Soybean - Bioenergy Crop Plants - page 512

Six elevated stearic acid germplasm lines were reported to carry homozygous recessive alleles:
A6 ( fas a ) with 30% (Hammond and Fehr 1983b), FA41545 ( fas b ) with 15% (Graef et al. 1985), A81-
606085 ( fas ) with 19% (Graef et al. 1985), KK-2 ( st 1 ) with 6% (Rahman et al. 1997), M25 ( st 2 ) with
19% (Rahman et al. 1997), and FAM94-41 ( fas nc ) with 9% (Pantalone et al. 2002) stearic acid were
reported as genetically altered genotypes. It is known that fas a , fas b , and fas are allelic (Graef et al.
1985) and that fas a and fas nc are allelic and are different mutations in the same gene (Pantalone et al.
2004). Rahman et al. (1997) reported that the single recessive genes st 1 and st 2 for elevated 18:0 are
nonallelic. The st 1 st 1 st 2 st 2 genotype had 30% 18:0 content, but it failed to grow after germination. It
is unknown whether st 1 or st 2 are allelic to fas a , fas b , or fas .
Molecular markers closely associated with stearic acid alleles have been discovered (Table 20.2).
A QTL associated with high stearic acid mapped to Chro. 16 (LG J) from a mapping popula-
tion, A81-356022 × PI468916 (Diers and Shoemaker 1992; Pantalone et al. 2004). A gene derived
from FAM94-41 for high 18:0 has been mapped to Chro. 14 (LG B2). Three SSRs—Satt070,
Satt474, and Satt556—were highly significant ( P < 0.0001) with major the QTL near Satt474,
having an R 2 value greater than 61% (Spencer et al. 2003). Hyten et al. (2004) also reported on
an Essex × Williams population in which two QTL on Chro. 6 (LG C2) and Chro. 19 (LG L)
were associated with stearic acid. Panthee et al. (2006) detected two markers, Satt168 [Chro. 14
(LG B2); R 2 = 18%] and Satt249 [Chro. 16 (LG J); R 2 = 12%] associated with stearic acid. They
reported that the gene near Satt249 on Chro. 16 (LG J) from N87-984-16 is a novel allele and gave
higher concentrations of stearic acid.
20.6 oleIc acId
Soybeans typically contain approximately 23% oleic acid (18:1). Increasing 18:1 to a range between
55 and 60% in combination with low 18:3 would have edible and industrial applications with high
oxidative stability. This oil would increase stability at high cooking temperatures and reduce the
need for hydrogenation reducing trans -fats. Oil with a high oleic acid content could be used in the
manufacture of soydiesel, lubricants, and hydraulic oils. Genes at the Fad2 locus have been shown
to be responsible for increasing levels of oleic acid (Wilson 2004). Other studies showed that high
18:1 in soybean oil was quantitatively inherited (Burton et al. 1983; Hawkins et al. 1983). The
germplasm line N78-2245 was perhaps the first soybean developed with higher levels (51%) of oleic
acid by recurrent selection (Wilson et al. 1981). N98-4445A, a mid-oleic soybean accession that
has an oleic acid concentration of 40-70% depending on the environmental growing conditions,
was developed from combining several oleic acid genes from a three-way cross: N94-2473 × (N93-
2007-4 × N92-3907) (Burton et al. 2006).
Molecular markers associated with oleic acid alleles have been disclosed (Table 20.2). Six QTL
have been mapped and confirmed for high 18:1 in line N00-3350, a derivative of N98-4445A, on
Chros. 5 (LGs A1) ( R 2 = 4%) at Satt211, 17 (D2) ( R 2 = 6%) at Satt389, 18 (G) ( R 2 = 13%) at Satt394,
18 (G) ( R 2 = 7%) at Satt191, 19 (L) ( R 2 = 9%) at Satt418, and 19 (L) ( R 2 = 25%) at Satt561 (Monteros
et al. 2008).
Rahman et al. (1994) developed M23 with 46% oleic acid content from irradiating seeds of Bay
soybean. The increase in oleic acid content in M23 was controlled by a single partially recessive
gene, designated as ol (Takagi and Rahman 1996). Another allele ol a at the same Ol locus was found
in mutant M11 and contains approximately 38% oleic acid (Rahman et al. 1996a).
A recent study revealed that the mutation of the ol gene in M23 was the result of a deletion at the
Fad2-1a locus (Sandhu et al. 2007). A polymerase chain reaction (PCR)-based DNA marker for the
high oleic genotype has made it easy to use MAS to select for genotypes with higher oleic acid levels
(Alt et al. 2005a). Because oleic acid content is significantly influenced by the environment in which
the seed is produced (Oliva et al. 2006), MAS for this trait should increase breeding efficiency.
Combining the M23 gene with genes from other mid-oleic acid sources has resulted in trans-
gressive segregation for higher oleic acid content. Transgressive segregation among lines in the