Progress for testcross performance within the flint heterotic pool of a public maize breeding program since the onset of hybrid breeding

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 commercial 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 remarkable 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 conditions as well as genetically broad testers to identify the most promising lines because interactions with testers and environments are larger in these materials compared with elite lines.