Oil Composition Variations - Genetics, Genomics and Breeding of Crop Plants - page 264

and their seed oil content was only 31.2% compared to 42.8% in the parental
cultivar. The inheritance of the mutant was oligogenic and was determined
by at least four genes. In the F 2 generation, palmitic acid content was
negatively correlated with oil content.
Wilson et al. (2001) have produced soybean cultivars with oil that varied
from less than 4% to about 35% palmitic acid, compared to about 11% palmitic
acid in typical cultivars. A number of recessive alleles associated with these
phenotypes have been described that represent different mutations at the
Fap loci. These metabolic studies narrowed the identification of fap 1 , fap 2 ,
and fap nc alleles to the genes that encode or regulate 3-keto-acyl-ACP
synthetase II, 166:0-ACP thioesterase, 186:0-ACP desaturase, or 186:1-ACP
thioesterase enzymes. This hypothesis was strongly supported by Northern
blot assays that revealed a significant reduction in the accumulation of
transcripts corresponding to the 166:0-ACP thioesterase in germplasm
homozygous for the fap nc allele.
8.2.2.2 Palmitic Acid in Sunflower
Pérez-Vich et al. (2000) have screened and studied sunflower genotypes
with increased levels of palmitic acid (C16:0) in the seed oil. Several mutants
were studied: CAS-5 displays more than 25% of the total oil fatty acids as
C16:0, whereas the parental line BSD-2-691 displays 5.4% C16:0. The
segregation fit a model of two alleles at one locus with partial dominance
for the low content. To determine the inheritance of the high C16:0 content
in the sunflower mutant line, the mutant was reciprocally crossed with
standard sunflower line HA-89 (5.7% C16:0) and with its parental line, and
F 1 , F 2 and BC 1 F 1 seeds were obtained from the crosses of CAS-5 with those
lines. The cross with HA-89 revealed a segregation that fit a ratio of 19:38:7
for low (<7.5%), middle (7.5-15%), and high (>25%) C16:0 content,
respectively. This segregation was explained on the basis of three loci (P1,
P2, and P3) each having two alleles showing partial dominance for low
content. Two of the loci revealed diversity present in the sunflower lines.
In contrast, low palmitic acid content has also been targeted. Miller and
Vick (1999) have determined the mode of inheritance of low stearic and low
palmitic acid content found in three sunflower mutant lines treated with
two mutagens, NMU and EMS. Two lines, HA 821 LS-1 and RHA 274 LS-2,
displayed lower stearic acid content (4.1% and 2.0%), compared to 4.7% for
their respective parental lines. Segregation ratios of F 2 and testcross progenies
indicated that the low stearic acid content in HA 821 LS-1 was controlled by
one gene, designated fas1 , with additive gene action. The low stearic acid
content in RHA 274 LS-2 was controlled by two genes with additive gene
action. The first gene was designated fas2 , and the second gene was
temporarily designated fasx . The allele fap1 was identified in RHA 274 LP-1