1a.Objectives (from AD-416):
Develop high yielding soybean germplasm with increased seed protein concentration in seeds and higher concentrations of both cysteine and methionine in the seed storage proteins.
1b.Approach (from AD-416):
In response to the recommendation that “PIs characterize and make available for use in breeding as many different source lines of each desired characteristic as possible and practical, in order to avoid ‘fixing’ the genome of soybean commonly used for breeding,” made in the review of the USB-sponsored soybean composition project, we are identifying QTLs for increased protein, methionine and cysteine contents in two populations. Once we complete our work in March 2011, we will select 2-3 QTLs to backcross once into a high yielding MGV line from our program. Our preliminary analysis indicates that there are no methionine and cysteine QTLs per se segregating in one population but that some protein QTLs are also QTLs for several amino acids including methionine and cysteine. So backcrossing the largest 2-3 protein QTLs that affect amino acid composition (including methionine and cysteine) may affect the overall composition. Alternatively, if we detect methionine and cysteine QTLs per se when we complete our current studies, we could backcross 1 QTL for each amino acid and 1 QTL for protein. Once we complete our work in March 2011, we will select 2-3 QTLs to backcross once into a high yielding MGV line from our program. We will cross one line that carries the favorable alleles at these 2-3 QTLs to a high yielding MG V line. F1 plants will be obtained and they will be used as males in crosses with the same MG V line to obtain 100 to 200 BC1F1 seeds. BC1F1 plants will be selected with markers flanking the 2-3 QTLs and those plants that carry the donor alleles at the QTLs will be genotyped at markers uniformly spaced every ~30 cM in the genome to increase the percentage of recurrent parent genome recovered. The selected BC1F1 plant will be selfed and BC1F2 seed obtained. BC1F2 plants will be genotyped at the flanking markers and several plants homozygous for both the favorable alleles and the non favorable alleles will be selected. In addition, these selected plants will be genotyped at marker loci uniformly spaced in the genome that are not fixed for the recurrent parent and plants that have the most number of loci homozygous for the recurrent parent allele will be selected. We will increase seed of selected BC1F2 lines and we will compare the performance of BC1F2:4 lines homozygous for alleles increasing protein/amino acid at 2-3 QTLs with BC1F2:4 lines homozygous for alleles decreasing protein/amino acid at 2-3 QTLs in yield trials in 2013.
This project is related to Objective 2 of the in-house project: To discover novel genes/alleles in soybean for seed composition, determine their inheritance, determine genomic location, transfer to adapted germplasm, and release. We continued the backcrossing of previously identified high sulfur amino acid quantitative trait loci (QTL). We completed the Backcross (BC) 2 generation in the summer and last winter, BC2F1 plants were genotyped and 9 BC2F1 plants were planted in the greenhouse for selfing. Each of those plants is heterozygous for a different combination of QTL. We grew BC2F1 plants and let them self-pollinate to obtain BC2F2 seeds. These lines have been planted in the field and will be genotyped to select for the sulfur amino acid QTL.