The researchers studied how different maize lines performed in terms of yield when grown at different plant densities. They found that some combinations of maize lines showed high yield increases, known as heterosis, especially when crossed with specific other lines. The best combinations accounted for a majority of the high-yielding crosses. The combining ability of the lines varied depending on the density at which they were grown, with some combinations showing better results at higher densities. Overall, the study highlights the importance of selecting the right maize lines and planting density to maximize yield per plant.