Soybean - Bioenergy Crop Plants - page 515

Two point mutations, one in GmFAD3A and the other in GmFAD3C , were detected in the low
linolenic acid line CX1512-44. They contributed unequally, but additively to the linolenic acid con-
tent (Bilyeu et al. 2005). QTL related to linolenic acid were mapped in two different studies using
normal linolenic acid soybean populations. Hyten et al. (2004) found major QTLs positioned at
50.6 cM ( R 2 = 14%) and 82.5 cM ( R 2 = 25%) on Chro. 19 (LG L), and Panthee et al. (2006) also
found molecular markers, Satt263 [Chro. 15 (LG E), R 2 = 14%], and Satt236 [Chro. 18 (LG G),
R 2 = 23%]. A major QTL that accounted for 78% of the phenotypic variability for low linolenic acid
content derived from RG10 soybean genotypes was found on Chro. 14 (LG B2) (Satt534 and Fad3i6)
(Reinprecht et al. 2006).
Mutations were discovered in all three GmFAD3 ω3 fatty acid desaturase genes in the soybean
line A29, which suggested that combinations of mutant alleles at the three GmFAD3 loci allowed
for the development of new germplasm containing 1% linolenic acid in the seed oil along with single
nucleotide polymorphism (SNP)-based molecular markers that can be used in a backcross breeding
strategy (Bilyeu et al. 2006).
There have been few studies in breeding and mapping for high linolenic acid levels in soybeans.
Accessions for this type of soybean are available in the USDA soybean germplasm collection.
Eleven G. max accessions with over 15% 18:3 and 20 G. soja accessions with over 20% 18:3 have
been reported in the USDA soybean germplasm collection (USDA, ARS 2007). Genetic regulation
of linolenic acid concentrations in wild soybean suggested that the high-linolenic trait in wild soy-
bean genotypes was determined by a set of desaturase alleles that were different from correspond-
ing alleles in G. max (Pantalone et al. 1997). Introgression of these alleles from G. soja to G. max
may lead to the production of high linolenic acid soybean oil for various applications such as ω3
fatty acid soy foods and industrial products.
20.9 envIronmental eFFect on oIl and Fatty
acId concentratIon In soyBean
Genotypes and environmental interactions that influence the oil concentration and fatty acid profile
of soybean oil have been addressed in many studies. Studies have indicated that temperature plays
an important role in the synthesis of oil and fatty acids. In general, higher temperature increases
oil content in soybean seed (Wilson 2004). Soybeans grown under high average temperatures have
reduced linoleic acid and linolenic acid and increased oleic acid content; however, contents of satu-
rated fatty acids were changed little by environmental factors (Howell and Collins 1957; Wolf et al.
1982; Rennie and Tanner 1989b; Dornbos and Mullen 1992; Wilson 2004; Hu et al. 2006).
Instability of oleic acid and linolenic acids under various temperature regimes is a concern.
Mid-oleic acid and low linolenic acid genotypes with genetically altered fatty acids developed by
mutagenesis were more stable across environments than genotypes with altered fatty acid genotypes
developed from conventional breeding techniques (Wilcox and Cavins 1992; Schnebly and Fehr
1993; Primono et al. 2002; Oliva et al. 2006). The higher the average linolenic acid content of a
genotype, the greater the instability it showed across various growing conditions (Oliva et al. 2006).
The 1% linolenic acid genotype IA 3017 was very stable, and the highest linolenic acid genotypes
were the least stable for 18:3 across ten growing environments. Thus, selecting for the lowest lino-
lenic acid content should produce the most stable genotypes for 18:3.
Oleic acid was influenced significantly by temperature during the final 30 days of the reproduc-
tive period (Oliva et al. 2006). The highest 18:1 genotypes were the least stable across growing envi-
ronments. In this study, N98-4445, an early group IV, had 55-60% 18:1 when grown in the southern
states of North Carolina and Mississippi and 39-45% when grown at Columbia, MO in the central
United States. The reduction in 18:1 as growing region moved from south to north was due to lower
average temperatures during seed development. On the other hand, M23 was more stable across
various environments than N98-4445A in the same study. Thus, genes for elevated oleic acid from