Durum wheat (AB genomes) is more salt-sensitive than bread wheat (ABD
genomes), a feature that restricts its expansion into areas with sodic or
saline soils. Salt tolerance in bread wheat is linked with a locus on the D
genome that results in low Na+ uptake and enhanced
K+/Na+
discrimination. In order to introduce salt tolerance into current durum wheats
from sources other than the D genome, a search for genetic variation in salt
tolerance was made across a wide range of tetraploids representing 5
Triticum turgidum sub-species
(durum, carthlicum,
turgidum, turanicum,
polonicum). Selections were screened for low
Na+ uptake and enhanced
K+/Na+
discrimination. This was assessed in seedlings grown in 150 mМ NaCl with
supplemental Ca2+, by measuring the
Na+ and K+ accumulated
in the blade of a given leaf over 10 days. Large and repeatable genetic
variation was found. Low Na+ accumulation and high
K+/Na+
discrimination of similar magnitude to that of bread wheat was found in the
sub-species durum. These selections have the potential
for improving salt tolerance in durum wheat breeding programs.
The association between osmoregulation and grain yield was examined using measurements of osmoregulation made on wheat plants grown in pots in a glasshouse and measurements of grain yields made in a wide range of field environments. Osmoregulation was determined from measurements of relative water contents and osmotic potentials made on the flag leaves of plants droughted near anthesis.The genotypes were advanced lines from two distinct breeding programsone for bread wheats and one for durum wheats. All the genotypes in each program (27 bread and 14 durum) were closely related in having a common parent. The grain yields of the bread wheats were evaluated in 56 field trials covering a period of 4 years, and those of the durum wheats were evaluated in seven field trials in one year. Both droughted and irrigated sites were represented. Four field environments were also included for F4 segregating lines reported previously. Considerable variation in osmoregulation occurred which was positively associated with grain yield over the full range of environments sampled for each genotype group. The yields of genotypes which were high in osmoregulation were 11-17% higher in bread wheats and 7% higher in durum wheats than those which were low in osmoregulation, when class differences were based on rnaximising the average yield differences between osmoregulation groups. These results add further evidence favouring the use of glasshouse measurements of osrnoregulation as a selection criterion in wheat breeding.
The possible use of gel electrophoresis of grain proteins to select for pasta-making quality in breeding durum wheats was studied in Australian durum cultivars and in 103 crossbred lines. Computer-based pattern analysis was used to compare gliadin electrophoregrams (38 band positions, each at three levels of intensity) and dough strength (considered as four quantitative estimates from mixograph testing). Close relationships were found between dough strength and a group of gliadin proteins (including band 43, and between dough weakness and a different group of gliadins (including band 42). All 27 breeding lines with weak dough had band 42 and its associated bands, while 90% of the strong-dough lines had gliadin 45. These relationships were shown not to be due to similarities in pedigree. The results indicate gel electrophoresis to be a valuable means of screening for grain quality at early generation in durum-wheat breeding.
The inheritance of gliadin protein differences was investigated because prior electrophoretic studies revealed a close relationship between certain endosperm proteins and gluten strength in durum wheat (Triticum turgidum L. var. durum). Particular attention was focused on gliadin band 45, as it is closely associated with dough strength, and on gliadin band 42, which is associated with poor viscoelastic properties. These inheritance studies were conducted on crosses between the two main biotypes of the Australian cv. Duramba. Results from F1, F2, and BC1F1, populations were consistent with the hypothesis that the syntheses of gliadin bands 45 and 42 are controlled by alleles at a single locus. Dosage effects were exhibited by both alleles; however, band 42 displayed a greater degree of dominance than did band 45. These results should prove useful in breeding durum wheat for improved pasta quality.
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