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A maize synthetic population was improved for resistance to the Mediterranean corn borer (MCB, Sesamia nonagrioides) while maintaining yield. The objectives of this research were to investigate whether yield and yield stability of the maize synthetic population named EPS12 were affected by selection for MCB resistance; also to determine which genotypic and environmental covariates could explain the genotype (G), environment (E) and genotype × environment (GE) effects for yield under corn borer infestation. Plants from three cycles of selection and their testcrosses to three inbred testers (A639, B93 and EP42) were evaluated at two locations in 2 years, under MCB and European corn borer infestations. After selection EPS12 was a more stable genotype. Hybrids derived from crosses between B93 and inbreds obtained from the initial cycles of selection could be recommended for cultivation in northern Spain. The yield of crosses between cycles of selection and testers increased when there were fewer days with temperatures >25°C and higher mean maximum temperatures. Differences in yield among these genotypes were mostly explained by resistance to corn borer attack. In general, among EPS12-derived materials, genetic characteristics that contribute to increased grain yield were also responsible for increased abiotic stress tolerance. [ABSTRACT FROM AUTHOR]

Abstract: In maize, the Mediterranean corn borer (MCB), Sesamia nonagrioides Lef, is the insect pest that causes the most significant yield losses in north-western Spain. A S1 recurrent selection program to improve resistance of EPS12 against MCB was evaluated previously. In the current study two experiments were conducted to determine if antibiosis and/or structural mechanisms were responsible for the improvement in resistance in this synthetic. Larval growth or survival of MCB was not significantly affected to consider the presence of antibiotic factors in the pith. Besides, pith puncture resistance, previously reported as a possible resistance trait in single inbred lines, did not show significant differences between cycles of selection. Length of the internode basal ring (LIBR) was the structural character most related to stem resistance improvement to MCB in the current evaluation. There was a high positive correlation between MCB tunnel length and LIBR (P ≤0.01, R 2 =0.99). The larvae would enter the plant throughout the internode basal area and, this way, they could avoid the increased thickness or hardness of the remaining rind area. LIBR might be a useful measure in future resistance breeding programs against this borer. [Copyright &y& Elsevier]

Sesamia nonagrioides causes high yield losses in maize in northwestern Spain. Therefore, a recurrent selection programme to improve resistance against this pest has been carried out in a maize synthetic population. The main purposes of this investigation were to determine which are the main components of genetic variance for stem tunnelling and yield under infestation, to determine the variance remaining after selection, and, finally, to establish the genetic relationship between traits used as selection criteria and other ear resistance and agronomic traits. A North Carolina Design I mating system was used. Individual analyses by year were carried out and additive variance was identified as the only significant component of the genetic variance for stem tunnel length while a dominant variance was significant for yield. Those variances have decreased due to selection, but not significantly. Selection could continue for more cycles as there is enough variance. Additive genetic correlation coefficients between tunnel length and yield could not be determined. Thereafter, we propose three different methodologies of the selection to determine the relationship between resistance and yield under infestation. [ABSTRACT FROM AUTHOR]

Abstract: In northwestern Spain, the grounded whole kernel of flint maize (Zea mays L.) landraces is traditionally used for making bread and other bakery products. We have identified some local varieties appropriate for traditional bakery. Thus far, evaluations have been made under low corn borer pressure, but to know their ability to compete for yield and quality in a wider area, evaluations should be done under higher corn borer, specifically targeting Sesamia nonagrioides (Lepidoptera: Noctuidae) and Ostrinia nubilalis (Lepidoptera: Crambidae) pressure. Therefore, the objectives of this study were to explore the stem and ear resistance to corn borer attack of maize landraces already evaluated for yield, kernel, and bread tasting qualities under organic farming conditions and to know possible relationships among yield, quality and corn borer damage traits. No significant correlation coefficients were detected between yield and quality-related traits. Therefore, simultaneous progress for yield and quality could be made. Many varieties providing high yield and kernel density under high insect pressure were similar to the ones selected by the same characteristics under low insect pressure in a previous study. However, under high insect pressure, varieties with less stem and shank damage by S. nonagrioides are recommended for reducing losses and the risk of kernel contamination with fumonisins. Among the late varieties, Bianco Perla would be the most appropriate to obtain high yield along with reduced stem damage by S. nonagrioides and reduced risk of fumonisin contamination. In areas with shorter growing season, EPS12 (T) C3 and Rebordanes would be the most suitable varieties for obtaining high-quality flours under high insect pressure. [Copyright &y& Elsevier]