Khushbu Verma

Population structure and association mapping studies for important agronomic traits in soybean

The present study was carried out with a set of 96 diverse soybean genotypes with the objectives of analysing the population structure and to identify molecular markers associated with important agronomic traits. Large phenotypic variability was observed for the agronomic traits under study indicating suitability of the genotypes for association studies. The maximum values for plant height, pods per plant, seeds per pod, 100-seed weight and seed yield per plant were approximately two and half to three times more than the minimum values for the genotypes. Seed yield per plant was found to be significantly correlated with pods per plant (r = 0.77), 100-seed weight (r = 0.35) and days to maturity (r = 0.23). The population structure studies depicted the presence of seven subpopulations which nearly corresponded with the source of geographical origin of the genotypes. Linkage disequilibrium (LD) between the linked markers decreased with the increased distance, and a substantial drop in LD decay values was observed between 30 and 35 cM. Genomewide marker-traits association analysis carried out using general linear (GLM) and mixed linear models (MLM) identified six genomic regions (two of them were common in both) on chromosomes 6, 7, 8, 13, 15 and 17, which were found to be significantly associated with various important traits viz., plant height, pods per plant, 100-seed weight, plant growth habit, average number of seeds per pod, days to 50% flowering and days to maturity. The phenotypic variation explained by these loci ranged from 6.09 to 13.18% and 4.25 to 9.01% in the GLM and MLM studies, respectively. In conclusion, association mapping (AM) in soybean could be a viable alternative to conventional QTL mapping approach.

Genetic Variability and Effect of Heat Treatment on Trypsin Inhibitor Content in Soybean [ Glycine max (L.) Merrill.]

Kunitz trypsin inhibitor (KTI), a major anti-nutritional factor present in soybean seed, is a major bottleneck in industrial use of soybean and public acceptance of soybean food products. Biochemical screening for trypsin inhibitor content was carried out in 145 genotypes of soybean comprising exotic collections and released varieties. The trypsin inhibitor content ranged from 14.15 to 186.27 mg g-1 of seed meal. Lowest level of trypsin inhibitor content was observed in genotype PI542044, (14.15 mg g-1 seed meal). Popular Indian soybean varieties viz., JS335, JS9305, NRC37, NRC7, PK1225, DS9712, JS9752, and DS9814 contained higher level of trypsin inhibitor. Heat treatment was able to reduce the TI content but to certain level leaving about 20% residual activity. The study indicated the need for other ways to create genotypes with reduced KTI for use in breeding program.

Genetic elimination of Kunitz trypsin inhibitors (KTI) from DS9712, an Indian soybean variety

In this study, the null allele of Kunitz trypsin inhibitor i.e. kti was transferred from PI542044, a germplasm line free from KTI in to a popular Indian soybean variety DS9712 through marker assisted backcross breeding (MABB) approach. Following foreground selection with 3 SSR markers viz., Satt228, Satt429 and Satt409 that are linked to kti, and background selection with 93 polymorphic SSR markers in BC1F1 and BC2F1 generations, target plants were selected that had 96–98% recovery of the recurrent parent genome (RPG). In BC2F2 generation, plants homozygous the for target allele (kti kti) were identified and harvested individually. In BC2F3 generation, seed proteins of the selected lines were extracted and analyzed through native polyacrylamide gel electrophoresis (PAGE) and confirmed absence of the KTI peptides. Four lines were identified that were free from Kunitz trypsin inhibitor but retained nearly all of the phenotypic features of DS9712. This study exemplified successful elimination of KTI from soybean seeds through MABB approach.

Biochemical screening for trypsin inhibitor factors and morphomolecular characterization of soybean (Glycine max L. Merr.)

A set of 101 diverse soybean genotypes were biochemically analyzed for trypsin inhibitor (TI) contents, and were characterized with morphological and molecular markers. The TI content in the seeds ranged from 14.65 to 175.52 mg g−1 soymeal. The Indian soybean varieties were found to contain higher amount of TI (58.79–126.78 mg g−1 soymeal) while PI542044, an exotic germplasm was found to contain the least (14.65 mg g−1 soymeal). Morphological characterization with 16 qualitative and quantitative traits revealed significant variations and grouped the genotypes in to three major groups with overall mean dissimilarity value of 0.30. Genetic diversity study conducted with 100 simple sequence repeat (SSR) markers detected higher level of polymorphism (71%). Of the total 221 alleles amplified, 65 were rare (frequency <0.2). The mean polymorphism information content (PIC) of the markers was 0.27 while the value for gene diversity was 0.44. UPGMA-based cluster analysis grouped the genotypes into four major clusters of which I, II and III were occupied by genotypes containing higher and moderate level of TI. PI542044, which was free from Kunitz trypsin inhibitor (KTI), grouped singly. Such genotype would be suitable for use in breeding program directed towards development of varieties with zero KTI.