Transgene effects vary among maize populations with implications for improving quantitative traits

The goal of transgenesis in plant breeding is to make step‐change improvements in traits of interest. However, improving quantitative traits, such as yield in maize ( Zea mays L.), with transgenes has been difficult. Traditionally, transgene testing is done on a few isogenic lines, and results are extrapolated to entire breeding populations. Testing on limited germplasm does not provide a robust estimate of a transgene's value. Incorporating transgenes directly into breeding populations could increase genetic variance and the rate of genetic gain. Here, we used a transgene that reduces ethylene as a case study and investigated event, transgene, family, and environment effects and their interactions. We also determined whether introduction of the transgene into a breeding population would result in transgenic lines being preferentially selected over nontransgenic lines for yield. We found significant variation in transgene effects across clustered environments and families for multiple traits including yield. In environmental Cluster 2, the transgenic lines yielded 0.4 Mg ha −1 more than nontransgenic lines in family KC22; yet, in family QY43, transgenic lines yielded 0.3 Mg ha −1 less. Similarly, within Cluster 4, the QY43 family had preferential selection of transgenic over nontransgenic lines, whereas in families YE41 and AY91, nontransgenic lines were selected more frequently. These results show the critical importance of evaluating transgenes across broad germplasm diversity to assess their general value to a program. Integrating transgenes, or using gene editing, directly in a breeding program can expand genetic variation for quantitative traits and potentially accelerate genetic gain. Using transgenes to improve quantitative traits like yield is difficult. Testing on few inbred lines does not reflect a transgene's value across an entire breeding program's germplasm. Transgenes for quantitative traits may improve yield in some genetic backgrounds but not others. Incorporating transgenes into a breeding program adds variation that could accelerate genetic gain. Transgenes have been used to improve crops for genetically simple traits like insect resistance, but using them to improving complex traits like yield has proven more difficult. In this experiment, we attempted to assess whether the effect of a transgene that affects yield of maize was higher or lower in certain breeding germplasm. We also wanted to know what proportion of individual maize lines