Biology Reference
In-Depth Information
EST database, of which 2 were mapped (Liu et al.
2012).
As regards the genetic architecture of dis-
ease resistance genes, candidate genome regions
that control disease resistance were identified by
Leal-Bertioli et al. (2009). For this, 34 sequence-
confirmed candidate disease resistance genes and
five QTLs for resistance against late leaf spot
were mapped in a diploid
A. duranensis
x
A.
stenosperma
cross. Candidate genes and QTLs
were distributed on all linkage groups except for
the smallest, but the distribution was not even.
Groupings were apparent on the upper region of
linkage group 4 and the lower region of link-
age group 2, indicating that these regions are
likely to control disease resistances. As noted
previously, these candidate regions showed shat-
tered synteny with
Lotus
and
Medicago
, indicat-
ing that RGA-containing regions are probably
faster evolving than some other genome regions.
In a different study, resistance to root-knot nema-
tode from the wild diploid
A. cardenasii
was
mapped to the A genome linkage group 9 (Nagy
et al. 2010). This region is particularly interest-
ing genetically because it displays strongly sup-
pressed recombination with the A genome of
A.
hypogaea
and appears to cover about one-third to
a half of a chromosome. Recently Ratnaparkhe
et al. (2011) sequenced two peanut BACs con-
taining six RGAs and concluded that synteny
was not high with
Lotus
,
Medicago
,or
Arabidop-
sis
, and that there was evidence of intergenic
and intragenic gene conversions and unequal
crossing-over in this region in peanut.
predominant pathogenic species to peanut are
M.
arenaria
(Neal) Chitwood,
M. hapla
Chitwood,
and
M. javanica
(Treub) Chitwood.
Meloidog-
yne haplanaria
(Eisenback et al. 2003) is a
peanut parasite with limited distribution in the
United States. Root-knot nematodes are found
on the commercial peanut in many parts of the
world, with
M. arenaria
being the predominant
pathogenic species in the southern United States,
especially in Alabama, Florida, Georgia, and
Texas.
Meloidogyne javanica
is more common
than
M. arenaria
on peanut in Africa and India
(Tomaszewski et al. 1994).
M. hapla
has a cooler
temperature optimum than
M. arenaria
or
M.
javanica
and is referred to as the northern root-
knot nematode. It is frequently found attacking
peanut in the more northern areas of peanut pro-
duction in the United States, specifically North
Carolina, Oklahoma, and Virginia, and is also
found on peanut in China.
Meloidogyne arenaria
and
M. javanica
are more aggressive pathogens
than
M. hapla
, causing greater yield losses at
lower nematode population densities (Koenning
and Barker 1992; Abdel-Momen and Starr 1997).
The effects of
Meloidogyne
spp. are due to
invasion of root tips cells by juvenile nema-
todes, followed by generation of giant cells in
the roots as feeding sites, damaging the root sys-
tem and impede nutrient transport in the plant
(Caillaud et al. 2008). A plant gene confer-
ring resistance to
M. incognita
, called
Mi
,was
first isolated from tomato by positional cloning
(Milligan et al. 1998), and encoded an NBS-
LRR type protein. Other genes associated with
response to nematode infection have been iso-
lated by several researchers in different species
(Lambert et al. 1999; Potenza et al. 2001).
More recently,
M. arenaria
-challenged resistant
species
A. stenosperma
(Guimaraes et al. 2010;
Morgante et al. 2011) identified many responsive
genes. Two have been identified by RT-PCR to
be upregulated upon infection.
High levels of resistance were identified in
11 of 15 diploid species tested against isolates
of
M. arenaria
, and several accessions were also
found with resistance to
M. hapla
(Nelson et al.
Marker-Assisted Breeding of
Peanut
Nematode Resistance: A Case Study in
the Effectiveness of Markers in
Breeding for a Simply Inherited Trait
Etiology
Meloidogyne
species (root-knot nematode) are
the most important nematode species limiting
yield in peanut (Porter et al. 1984). Of these, the
Search WWH ::
Custom Search