*Article* **Effects of Different Growth Hormones on Rooting and Endogenous Hormone Content of Two** *Morus alba* **L. Cuttings**

**Hanlei Chen, Youzhen Lei, Jiajia Sun, Mingyue Ma, Peng Deng, Jin'e Quan \* and Huitao Bi \***

College of Forestry, Henan Agricultural University, Zhengzhou 450046, China; 18336253160@163.com (H.C.); leiyouzhen1021@163.com (Y.L.); dearperi@163.com (J.S.); 15178061569@163.com (M.M.); dengpeng@henau.edu.cn (P.D.)

**\*** Correspondence: quanjine@163.com (J.Q.); bihuitao@126.com (H.B.)

**Abstract:** This study aimed to explore the effects of different concentrations of indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), and indene-naphthaleneacetic acid (ABT-1) on the rooting and dynamic changes of the endogenous hormone content of Australian Mulberry (vegetable Mulberry) and Kirin mulberry (Fruit Mulberry) hardwood cuttings. As exhibited by the results, the rooting process of both vegetable mulberry and fruit mulberry could be divided into three stages, namely the initiation stage (1–18 days), the callus formation stage (18–28 days), and the adventitious root formation and elongation stage (28–48 days). The two treatments with 1000 mg·L−<sup>1</sup> ABT-1 and 500 mg·L−<sup>1</sup> ABT-1 achieved the highest rooting efficiencies of vegetable mulberry and fruit mulberry, significantly higher than those of other treatments (*p* < 0.01), with average rooting rates of 63.3% and 68.7%, and rooting efficiency indices of 25.3 and 34.3, respectively. During the rooting process, the contents of endogenous IAA and zeatin riboside (ZR) and the ratios of IAA/ABA and IAA/ZR presented a trend of decreasing before increasing, while the abscisic acid (ABA) and jasmonic acid (JA) contents exhibited a trend of increasing before decreasing, and the gibberellin (GA3), strigolactone (SL), and IBA contents showed a continuous decreasing trend. Hence, ABT-1 was effective in inducing the synthesis of IAA, IBA, JA, and SL, reducing the contents of ABA, ZR, and GA3, and promoting the rooting of vegetable mulberry and fruit mulberry cuttings. For fruit mulberry and vegetable mulberry cuttings, the optimal concentrations of ABT-1 were 500 mg·L−<sup>1</sup> and 1000 mg·L−1, respectively, demonstrating applicability for the efficient propagation of *Morus alba* L. cuttings.

**Keywords:** growth hormones; *Morus alba* L.; hardwood cuttings; endogenous hormones
