Biology Reference
In-Depth Information
Chapter 8
Marker-Assisted Selection for Biotic Stress
Resistance in Peanut
MarkD.Burow,SorayaC.M.Leal-Bertioli,CharlesE.Simpson,PeggyOzias-Akins,
YeChu,NicholasN.Denwar,JenniferChagoya,JamesL.Starr,MarcioC.Moretzsohn,
ManishK.Pandey,RajeevK.Varshney,C.CorleyHolbrook,and DavidJ.Bertioli
Abstract
Peanut is the second-most important legume grown worldwide. Cultivated peanut is a disomic
tetraploid, 2n
40, with limited genetic diversity due to a genetic bottleneck in formation of
the polyploid from ancestors
A. duranensis
and
A. ipaensis
. Consequently, resistance to biotic stresses
is limited in the cultigen; however, wild species possess strong resistances. Transfer of these re-
sistances is hindered by differences of ploidy, but production of synthetic amphidiploids, coupled
with use of molecular markers, enables efficient gene transfer. Marker maps have been made from
interspecific crosses, and SSR-based maps from cultivated parents have been developed recently. At
least 410 resistance gene analogues have been identified. The first markers for biotic stress tolerance
were for root-knot nematode resistance and introgressed from one
A. cardenasii
chromosome. These
and improved markers have been used for marker-assisted backcrossing, contributing to release of
three cultivars. Additional QTLs have been identified since. Early and late leafspots cause significant
yield losses worldwide, and resistance depends on multiple genes. Using interspecific populations,
five resistance QTLs for early leafspot were identified using greenhouse inoculations, and five QTLs
for late leafspot were identified using detached leaf assays. Using cultivated species populations, 28
QTLs were identified for LLS resistance; all but one were minor QTLs; the major QTL was donated
by an interspecific introgression line parent. Rust often occurs alongside leafspots, and rust resistance
was characterized as one major QTL, plus several smaller QTLs. Marker-assisted backcrossing of this
major QTL has been performed into different populations. QTLs for resistance to other biotic stresses
have been identified, namely to groundnut rosette virus, Sclerotinia blight, aflatoxin contamination,
aphids, and tomato spotted wilt virus. Marker-assisted breeding is still in early stages, and develop-
ment of more rapid and inexpensive markers from transcriptome and genome sequencing is expected
to accelerate progress.
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