Research on the identification and
quality effects of the 1B-1R
translocation has continued. An electrophoretic procedure was
developed to obtain patterns of water-soluble proteins from seeds
to detect the 1B-1R
translocation in wheat cultivars. The water soluble proteins
were precipitated with Coomassie Brilliant Blue R-250 and separated
on an SDS-PAGE gel. The procedure extracted protein bands corresponding
to the FONT SIZE=2 FACE="WP Greek Century"o-secalins
of the rye parent that were present only in lines carrying the
1B-1R
translocation. By simplifying extract preparation and providing
clear band resolution, this procedure facilitates large-scale
screening of wheat lines for the rye translocation.
Mixing curves of 100 g, full-formula doughs made from 1B-1R wheats can be used to provide an objective test for estimating dough breakdown and stickiness. Dough breakdown occurred within 2 min after peak development in all 1B-1R wheats. Variation in genetic background, particularly HMW glutenin composition, affected the degree of dough
breakdown. Recommendations can now
be made to breeders on the optimum allelic composition of endosperm
proteins required to maintain acceptable dough strength, even
in the presence of the 1B-1R
translocation.
Low molecular weight glutenin subunits
and durum wheat pasta quality.
M.I.P. Kovacs1, N.K. Howes1, D. Leisle1, and J. Zawiskowski2.
1 Agriculture & Agri-Food Canada, Winnipeg Research Centre, Winnipeg, MB R3T 2M9, Canada; and
2 Department
of Food Science, University of Manitoba, Winnipeg, MB R3T 2N2,
Canada.
It has been shown previously that two
types of the low molecular weight glutenin subunit-2
(LMWGS 2 and 2-) exist in durum wheat cultivars. We
examined the effect of these alleles upon quality parameters generally
examined in the Canadian durum wheat breeding programs. F2-derived
F4 and F5 durum wheat families from the
cross `DT471/DT624',
homozygous for either of two low molecular weight glutenin subunits
(LMWGS 2 and LMWGS 2-), were used in a study to determine the
effect of these subunits on protein content (PROT), cooked pasta
disc viscoelasticity (PDV), cooked gluten viscoelasticity (CGV),
sodium dodecyl sulphate sedimentation volume (SV), mixograph mixing
development time (MDT), mixograph peak height (MPH), and mixograph
total energy (MTE). These subunits were identified using a monoclonal
antibody (MAb45/8) specific for the LMWGS 2 allele. Both parents
and progeny were homozygous for the HMWGS 6+8 and gliadin band
45. The major effect of the LMWGS 2 type was on PDV and SV rather
than on measures of gluten strength (MDT, CGV). PDV and SV values
were not influenced greatly by either MDT or CGV values, indicating
that the former two are being influenced by additional quality
components other than gluten strength. This study showed that
the LMWGS 2 allele is beneficial to improve the pasta cooking
quality of future cultivars and that selection can be accomplished
readily using the monoclonal antibody MAb45/8.
Low molecular weight (LMW) glutenin subunit composition of Canadian-grown wheat cultivars.
O.M. Lukow.
The proteins of 120, Canadian-grown
hexaploid wheat cultivars were fractionated by SDS-PAGE to determine
their LMW glutenin subunit composition. Considerable variation
occurred in the B-zone gel region; 31 distinct banding patterns
were identified. Each banding pattern varied in band number from
3 to 9. Twenty-four bands differing in mobility were identified.
High quality bread wheats, as assessed by their baking strength
index, were characterized by a common LMW pattern composed of
five bands. Nine LMW-patterns were unique and were found in only
one cultivar. A numerical designation and schematic representation
of banding patterns has been devised. The importance of specific
LMW-glutenin patterns to end-use quality must be evaluated in
conjunction with the HMW-glutenin composition, particularly for
breeding material.
J.D. Procunier and M. Wolf.
PCR-based DNA markers have many advantages over conventional RFLP markers. High molecular weight DNA is necessary for RFLP analysis, whereas smaller DNA fragments are adequate for PCR. Only small DNA amounts are needed for PCR, and the DNA can be isolated from a single seed, leaving the embryo intact. The PCR procedure is quick and simple and numerous, independent resistance genes can be analyzed simultaneously (multiplex PCR). Near-
isogenic lines (NILs), carrying leaf
rust resistance genes Lr29 and Lr25, were screened
for molecular markers that showed linkage to the Lr genes.
By combining the RAPD (random amplified polymorphic DNA) technique
with the DGGE (denaturing gradient gel electrophoresis) method
of fragment separation, a tightly linked RAPD/DGGE marker for
each Lr gene was identified.
The RAPD primer for each Lr
gene was converted to a SCAR (sequence characterized amplified
region) primer by TA cloning and DNA sequencing the polymorphic
band. Eighteen to 24 base-long oligonucleotide primers were chosen
from each sequence and included the original RAPD primer sequence.
The oligonucleotides were synthesized by an Applied Biosystems
DNA synthesizer, model 391. At a specific annealing temperature
and primer length, the polymorphism between the resistant and
susceptible lines was retained for each Lr gene. A single
band was present on agarose gels for each NIL line and absent
for the recurrent, susceptible parent (Thatcher).
The use of longer and specific SCAR
primers allowed a more robust PCR reaction, the elimination of
the multiple banding patterns of RAPD primers, the detection of
Lr genes in different wheat backgrounds, and multiplex
PCR. For a single PCR reaction, the four SCAR primers were used
to simultaneously identify both Lr29 and Lr25 genes
from DNA having both of them. Both the Lr29 and Lr25
bands were visualized in a single lane on an agarose gel. Touchdown
PCR eliminated spurious bands caused by a primer pair annealing
nonspecifically at the lower temperature. This method can identify
numerous resistance genes simultaneously, as long as the PCR products
have different molecular weights.
Quality evaluation of durum wheat by measuring pasta viscoelasticity.
M.I.P. Kovacs, G. Dahlke, J.S. Noll, and D. Leisle.
The usefulness of pasta disc viscoelasticity
to predict pasta cooking quality in the durum wheat breeding program
was evaluated. Cooked pasta disc viscoelasticity (PDV) was calculated
from the creep curve of the viscoelastogram. Two sets of samples
with different quality characteristics were tested for protein
content, sedimentation volume (SV), mixograph mixing characteristics,
cooked gluten viscoelasticity (CGV), and cooked PDV. Pearson
correlation coefficients indicated that cooked PDV was associated
with the mixograph values SV and CGV, but not with protein content.
The results indicate that the PDV test is useful in breeding
programs because it requires small quantities of sample, it is
simple, and it more closely mimics rheological tests used on the
final product, pasta.
Wheat leaf rust in Canada in 1994.
J.A. Kolmer.
Incidence and Severity.
Wheat fields and uniform nurseries of known cultivars and breeding
lines in Manitoba and eastern Saskatchewan were surveyed for incidence
and severity of leaf rust in June, July, and August. The initial
observation of leaf rust was on winter wheat at Carmen, Manitoba,
on June 19. Warm and dry weather in the eastern prairies during
the latter half of June and first week of July slowed development
of the leaf rust epidemic. In the second week of July, leaf rust
was found at trace levels on spring wheat throughout southern
Manitoba. By the first week of August in the Red River Valley
of Manitoba, leaf rust levels on the moderately resistant cultivar,
Katepwa, had reached 40 %, and were up to 10 % on the more resistant
cultivar, Roblin. Susceptible winter wheats had infection levels
up to 100 % in southern Manitoba. Levels of leaf rust infections
on spring wheat were very light in other areas of southern Manitoba
and eastern Saskatchewan. Yield losses were not expected in these
areas.
Physiologic Specialization. In 1994, phenotypes of P. recondita with virulence to Lr3ka and Lr30 continued to increase in the Manitoba and Saskatchewan population. The Kansas winter wheat Karl, with Lr3ka, has selected phenotypes with virulence to this resistance gene. Virulences to these two genes were at very low levels (0-1 %) as recently as 1992.
Virulences to Lr3ka and Lr30
are linked tightly in P. recondita. It is possible
that a mutation affecting both virulence loci had occurred and
this may explain why virulence to Lr30 has increased, although
it is not known if any winter wheat cultivars have this gene.
The Canadian hard red spring wheat cultivar Pasqua has Lr30.
However, this cultivar has not yet been grown widely, and it
is unlikely that the sudden increase in virulence to Lr30
can be attributed only to Pasqua.
Leaf rust collections were received
from Quebec (winter and spring wheats); Ontario (mostly winter
wheats); and Manitoba, Saskatchewan, and Alberta (spring wheats).
The collections were increased on susceptible seedlings of the
wheat cultivar Little Club, and single pustules were inoculated
onto 15 Thatcher lines isogenic for leaf rust resistance genes
to identify the virulence phenotypes.
Frequencies of virulences to specific
Lr genes are shown in Table 1.
Table 1. Frequency (%) of virulence to leaf rust resistance genes in
isogenic Thatcher lines of Puccinia recondita f.sp. tritici single pustule
isolates in Canada in 1994.
_________________________________________________________
Gene Quebec Ontario Man./Sask. Alberta
_________________________________________________________
Lr1 98.2 98.7 98.4 92.3
Lr2a 1.8 3.9 18.6 26.9
Lr2c 82.1 79.2 19.1 50.0
Lr3 52.0 98.7 100.0 88.5
Lr9 0.0 0.0 0.0 0.0
Lr16 0.0 0.0 0.0 0.0
Lr24 0.0 3.9 47.0 15.4
Lr26 0.0 0.0 31.1 3.8
Lr3ka 82.1 83.1 80.9 30.9
Lr11 16.1 22.1 66.1 50.0
Lr17 1.8 2.6 0.5 11.5
Lr30 7.1 11.7 73.8 30.8
LrB 80.4 75.3 1.1 11.5
Lr14a 17.9 23.4 99.5 80.8
Lr18
80.4 75.3 0.5 11.5
Number of
phenotypes 8 12 23 11
Number of
Isolates 56 77 183 26
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A total of 38 different virulence phenotypes
of P. recondita were identified in Canada in 1994.