Peanut Improvement for Human Health - Plant Breeding Reviews - page 167

Pod and seed characteristics (pod/seed number, pod/seed weight, and
pod/seed length and width) are signi

cantly associated in peanut
(Nigam et al. 1984; Gomez Selvaraj et al. 2009). To date, few QTL
with major effects ( 10% phenotypic variance) on pod weight, pod

length and width, pod thickness, seed weight, and oil content and fatty
acids have been reported in cultivated peanut (Gomez Selvaraj et al.
2009; Zhang et al. 2011; Shirasawa et al. 2012b). The phenotypic
variance explained by these QTL ranged from 10% to 28%. Interestingly,
the QTL for seed weight and seed number did not overlap but mapped to
the same linkage group LG08.2, while a signi

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cant association involving
QTL for pod thickness and width on LG07.1 indicate that these QTL
regulate lateral growth of pods (Shirasawa et al. 2012b). Likewise, a few
SSRs have been associated with major QTL as well as several minor QTL
for oil and fatty acids have also been reported in cultivated peanut
(Gomez Selvaraj et al. 2009; Sarvamangala et al. 2011; Zhang et al. 2011).
The ahFAD2A and ahFAD2B genes, respectively, are mapped on to
LG09.2 and LG09.1 (Qin et al. 2011; Shirasawa et al. 2012b). Further-
more, Li et al. (2011) found that SSRs, 2A5 250 and 2A5 240 , are tightly
linked with oil content in peanut. The 2A5 250 allele is associated
with low oil content, whereas 2A5 240 is associated with high oil content,
with 95% and 89% predictability, respectively, for differentiating the
RILs or 91% and 63% predictability for differentiating the peanut
cultivars with low or high oil content. Clearly, 2A5 250 /2A5 240 may be
used for marker-assisted selection to improve oil content in cultivated
peanut.
High O/L ratio in peanut is controlled by two recessive alleles of the
FAD2 genes and direct selection of these alleles will facilitate high oleate
peanut breeding. Markers and assays are now available to facilitate
molecular breeding for the high oleate trait in peanut. These include
CAPS markers for ahFAD2A and ahFADB (Chu et al. 2007, 2009) and
real-time PCR markers (Barkley et al. 2010, 2011) or allele-speci

c PCR
markers (Chen et al. 2010) for detecting FAD2A and FAD2B alleles.
Using these tools, Chu et al. (2007) detected 31.6% of the U.S. peanut
mini core accessions containing the ahFAD2A mutant allele among
subspecies hypogaea accessions, but absent in subspecies fastigiata
accessions and A. duranensis (A-genome ancestor of peanut). Likewise,
the two mutant ahFAD2B alleles were reported present in the high oleate
U.S. peanut cultivars and breeding lines (Chu et al. 2009). The associa-
tion analysis involving the U.S. peanut mini core revealed that a
functional SNP marker from the FAD2A gene is signi

cantly associated
with variation in oleic (O) and linoleic (L) acids and O/L ratio in peanut
(Wang et al. 2011a). Furthermore, Wang et al. (2011b) differentiated