Dynamic changes in the genetic parameters of growth traits with age and their associations with heterosis in hybrid Liriodendron

Liriodendron plants have been cultivated in many regions of the world for both wood production and landscape ornamentation. Hybrid Liriodendron varieties show obvious growth and resistance heterosis; thus, interspecies hybridization and heterosis utilization constitute the major breeding strategy for Liriodendron plants. Choosing superior crossing parents/combinations and predicting the heterosis of potential hybrid combinations will greatly improve breeding efficiency and accelerate the breeding process. To explore the relationships between genetic parameters and heterosis, we investigated dynamic changes in the genetic parameters of growth traits with age by testing 57 progeny combinations derived from six cross types in Liriodendron. Tree height (H) and diameter at breast height (DBH) were under intermediate to strong genetic control and varied among combinations, indicating that parent-pair selection or combination selection is feasible. Both heritability and combining ability (general combining ability, GCA; specific combining ability, SCA) changed with age, with narrow-sense heritability fluctuating greatly in the early stage and increasing in the late stage, and the combining abilities varied among combinations. Additionally, the GCA of Liriodendron chinense parents was higher than that of Liriodendron tulipifera and hybrid Liriodendron parents, and the SCA of L. tulipifera x L. chinense combinations fluctuated less than that of other combinations. Further, midparent heterosis (MPH) and SCA were significantly positively correlated, suggesting that SCA could be a suitable criterion for predicting growth heterosis. Our findings provide useful clues for selecting parent pairs/combinations and predicting heterosis, which will accelerate Liriodendron tree breeding and shed light on cross-breeding in other plants.