Heterosis × environment interaction in maize: What drives heterosis for grain yield?

Abstract

Variation in mean heterosis over a range of environments is expected when maize hybrids and inbred lines respond differently to environmental stimuli. However, the magnitude and nature of the heterosis × environment interaction (H × E) has not been adequately described. The objectives of this work were to determine (i) the effects of environmental variability on the expression of heterosis for plant grain yield (PGY) and related ecophysiological traits and (ii) to what extent H × E is of general importance for the expression of heterosis for these traits. Field experiments included a set of six inbred lines and twelve derived hybrids grown in 14 environments (year × nitrogen × water regime combinations) in the temperate region of Argentina. Main physiological and quantitative determinants of PGY were measured and mid parent heterosis (MPH) computed for each trait. Genotype × environment interaction was investigated using the joint regression analysis. For PGY, hybrids had a significant but moderate association between sensitivity to the environment and mean genotype value, whereas inbred lines did not show association. For harvest index (HI) hybrids showed greater mean values than inbreds, however, regression coefficients of both genotype groups tended to overlap slightly. A decrease in environmental quality led to a decline in the expression of heterosis for PGY but not for HI. A bilinear with plateau model adequately described the association between heterosis for PGY and environmental quality, because a threshold value was detected beyond which further increases in environment mean did not translate into higher heterosis for PGY. A similar response pattern was found between PGY MPH and biomass at physiological maturity (Biomass PM) MPH. Despite the greater heterosis for Biomass PM, further increases in PGY MPH could not be realized above a threshold value of 115 g pl −1 for Biomass PM MPH. HI MPH was the major factor that set a limit to PGY MPH under favorable environments.