Genetics of Na+ exclusion and salinity tolerance in Afghani durum wheat landraces

Abstract

Background: Selecting for low concentration of Na⁺ in the shoot provides one approach for tackling salinity stress that adversely affects crop production. Novel alleles for Na⁺ exclusion can be identified and then introduced into elite crop cultivars.

Results: We have identified loci associated with lower Na⁺ concentration in leaves of durum wheat landraces originating from Afghanistan. Seedlings of two F₂ populations derived from crossings between Australian durum wheat (Jandaroi) and two Afghani landraces (AUS-14740 and AUS-14752) were grown hydroponically and evaluated for Na⁺ and K⁺ concentration in the third leaf. High heritability was found for both third leaf Na⁺ concentration and the K⁺/Na⁺ ratio in both populations. Further work focussed on line AUS-14740. Bulk segregant analysis using 9 K SNP markers identified two loci significantly associated with third leaf Na⁺ concentration. Marker regression analysis showed a strong association between all traits studied and a favourable allele originating from AUS-14740 located on the long arm of chromosome 4B.

Conclusions: The candidate gene in the relevant region of chromosome 4B is likely to be the high affinity K⁺ transporter B1 (HKT1;5-B1). A second locus associated with third leaf Na⁺ concentration was located on chromosome 3BL, with the favourable allele originating from Jandaroi; however, no candidate gene can be identified.

Keywords: Bulk Segregant analysis; HKT1;5; K+/Na+ ratio; Leaf Na+ concentration; SNP markers; Salinity tolerance.

Fig. 1

Distribution of third leaf Na⁺ and third leaf K⁺ concentration and the K⁺/Na⁺ ratio in F₂ progeny of two crosses of durum wheat - Jandaroi × AUS-14740 (112 plants) and Jandaroi × AUS-14752 (176 plants). Bars represent number of plants for: (a) Third leaf Na⁺ concentration, (b) Third leaf K⁺ concentration and (c) K⁺/Na⁺ ratio. Black arrows indicate means for paternal parents, AUS-14740 and AUS-14752 (n = 10), and clear arrows indicate means for maternal parent, cv. Jandaroi (n = 10). Salt stress (100 mM NaCl) was gradually applied at the time of third leaf emergence. Na⁺ and K⁺ concentrations were measured in the fully expanded third leaf, 10 d after beginning of NaCl application

Fig. 2

Mapping of two SNP markers, Xm5511 and Xm564, on chromosomes 3B and 4B and comparison with known locations of HKT1;5 genes in wheat. Both homoeologous genes in genomes A and D have similar genetic locations along the corresponding chromosomes. HKT1;5-A (Nax2) has been mapped onto the distal part of chromosome 5A with an estimated genetic distance of about 17 cM from the end of chromosome 5AL [15]. Part of chromosome 5AL originated from part of chromosome 4AL due to an ancient reciprocal translocation between the distal ends of chromosomes 4AL and 5AL [23]. HKT1;5-D (Kna1) has been identified in the genetic region about 14% from the end of chromosome 4DL [20]. Two genes; HKT1;5-B1 and HKT1;5-B2 on chromosome 4BL. HKT1;5-B1 is very close to the locus of Xm564 which is 17 cM from the end of chromosome 4BL, HKT1;5-B2 sits closer to the centromere on this chromosome