Abstract:
Among the diseases threatening maize production in Africa are gray leaf spot (GLS)
caused by Cercospora zeina and northern corn leaf blight (NCLB) caused by
Exserohilum turcicum. The two pathogens, which have high genetic diversity,
reduce the photosynthesizing ability of susceptible genotypes and, hence, reduce
the grain yield. To identify population-based quantitative trait loci (QTLs) for GLS
and NCLB resistance, a biparental population of 230 lines derived from the tropical
maize parents CML511 and CML546 and an association mapping panel of
239 tropical and sub-tropical inbred lines were phenotyped across multienvironments
in western Kenya. Based on 1,264 high-quality polymorphic
single-nucleotide polymorphisms (SNPs) in the biparental population, we
identified 10 and 18 QTLs, which explained 64.2% and 64.9% of the total
phenotypic variance for GLS and NCLB resistance, respectively. A major QTL
for GLS, qGLS1_186 accounted for 15.2% of the phenotypic variance, while
qNCLB3_50 explained the most phenotypic variance at 8.8% for NCLB
resistance. Association mapping with 230,743 markers revealed 11 and 16 SNPs
significantly associated with GLS and NCLB resistance, respectively. Several of the
SNPs detected in the association panel were co-localized with QTLs identified in
the biparental population, suggesting some consistent genomic regions across
genetic backgrounds. These would be more relevant to use in field breeding to
improve resistance to both diseases. Genomic prediction models trained on the
biparental population data yielded average prediction accuracies of 0.66–0.75 for
the disease traits when validated in the same population. Applying these prediction
models to the association panel produced accuracies of 0.49 and 0.75 for GLS and
NCLB, respectively. This research conducted in maize fields relevant to farmers in
western Kenya has combined linkage and association mapping to identify new QTLs and confirm previous QTLs for GLS and NCLB resistance. Overall, our findings imply that genetic gain can be improved in maize breeding for resistance to
multiple diseases including GLS and NCLB by using genomic selection.
