Soybean seeds contain large amounts of isoflavones or
phytoestrogens such as genistein, daidzein, and glycitein that
display biological effects when ingested by humans and animals.
In seeds, the total amount, and amount of each type, of
isoflavone varies by 5 fold between cultivars and locations.
Isoflavone content and quality are one key to the biological
effects of soy foods, dietary supplements, and nutraceuticals.
Previously we had identified 6 loci (QTL) controlling isoflavone
content using 150 DNA markers. This study aimed to identify and
delimit loci underlying heritable variation in isoflavone content
with additional DNA markers. We used a recombinant inbred line
(RIL) population (n=100) derived from the cross of “Essex” by
“Forrest,” two cultivars that contrast for isoflavone content.
Seed isoflavone content of each RIL was determined by HPLC and
compared against 240 polymorphic microsatellite markers by
one-way analysis of variance. Two QTL that underlie seed
isoflavone content were newly discovered. The additional markers
confirmed and refined the positions of the six QTL already
reported. The first new region anchored by the marker
BARC-Satt063 was significantly associated with genistein
(P=0.009, R2=29.5%) and daidzein (P=0.007, R2=17.0%).
The region is located on linkage group B2 and derived the
beneficial allele from Essex. The second new region defined by
the marker BARC-Satt129 was significantly associated with total
glycitein (P=0.0005, R2=32.0%). The region is located on
linkage group D1a+Q and also derived the beneficial allele from
Essex. Jointly the eight loci can explain the heritable variation
in isoflavone content. The loci may be used to stabilize seed
isoflavone content by selection and to isolate the underlying
genes.