Striga species are parasitic weeds that are widespread
constraints to the production of staple cereal crops
in semiarid areas, principally attacking maize, sorghum,
finger millet and upland rice. They have been estimated
to infest some 40 per cent of the cereal producing areas
of sub-Saharan Africa; Striga hermonthica alone may
now infest over 10 million hectares and those most severely
affected are subsistence farmers. Loss of grain yield
from parasitized cereal crops is difficult to estimate
with any reliability due to variations in soil fertility,
infestation levels and different sensitivity of local
varieties. The aim of this project is to identify key
genes involved in resistance of rice cultivar APS1101
to Striga hermonthica (using the whole genome array
Rice Gene Chip).
Understanding the genetic
basis of post attachment resistance to Striga species
Understanding the molecular basis of host resistance to
Striga species is a critical step in the identification
of genes that can be used for improving crop productivity
either via biotechnology based approaches such as crop
transformation or via the development of molecular markers
for use in marker assisted selection programmes. We have
screened the model cereal rice for post attachment resistance
to Striga hermonthica and we have identified cultivars
that exhibit varying degrees of resistance to this parasite.
In order to begin the identification of the molecular
genetic basis of post-attachment resistance in rice we
have taken two complementary approaches.
- First we have carried out a QTL analysis using a mapping
population (Nipponbare/Kasalath//Nipponbare) of Backcross
Inbred Lines.
- second we have profiled changes in gene expression in
roots of a susceptible and resistant cultivar of rice
following infection by S. hermonthica.
QTL explaining a large proportion of the resistance were
discovered on five chromosomes; 4 alleles providing resistance
from Nipponbare and 1 allele from Kasalath. Each of these
QTL were statistically significant at the stringent genome-wide
P 0.001 threshold. All of these QTL were of magnitude
in excess of the usual definition of a major gene, thus
although the resistance trait is polygenic, it is likely
that this may indicate a few genes of major effect. To
dissect the Nipponbare QTL into their underlying genetic
determinants, an analysis of changes in gene expression
in Striga-infected roots has been carried out using the
Affymetrix whole genome rice oligonucleotide array. To
date a small number of genes have been identified that
are significantly differentially expressed within the
major resistance QTL; such genes are potential candidates
for Striga resistance and could also be used to develop
molecular markers of resistance. |
