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stunting of the peanut plant and loss of yield.
Until recently, there were no resistant culti-
vars, but resistant germplasm was identified (de
Berchoux 1958, 1960; Subrahmanyam et al.
1998) and is being used for varietal development.
In an effort to identify markers for GRV
resistance, Herselman et al. (2004) tested 308
AFLP primer combinations and were able to
devise 5 linkage groups consisting of 12 markers;
1 marker was linked to aphid resistance.
unigenes that were probed under different con-
ditions. Twenty-five ESTs potentially associated
with drought stress and response to
A. parasiti-
cus
were identified. Subsequently, a microarray
of 14,000 unigenes was developed from public
peanut EST sequences (Kottapalli et al. 2009).
Guo et al. (2011), using an oligoarray, profiled
Aspergillus flauvus
infection-responding genes
in two contrast peanut genotypes. Additional
work is still needed to find useful markers for
aflatoxin resistance.
AflatoxinResistance
TomatoSpottedWiltVirus(TSWV)
Aflatoxin is a family of potent hepatotoxins and
carcinogens that are also responsible for sup-
pression of immune system function (Williams
et al. 2004). Aflatoxin contamination occurs on
several crops, including maize and peanut. The
causative organism is
Aspergillus flavus
, which
colonizes seeds and under certain conditions in
the field and post-harvest storage may produce
toxins.
Several attempts have been made to develop
peanut varieties with low potential for develop-
ing aflatoxin, but this goal has been difficult to
attain due to high variability in measurements,
requiring up to 10 replications in the field. Eleven
peanut accessions with at least a 70% reduc-
tion in aflatoxin have been identified (Holbrook
et al. 2009), and advanced breeding lines have
been developed. Additional materials have been
identified (Nigam et al. 2009); however, high
genotype x environment effects have been noted.
Development of markers for this trait would be
very useful in breeding.
Only one report exists to date on markers
for resistance to aflatoxin contamination. Milla
et al. (2005a) reported AFLP-based markers for
A. cardenasii
-derived resistance to aflatoxin con-
tamination. Of 38 markers screened in the
A.
hypogaea
x
A. cardenasii
population, 6 were
found associated with aflatoxin concentration
in the F
2
population at a low statistical thresh-
old. Several proteins have been associated with
infection of peanut with
Aspergillus
(Basha and
Pancholy 1986). Luo et al. (2005) developed an
EST-derived microarray of approximately 400
Tomato spotted wilt virus causes serious losses
in the United States in fields where the virus is
prevalent. The virus is transmitted by tobacco
thrips (
Frankinellia
sp.) A segregating popula-
tion of F
2
plants of an A-genome diploid cross
A. kuhlmannii
x
A. diogoi
was screened for resis-
tance to TSWV, and five linked AFLP markers
on one chromosome were associated with resis-
tance at a high statistical threshold (Milla 2003;
Milla et al. 2004). In Brazil, interspecific popu-
lations and wild species have also been found as
promising for introgression of resistance to the
thrips
Enneothrips flavens
(Janini et al. 2010).
Recently, one QTL each in Tifrunner x
GT-C20 (T population) and SunOleic 97R x
NC94022 (S population) crosses, explaining
12.9% and 35.8% phenotypic variance, respec-
tively, was reported (Qin et al. 2012). The
linked markers (IPAHM287 and Seq12F7) pro-
vide hope for marker-assisted improvement of
this disease, but validation of markers as well as
QTLs are required as these were identified based
on single environment data.
SclerotiniaMinor
Sclerotonia blight (
Sclerotinia minor
Jagger) is a
major problem in U.S. areas with cool autumns.
The fungal form, sclerotia, can survive in the
field for many years. Yield losses are typically
about 10% but have been reported to be as high
as 50% (Melouk and Backman 1995). Several
resistant cultivars have been developed, but this
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