
seven
cultures
are
avirulent
on
seedlings
withSr13
(infection
type
"2+3
=").
Virulence
on
seedlings
with
Sr8
is
denoted
by
"-6"
in
the
strain
designations
for
cultures
68-L-4,
70-L-5,
and
334.
Infection
types
produced
when
seedlings
with
Sr8
were
inoculated
with
avirulent
cultures
were
"2"
to
"3
=".
Seedling
populations
were
inoculated
and
tested
by
usual
procedures.
Mitotic
studies
were
performed
on
root
tips
that
had
been
treated
in
cold
water
or
in
a
saturated
solution
of
",-bromo-
naphthalene,
fixed
in
Farmer's
fixative,
hydrolysed
in
IN HCl,
and
stained
in
leuco-basic fuchsin.
For
meiotic
studies,
anthers
were
fixed
in
Farmer's
fixative,
hydrolysed
in
IN HOI,
and
stained
in
leuco-basic fuchsin.
TABLE
1
SEGREGATION
OF
REACTION
TO
PUOOINIA
GRAMINIS
CULTURE
64726
IN
F2
POPULATIONS
FROM
MONOSOMIC
Fl
PLANTS
OF
CROSSES
BETWEEN
CHINESE
SPRING
MONOSOMICS
AND
KHAPSTEIN
R,
resistant;
S, susceptible
Chromo-
Reaction
Chromo-
Reaction
Ch
Reaction
~
2 *
~
2 *
romo-~
2 *
X3:1
some
X3:1 X3:1
some
R S R S
some
R S
lA
91
29
0·04
1B
71
36
4·26
1D
68 22
0·01
2A
87 25
0·43
2B
102
41
1·03
2D
68 22
0'01
3A
71
29
0·85
3B
64 21 0
3D
73 15
2·97
4A
78 38
3·72
4B
61
25
0·76
4D
52 37
13·04
5A
9,( 23
1·78
5B
88 28
0·04
5D
68
24
0·06
6A 98 18
5·56
6B 67 17
1·02
6D 66 20
0·14
7A 77 37
3·38
7B 74 19
1·04
7D
61
28
1·98
Total
(excluding 6A): 1481
resistant,
536 susceptible,
X~:l
2·66
*
Values
for significance:
3·84
(P
=
0·05);
6·64
(P
=
0·01).
III.
RESULTS
(a)
Chromosome Location
of
Srl3
Seedling segregation ratios
in
progenies
of
Fl
plants from crosses between
the
various Chinese Spring monosomics
and
Khapstein
(Table
1)
deviated from those
expected
at
the
P =
0·05
level for single-factor
pair
segregation
in
three
instances.

Fl
F2
CYTOGENETICAL
STUDIES
IN
WHEAT.
VI
TABLE
2
SUMMARY
OF
STEPS
INVOLVED
IN
ANALYSIS
OF
Sr13
o = selfed cross
Chinese
Spring
mono-6A
X
Khapstein
I
1 I
h=~
h=~
10 10
48 : 9
(resistant:
susceptible)
50
: 9
Approx.
one-half
of
F2
population
transplanted
I I
22 : 5 23 : 7
1
0
.-----1-
10
_----.
767
I I I I
Homozygous
Four
monosomic,
Homozygous
Four
monosomic,
Fa
resistant
or
homozygous
resistant
or
homozygous
segregated
susceptible;
one
segregated
susceptible;
abnormally
nullisomic, sterile
abnormally
three
monotelo-
somic,
one
of
which
is 6A",
Fa
family
1581
segregated
as
follows:
30
resistant
: I
chimaera
: 6
susceptible
20"
+
t'
o
16
plants
progeny-
tested
(Table
4);
select
20"
+
t'
cross
with
diteio-
6A",
;
select 2n = 42tt
Q9
20"
+
t'
+
t'
Select
three
plants:
1
I I I
2n
= 42tt 41t 40
10 10 10
Cross
A:
three
plants
2n
=
41;
one
plant
2n
= 42t
I
cross
with
Chinese
Spring
Cross
B:
eight
plants
2n
=
41
Segregation
as
in
Table
3
cross
with
Chinese
Spring
Select
2n
= 42t
o
Homozygous
Segregated
resistant
Homozygous
susceptible
Segregation
as
in
Table
3
cross
with
Chinese
Spring
Segregation
as
in
Table
5

768
R.
A. MoINTOSH
Ratios for chromosomes
IB
and
4D
deviated
in
the
direction
of
excess susceptible
seedlings, whereas for
the
critical cross, a deviation
in
the
opposite direction was
expected. Hence chromosome 6A appeared
to
be
involved,
but
as this result was
not
considered
to
be
conclusive, approximately one-half
of
the
F2 populations were
transplanted
to
obtain
F3lines for
further
study.
F3
data,
obtained
using culture
68-L-4,
confirmed
that
Sr13 was located
in
chromosome 6A. Mitotic chromosome counts
on
two, three,
or
four seedlings within
each F3 line from
the
6A cross
permitted
deduction
of
the
chromosome constitution
of
each F2
plant.
Disomic F2
plants
which were resistant produced homozygous resistant
F3 families, whereas monosomic F2
plants
which were resistant gave progenies
with
clearly abnormal segregation ratios. On
the
other
hand
tests
on
F3 lines from
the
20 non-critical crosses confirmed single-gene segregation
in
each instance.
The F2
data
for chromosome 6A
and
the
various steps involved
in
subsequent
studies
are
summarized
in
Table
2.
Of
the
18
susceptible seedlings,
in
the
F2 popula-
tion
involving chromosome 6A,
12
were
transplanted.
One
of
these was nullisomic
in
appearance
and
proved
to
be sterile.
From
mitotic studies
of
progenies
it
was inferred
that
eight were monosomic, while three, which
had
been nullisomic-like
but
partially
fertile, were inferred
to
have
been monotelosomic. The telocentric derivative
in
one
of
these was identified as
6Aoc.
Since these derivatives were susceptible
to
P.
graminis,
the
test
established
that
the
population was indeed aneuploid for chromosome 6A
and
that
Sr13 was
not
located
in
the
ex
arm. The inclusion
of
eight presumed monosomic
plants
in
the
susceptible group was unexpected,
but
since
their
constitutions were
determined from mitotic chromosome counts
on
progenies,
other
explanations
are
possible. These plants
may
have been
monoisosomic-an
isochromosome would
not
be
identified
somatically-or
they
may
have been nullisomic for chromosome 6A
and
trisomic for a compensatory homoeologous chromosome. However,
their
normal
plant
vigour reduced
the
first possibility. A more likely explanation is
that
they
resulted from
out
crossing-the
pollination
of
20-chromosome eggs lacking chromosome
6A
by
21-chromosome pollen grains carrying
the
susceptible allele from a
plant
in
another
cross
or
from
an
outside source.
Poor
fertility
of
many
of
the
monosomic
Fl
plants
from
the
cv. Chinese Spring X
Khapstein
crosses was
noted
and
definite
instances
of
out
crossing were established in certain crosses.
(b)
Telocentric Mapping
of
Sr13
A seedling displaying a chimaeric reaction
to
P.
graminis
appeared
in
one
Fa
family from a resistant F2
plant.
This seedling was
transplanted
and
was found
to
have 20 bivalents
and
a telocentric univalent chromosome (20" +
t')
at
meiosis. Two
spikes were pollinated
with
cv. Chinese Spring
and
the
remaining spikes were
permitted
to
self.
The
telocentric chromosome was recovered
in
only one (1581/Chinese Spring
A.4)
of
12 seedlings obtained from
the
crosses. Chromosome counts
and
seedling
reactions
of
19
progeny
of
this individual
are
presented in Table 3. Mitotic chro-
mosome counts were obtained for
16
selfed seedlings from
the
chimaera. Their
frequencies, meiotic constitutions,
and
behaviour when progenies were tested,
are
given
in
Table
4.
Because
of
trisomy
of
the
ditelocentric individual, plants
with
20"
+
t'
were chosen for
further
study.
Firstly
an
individual with
two
telocentric

CYTOGENETICAL
STUDIES
IN
WHEAT.
VI
769
chromosomes from a cross
with
a Chinese Spring
plant
ditelocentric for
6Aot:
displayed,
at
meiosis, 20 bivalents
and
two telocentric univalents (20" +
t'
+ t'). This estab-
lished
that
the
telocentric being
tested
involved chromosome 6A
and
that
it
was
the
fJ
TABLE
3
CHROMOSOME
CONSTITUTIONS
AND
REACTIONS
TO
P.
GRAMINIS
CULTURE
70-L-5
IN
PROGENIES
OF
MONOTELODISOMIC
PLANTS
HETEROZYGOUS
FOR
Sr13
Reactions
of
Reactions
of
Chromosome 1581/Chinese
Spring
A.4
1581. 7/Chinese
Spring
Constitution
progeny progeny
1\
Resistant
Susceptible
Resistant
Susceptible
Total
42tt* 1
42tt
9 1
42 5 1
41
1 1
16 3
*
Including
two
telocentric
chromosomes.
t
Including
one
telocentric
chromosome.
1
4 2
11
4
1
17
6
arm
of
this chromosome. Secondly,
three
plants were selected from a selfed mono-
telocentric individual. One was ditelocentric
and
progeny
tests
established
that
it
was homozygous for Sr13. One was monotelocentric
and
mitotic counts
of
nine
progeny showed four with 2n =
41
t
and
five
with
2n = 40. The
41
t seedlings were
TABLE
4
CHROMOSOME
CONSTITUTIONS,
MEIOTIC
CONFIGURATIONS,
AND
REACTIONS
TO
P.
GRA-MINIS
CULTURE
70-L-5
OF
16
PLANTS
FROM
THE
SELFING
OF
Sr13
CHIMAERA
No.
of
Mitotic
Meiotic
Progeny
plants
count*
configuration
*
test
1
2n
= 43tt
19"
+
1'"
+
t"
Homozygous
resistant
1
2n
= 42t
20"
+
i'
+
t'
or
Segregating
20"
+
it"
1
2n
=
41
20"
+
i'
Segregating
10
2n
= 41t
20"
+
t'
Segregating
3
2n
= 40
20"
Homozygous
susceptible
* t =
telocentric;
i = isochromosome;
univalent;
bivalent;
=
trivalent.
resistant,
and
those
with
40 chromosomes susceptible,
to
culture
70-
L-5.
Three
seedlings with
2n
= 40 from a
third
plant
with 20" were susceptible as expected.
This
study
conclusively demonstrated
that
Sr13 was located in
the
telocentric
chromosome.

770
R.
A.
McINTOSH
In
a
third
study
involving a cross
with
Chinese Spring, a monotelodisomic
progeny
was
further
test-crossed
with
Chinese Spring.
Table
5 lists
the
somatic
counts
and
reaction
frequencies
of
the
progeny. One susceptible
individual
with
2n
= 43t, was considered
to
be
a recombination.
Of
two
seedlings
with
2n
=
41
t,
one was considered a
recombinant
and
the
other
a
parental
type.
As
the
telocentric
chromosome was
transmitted,
aneuploidy
must
have
involved
a different chromosome.
Of
two
plants
with
2n
= 41,
the
resistant
individual
was considered a
recombinant,
whereas
the
second, being susceptible, could
not
be
included
in
the
analysis since
it
may
have
been
deficient,
rather
than
parental,
for chromosome 6A.
Hence
of
20
gametes
sampled, 12 were
recombinant,
indicating
that
Sr13 is
independent
of
the
centromere
(recombination =
0·60±0·U).
TABLE
5
CHROMOSOME
CONSTITUTIONS
AND
REACTIONS
TO
P.
GRAMINIS
CULTURE
70-L-5
OF
21
SEEDLINGS
FROM
TEST·CROSS
OF
HETEROZYGOUS
MONOTELODISOMIC
PLANT
Chromosome
Reaction*
constitution
Resistant
Susceptible
43t
lR
42t
4P
6R
41t
IP
lR
42
3R
3P
41
lR
1-
* R =
recombinant;
P =
parental.
Data
for 23 selfed
progeny
from
the
test-crossed
plant
(1581.7 jChinese Spring)
are
included
in
Table
3.
Recombination
based
on
the
method
of
maximum
likelihood
for
the
combined
data
in
Table
3,
but
omitting
individuals
with
2n = 41, was
estimated
to
be
0·49±0·10.
A
recombination
estimate
using
the
pooled
test-cross
and
self
data
was
0·54±0·07.
(c)
Linkage
of
Sr8
and
Srl3
Thirty-six
F3lines
from
a cross
between
the
appropriate
near-isogenic lines were
tested
with
culture
334 which is
virulent
on
plants
with
Sr8,
and
with
culture
64726
which is
avirulent
on
plants
with
either
Sr8
or
Sr13. Because
oflow
seedling
numbers
in
some lines,
determinations
as
to
whether
lines were homozygous
resistant
or
segregating were
not
possible, especially
with
the
second
culture
where two-gene
segregation was expected.
Hence
lines were classified
into
three
groups,
the
expected
frequencies for which,
if
independence is assumed,
are:
12 homozygous
resistant
or
segregating
with
both
cultures, i.e.
genotypes
Sr13Sr13 - - andSr13sr13
--;
3 homozygous
resistant
or
segregating
with
culture
64726 only, i.e.
genotypes
sr13sr13 Sr8Sr8
and
sr13sr13 Sr8sr8;
1 homozygous susceptible
with
both
cultures, i.e.
genotypes
sr13sr13 sr8sr8.

CYTOGENETICAL
STUDIES
IN
WHEAT.
VI
771
The
realized
ratio
of
30 : 4 : 2 does
not
differ significantly from
the
expected distribu-
tion
(xL
(30 :
6)
=
1·33;
P>0·25).
This result indicated
that
Sr13
andSr8
are
not
linked.
(d)
Telocentric Mapping
of
Sr8
A monotelodisomic
plant
from
the
cross Ohinese Spring monotelo-6Aot *
5JMen-
tana
(a 2n =
41
individual being selected for each backcross) was test-crossed
with
Ohinese Spring. Mitotic chromosome counts
and
reactions
of
the
progenies
with
culture 70290, which is avirulent
on
seedlings
with
Sr8, are given
in
Table
6.
Among
91
gametes sampled,
41
recombinants were recovered. Recombination between Sr8
and
the
centromere was
estimated
to
be
0·46±0·05.
TABLE
6
MITOTIC
CHROMOSOME
COUNTS
AND
REACTIONS
TO
P.
GRAMINIS
CULTlTRE
70290
OF
TEST-CROSS
PROGENIES
OF
MONOTELODISOMIC
PLANT
FROM
CHINESE
SPRING
MONOTELO-6Acx
*
5/MENTANA
Direction
Chromosome
Reactiont
of
cross
No.
-,
Resistant
Susceptible
Male 42 16 10
42t 3
Female
42 14 12
42t
20
16
Total
42
30P
22R
42t
20R
19P
t P =
parental;
R =
recombinant.
TABLE
7
CHROMOSOME
COUNTS
AND
REACTIONS
TO
P.
GRAMINIS
CULTlTRE
59-51A
OF
PROGENY
OF
SELFED
MONOTELODISOMIC
PLANT
FROM
CHINESE
SPRING
MONOTELO-6Acx
*
4/MENTANA
Chromosome
Reaction
Total
No.
Resistant
Susceptible
42 22 4 26
42t 13 2 15
42tt 1 1 2
Total
36 7 43
A selfed population from a monotelodisomic
plant
in
cross Ohinese Spring
monotelo-6Aot * 4JMentana was scored mitotically for chromosome
number
and
tested
with
culture 59-51A. Frequencies
and
reaction classes are presented
in
Table
7.
Some reactions considered doubtful
on
a single-plant basis were confirmed
by

772
R.
A.
McINTOSH
progeny
testing.
Recombination,
based
on
the
method
of
maximum
likelihood, was
estimated
at
0·37±0·09.
Using
the
pooled test-cross
and
self
data,
recombination
between
Sr8
and
the
centromere
was
estimated
to
be
0·44±0·05.
IV.
DISCUSSION
Genes Sr8
and
Sr13 concerned
with
reaction
to
P.
graminis were
located
in
opposite
arms
of
chromosome 6A. Sr8 was localized
to
the
IX
(standard)
arm
and
showed
recombination
of
0·44±0·05
with
the
centromere, whereas
the
estimate
of
0·54±0·07
suggests
that
Sr13 is
independent
of
the
centromere
in
the
(3
arm.
These
findings were
supported
by
a
concurrent
genetic
study
indicating
that
Sr8
and
Sr13
were
independently
inherited.
The
studies
with
Sr13
demonstrated
the
value
of
occasional chimaeric
plants
which
may
appear
in
segregating populations.
Such
chimaeras
frequently
carry
chromosome misdivision
products
which
can
be
used
for chromosome
arm
determina-
tions
and,
if
telocentric as
in
this
study,
for telocentric mapping. However, misdivi-
sion
products
are
not
always stable.
From
a chimaeric seedling
with
part
of
its
tissue
having
a telocentric,
or
isochromosome,
bearing
the
particular
dominant
(or hemi-
zygous effective)
marker,
subsequent
growth
appears
to
be
random.
Hence
the
misdivision
products
are
not
always recovered,
or
they
may
be
somatically
unstable
(Steinitz-Sears 1966).
The
detection
of
a
chimaera
in
these
studies
not
only
permitted
the
determination
of
the
particular
arm
bearing Sr13,
but
also allowed
the
isolation
of
a telocentric chromosome which was previously
unavailable
in
wheat.
Moreover,
the
newly isolated telochromosome is
marked
with
Sr13 which should
enhance
its
value for
future
mapping
purposes. As
the
result
of
recombination
and
further
selec-
tion, ditelocentric
6Aoc
stocks homozygous for Sr8 also should be available.
Although
Sr13 confers resistance
to
all
current
Australian
field
strains
of
P.
graminis
there
has
been
difficulty
in
exploiting
it
as a resistance source in commercial
wheat
cultivars. A physiological "black-chaff" condition
appears
to
be
associated
with
its
presence.
This
detracts
from
agronomic
appearance
and,
under
certain
conditions
at
least,
undoubtedly
leads
to
yield depression.
In
these
studies,
the
black-chaff condition
has
persisted
in
Sr
13-bearing
monotelodisomic individuals
after
backcrossing
to
Chinese Spring. This association requires
further
investigation
to
determine
the
intensity
of
linkage,
and
to
determine
the
relationship,
if
any,
between
the
black-chaff
characteristic
and
leaf
necrosis
characters
which
have
been
associated
with
chromosomes
of
homoeologous
group
6 (Sears 1954, 1966; Morris,
Schmidt,
and
Johnson
1970; Wenzel 1971). A well-known black-chaff
phenotype
allegedly
linked
with
field resistance
to
P.
graminis
has
been
associated
with
chromo-
some
3B
of
cv.
Hope
which, like
Khapstein,
resulted
from
a cross
of
tetraploid
with
hexaploid
wheat,
but
there
is
no
evidence
to
suggest
these
occurrences
are
related
in
any
way.
V.
ACKNOWLEDGMENTS
Financial
assistance
and
a
travel
grant
was
provided
by
the
Wheat
Industry
Research
Council
of
Australia. Segments
of
the
study
were
conducted
at
the
Univer-

CYTOGENETICAL
STUDIES
IN
WHEAT.
VI
773
sity
of
Missouri, where
the
author
was
the
recipient
of
a
Postdoctoral
Research
Fellowship
provided
by
the
Graduate
School.
Dr.
E. R. Sears
contributed
a cytological
analysis
and
Dr.
W.
Q. Loegering
provided
a P. graminis culture used
in
the
study.
I
am
grateful
to
Dr.
D.
G. Pederson
ofthis
Department
for calculation
ofthe
recombina-
tion
values. Technical assistance was
provided
by
Mr.
J.
Green
and
Miss
M.
Lowe.
VI.
REFERENCES
ATBW
AL,
D.
S.,
and
WATSON,
I.
A.
(1956).-
Resistance
to
Puccinia
graminis tritici
in
Khapstein,
8
vulgare
derivative
of
Khapli
emmer.
Proc.
Linn.
Soc.
N.S.
W.
81,
71-7.
KNOTT, D.
R.
(1962).-The
inheritance
of
rust
resistance.
IX.
The
inheritance
of
resistance
to
races
15B
and
56
of
stem
rust
in
wheat
variety
Khapstein.
Oan.
J.
Plant
Sci.
42,
415-19.
MORRIS,
R.,
SCHMIDT,
J.
W.,
and
JOHNSON, V.
A.
(1970).-Association
of
homoeologous
group
6
aneuploids
with
leaf
necrosis
in
hexaploid
wheat
varieties.
Wheat
Inform.
Servo
30,
6-7.
PURDY,
L.
H.,
LOEGERING,
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Q.,
KONZAK,
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(1968).-A
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Orop. Sci.
8,
405-6.
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E.
R.
(1954).-The
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Mo.
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Stn.
No.
572.
SEARS,
E.
R.
(1966).-Chromosome
mapping
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the
aid
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Proc.
2nd
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[Heredita8,
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SEARS,
E.
R.,
LOEGERING,
W.
Q.,
and
RODENHISER,
H.
A.
(1957).-Identification
of
chromosomes
carrying
genes
for
stem
rust
resistance
in
four
varieties
of
common
wheat.
Agron.
J.
49,
208-12.
STEINITZ-SEARS,
L.
M.
(1966).-Somatic
instability
of
telocentric
chromosomes
in
wheat
and
the
nature
of
the
centromere.
Genetics, Princeton
54,
241-8.
WATSON,
I.
A.,
and
LUIG,
N.
H.
(1963).-The
classification
of
Puccinia
gramini8
var.
tritici
in
relation
to
breeding
resistant
varieties.
Proc.
Linn.
Soc.
N.S.
W.
88,
235-58.
WATSON,
I.
A.,
and
LUIG,
N.
H.
(1965).-Sr15-Anew
gene
for
use
in
the
classification
of
Puccini
a
graminis
var.
tritici.
Euphytica
15,
239-50.
WENZEL,
W.
G.
(1971).-Monosomic
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Genet. Oytol. 13,
227-30.