Progress for testcross performance within the flint heterotic pool of a public maize breeding program since the onset of hybrid breeding Armin C. Ho ¨lker . Wolfgang Schipprack . H. Friedrich Utz . Willem S. Molenaar . Albrecht E. Melchinger Received: 12 October 2018 / Accepted: 6 February 2019 Ó Springer Nature B.V. 2019 Abstract Maize (Zea mays L.) grain yields have risen due to agronomic improvements and plant breeding, especially since the introduction of hybrid breeding. This study was conducted to measure the breeding progress within the flint heterotic pool of a public maize breeding program since the onset of hybrid breeding. Testcrosses with two dent testers of four flint founder lines (FL), four elite flint lines from three time periods each (EL1, EL2, EL3), and seven preselected doubled haploid (DH) lines from landraces (DH-LR) were evaluated together with four commer- cial check hybrids (CH). Grain yield (GY) and grain dry matter content (GDMC) were assessed in six diverse environments in southwestern Germany and northeastern France in 2016. We estimated a highly significant (P \ 0.001) linear increase in GY of 48 kg ha -1 yr -1 . The average testcross performance of DH-LR was significantly higher than of FL. Interestingly, two of the DH-LR lines had a higher yield than all EL2 lines. We conclude that a remark- able breeding progress has been achieved and annual gain in GY does not level off yet. However, an integration of new genetic material into the flint heterotic pool for maintaining sufficient genetic diversity is needed to ensure long-term selection gain. DH lines from landraces could be used for this purpose but we recommend using multiple test environments with contrasting yield levels and agronomic condi- tions as well as genetically broad testers to identify the most promising lines because interactions with testers and environments are larger in these materials com- pared with elite lines. Keywords Breeding progress Á Doubled haploid lines Á Flint heterotic pool Á Founder lines Á Maize landraces Abbreviations CH Commercial check hybrids DH Doubled haploid DH-LR Doubled haploid lines from landraces EL Elite lines EL1 Elite lines time period 1 EL2 Elite lines time period 2 EL3 Elite lines time period 3 FL Flint founder lines Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10681-019-2370-0) con- tains supplementary material, which is available to authorized users. A. C. Ho ¨lker Á W. Schipprack Á H. F. Utz Á W. S. Molenaar Á A. E. Melchinger (&) Institute of Plant Breeding, Seed Sciences and Population Genetics, University of Hohenheim, Fruwirthstraße 21, 70599 Stuttgart, Germany e-mail: Melchinger@uni-hohenheim.de Present Address: A. C. Ho ¨lker Plant Breeding, TUM School of Life Sciences Weihenstephan, Technical University of Munich, Liesel-Beckmann-Str. 2, 85354 Freising, Germany 123 Euphytica (2019)215:50 https://doi.org/10.1007/s10681-019-2370-0