Trypsin inhibitor assessment with biochemical and molecular markers in a soybean germplasm collection and hybrid populations for seed quality improvement

A soybean germplasm collection was studied for the identification of accessions with low trypsin inhibitor content in seeds. Twenty-nine accessions, parental plants, and two hybrid populations were selected and analyzed using genetic markers for alleles of the Ti3 locus, encoding Kunitz trypsin inhibitor (KTI). Most of the accessions had high or very high KTI (49.22–73.53 Trypsin units inhibited (TUI/mg seeds), while the two local Kazakh cultivars, Lastochka and Ivushka, were found to have a moderately high content of KTI, at 54.16–54.87 TUI/mg. In contrast, two soybean cultivars from Italy, Hilario and Ascasubi, showed the lowest levels of trypsin units inhibited, at 25.47–27.87 TUI/mg. Electrophoresis of seed proteins in a non-denaturing system showed a simple discrimination pattern and very clear presence/absence of bands corresponding to KTI. The SSR marker Satt228 was the most effective diagnostic marker among the three examined, and it confirmed the presence of the homozygous null-allele ti3/ti3 in cultivars Ascasubi and Hilario, which were used for hybridization with the local cv. Lastochka. Heterozygote F1 hybrid plants and homozygous ti3/ti3 lines in F2 segregating populations were successfully identified using Satt228. Finally, through marker-assisted selection with Satt228, prospective homozygous ti3/ti3 lines were produced for further application in the breeding program aimed at improving soybean seed quality in Kazakhstan.