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.

Kunitz trypsin inhibitor, a proteinaceous antinutritional factor present in soybean seeds, is responsible for inferior nutritional quality of raw soybean and incompletely processed soy products.

The ratio of oleic acid to the combined value of linoleic and α-linolenic acids determines the oxidative stability, and the ratio of linoleic acid to α-linolenic acid is the key to the nutritional value of soybean oil. The present study was conducted to identify genomic regions associated with oleic, linoleic, and α-linolenic acids in recombinant inbred lines (RIL), developed from LSb1 × NRC7, across 5 cropping years. These RIL were genotyped using 105 polymorphic SSR markers across soybean genome and analyzed for fatty acid composition. SSR markers, namely, Satt245 (LGp M), Satt556 (LGpB2), Sat_042 (LGp C1), Staga002 (LGp D1b), Satt684 (LGp A1), and AI856415 (LGpD1b) showed significant (P < 0.05) association with oleic acid for all the 5 years, though this association was weak in the years when the growing temperature during active seed formation stage was high. Quantitative trait loci (QTL) linked to Satt684 (LGp A1), Satt556 (LGp B2), Sat_042 (LGp C1), and AI856415 (LGp D1b) showed pleiotropic influence on the levels of unsaturated fatty acids. Complementation of favorable QTL from LSb1 and NRC7 generated 60% oleic acid and less than 4% α-linolenic acid RIL, stable across 5 cropping years. New SSR markers, namely, Satt245, AI856415, and Staga002 identified to be associated with different unsaturated fatty acids may be useful in improving the efficiency of markerassisted breeding for enhancing the monounsaturated to polyunsaturated fatty acids ratio of soybean oil.

No abstract