Abstract
Several species of herbivores feed on maize in field and storage setups, making the development of multiple insect resistance a critical breeding target. In this study, an association mapping panel of 341 tropical maize lines was evaluated in three field environments for resistance to fall armyworm (FAW), whilst bulked grains were subjected to a maize weevil (MW) bioassay and genotyped with Diversity Array Technology’s single nucleotide polymorphisms (SNPs) markers. A multi-locus genome-wide association study (GWAS) revealed 62 quantitative trait nucleotides (QTNs) associated with FAW and MW resistance traits on all 10 maize chromosomes, of which, 47 and 31 were discovered at stringent Bonferroni genome-wide significance levels of 0.05 and 0.01, respectively, and located within or close to multiple insect resistance genomic regions (MIRGRs) concerning FAW, SB, and MW. Sixteen QTNs influenced multiple traits, of which, six were associated with resistance to both FAW and MW, suggesting a pleiotropic genetic control. Functional prioritization of candidate genes (CGs) located within 10–30 kb of the QTNs revealed 64 putative GWAS-based CGs (GbCGs) showing evidence of involvement in plant defense mechanisms. Only one GbCG was associated with each of the five of the six combined resistance QTNs, thus reinforcing the pleiotropy hypothesis. In addition, through in silico co-functional network inferences, an additional 107 network-based CGs (NbCGs), biologically connected to the 64 GbCGs, and differentially expressed under biotic or abiotic stress, were revealed within MIRGRs. The provided multiple insect resistance physical map should contribute to the development of combined insect resistance in maize.
Highlights
Despite the importance of maize (Zea mays L.) for food security, income, livestock feed, and biofuel products, and its large production area, grain yield remains low in sub-Saharan African (SSA) countries, averaging less than 1.8 ton/ha due to a barrage of biotic and abiotic stresses [1]
The association mapping panel (AMP) used in this study consisted of 358 maize lines from a diverse genetic and geographic background sourced from the National Crop Resources Research Institute (NaCRRI of Namulonge, Uganda), the International Institute for Tropical Agriculture (IITA of Ibadan, Nigeria), and The
African environments was evaluated in three environments
Summary
Despite the importance of maize (Zea mays L.) for food security, income, livestock feed, and biofuel products, and its large production area, grain yield remains low in sub-Saharan African (SSA) countries, averaging less than 1.8 ton/ha due to a barrage of biotic and abiotic stresses [1]. Maize faces several yield-limiting factors, among which biotic stresses such as insect pest attacks [1,2,3] start in the field with a range of voracious phytophagous pests that include stem borers, leaf feeders, phloem feeders, and root feeders [4]. The pest is a threat to food security in Africa owing to its voracious and polyphagous nature, resulting in substantial yield losses in maize production [1]. Storage pests (SP) such as the maize weevil (MW), Sitophilus zeamais Motsch (Coleoptera: Curculionidae), and the larger grain borer (LGB), Prostephanus truncatus Horn (Coleoptera: Bostrichidae), have a substantial share in these losses, especially in Africa where poor storage facilities expose stored grains [5,9]
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