Introgression of a 4D chromosomal fragment into durum wheat confers aluminium tolerance

Aluminium (Al(3+)) inhibits root growth of sensitive plant species and is a key factor that limits durum wheat (Triticum turgidum) production on acid soils. The aim of this study was to enhance the Al(3+) tolerance of an elite durum cultivar by introgression of a chromosomal fragment from hexaploid wheat (Triticum aestivum) that possesses an Al(3+) tolerance gene.

A 4D(4B) substitution line of durum wheat 'Langdon' was backcrossed to 'Jandaroi', a current semi-dwarf Australian durum. In the second backcross, using 'Jandaroi' as the recurrent parent, a seedling was identified where TaALMT1 on chromosome 4D was recombined with the Rht-B1b locus on chromosome 4B to yield an Al(3+)-tolerant seedling with a semi-dwarf habit. This seedling was used in a third backcross to generate homozygous sister lines with contrasting Al(3+) tolerances. The backcrossed lines were characterized and compared with selected cultivars of hexaploid wheat for their Al(3+) and Na(+) tolerances in hydroponic culture as well as in short-term experiments to assess their growth on acid soil.

Analysis of sister lines derived from the third backcross showed that the 4D chromosomal fragment substantially enhanced Al(3+) tolerance. The ability to exclude Na(+) from leaves was also enhanced, indicating that the chromosomal fragment possessed the Kna1 salt tolerance locus. Although Al(3+) tolerance of seminal roots was enhanced in acid soil, the development of fine roots was not as robust as found in Al(3+)-tolerant lines of hexaploid wheat. Analysis of plant characteristics in the absence of Al(3+) toxicity showed that the introgressed fragment did not affect total grain yield but reduced the weight of individual grains.

The results show that it is possible to increase substantially the Al(3+) tolerance of an elite durum wheat cultivar by introgression of a 4D chromosomal fragment. Further improvements are possible, such as introducing additional genes to enhance the Al(3+) tolerance of fine roots and by eliminating the locus on the chromosomal fragment responsible for smaller grain weights.