**11.2 Isoflavones**

*Legume Crops - Prospects, Production and Uses*

Stachyose and raffinose are not readily digestible and cause flatulence when soy foods are consumed. Therefore, breeders aim to develop soybean seeds with reduced oligosaccharide content. Stachyose and raffinose content among soybean germplasm range from 1.4 to 6.7%, and 0.1 to 2.1%, respectively. Breeding lines with less than 1% stachyose and raffinose have been developed [13]. Soybean germplasm "V99–5089" was developed with high sucrose, low raffinose, and low stachyose content to use as a parent in food-grade soybean breeding programs [118]. The genetic variability of seed sugars has significant allelic difference in the genes controlling the biosynthetic enzymes. QTL mapping of soluble sugars in soybean seed were reported and of which 28 were for seed sucrose (**Table 1**). These 28 QTLs were mapped on LGs A1 and E; 3 QTLs on A2, I, and F, and 3 QTLs on L, M, and B1 [73], two QTLs on L, D1b, 7 QTLs on L [74], and B2, D1B, E, H, J [75]. The genomic regions associated with sucrose, raffinose, and stachyose were identified in segregating F2–10 RILs [74]. Alkond et al. [76] reported 14 significant QTLs associated with sucrose and oligosaccharides that were mapped on 8 different linkage groups (LGs) and chromosomes (Chr). Seven QTL were identified for raffinose content on LGs D1a (Chr1), N (Chr3), C2 (Chr6), K (Chr9), B2 (Chr14), and J (Chr16). Four QTL for stachyose content were identified on LG D1a (Chr1), C2 (Chr6), H (Chr12), and B2 (Chr14) [76]. Three QTL for seed sucrose content were identified on LGs N (Chr3), K (Chr9), and E (Chr15). The region of Chr15 (LG E) that has been reported to be associated with sucrose was detected by others [73, 75, 77, 78], but the position of the QTL was different [76]. The two of the regions underlying seed sucrose QTLs identified on LG N (Chr3) and K (Chr9) are additions to the loci previously reported on LGs D1b (Chr2), A1 (Chr5), M (Chr7), A2 (Chr8), B1 (Chr11), H (Chr12), F (Chr13), G (Chr18), J (Chr16), L (Chr19), and I (Chr20) [73, 75, 77, 78]. The selection for beneficial alleles of these QTLs could facilitate breeding strategies to develop soybean lines with higher

concentrations of sucrose and lower levels of raffinose and stachyose.

Normal soybean seeds contain three lipoxygenase isozymes that are responsible

for the grassy beany flavor and bitter taste of soy food. Research is being conducted for the genetic elimination of lipoxygenase from soybean seeds to reduce undesirable flavors in soy food products. Soybean seed lipoxygenase exists in three isozymic forms, namely lipoxygenase-1, −2, and −3 controlled by single dominant genes, viz. *Lx1*, *Lx2*, and *Lx3*, respectively. Their recessive forms, i.e., *lx1*, *lx2*, and *lx3* cause the loss in activity of corresponding isozyme [119]. Several combinations of lipoxygenase null mutants have already been developed: 0-, 00-, and 000-genotypes with one, two, and three of the isozymes eliminated respectively, In the 000-genotype, absence of the grassy and beany flavor was observed, as there was no detectable level of the lipoxygenase proteins in mature soybean seeds. The presence or absence of three lipoxygenase isozymes is determined by gel electrophoresis and spectrophotometer or by immunological or colorimetric methods [13]. Of the three lipoxygenases, *Lx2* locus has been mapped on *chr13*, which corresponds to linkage group F, and has been reported tightly linked with *Lx1* locus [120]. *Lx3* gene has been reported to be present on *chr15* and is inherited independent of *Lx1* and *Lx2.* SSR marker Satt656 tightly linked with Lox2 [121] has been deployed in the development of Lox-2 free soybean genotypes NRC109 and NRC110 in India [121].

**11. Breeding for functional components**

**11.1 Lipoxygenase**

**10.2 Oligosaccharides content**

**64**

Soybean cultivars with good isoflavone content are desirable as it contributes health benefits. High-isoflavone soybeans contain more than 0.4% isoflavones compared to levels of 0.15–0.25% for traditional soybean varieties [13]. Isoflavone content is influenced by genetic factors and environmental factors such as temperature and irrigation during seed maturation [13]. For instance, the total isoflavone content of soybean seeds appears to be negatively related to growth temperature [5]. Understanding the genetic regulation of this pathway may be necessary for obtaining cultivars with good isoflavone levels. Interest has been put in the phenylpropanoid synthetic pathway which is catalyzed in its first step by isoflavone synthase (IFS). Two genes for IFS have been identified in soybean. Furthermore, negative correlation has been found between total isoflavone content and linolenic acid (18:3) concentration. Other data suggest negative correlation between isoflavone content and protein content [5]. QTLs affecting isoflavones were identified using recombinant inbred line population and found five QTLs contributed to the concentration of isoflavones, having single or multiple additive effects on isoflavone component traits [123]. Similarly, six QTLs were identified using the linkage map constructed with specific length amplified fragment sequencing, of which one major QTL (qIF20-2) contributed to a majority of isoflavone components across various environments and explained a high amount of phenotypic variance (8.7–35.3%) [124]. Akond et al. [125] identified QTL controlling isoflavone content in a set of recombinant inbred line (RIL) populations of soybean derived from "MD96–5722" by "Spencer" cultivars. Wide variations were found for seed concentrations of daidzein, glycitein, genistein, and total isoflavones among RIL populations. Three QTLs were identified on three different linkage groups (LG). One QTL that controlled daidzein content was identified on LG A1 (Chr 5) and two QTLs that underlay glycitein content were identified on LG K (Chr 9) and LG B2 (Chr 14). Identified QTLs could be used to develop soybean with preferable isoflavone concentrations in the seeds through MAS.
