Biology Reference
In-Depth Information
the hybrid chromosome number with colchicine
to the hexaploid level (60 chromosomes).
The progeny is backcrossed repeatedly to A.
hypogaea until the progeny regained the nor-
mal chromosome number of 40. This method
was used in crosses between A. hypogaea and
seven diploid species, among them A. carde-
nasii (Smartt and Gregory 1967; Smartt et al.
1978; Stalker and Moss 1987; Wynne and
Halward 1989). The progeny of the A. hypogaea
x A. cardenasii cross have been used for develop-
ment of marker maps, introgression populations,
and germplasm releases (Stalker et al. 2002a,
2002b) or varieties with nematode, rust, and late
leaf spot resistance, such as GPBD-4 (Gowda
et al. 2002) (see discussion that follows).
The autotetraploid route involves the treat-
ing of two wild diploid species with AA and
BB genomes types with colchicine to create
synthetic autotetraploids. The synthetic auto
tetraploids, with genomic composition AAAA or
BBBB, are crossed to obtain plants with geno-
type AABB. Three autotetraploids were gener-
ated by Singh (1985) and crossed to A. hypogaea .
Fertility of the autotetraploids varied, but fertil-
ities of progenies backcrossed by A. hypogaea
were higher.
The allotetraploid route involves the cre-
ation of synthetic amphidiploids by crossing two
diploids of different genomes, followed by dou-
bling with colchicine to the tetraploid level. This
method was used to develop the TxAG-6 breed-
ing line (Simpson 1991; Simpson et al. 1993),
although by a slight variation of the procedure
(Figure 1).
The hybrid TxAG-6 was backcrossed repeat-
edly to recover the cultivated phenotype to
develop various varieties most notably incorpo-
rating resistance against root-knot nematode (see
discussion later in the chapter).
Since the development of TxAG-6, a number
of new synthetic amphidiploids have been cre-
ated. For example, in a probable “resynthesis” of
A. hypogaea , an amphidiploid was made from A.
ipaensis and A. duranensis (Favero et al. 2006).
From this amphidiploid, a series of structured
introgression lines and agronomically adapted
selected lines with some level of late leaf spot
resistant have been made (Fonceka et al. 2009;
Galhardo et al. 2011). Subsequently, additional
amphiploids have been developed (Favero et al.
2011; Leal-Bertioli et al. 2011; Santos et al.
2011). Almost all had greater resistance to leaf
spot and rust than the cultivated species, with
the most resistant amphiploids being A. magna
x A. cardenasii , A. magna x A. stenosperma , A.
batizocoi x A. stenosperma , and A. gregoryi x A.
stenosperma (Favero et al. 2011; Leal-Bertioli
et al. 2011).
Genetic Linkage Maps of Arachis
Molecular Markers for Arachis
The development of molecular markers for
peanut has followed the technical trends of
the times. The first studies were based on
isozymes and proteins (Krishna and Mitra 1988;
Grieshammer and Wynne 1990; Lu and Pick-
ersgill 1993), followed by Restriction Frag-
ment Length Polymorphism—RFLPs (Kochert
et al. 1991; Paik-Ro et al. 1992; Kochert et al.
1996), Random Amplified Polymorphic DNA—
RAPDs (Halward et al. 1991, 1992; Hilu and
Stalker 1995; Subramanian et al. 2000), Ampli-
fied Fragment Length Polymorphism—AFLPs
(He and Prakash, 1997; Gimenes et al. 2000; He
and Prakash 2001; Gimenes et al. 2002; Hersel-
man, 2003; Milla et al. 2005a, 2005b; Tallury
et al. 2005), and more recently microsatellite
markers (Hopkins et al. 1999; Palmieri et al.
[ A. batizocoi x ( A. cardenasii x A. diogoi )]
'AA'
'BB'
'AA'
2x hybrid
'AB'
colchicine
TxAG-6
'AABB'
Search WWH ::




Custom Search