Biology Reference
In-Depth Information
high-stimulant-producing sorghum) allowed the
Lhf
(low haustorial factor) locus to be mapped to
19.3 cM from the microsatellite marker
Xtxp358
on linkage group nine (
ence of other resistance mechanisms. In RIL-2,
five QTL (derived from N13) were stable across
years and environments and explained between
12% and 30% of the observed genetic variation
for resistance indicating that flanking molecular
markers would be excellent candidates for MAS.
Recently Satish et al. (2012) fine-mapped the
lgs
locus on sorghum chromosome SBI-05 toward
distal end. Four tightly linked SSRs were also
tagged and validated for their linkage with
lgs
locus.
sorghum chromosome
SBI-09 short arm) (Grenier et al. 2007). Simi-
larly, a cross between the wild sorghum species
S
.
arundinaceum
, which exhibits a hypersensi-
tive like resistance response, with two cultivated
sorghum species revealed that the resistance
trait was controlled by two nuclear genes
HR1
and
HR2
, which were mapped at 7.5 cM from
Xtxp096
on SBI02 and 12.5cM from
SbKAFGK1
on SBI05, respectively (Mohamed et al. 2003;
Grenier et al. 2007).
Analyzing gene expression profiles within a
segregating population such as NILs or selected
backcross inbred lines (BILs) or Recombinant
Inbred Lines (RILs) allows the identification of
both cis and trans acting QTL, thus providing
information about factors that control the expres-
sion of a gene as well as its location on a genetic
map (Schadt et al. 2003). Although it is often
assumed that QTL do not accurately reflect the
physical location of genes on the genome under-
lying a polygenic trait, in many cases, the gene
was located within 1-2 cM of the QTL peak
(Price et al. 2006). Combining QTL analysis with
transcriptomic data can help determine whether
genes that are differentially regulated within the
QTL regions are putative candidate resistance
genes.
Haussmann et al. (2004) reported a QTL
analysis of field resistance to
Striga
using two
mapping populations of RILs derived from a
cross between IS9830, a low germination stim-
ulant producer, and a E36-1, a susceptible geno-
type (RIL-1); and N13 (mechanical resistance)
and E36-1 (RIL-2). Each mapping population
was divided into two sets, which were tested
in sequential years at five sites in Mali and
Kenya (Haussmann et al. 2001). Composite
interval mapping revealed some QTL in each
RIL that were stable across years and environ-
ments and some that were not. In RIL-1, the
most significant QTL corresponded to the
lgs
locus but other QTL also indicated the pres-
=
Recent Development in
Marker-Assisted Backcrossing for
Development of
Striga
Resistance
Products
The QTLs identified by Haussmann et al (2004)
in RIL-2 (based on cross N13
E36-1) were sub-
ject to two MABC projects over last few years.
Following the initial QTL mapping studies, a
collaborative project of ICRISAT, IER, and the
University of Hohenheim, two locally adapted,
farmer-preferred sorghum varieties from Mali
were introgressed with up to four of the five
resistance QTL by marker-assisted backcrossing
(MABC) (Muth et al. 2011). In this project, 32 of
the resulting backcross-two lines (BC2S3) were
field-evaluated for their
Striga
resistance under
natural and artificial
Striga
infestation at three
sites in Mali in 2009 and 2010. Together with
yield data and agronomic properties, the number
of emerged
Striga
plants per experimental plot
was evaluated at regular intervals over the crop-
ping season as an integrative measure of disease
severity. In parallel, the presence/absence of the
targeted genomic regions from N13 neighbor-
ing the QTL was tested in all lines using flank-
ing SSR markers mapped to the vicinity of the
targeted QTLs. Preliminary analyses of the data
show a resistance of the best sorghum lines equal
to or exceeding the resistance of the donor parent
N13. However, yield of BC2-lines was on aver-
age inferior to the recurrent parents. A strong
environmental influence on resistance between
trial sites was observed in the field experiments.
×
Search WWH ::
Custom Search