2.2.1. Study of Cuttings

In this study, a randomized complete block design was adopted, and a total of 26 treatment groups were included, with three replicates per group and 50 cuttings per replicate. A total of 3900 cuttings were required. The cuttings were uniform in thickness and length, with a diameter between 0.6–0.8 cm and a length between 12–15 cm. The upper end of the cutting was trimmed flat, and the lower end was cut at a 45◦ angle. In total, 50 cuttings were selected for each group, followed by soaking in an 800-fold dilution of a 50% wettable powder of carbendazim for 1 min at the base and three growth regulators, namely ABT-1 (Abiti Biotechnology Co., Ltd., Beijing, China), IAA, and IBA (Solaibao Technology Co., Ltd., Beijing, China) with 99% purity. Furthermore, 100% alcohol was used for dissolving IAA, IBA, and ABT-1 at 0.2 g, 0.5 g, 1 g and 1.5 g, respectively, and then 1 L of water was employed to dilute them to concentrations of 200, 500, 1000, and 1500 mg·L−<sup>1</sup> [21], respectively, followed by soaking the base of cuttings for 4 h. The specific study design is exhibited in Tables 2 and 3. The cuttings were inserted into the substrate to a depth of approximately 7–8 cm, with a spacing of 10 cm between every two cuttings, and the cuttings were maintained slanted downwards with the buds facing upwards. Successively, the soil was compacted and watered, thereby guaranteeing close contact between the cutting base and the substrate and ensuring adequate water supply. Every 9 days after the cuttings, carbendazim was sprayed with an 800-fold dilution for disinfection, and field water management was needed, aiming at keeping the soil moisture at around 50% and removing weeds manually at proper time.


**Table 2.** Treatment of three plant growth hormones on vegetable mulberry cuttings.

Note: CK1: the vegetable mulberry cuttings control group. A1: the treatment group with 200 mg·L−<sup>1</sup> ABT-1, A2: the treatment group with 500 mg·L−<sup>1</sup> ABT-1, A3: the treatment group with 1000 mg·L−<sup>1</sup> ABT-1, A4: the treatment group with 1500 mg·L−<sup>1</sup> ABT-1, A5: the treatment group with 200 mg·L−<sup>1</sup> IAA, A6: the treatment group with 500 mg·L−<sup>1</sup> IAA, A7: the treatment group with 1000 mg·L−<sup>1</sup> IAA, A8: the treatment group with 1500 mg·L−<sup>1</sup> IAA, A9: the treatment group with 200 mg·L−<sup>1</sup> IBA, A10: the treatment group with 500 mg·L−<sup>1</sup> IBA, A11: the treatment group with 1000 mg·L−<sup>1</sup> IBA, A12: the treatment group with 1500 mg·L−<sup>1</sup> IBA.

#### 2.2.2. Observation and Statistical Analysis of Rooting Morphology

The first sampling was performed on the day after the cuttings, and subsequent samplings were conducted every 9 days. After being randomly sampled from each treatment, 5 cuttings were washed with water, and the bark was peeled off within 2 cm of the base. Afterwards, the samples were stored in a −80 ◦C ultra-low temperature freezer for determining the endogenous hormone content. At the sixth sampling, all cuttings were pulled out, thereby exploring number of rooted cuttings, number of roots per cutting, and root length.

Rooting rate = number of rooted cuttings/total number of cuttings × 100%

Average number of roots = sum of the number of roots/total number of cuttings

Average root length = sum of root length/total number of cuttings

Root system effectiveness index = (rooting rate × average number of roots) × average root length [22].


**Table 3.** Treatment of three plant growth hormones on fruit mulberry cuttings.

Note: CK2: the fruit mulberry cuttings control group. B1: the treatment group with 200 mg·L−<sup>1</sup> ABT-1, B2: the treatment group with 500 mg·L−<sup>1</sup> ABT-1, B3: the treatment group with 1000 mg·L−<sup>1</sup> ABT-1, B4: the treatment group with 1500 mg·L−<sup>1</sup> ABT-1, B5: the treatment group with 200 mg·L−<sup>1</sup> IAA, B6: the treatment group with 500 mg·L−<sup>1</sup> IAA, B7: the treatment group with 1000 mg·L−<sup>1</sup> IAA, B8: the treatment group with 1500 mg·L−<sup>1</sup> IAA, B9: the treatment group with 200 mg·L−<sup>1</sup> IBA, B10: the treatment group with 500 mg·L−<sup>1</sup> IBA, B11: the treatment group with 1000 mg·L−<sup>1</sup> IBA, B12: the treatment group with 1500 mg·L−<sup>1</sup> IBA.
