A novel approach for enhancing sprouting to increase yield and its mechanism in Fraxinus mandshurica Rupr.

Fraxinus mandshurica is a valuable timber and landscaping tree species in northern China. However, its clonal propagation faces significant challenges, including limited sprouting of young mother trees, insufficient scion sources, low yields and short usage cycles. This study introduced a novel method to promote sprouting in F. mandshurica, focusing on factors like trunk cutting, continuous rejuvenation and leaf trimming. The method initially determined the optimal conditions for trunk cutting, considering tree age, height, and timing. Plants that met these conditions were then subjected to coppicing, basal girdling and hormone sprays rejuvenation treatments in sequence. Leaf trimming was conducted during sprouting branches collection. The results showed that for trees over 4 years old, trunk cutting treatment was performed 30∼50 cm above the ground 3 weeks after sap flow in spring, followed by rejuvenation treatment (coppicing + basal girdling + hormone sprays), which improved the cutting yield by 10.4-fold. Furthermore, retaining a pair of axillary buds at the base while removing the compound leaves during branch harvesting can increase cutting yield by an additional 47.1 %. This approach effectively promoted sprouting and produced cuttings suitable for propagation. To further elucidate the mechanism of sprouting promotion, the hormone levels and key gene expression during shoot regeneration after F. mandshurica trunk cutting were analyzed, leading to the identification of the key shoot regeneration gene FmESR1. By transforming the F. mandshurica hypocotyl with FmESR1, overexpressing transgenic plants were obtained. Combined with the changes in adventitious shoot development, hormone levels and regeneration-related gene expression, it was revealed that FmESR1 played a crucial role in shoot regeneration. Thus, it was concluded that sprouting promotion significantly improved regeneration ability and cutting yield by activating the expression of FmESR1. This technology lays a solid foundation for the efficient reproduction and widespread application of superior and new varieties of F. mandshurica. The elucidation of FmESR1 function not only enriches the theoretical understanding of shoot regeneration and the gene function database but also provides theoretical and technical support for asexual propagation.