Seed quality QTL in a prominent soybean population.

Soybean [Glycine max (L.) Merr.] is a versatile crop due to its multitude of uses as a high protein meal and vegetable oil. Soybean seed traits such as seed protein and oil concentration and seed size are important quantitative traits. The objective of this study was to identify representative protein, oil, and seed size quantitative trait loci (QTL) in soybean. A recombinant inbred line (RIL) population consisting of 131 F6-derived lines was created from two prominent ancestors of North American soybeans ('Essex' and 'Williams') and the RILs were grown in six environments. One hundred simple sequence repeat (SSR) markers spaced throughout the genome were mapped in this population. There were a total of four protein, six oil, and seven seed size QTL found in this population. The QTL found in this study may assist breeders in marker-assisted selection (MAS) to retain current positive QTL in modern soybeans while simultaneously pyramiding additional QTL from new germplasm.

Mapping the Fas locus controlling stearic acid content in soybean.

Increasing the stearic acid content to improve soybean [ Glycine max (L) Merr] oil quality is a desirable breeding objective for food-processing applications. Although a saturated fatty acid, stearic acid has been shown to reduce total levels of blood cholesterol and offers the potential for the production of solid fat products (such as margarine) without hydrogenation. This would result in the reduction of the level of trans fat in food products and alleviate some current health concerns. A segregating F(2) population was developed from the cross between Dare, a normal stearic acid content cultivar, and FAM94-41, a high stearic acid content line. This population was used to assess linkage between the Fas locus and simple sequence repeat (SSR) markers. Three SSR markers, Satt070, Satt474 and Satt556, were identified to be associated with stearic acid (P < 0.0001, r(2) > 0.61). A linkage map consisting of the three SSR markers and the Fas locus was then constructed in map order, Fas, Satt070, Satt474 and Satt556, with a LOD score of 3.0. Identification of these markers may be useful in molecular marker-assisted breeding programs targeting modifications in soybean fatty acids.

Map order and linkage distances of molecular markers close to the supernodulation (nts-1) locus of soybean.

The molecular characteristics of markers in the chromosome region surrounding the supernodulation gene (nts-1) of soybean (Glycine max L. Merr.) were investigated in 187 F2 plants from a cross of G. max cv. Bragg (nts) and G. soja PI468.397 (wild-type nodulation). RFLP marker pUTG-132a, linked tightly (0.7+/-0.5 cM) to nts-1, was converted to a PCR marker. The polymorphism resides within a 1.72 kb PstI fragment and consists of an 832 bp insertion in G. max relative to the wild progenitor G. soja. The insertion is flanked by a 35 bp direct duplication that was found only once in G. soja. Data suggest that the pUTG-132a sequence exists only once in the genome, which is compatible with the recessive nature of nts-1. Accordingly, pUTG-132a is a valuable marker for map-based cloning. Another RFLP marker, pA-381, was mapped 4.8 cM distal to nts-1. Marker order, established by Maximum Likelihood Analysis, placed nts-1 between pUTG-132a and pA-381. To generate additional molecular markers, a segregating F2 population was analysed using bulked segregant analysis (BSA) and single oligonucleotide primer-based PCR (DNA amplification fingerprinting; DAF). PCR marker pcr5-4L was mapped to soybean linkage group H and sequenced. The data revealed (i) recombination events and marker order in the nts-1 region; (ii) the molecular nature and cause of polymorphisms in linked molecular markers; (iii) a low density of polymorphisms around nts-1, and (iv) diploidy of the distal region of linkage group H of soybean.

The genetic locus controlling supernodulation in soybean (Glycine max L.) co-segregates tightly with a cloned molecular marker.

The genetic locus (nts) controlling nitrate-tolerant nodulation, supernodulation, and diminished autoregulation of nodulation of soybean (Glycine max (L.) Merill) was mapped tightly to the pA-132 molecular marker using a restriction fragment length polymorphism (RFLP) detected by subclone pUTG-132a. The nts (nitrate-tolerant symbiotic) locus of soybean was previously detected after its inactivation by chemical mutagenesis. Mutant plant lines were characterized by abundant nodulation (supernodulation) and tolerance to the inhibitory effects of nitrate on nodule cell proliferation and nitrogen fixation. The large number of RFLPs between G. max line nts382 (homozygous for the recessive nts allele) and the more primitive soybean G. soja (PI468.397) allowed the detection of co-segregation of several diagnostic markers with the supernodulation locus in F2 families. We located the nts locus on the tentative RFLP linkage group E about 10 cM distal to pA-36 and directly next to marker pA-132. This very close linkage of the molecular marker and the nts locus may allow the application of this clone as a diagnostic probe in breeding programs as well as an entry point for the isolation of the nts gene.