**1. Introduction**

As a deciduous tree of the genus Morus in the family Moraceae, *Morus alba* L. [1] derives from northern and central China. Characterized by drought resistance, barren land tolerance" waterlogging resistance, cold tolerance, and strong adaptability to soil, *Morus alba* L. is an excellent timber, as well as environmental protection and economic tree species [2]. In addition, as a valuable plant, *Morus alba* L. can be used both medicinally and as a food source, with its fruit, leaves, branches, and roots being highly prized. Furthermore, known as the "Chinese holy tree", *Morus alba* L. has been listed by the Ministry of Health as a dual-purpose plant for food and medicine on account of its high development and utilization value [2]. Following the promotion of scientific and technological innovation in the sericulture industry, this industry is gradually developing towards a diversified and multi-purpose direction, including fruit mulberry, vegetable mulberry, medicinal mulberry, and ecological feed mulberry [3]. In view of the large demand for *Morus alba* L. seedlings, it is essential to develop asexual propagation techniques, especially cutting propagation techniques, thereby ensuring high-quality seedlings [4].

Cutting propagation has many advantages, such as easy access to materials, simple operation, short seedling cycle, and low cost [5]. As discovered by most studies, plant growth

**Citation:** Chen, H.; Lei, Y.; Sun, J.; Ma, M.; Deng, P.; Quan, J.; Bi, H. Effects of Different Growth Hormones on Rooting and Endogenous Hormone Content of Two *Morus alba* L. Cuttings. *Horticulturae* **2023**, *9*, 552. https://doi.org/10.3390/ horticulturae9050552

Academic Editor: Sergio Ruffo Roberto

Received: 13 April 2023 Revised: 28 April 2023 Accepted: 29 April 2023 Published: 4 May 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

hormones can greatly promote the rooting rate of cutting propagation [6–10]. Indole-3 acetic acid (IAA) [9], indole-3-butyric acid (IBA) [11], and indene-naphthaleneacetic acid (ABT-1) [12] (Table 1) are widely employed in the rooting of plant cuttings. Hormone treatment has been found to accelerate the rooting of cuttings of various plants such as *camptotheca acuminata* [13], *Cyclocarya paliurus* [14], *Picea abies* (L.) Karst [15] and *Malus hupehensis* [9]. As exhibited by numerous studies, the dynamic balance of endogenous hormones in cuttings is crucial for the formation of adventitious roots [16], and exogenous plant growth hormones can regulate the balance of endogenous hormones in cuttings [17]. For instance, during critical periods of adventitious root formation in *Sapindus mukorossi* [18], *Picea abies* [19] and *Tamarix taklamakanensis* [20], various endogenous hormones show dynamic change, thus enhancing rooting of cuttings. Nonetheless, there are few studies on the dynamic change of endogenous hormone content in *Morus alba* L. cuttings resulted by growth hormones, and the mechanism of the correlation between *Morus alba* L. cuttings and endogenous hormones is still unclear. Hence, to clarify the inherent mechanism of *Morus alba* L. cuttings rooting, we conduct studies on *Morus alba* L. cuttings and explore the relationship between growth hormones and endogenous hormones in rooting of cuttings.

**Table 1.** Introduction to plant growth hormones.


Note: Indene-naphthaleneacetic acid (ABT-1) is made from a mixture of plant hormones, so the formula is not specified. Indene-naphthaleneacetic acid (ABT-1) contains 50% active ingredients, including α-Naphthalene acetic acid (NAA) 20% and Indole-3-acetic acid (IAA) 30%.

## **2. Materials and Methods**

In this study, a new variety of Australian Mulberry (vegetable Mulberry) introduced from McLaren Vale in 2016 and a new variety of Kirin mulberry (Fruit Mulberry) introduced from China Agricultural University in 2018 were selected as study objects, and rooting responses of vegetable mulberry and fruit mulberry hardwood cuttings to different concentrations of growth hormones and endogenous hormones were explored, thereby screening for high-efficiency cutting schemes for large-scale and rapid propagation of vegetable mulberry and fruit mulberry.
