Marker-Assisted Selection for Biotic Stress Resistance in Peanut - Translational Genomics for Crop Breeding: Biotic Stress - page 127

leaflets, A. tuberosa and A. guaranitica .From
these ancient progenitors developed the sections
Erectoides , Extranervosae , Triseminatae , and
Heteranthae . The species of these four sections
have varying affinities to the primitive section,
as reported by Gregory and Gregory (1979) and
Krapovickas and Gregory (1994). The more
advanced sections include the Caulorrhizae ,
Procumbentes , and Rhizomatosae . The affinities
of these latter species groups are varied as
well, but with very limited successes reported
in crossing with species of the most advanced
section, Arachis (Gregory and Gregory 1979;
Krapovickas and Gregory 1994). Krapovickas
and Gregory (1994) described 69 species and
Valls and Simpson (2005) added descriptions of
11 more, for a total of 80 species. There are at
least 11 more species that have been collected
but not yet described (Valls 2011).

species have been described (Krapovickas and
Gregory 1994); among these are perennials A.
cardenasii , A. diogoi , A. helodes , A. villosa , and
A. correntina and annuals A. duranensis and A.
stenosperma . Based on cytological evidence and
cross-hybridization data, A. cardenasii was con-
sidered originally to be the most probable A-
genome ancestor of A. hypogaea (Smartt et al.
1978). More recently, it has been proposed that
this genome type can be divided into three groups
based on karyotype (Robledo and Seijo 2010).
Initially only one annual B-genome species,
A. batizocoi , was identified (Smartt et al. 1978),
the B genome being associated with the absence
of a specific small pair of A chromosomes
(Fernandez and Krapovickas 1994). Accord-
ingly, A. batizocoi was first proposed as the B
genome donor to the cultigen (Smartt et al. 1978).
However, cytological measurements discounted
this hypothesis (Stalker and Dalmacio 1986).
Subsequently, cross-compatibility, molecular,
and cytological studies provided evidence for
up to 10 B-genome species (Krapovickas and
Gregory 1994; Kochert et al. 1996; Milla et al.
2005b; Tallury et al. 2005; Valls and Simpson
2005; Burow et al. 2009). However, the low
pollen fertility, sterility, and separate molecu-
lar phylogenetic groupings of A. ipaensis and
A. batizocoi led Burow and coworkers to ques-
tion whether A. ipaensis and A. batizocoi belong
to the same genome (Burow et al. 2009). Based
on FISH, GISH, and geographic origin, Robledo
and Seijo (2010) proposed that the B genome
classification is not accurate and should be split
into three genome types. Arachis ipaensis , A.
magna , A. gregoryi , A. vallsii , and A. william-
sii are B genome sensu stricto , A. batizocoi , A.
cruziana and A. krapovickasii being reclassified
as K genome, and A. benensis and A. trinitensis
as F genome.
The D genome consists of one species, A.
glandulifera . This species is characterized by
extensive genome rearrangements relative to
other section Arachis species, as observed cyto-
logically (Stalker 1991).
In addition, there are three diploid species that
possess 18 instead of 20 chromosomes. These

Section Arachis

The Arachis section is the most advanced of
the 9 sections and encompasses 31 described
species, including the cultigen, A. hypogaea and
one other cross-compatible tetraploid species, A.
monticola Krapov. & Rigoni, plus 29 diploid
annual and perennial species (Krapovickas and
Gregory 1994; Valls and Simpson 1994; Valls
and Simpson 2005). All but one of these species
can be crossed to A. hypogaea and A. monticola
with varying degrees of difficulty (Krapovickas
and Gregory 1994; Singh and Simpson 1994).
The distribution of the Arachis section has over-
lapped that of the other sections in many areas.
It is not unexpected that the most advanced
species would be more adaptable and thus col-
onize a larger geographical area. Also, people
have played a role in the distribution of several
species, most of which belong to section Arachis ,
including A. stenosperma and A. hypogaea .This
latter species is the most widely cultivated mem-
ber of the genus.
The remaining species of section Arachis are
diploid and had been grouped until recently into
three genomes (A, B, and D) each having 20
chromosomes. To date, 20 A-genome diploid