Genetic mapping of QTL for maize weevil resistance in a RIL population of tropical maize

A tropical RIL maize population was subjected to phenotypic and genotypic analysis for maize weevil resistance during four seasons, and three main genomic areas were detected as main QTLs. The maize weevil (Sitophilus zeamais) (MW) is a common and important pest of stored maize (Zea mays) worldwide, especially in tropical areas. Quantitative trait loci (QTLs) associated with the MW have been analyzed previously in an F2 maize population. In this work, new germplasm-based F6 recombinant inbred line (RIL) families, derived from the cross of Population 84 and Kilima, were analyzed using insect bioassays during four seasons. The parameters analyzed for MW resistance were grain weight losses (GWL), adult progeny (AP), and flour production (FP). Composite interval mapping identified a total of 15 QTLs for MW parameters located on six chromosomes, explaining between 14 and 51 % of phenotypic variation (σ p (2) ) and 27 and 81 % of genotypic variation (σ g (2) ). The QTL obtained for GWL was located in bin 2.05, which explained 15 % of σ p (2) . For AP and FP, the QTLs were located on regions 1.09 and 2.05, explaining 7 and 15 % of σ p (2) , respectively. Comparative analysis between F2 and F6 families showed similarities in QTL localization; three main regions were co-localized in chromosomes 4.08, 10.04, and 10.07, where no resistance-associated genes have been reported previously. These regions could be used for a marker-assisted selection in breeding programs for MW resistance in tropical maize.

Leaf profile of maize resistance factors to European corn borer,Ostrinia nubilalis

The feeding preference of European corn borer larvae for immature whorl tissue of maize was examined by conducting leaf bioassays and quantifying resistance factors along the length of mid-whorl leaves from the maize synthetic BS9(C4) developed by recurrent selection for resistance. Potential resistance factors that were quantified included percent foliar nitrogen, gravimetric determination of soluble metabolites and fiber, soluble phenolics and hydroxamic acids, cell-wall-bound phenolics, leaf toughness, and UV absorbance of the epidermal cell wall determined by microspectrophotometry. Larvae consumed immature tissue at a higher rate than more mature tissue outside of the whorl, despite higher levels of DIMBOA in immature tissue. Consumption rate was highly negatively correlated with epidermal cell wall absorbance and leaf toughness. Fiber content and phenolic fortification of cell walls are proposed as the major resistance components that influence European corn borer feeding preference within the resistant synthetic BS9(C4).

Grain and tortilla quality in landraces and improved maize grown in the highlands of Mexico

The maize produced in the highlands of Mexico (>2,400 masl) is generally not accepted by the flour and masa and tortilla industry. The objective of this work was to evaluate the grain quality and tortilla properties of maize landraces commonly grown in the highlands of Mexico and compare them with improved germplasm (hybrids). Germplasm analysis included 11 landraces, 32 white hybrids, and six yellow hybrids. Grain quality was analyzed for a range of physical and chemical factors, as well as for alkaline cooking quality. Landrace grains tended to be heterogeneous in terms of size, hardness and color. All landraces had soft-intermediate grains with an average flotation index (FI) of 61%. In contrast, hybrid grains were homogenous in size and color, and harder than landrace grains, with a FI of 38%. Protein, free sugars, oil and phenolic content in landraces were higher than in the hybrids. Significant correlations were found between phenolic content and tortilla color (r= -0.60; p<0.001). Three landraces were identified as appropriate for the masa and tortilla industry, while all the hybrids evaluated fulfilled the requirements of this industry.