Impact of parent inbred lines on heterosis expression for agronomic characteristics in sunflower

To study the impact of parent-inbred lines on the heterosis expression of the agronomic characteristics in sunflower hybrids, 24 sunflower hybrids along with the parent lines were evaluated for their agronomic characteristics as a randomised complete block design with three replications in the 2018-2019 growing seasons in Karaj, Iran. According to the results, the hybrids R29 × A346, R19 × A346, R29 × A40 had the highest achene yield (4 159, 4 143 and 4 108 kg/ha, respectively), but the highest heterosis was observed in R29 × A212 and R19 × A212 (182 and 181%, respectively) suggesting that the incidence of heterosis is related to the relative performance of both the parents and hybrids. The results confirmed the heterosis expression for most of the agronomic traits. The heterosis for the days to flowering and maturity were negative. All the mid-parent heterosis (MPH) for the plant height, head diameter, stem diameter and achene number were positive, while only the plant height was positive for the best parent heterosis (BPH). Almost all the MPH and BPH of the crosses for the achene and oil yield were positive, which indicates a considerable heterosis for the achene and oil yield. The results showed that the relative impact of the restorer (R)-lines was higher than the cytoplasmic mail sterile (CMS)-lines on the heterosis expression for the days to maturity, stem diameter, achene number per head and achene and oil yield. The CMS-lines had more of an impact on the heterosis expression for the plant height and the relative impact of the R-lines and CMS-lines were almost similar for the days to flowering, head diameter, achene weight and oil content. Due to the higher relative impact of the paternal lines on the heterosis expression for half of the studied characteristics in this study, choosing suitable parental lines will have a crucial role in breeding the sunflowers for a desired trait.