Interspecific hybridizations of Fraxinus L. (F. mandshurica x F. americana and F. mandshurica x F. velutina) and heterosis analysis and selection of F1 progenies

The interspecific hybridizations of Fraxinus mandshurica Rupr. x Fraxinus americana L. (MA) and Fraxinus mandshurica x Fraxinus velutina Torr. (MV) were conducted to solve the problems of poor cold adaption associated with the introduction of Fraxinus in Heilongjiang province. High-voltage electrostatic field (HVEF) treatment to pollen was performed to overcome the prefertilization barriers. The hybrids adapted more strongly and grew better than the pure species (heterosis over higher parent (HHP) of the 9-year volume index was 5.5% for MA and 23.1% for MV) in Heilongjiang province. HVEF treatment greatly improved the number of seeds (0.25- to 5.52-fold) and seedlings (1.63- to 8.71-fold) of the hybrids. Additionally, three excellent female parents (nos. 15, 16, and 17) and seven hybrid combinations of MA(D94, D70, and D100) and MV (D103, D116, D105, and D104) with excellent growth traits were selected. The HHPs of volume index were 39.1%-112.5% for selected hybrids. Additionally, predicted growth trends of the hybrids showed that the hybrids will maintain a 7.7% to 9.3% height advantage over F. mandshurica through ages 10 to 15 years in Mao Ershan. These findings will accelerate the genetic breeding process of Fraxinus species.