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Genetic
analysis of resistance to Striga
hermonthica introgressed from Zea
diploperennis to tropical maize
Striga
is the single most severe biological constraint to cereal production in
sub-Saharan Africa. Maize is highly susceptible to Striga
and can sustain yield losses of up to 100% in highly infested
fields. Host plant resistance is regarded as the most feasible and
potentially durable method to reduce losses to Striga.
In the 1980’s, IITA developed inbred lines and hybrids with partial
resistance and/or tolerance to Striga
hermonthica. However, none of
the lines and hybrids completely prevented the successful development of
Striga. Also, the level of
genetic variation resistance is too low to permit adequate progress from
selection. It was, therefore, necessary to search for novel resistance
genes that suppress the emergence of Striga
in diverse sources of maize germplsm. An accession of teosinte, Zea diploperennis, that supported little or no emergence of S.
hermonthica was identified at IITA and crossed to adapted tropical
maize. Several lines supporting few emerged Striga
plants were derived from a backcross population of Z.
diploperennis after two generations of inbreeding and repeated
selection under artificial infestation in the field and screen house.
The purpose of the study presented in this report was to use molecular
markers to identify genetic loci associated with resistance to Striga
in maize using F2:3 families derived from a cross of a Striga resistant line derived from Z. diploperennis BC4 population with a Striga-susceptible inbred line. The F2:3 families along
with the parents were evaluated in three environments under artificial
infestation with Striga and
genotyped with 47 SSR and 80 AFLP markers suing standard protocols. The
mapping population exhibited significant differences among families for Striga
damage symptom rating, numbers of emerged Striga
plants, numbers of ears at harvest and grain yield under Striga
infestation. Analyses of genotypic and phenotypic data led to the
identification of SSR and AFLP markers associated with QTLs affecting Striga
damage symptom rating, the numbers of ears at harvest and grain yield
under Striga infestation. These QTLs were consistently expressed across
test environments representing different Striga
populations and were anchored at a few common marker intervals in the
same linkage groups. Although some QTLs were significantly associated
with the numbers of emerged Striga
plants, they were not consistent across environments. The markers with
significant association to reduced Striga
damage symptom and increased number of ears at harvest and grain yield
can be used as potential candidate markers for simultaneous improvement
of these traits in maize. Future efforts should focus on search for
markers consistently linked to the number of emerged Striga
plants across environments to facilitate marker-assisted selection to
drastically deplete the reservoir of Striga
seeds from the soil.
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