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

Abstract

Background and aim: 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.

Methods: 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.

Key results: 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.

Conclusions: 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.

Keywords: 4D chromosomal fragment; Kna1; TaALMT1; Triticum aestivum; Triticum turgidum; acid soil; aluminium tolerance; durum wheat; malate; rhizosheath; root growth; salt tolerance.