Effects of exogenous IAA and GA3 on formation of compression wood of Pinus massoniana Lamb.

The effect of exogenous hormones on the formation of compression wood of Masson pine (Pinus massoniana Lamb.) was explored to enrich ideas and methods for the cultivation and quality improvement of Masson pine plantation. Three-year-old Masson pine seedlings were artificially inclined at angle of 45° at first, and then different concentrations of IAA, GA3 and IAA+GA3 were added into the seedlings through cutting wound to adjust the growth of branches. In order to analyze the effects of these two exogenous hormones on the formation of compression wood of Masson pine, the differences and changes in longitudinal growth of previous-year (1-year-old) branches, radial widths of xylem and phloem, tracheid length, wall thickness, tracheid production and the severity of compression wood were observed and analyzed. The results showed that the longitudinal growths of previous-year (1-year-old) branches were increased in all hormone treatments (89.6%-179.1%). Radial widths of phloem and xylem were increased by adding GA3 and IAA +GA3; however, the effects of IAA on radial widths of phloem and xylem were not significant. Compared with the control group, tracheid production was inhibited on the lower side (14-17 layers) of tilt branch but was increased at the upper side (5-11 layers) in all hormone treatments. Adding GA3 or IAA +GA3 promoted the formation of mild compression wood at the lower sides of tilt previous-year (1-year-old) branches. Meanwhile, severe compression woods were formed at control group and IAA treatments for the same materials. Above results indicated that exogenous hormones can increase the top growth of Masson pine’s tilt branches, and the formation of compression wood was inhibited by applying exogenous hormones on the upside of the Masson pine’s tilt branches.