Response of Sprouting and Tillering Growth of Pinus yunnanensis Seedlings to Exogenous IAA and ZT Application

To investigate the effects of different exogenous hormones on the sprout growth of Pinus yunnanensis seedlings after stump cutting, two-year-old P. yunnanensis were selected as the study subjects. These P. yunnanensis were sprayed with different concentrations of the exogenous hormones indole-3-acetic acid (IAA) and zeatin (ZT). The results showed that the optimal hormone combination for the height growth of P. yunnanensis seedlings after cutting was IAA 300 mg/L and ZT 0 mg/L. Within a certain range, IAA promoted the height growth of the seedlings, with the cumulative growth of seedling height over time showing a slow-fast-slow growth trend. The rapid growth point and period of seedling height were delayed with increasing concentrations of IAA. The optimal hormone combination for the diameter growth at the ground level of P. yunnanensis seedlings after cutting was IAA 0 mg/L and ZT 100 mg/L. Within a certain range, ZT promoted the diameter growth of the seedlings, with the cumulative growth of diameter at the ground level also showing a slow-fast-slow trend. When sprayed with IAA 300 mg/L and ZT 100 mg/L, the number of sprouts per P. yunnanensis seedling was the highest after stump cutting, although there were no significant differences. The combination of IAA and ZT influenced the growth of P. yunnanensis seedlings, with ZT specifically promoting the diameter growth and favoring an increase in the number of sprouts. The role of ZT in the growth and development of P. yunnanensis sprouts was superior to that of IAA, indicating that finding the appropriate hormone and concentration can maximize the sprouting ability of P. yunnanensis seedlings.