Background: Triticum aestivum (wheat) is one of the world’s oldest crops and has been used for >8000 years as a food crop in North Africa, West Asia and Europe. Today, wheat is one of the most important sources of grain for humans, and is cultivated on greater areas of land than any other crop. As the human population increases and soil salinity becomes more prevalent, there is increased pressure on wheat breeders to develop salt-tolerant varieties in order to meet growing demands for yield and grain quality. Here we developed a mutant wheat population using the moderately salt-tolerant Bangladeshi variety BARI Gom-25, with the primary goal of further increasing salt tolerance. Results: After titrating the optimal ethyl methanesulfonate (EMS) concentration, ca 30,000 seeds were treated with 1% EMS, and 1676 lines, all originating from single seeds, survived through the first four generations. Most mutagenized lines showed a similar phenotype to BARI Gom-25, although visual differences such as dwarfing, giant plants, early and late flowering and altered leaf morphology were seen in some lines. By developing an assay for salt tolerance, and by screening the mutagenized population, we identified 70 lines exhibiting increased salt tolerance. The selected lines typically showed a 70% germination rate on filter paper soaked in 200 mM NaCl, compared to 0–30% for BARI Gom-25. From two of the salt-tolerant OlsAro lines (OA42 and OA70), genomic DNA was sequenced to 15x times coverage. A comparative analysis against the BARI Gom-25 genomic sequence identified a total of 683,201 (OA42), and 768,954 (OA70) SNPs distributed throughout the three sub-genomes (A, B and D). The mutation frequency was determined to be approximately one per 20,000 bp. All the 70 selected salt-tolerant lines were tested for root growth in the laboratory, and under saline field conditions in Bangladesh. The results showed that all the lines selected for tolerance showed a better salt tolerance phenotype than both BARI Gom-25 and other local wheat varieties tested. Conclusion: The mutant wheat population developed here will be a valuable resource in the development of novel salt-tolerant varieties for the benefit of saline farming.

Salinity tolerance-associated phenotypes of 35 EMS mutagenized wheat lines originating from BARI Gom-25 were compared. Vegetative growth was measured using non-destructive image-based phenotyping. Five different NaCl concentrations (0 to 160 mM) were applied to plants 19 days after planting (DAP 19), and plants were imaged daily until DAP 38. Plant growth, water use, leaf Na⁺, K⁺ and Cl⁻ content, and thousand kernel weight (TKW) were measured, and six lines were selected for further analysis. In saline conditions, leaf Na⁺, K^+, and Cl⁻ content variation on a dry weight basis within these six lines were ~9.3, 1.4, and 2.4-fold, respectively. Relative to BARI Gom-25, two (OA6, OA62) lines had greater K⁺ accumulation, three (OA6, OA10, OA62) had 50–75% lower Na⁺:K⁺ ratios, and OA62 had ~30% greater water-use index (WUI). OA23 had ~2.2-fold greater leaf Na⁺ and maintained TKW relative to BARI Gom-25. Two lines (OA25, OA52) had greater TKW than BARI Gom-25 when grown in 120 mM NaCl but similar Na⁺:K⁺, WUI, and biomass accumulation. OA6 had relatively high TKW, high leaf K^+, and WUI, and low leaf Na⁺ and Cl⁻. Phenotypic variation revealed differing associations between the parameters measured in the lines. Future identification of the genetic basis of these differences, and crossing of lines with phenotypes of interest, is expected to enable the assessment of which combinations of parameters deliver the greatest improvement in salinity tolerance.

Twenty-three lines from a mutagenized Bangladeshi BARI Gom-25 wheat population that included previously identified salt-tolerant lines, and the BARI Gom-25 control variety, were cultivated in a drip-irrigated salinity test field at Salt Farm Texel, Netherlands, to assess their performance during salt stress in European climatic conditions. Lines were tested at irrigation salinity levels of 1, 4, 8, 12, 16, and 20 dS m⁻¹ in four repetitions of plots with 24 plants per plot. Average plant height, tiller number, spike length, frequency of live plants, and total grain weight (TGW) were recorded as functions of seasonal mean pore water salinity in the soil. Increases in salinity triggered reductions in all evaluated variables of the assessed lines and the control variety. However, nine mutagenized lines had at least twofold higher mean TGW than the control variety, 18.73 ± 4.19 g/plot at 1–16 dS m⁻¹ salinity levels. Common models of salt tolerance confirmed this pattern, but there were no clear differences in salinity tolerance parameter estimates between the mutagenized lines and the control variety. Thus, despite the apparent similarity in responses of all lines to salinity increase, we clearly identified lines that tended to have higher TGW at given salinities than the control variety. This higher TGW at the full range of salinity treatments indicates not only a possible higher salinity tolerance but a higher yield potential as well. The mechanisms involved clearly warrant further attention.