Abstract
Soil acidity poses a major threat to productivity of several crops; mainly due to the prevalence of toxic levels of Al3+ and Mn2+. Crop productivity could be harnessed on acid soils via the development of plant varieties tolerant to phytotoxic levels of these cations. In this study, we investigated the extent of natural variation for Mn2+ tolerance among ten parental lines of the Australian and International canola mapping populations. Response to Mn2+ toxicity was measured on the bases of cotyledon chlorosis, shoot biomass, and leaf area in nutrient solution under control (9 μM of MnCl2⋅4H2O) and Mn treatment (125 μM of MnCl2⋅4H2O). Among parental lines, we selected Darmor-bzh and Yudal that showed significant and contrasting variation in Mn2+ tolerance to understand genetic control and identify the quantitative trait loci (QTL) underlying Mn2+ tolerance. We evaluated parental lines and their doubled haploid (DH) progenies (196 lines) derived from an F1 cross, Darmor-bzh/Yudal for Mn2+ tolerance. Mn2+-tolerant genotypes had significantly higher shoot biomass and leaf area compared to Mn2+-sensitive genotypes. A genetic linkage map based on 7,805 DArTseq markers corresponding to 2,094 unique loci was constructed and further utilized for QTL identification. A major locus, BnMn2+.A09 was further mapped with a SNP marker, Bn-A09-p29012402 (LOD score of 34.6) accounting for most of the variation in Mn2+ tolerance on chromosome A09. This is the first report on the genomic localization of a Mn2+ tolerance locus in B. napus. Additionally, an ortholog of A. thaliana encoding for cation efflux facilitator transporter was located within 3,991 bp from significant SNP marker associated with BnMn2+.A09. A suite of genome sequence based markers (DArTseq and Illumina Infinium SNPs) flanking the BnMn2+.A09 locus would provide an invaluable tool for various molecular breeding applications to improve canola production and profitability on Mn2+ toxic soils.
Highlights
Canola (Brassica napus L., 2n = 4× = 38, genome = AnAnCnCn) is the second major oilseed crop grown worldwide, followed by soybean1
This study describes the (i) evaluation of 10 parental lines of different mapping populations, currently being used in the Australian Brassica Germplasm Improvement Program (NBGIP), for Mn2+ tolerance, (ii) construction of a highdensity linkage map consisting of 7,805 DArTseq markers corresponding to 2,094 unique bin loci in the Darmor-bzh/Yudal doubled haploid (DYDH) mapping population, (iii) genetic mapping and identification of molecular markers associated with Mn2+ tolerance locus in the DYDH population, (iv) physical localization of the DArTseq sequences linked with Mn2+ tolerance locus and (v) identification of putative candidate gene involved in Mn2+ tolerance in B. napus using A. thaliana orthologs/paralogs implicated in Mn2+ uptake, accumulation and transport on the reference genomic scaffolds of B. napus cv
Roots were discolored under ++Mn treatment, we could not clearly establish whether this is due to Mn2+ toxicity
Summary
Canola (Brassica napus L., 2n = 4× = 38, genome = AnAnCnCn) is the second major oilseed crop grown worldwide, followed by soybean1 It is used as a source of healthy vegetable oil for human consumption, fodder and canola meal for animals, biodiesel for renewable energy and for other pharmaceutical applications (Friedt and Snowdon, 1999). At low pH (≤5), di- and trivalent cations (Mn2+ and Al3+) become solubilized into solution form and inhibit growth of sensitive plants (Pittman, 2005) Extreme environment conditions such as high temperatures in summer, and waterlogging at the end of winter, can increase the levels of exchangeable Mn2+ in soil and increase the incidence of toxicity (Sparrow and Uren, 1987; Slattery and Ronnfeldt, 1992). It is very difficult to incorporate lime in the deeper layers of subsoils
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