Marker assisted accelerated introgression of null allele of kunitz trypsin inhibitor in soybean.

Development of kunitz trypsin inhibitor (KTI)-free soybean is crucial for soy-food industry as the heat inactivation employed to inactivate the anti-nutritional factor in regular soybean incurs extra cost and affects protein solubility. In the presented work, a null allele of KTI from PI542044 was introgressed into cultivar 'JS97-52' (recurrent parent) through marker assisted backcrossing. Foreground selection in BC1F2, BC2F2 and BC3F2 was carried out using the null allele-specific marker in tandem with SSR marker Satt228, tightly linked with a trypsin inhibitor Ti locus. Background selection in null allele-carrying plants through 106 polymorphic SSR markers across the genome led to the identification of 9 KTI-free lines exhibiting 98.6% average recurrent parent genome content (RPGC) after three backcrosses, which otherwise had required 5-6 backcrosses through conventional method. Introgressed lines (ILs) were free from KTI and yielded at par with recurrent parent. Reduction of 68.8-83.5% in trypsin inhibitor content (TIC) in ILs compared to the recurrent parent ('JS97-52') was attributed to the elimination of KTI.

Deployment of gene specific marker in development of kunitz trypsin inhibitor free soybean genotypes.

Genetic elimination of kunitz trypsin inhibitor in soybean seed would obviate the need for boiling required to inactivate the antinutritional factor and therefore economize the soy processing. PI542044, the source of null variant of kunitz trypsin inhibitor gene is being used in the development of kunitz trypsin inhibitor free soybean genotypes in India. Gene specific marker can expedite the genetic elimination of this undesirable trait from popular soybean genotypes. In the present study, we tested the DNA amplification of soybean genotype PI542044 and kunitz trypsin inhibitor null lines derived from this genotype with a gene specific primer developed from the null variant of PI157740. The amplicons so obtained corresponded to the absence of kunitz trypsin inhibitor protein band on 10% polyacrylamide gel. The gene specific marker also amplified the null allele of template DNA of F1, BC1F1 and BC2F1 plants developed during marker assisted introgression of null allele of kunitz trypsin inhibitor into elite soybean cultivar JS97-52. The results presented show the utility of this gene specific marker developed from null allele of kunitz trypsin inhibitor for identification of kunitz trypsin inhibitor free genotypes developed from PI542044, the only source of null variant available in India.