**14. Developing markers for marker-assisted selection of low Cd accumulation**

Marker-assisted selection (MAS) could be an alternative to phenotypic selection. In soybean, DNA markers linked to low Cd accumulation were identified using RIL population (*F*6:8) derived from the cross AC Hime (high Cd accumulation in seeds) and Westag-97 (low Cd accumulation in seeds). The distribution of Cd concentration of 166 RILs ranged from 0.067 to 0.898 mg kg<sup>−</sup><sup>1</sup> , with a mean of 0.268 ± 0.013 mg kg<sup>−</sup><sup>1</sup> [134]. Using the RIL population, seven simple sequence repeat (SSR) markers, SatK138, SatK139, SatK140 (0.5 cM), SatK147, SacK149, SaatK150, and SattK152 (0.3 cM), were reported to be linked to *Cda1* in soybean seed. It was also reported that all the linked markers were mapped to the same linkage group (LG) K. SSR markers closely linked to *Cda*1 in soybean seeds have the potential to be used for MAS to develop low Cd-accumulating cultivars in a breeding program [134]. In a similar mapping approach, Benitez et al. [137] identified a major QTL cd1 on chromosome 9 (LG-K) across years and generations which accounted for 82, 57, and 75% of the genetic variation. Near-isogenic lines (NILs) were used to confirm the effect of the QTL and the peak of the QTL that was located in the vicinity of two SSR markers, Gm09:4770663 and Gm09:4790483. Both the studies revealed a major QTL for seed *Cd* content, *Cda*1 at a similar genomic location, suggesting that *cd*1 and *Cda1* may be identical. Candidate genes related to heavy metal transport or homeostasis were located in the vicinity of the identified QTL (Cda1). Protein kinase, putative adagio-like protein, and plasma membrane H+ -ATPase were found in the QTL vicinity. The presence of protein kinase and plasma membrane H+ -ATPase genes near the tightly linked SSR markers suggests that the regulation of this enzyme may play a vital role in Cd stress [134]. This was later supported by a major QTL-controlling Cd concentration (*cd*1) identified in soybean [137]. The gene was designated as *GmHMA1.* In *GmHMA1a*, one base substitution from G to A at nucleotide position 2095 resulted in a loss of function of the ATPase and was found to be associated with Cd uptake [137]. The SSR markers linked to the *Cda*1 and*Cd*1gene(s)/or QTLs and the SNP marker in the P1B-ATPase metal ion transporter gene in soybean can be utilized in MAS for developing soybean cultivars with low Cd content.
