Breeding early maturing European dent maize (Zea mays L.) for improved agronomic performance and resistance against the european corn borer (Ostrinia nubilalis Hb.)

The prime objective of maize breeding programs in Western Europe is improving yield, maturity, and stalk quality. Increasing the resistance to the European corn borer (Ostrinia nubilalis Hb., ECB) is of secondary importance, despite its significance as a major pest of maize in Western Europe. Given this priority setting, die overall goal of the Hohenheim ECB breeding program, initiated in 1992, was to select lines with improved per se and testcross performance for multiple agronomic traits and ECB resistance. Objectives of this study were to describe the used breeding scheme and the results obtained after ten years of intensive selection work. In the standard breeding scheme, line development started from a segregating S ₁ population. Genotypes were evaluated for their line per se ECB resistance in generations S ₁, S ₃, and S ₅. Lines from the S ₂, S ₄, and S ₅ generations were testcrossed and evaluated for their agronomic performance. Selection was based on ECB resistance and TC performance for grain yield and maturity. The five newly developed lines showed only a minor improvement for ECB resistance. This can be explained by the negative correlation between the used selection index for agronomic traits and ECB resistance. The population fraction selected based on index performance did not contain the lines with the highest level of resistance. None of the selected lines showed associations between SSR haplotypes at ECB resistance gene clusters and their level of ECB resistance. These results demonstrated that a simultaneous improvement of important agronomic traits and ECB resistance is difficult to accomplish, if conventional tools typically used by maize breeders are applied. Further research is needed to develop new breeding methods to overcome these limitations.