Breeding method of off-season fast-growing introduced mangrove plant rhizophora mucronata seed sterile seedling

Abstract

The application relates to a breeding method of sterile seedlings of an alien fast-growing introduced mangrove plant, and relates to the technical field of plant breeding. In view of the problems of possible ecological invasion risk of seed breeding and blank of asexual reproduction technology, healthy male plants are selected and labeled according to flower shape difference in the flowering period from May to July; 3-5 year old high-quality male plants are selected, 6-10 cm annual wood branches are cut, 2-3 bud points are reserved, and 1-2 half leaves are reserved on the upper branches; the branches are inserted into the substrate by 1 / 3, the plastic film is sealed to keep the branches moist, and air holes are drilled, and the branches are cultivated to root in the seedling base. The asexual reproduction system of the male plants of the Laganum is established for the first time, the seed diffusion risk is blocked from the source, the seasonal breeding limitation of the mangrove plants is broken through, the seedling breeding can be realized all year round, the difficult site afforestation problem is solved, and the wetland carbon sink forest construction is promoted. The survival rate of the sterile seedlings reaches more than 80%, and the sterile seedlings can be widely applied to coastal wetland ecological restoration engineering.

Description

Technical Field

[0001] This invention relates to the field of plant propagation technology, specifically to a method for propagating sterile seedlings of the introduced fast-growing mangrove plant *Lagerstroemia indica*, which cultivates sterile seedlings through cutting propagation for use in afforestation in difficult wetland sites. Background Technology

[0002] Mangrove wetland ecosystems, as one of the most recognized ecosystem services in the context of climate change, possess enormous potential for carbon storage (blue carbon). Studies have shown that fast-growing plants play a crucial role in increasing carbon sink potential to mitigate the rate of global temperature rise (Pittau F, et al., Retrofit as a carbon sink: The carbon storage potentials of the EU housing stock [J]. Journal of Cleaner Production, 2019, 214: 365-376). Laguncularia racemosa, a fast-growing mangrove belonging to the Combretaceae family, is a cryptophytic mangrove widely distributed in South America, the West Indies, and along the Florida coast. Because Laguncularia racemosa can grow in a wide range of soil types, such as being tolerant of high salinity, poor sandy loam, and heavy metal pollution, it is a pioneer species for afforestation in challenging wetland projects.

[0003] The sexual systems of *Lagerstroemia indica* exhibit diversity among different populations (Nadia TDL, Machado I C. Interpopulation variation in the sexual and pollination systems of two Combretaceae species in Brazilian mangroves [J]. Aquatic Botany, 2014, 114(1): 35-41). *Lagerstroemia indica* in Florida and the Bahamas, USA, has been reported to be dioecious and monoecious, while *Lagerstroemia indica* in Brazil has been reported to be dioecious. However, *Lagerstroemia indica* communities introduced to China are primarily dioecious (Wang Xiuli. Research on the ecological risks and main ecological benefits of the introduced mangrove plant *Lagerstroemia indica* [D]. Doctoral dissertation, Xiamen University, 2018). Dioeciousness refers to the presence of both male and hermaphroditic plants within the same plant population. It is the rarest reproductive system among angiosperms, accounting for an extremely low proportion. Only 10 plant species exhibit stable dioeciousness, including the mangrove plant *Lagerstroemia indica*. The offspring of male *Lagerstroemia indica* plants propagated by cuttings are sterile. In wetland afforestation projects, this can effectively control the ecological niche distribution of *Lagerstroemia indica* communities and address concerns about the natural dispersal of *Lagerstroemia indica* offspring in special habitats.

[0004] To ensure the sustainable utilization of carbon sink resources from the fast-growing mangrove plant *Lagerstroemia indica*, the rapid and efficient cultivation of sterile offspring seedlings as an important seedling resource for wetland ecological engineering afforestation is a critical scientific and technological issue that urgently needs to be addressed. Currently, there are no reports on a propagation technology system for male *Lagerstroemia indica* plants using stem cuttings. Summary of the Invention

[0005] The purpose of this invention is to address the ecological invasion risks that may arise from the natural dispersal of offspring from the seed propagation of the introduced fast-growing mangrove species *Lagerstroemia indica*, and to provide a method for propagating sterile offspring seedlings by cuttings from male branches of the introduced fast-growing mangrove species *Lagerstroemia indica*. This method can block the seed dispersal pathway and maintain its carbon sequestration function, enabling the large-scale planting of sterile offspring seedlings of *Lagerstroemia indica*, and meeting the functional requirements of ecological restoration of difficult wetlands, controlling the natural distribution of communities, and creating high-carbon-sink wetland ecological forests.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] The propagation technology of sterile lines of the introduced fast-growing mangrove plant *Laguania* includes the following steps:

[0008] 1) Selection of tree species and sex of mother trees for cuttings: During the peak flowering period of Laguanmu from May to July each year, healthy male plants are selected and labeled according to the differences in morphology and structure between hermaphroditic and male flowers; this is to quickly obtain the cutting materials needed for the cultivation of Laguanmu male sterile lines and avoid the influence of seasonal factors on the identification of male plants.

[0009] 2) Selection of mother tree age for cuttings: Select male Lagerstroemia indica plants aged 3 to 5 years as mother trees for cuttings; 3 to 5-year-old Lagerstroemia indica trees are not only of flowering age, but also have many branches, which provides an important resource for obtaining male Lagerstroemia indica cuttings.

[0010] 3) Treatment of cuttings: In spring, summer and autumn, select healthy and high-quality current-year lignified branches from the labeled male Laguanmu plants, cut them into 6-10 cm lengths, retain 2-3 buds on each branch, cut the upper end flat and the lower end at an angle, no leaves are retained on the lower current-year branches, and 1-2 leaves are retained on the upper current-year branches.

[0011] 4) Cuttings: Place the seedling tray filled with substrate into the plastic seedling frame, pour water into the seedling frame to moisten the substrate, and then insert the prepared cuttings into the substrate to a depth of 1 / 3 of the length of the cuttings, and compact the substrate around the cuttings.

[0012] 5) Post-cutting management: Seal the seedling frame with plastic film, and drill 8-10 ventilation holes in the sealing film for gas exchange. Place the treated seedling frame in a sunny seedling base for cultivation. After the cuttings sprout and take root, remove the plastic film to complete the propagation of sterile seedlings of the fast-growing introduced mangrove plant, Laguanmu.

[0013] In step 1), the morphological and structural differences between the hermaphroditic and male flowers are as follows: Male plants of *Lagerstroemia indica* produce male flowers, which are light yellow in color. The buds of male flowers are round, and the structure of the ovary is V-shaped. The stigma and style are short and thin, and the anthers surround the short and thin style. The ovules of male flowers are underdeveloped and degenerate, making them plants that only flower but do not bear fruit. In contrast, hermaphroditic plants of *Lagerstroemia indica* produce hermaphroditic flowers, which are green in color. The buds of hermaphroditic flowers are nearly elliptical, and the pistil and stigma are relatively thick and long. The pollen sacs surround the style, and the structure of the ovary is nearly U-shaped. The ovaries of hermaphroditic flowers are fully developed, making them plants that can flower and bear fruit.

[0014] In step 2), the selection of male *Lagerstroemia indica* plants aged 3 to 5 years as mother trees for cuttings includes the following specific conditions: tree height: 2.6 to 4.5 m, crown width: 2.7 to 4.3 m, number of branches: 10 to 16, which can provide abundant current-year branches.

[0015] In step 3), the branch retains 1 to 2 leaves, with each leaf retaining only 1 / 3 to 2 / 3 of its area.

[0016] In step 4), the substrate can be coconut coir, river sand or vermiculite; the water level in the substrate should be level with the top of the substrate. Since mangroves are coastal wetland plants, their branches need to grow under high humidity conditions. Therefore, the water depth in the seedling tray should be level with the top of the substrate.

[0017] In step 5), the diameter of the ventilation hole can be 1-2 mm; the seedling base can be a white plastic film greenhouse or a glass greenhouse; the cultivation conditions can be as follows: First, the seedling trays of the cutting substrate (such as river sand) must be fully soaked in water to ensure that the water level in the seedling frame is level with the substrate level in the seedling tray. This is an important condition to ensure that the mangrove cuttings are soaked in the water environment substrate and that the cuttings retain water; Second, to ensure that the male cuttings of *Lysimachia christinae* can quickly take root and sprout, the ambient temperature of the seedling base should be controlled at 20-30℃, the humidity should be controlled at 80%-90% (increased by covering the seedling frame with film), and the daytime light intensity should be controlled at 1000-3000 Lux in the early stage of cutting.

[0018] This invention addresses the concerns of some professionals in the field of mangrove wetland ecological restoration regarding the natural dispersal of offspring propagated from seeds of *Lagerstroemia indica*, and has the following beneficial effects: (1) Using cuttings from male *Lagerstroemia indica* plants for propagation completely solves the problem of the natural dispersal and distribution of offspring propagated from seeds, which could potentially affect the ecological niche of native mangrove plants in the protected area; (2) Propagation from male *Lagerstroemia indica* plants through cuttings is a form of asexual reproduction, which can be cultivated year-round, avoiding the impact of seasonal factors on mangrove plants. The problem of seedling cultivation; (3) The male plants of Laguanmu belong to the tree category, with a large supply of branches. The offspring sterile line cuttings can meet the large-scale promotion of wetland ecological restoration projects across the country, effectively realize the construction of wetland fast carbon sink forests, and accelerate the realization of my country's "dual carbon" goal; (4) The offspring sterile line seedlings of Laguanmu have a wide adaptability to ecological niches and can be used as pioneer tree species for afforestation in difficult areas, solving the technical problem that native mangrove species in my country cannot adapt to afforestation in difficult areas in the early stage. Attached Figure Description

[0019] Figure 1 These are hermaphroditic and male plants of the fast-growing mangrove plant *Lagerstroemia indica*, which is introduced from abroad and blooms during its peak flowering period from May to July.

[0020] Figure 2 This is a schematic diagram of the structure of hermaphroditic and male flowers under a microscopic environment for *Laguanmata*, a fast-growing mangrove plant introduced from abroad.

[0021] Figure 3This image shows the growth of male *Lagerstroemia indica* plants of different ages, which are fast-growing mangrove species introduced from abroad.

[0022] Figure 4 A schematic diagram illustrating the pretreatment of cuttings from introduced fast-growing mangrove plants.

[0023] Figure 5 Cuttings and water retention measures for the male plants of the fast-growing mangrove species *Lysimachia christinae* introduced from abroad.

[0024] Figure 6 This image shows the sprouting and rooting of male cuttings from *Lagerstroemia indica*, an introduced fast-growing mangrove species. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the following embodiments will be used in conjunction with the accompanying drawings to further illustrate the invention. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Rather, the invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the invention as defined in the claims.

[0026] The embodiments of the present invention include the following steps:

[0027] 1) Selection of tree species and sex for mother trees used for cuttings

[0028] Because the population sex system of *Lagerstroemia indica*, a fast-growing mangrove plant introduced to my country, is dioecious (male and female), it is difficult to visually distinguish between hermaphroditic and male plants in terms of leaf and stem structure. However, there are significant differences in the morphology and structure of their hermaphroditic and male flowers. Specifically: male *Lagerstroemia indica* plants produce male flowers, which are light yellow, with round buds and a V-shaped ovary structure. The stigma and style are short and thin, and the anthers surround the short and thin style. The ovules of male flowers are underdeveloped and degenerate, indicating plants that only flower but do not bear fruit. Hermaphroditic *Lagerstroemia indica* plants produce hermaphroditic flowers, which are green. The buds are nearly elliptical, and the pistil and stigma are relatively thick and long. The pollen sacs surround the style, and the ovary structure is nearly U-shaped. The ovaries of hermaphroditic flowers are fully developed, indicating plants that can flower and bear fruit. The peak flowering period of *Lagerstroemia indica* is from May to July each year. Therefore, this period is crucial for selecting healthy male plants for labeling. By using labels, cuttings needed for the cultivation of male-sterile lines of *Laguanmu* can be obtained quickly, avoiding the influence of seasonal factors on the identification of male plants.

[0029] Figure 1 This document presents schematic diagrams of hermaphroditic and male plants of the introduced fast-growing mangrove species *Lagerstroemia indica* during its peak flowering period from May to July. The left image shows a hermaphroditic plant, and the right image shows a male plant. Figure 1 The overall morphological differences between hermaphroditic and male plants during their peak flowering period are clearly visible, making them easy to distinguish visually. Figure 2This paper presents structural diagrams of the hermaphroditic and male flowers of the introduced fast-growing mangrove plant *Lagerstroemia indica* under a stereomicroscopic environment. A represents the male flower bud; B represents the longitudinal section of the male flower; C represents the style and sterile ovary of the male flower; D represents the hermaphroditic flower bud; E represents the longitudinal section of the hermaphroditic flower; and F represents the style and fully developed ovary of the hermaphroditic flower. Figure 2 The differences in microstructure between hermaphroditic and male flowers, such as the shape of the ovary, the length of the stigma and style, can be observed, which helps to accurately identify the sex of the flower.

[0030] 2) Selection of the age of the mother tree for cuttings

[0031] Long-term field tracking surveys have revealed that *Laguania* exhibits different growth patterns as the forest age increases (e.g., ... Figure 3 As shown in the diagram, young *Lagerstroemia indica* trees primarily acquire resources through lateral growth (numerous branches and low canopy), while older trees mainly utilize resources through longitudinal growth (fewer branches and higher canopy). Therefore, mature *Lagerstroemia indica* trees, due to their tall trunks and few branches, are not conducive to obtaining cuttings. However, 3-5 year old young trees, having reached flowering age and possessing numerous branches, provide abundant resources for obtaining male cuttings.

[0032] The 3- to 5-year-old male *Lagerstroemia indica* plants have a height of 2.6 to 4.5 m, a crown width of 2.7 to 4.3 m, and 10 to 16 branches, providing abundant current-year shoots.

[0033] Male *Lysimachia christinae* plants that are 10 years or older have a height of 8.3–12.4 m, a crown width of 3.5–8.4 m, and 1–4 branches. Due to their large size, the current year's branches are distributed at high and few points, making it difficult to prune them.

[0034] Figure 3 shows the growth of male *Lagerstroemia indica* plants of different ages introduced from abroad. A is a panoramic view of a representative male *Lagerstroemia indica* plant aged 3–5 years; A1 shows the canopy position of a representative male *Lagerstroemia indica* plant aged 3–5 years; A2 is a schematic diagram of the tagging of a male *Lagerstroemia indica* plant; and A3 shows the base of the stem of a representative male *Lagerstroemia indica* plant aged 3–5 years. These plants have a high number of branches, reaching 10–16, indicating that the abundant branching and suitable tree height of 3–5 year old male *Lagerstroemia indica* plants ensure the rapid acquisition of abundant current-year shoots. B is a panoramic view of a male *Lagerstroemia indica* plant over 10 years old. B1 shows the canopy position of a male *Lagerstroemia indica* plant over 10 years old, with a canopy width of 3.5–8.4 m and a high canopy position. B2 shows the base of the stem of a representative male *Lagerstroemia indica* plant over 10 years old, with few branches, only 1–4. It is evident that male *Lagerstroemia indica* plants over 10 years old, due to their excessive height and few branches, cannot provide a large number of current-year shoots. From... Figure 3 It can be seen that the differences in tree height, crown width and number of branches among male *Lagerstroemia indica* plants of different ages provide a basis for selecting mother trees of suitable age for cuttings.

[0035] 3) Treatment of cuttings

[0036] In spring, summer, and autumn, select healthy, high-quality, current-year lignified branches from tagged male *Lagerstroemia indica* plants. Cut these branches into 6-10 cm long sections, retaining 2-3 buds on each branch. Make a flat cut at the top and a slanted cut at the bottom. Lower current-year branches should have no leaves, while upper current-year branches should have 1-2 leaves, with each leaf retaining only 1 / 3 to 2 / 3 of its surface area. The selected male *Lagerstroemia indica* branches, if... Figure 4 As shown in A, the upper half of the branch near the top has green leaves, but the lower half has no leaves (because the leaf arrangement of the branch is mostly 5 to 8 pairs, and the leaves are concentrated at the top of the branch. Old leaves will fall off naturally due to leaf aging. Therefore, the lower half of the branch is also used as a cutting. When cutting the branch, the lower half of the branch will be leafless). Therefore, when cutting the cutting, retain 1 to 2 of the original leaves of the upper half of the branch, while the lower half of the branch will be leafless because it has no leaves.

[0037] Figure 4 This diagram illustrates the pretreatment of cuttings from introduced fast-growing mangrove plants. A represents current-year shoots from male mangrove plants; B represents 6-10 cm cuttings; C shows the bundling of 50 cuttings together; and D represents the pretreatment of the cuttings (including immersing the lower end of the cuttings in water to retain moisture or soaking them in a rooting hormone solution before insertion). Figure 4 It can be seen that the length of the cuttings, the retention of buds, the shape of the cuts at the top and bottom, and the way the leaves are retained are all important details.

[0038] 4) Propagation by cuttings

[0039] Place the seedling tray filled with substrate into the plastic seedling frame, fill the frame with water to moisten the substrate, and then insert the prepared cuttings as described above into the substrate, inserting 1 / 3 of the cutting length into the substrate. Gently compact the substrate around the cutting (e.g., ...). Figure 5 (As shown in the figure); the substrate can be coconut coir, river sand or vermiculite, etc. Since mangrove plants are coastal wetland plants, their branches need to grow under high humidity conditions. Therefore, the water depth in the seedling frame needs to reach the same level as the top of the substrate in the seedling tray.

[0040] Figure 5This paper presents a schematic diagram illustrating the propagation of male *Lagerstroemia indica*, a fast-growing introduced mangrove species, and water retention measures. It demonstrates the process of inserting cuttings into the substrate and the specific operation of sealing the container with white plastic film to maintain humidity. In diagram A, the cuttings are inserted into a seedling tray containing river sand substrate. In diagram B, the water level in the seedling frame is level with the substrate in the tray. The top of the seedling frame is sealed with white plastic film, with 8-10 small holes drilled to facilitate gas exchange. Humidity is increased by covering the seedling frame with the film.

[0041] 5) Post-cutting management

[0042] To ensure that the male cuttings of *Lagerstroemia indica* are cultivated in a high-humidity microenvironment in the early stages, the prepared seedling frames are sealed with white plastic film, and 8-10 small holes are drilled in the sealing film with a toothpick to facilitate gas exchange inside the seedling frames. The prepared seedling frames are then placed in a sunny seedling nursery. Once the cuttings have sprouted and rooted, the plastic film is removed. The seedling nursery can be a white plastic film greenhouse or a glass greenhouse. The cultivation conditions are as follows: First, the seedling trays containing the cutting substrate (such as river sand) must be fully soaked in water, ensuring that the water level in the seedling tray is level with the substrate level. This is to ensure that the mangrove cuttings are immersed in the aquatic substrate. The top of the seedling tray must be sealed with a white plastic film, and 8-10 small holes should be drilled to facilitate gas exchange. These two treatments are important conditions for the cuttings to retain water. Second, to ensure that the male cuttings of *Lysimachia christinae* can quickly take root and sprout, the ambient temperature in the seedling base should be controlled at 20-30℃, the humidity at 80%-90%, and the daytime light intensity at the beginning of the cuttings should be controlled at 1000-3000 Lux.

[0043] Example 1: Propagation method of sterile lines of introduced fast-growing mangrove plant *Laguania*

[0044] In March 2025, at the Xiatanwei Mangrove Wetland in Xiang'an District, Xiamen City, Fujian Province, healthy, high-quality, current-year lignified branches were selected from 3-5 year old (tree height: 2.6 m-4.5 m, crown width: 2.7 m-4.3 m, number of branches: 10-16) male *Lagerstroemia indica* plants that were in full bloom, had confirmed male flower characteristics, and were labeled. These current-year lignified branches were taken back to the laboratory and further divided into 6-10 sections. Cuttings should be taken at 1 cm intervals, retaining 2-3 buds. Leaves on the upper branches should be trimmed to 1 / 3-2 / 3 of their area. The substrate in the seedling tray is river sand. Place the tray in the seedling frame, insert the cuttings, and water the frame until the water level is level with the substrate. Cover the top of the frame with a thin film with 8-10 small holes. Maintain the temperature in the seedling nursery between 20-30℃ and the humidity between 80%-90%. Cover the top of the frame with white plastic film (the plastic film traps transpiration, and the water droplets on the film can return to the substrate). No additional watering is needed during the entire seedling process. In the early stages of propagation, the daytime light intensity in the seedling nursery should be controlled at 1000-3000 Lux. The germination rate of cuttings from the male-sterile line of *Laguanmu* reaches over 80%. Six cuttings with sprouting were randomly selected from each seedling frame (each seedling frame contained 50 cuttings). A total of 18 cuttings were selected from 3 seedling frames. The rooting and sprouting status of these cuttings were recorded (as shown in Table 1). Photos of the sprouting and rooting of the Laguan male-sterile line cuttings are attached. Figure 6 As shown, A represents the sampled cuttings and the total number, while B and C are detailed diagrams of the rooting and sprouting of the sampled cuttings.

[0045] Table 1. Growth Indicators of Sampled Progeny Sterile Lines of the Introduced Fast-Growing Mangrove Plant *Laguania*

[0046]

[0047] Experimental data confirmed the feasibility of this invention in the propagation of sterile lines, providing an efficient propagation solution for mangrove ecological restoration. This invention establishes for the first time a sexual propagation system for male *Lagerstroemia indica* plants, featuring three major innovations: ① blocking the risk of seed dispersal; ② overcoming seasonal limitations for year-round seedling cultivation; ③ solving the problem of afforestation in challenging sites. The survival rate of the cultivated sterile seedlings reached over 85%, making them suitable for coastal wetland ecological restoration projects and promoting the construction of blue carbon ecological forests.

[0048] The above embodiments are merely preferred embodiments of the present invention and should not be considered as limiting the scope of the present invention. All equivalent variations and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for propagating sterile lines of introduced fast-growing mangrove species *Laguania*, characterized in that... Includes the following steps: 1) Selection of tree species and sex of mother trees for cuttings: During the peak flowering period of Laguanmu from May to July each year, healthy male plants are selected and labeled according to the differences in morphology and structure between hermaphroditic and male flowers; this is to quickly obtain the cutting materials needed for the cultivation of Laguanmu male sterile lines and avoid the influence of seasonal factors on the identification of male plants. 2) Selection of mother tree age for cuttings: Select male Lagerstroemia indica plants aged 3 to 5 years as mother trees for cuttings; 3 to 5-year-old Lagerstroemia indica trees are not only of flowering age, but also have many branches, which provides an important resource for obtaining male Lagerstroemia indica cuttings. 3) Treatment of cuttings: In spring, summer and autumn, select healthy and high-quality current-year lignified branches from the labeled male Laguanmu plants, cut them into 6-10 cm lengths, retain 2-3 buds on each branch, cut the upper end flat and the lower end at an angle, the lower half of the current-year branch has no leaves, and the upper half of the current-year branch retains 1-2 leaves; 4) Cuttings: Place the seedling tray filled with substrate into the plastic seedling frame, fill the seedling frame with water to moisten the substrate, and then insert the prepared cuttings into the substrate to a depth of 1 / 3 of the cutting length, and compact the substrate around the cuttings; the water level in the seedling frame should be level with the top of the substrate when moistening the substrate. 5) Post-cutting management: Seal the seedling frame with plastic film, and drill 8-10 ventilation holes in the sealing film for gas exchange. Place the treated seedling frame in a sunny seedling base for cultivation. After the cuttings sprout and root, remove the plastic film to complete the propagation of sterile seedlings of the fast-growing introduced mangrove plant, Laguanmu. The cultivation conditions are as follows: the ambient temperature of the seedling base is controlled at 20-30℃, the humidity is controlled at 80%-90%, and the daytime light intensity is controlled at 1000-3000 Lux.

2. The method for propagating sterile lines of introduced fast-growing mangrove species *Lagerstroemia indica* as described in claim 1, characterized in that... In step 1), the morphological and structural differences between the hermaphroditic and male flowers are as follows: Male plants of *Lagerstroemia indica* produce male flowers, which are light yellow in color. The buds of male flowers are round, and the structure of the ovary is V-shaped. The stigma and style are short and thin, and the anthers surround the short and thin style. The ovules of male flowers are underdeveloped and degenerate, making them plants that only flower but do not bear fruit. In contrast, hermaphroditic plants of *Lagerstroemia indica* produce hermaphroditic flowers, which are green in color. The buds of hermaphroditic flowers are nearly elliptical, and the pistil and stigma are relatively thick and long. The pollen sacs surround the style, and the structure of the ovary is nearly U-shaped. The ovaries of hermaphroditic flowers are fully developed, making them plants that can flower and bear fruit.

3. The method for propagating sterile lines of introduced fast-growing mangrove species *Lagerstroemia indica* as described in claim 1, characterized in that... In step 2), the selection of male *Lagerstroemia indica* plants aged 3 to 5 years as mother trees for cuttings includes the following specific conditions: tree height: 2.6 to 4.5 m, crown width: 2.7 to 4.3 m, number of branches: 10 to 16, which can provide abundant current-year branches.

4. The method for propagating sterile lines of introduced fast-growing mangrove species *Lagerstroemia indica* as described in claim 1, characterized in that... In step 3), the upper half of the current year's shoot retains 1 to 2 leaves, and the leaves retain only 1 / 3 to 2 / 3 of their area.

5. The method for propagating sterile lines of introduced fast-growing mangrove species *Lagerstroemia indica* as described in claim 1, characterized in that... In step 4), the substrate is coconut coir, river sand or vermiculite.

6. The method for propagating sterile lines of introduced fast-growing mangrove species *Lagerstroemia indica* as described in claim 1, characterized in that... In step 5), the diameter of the vent hole is 1 to 2 mm.

7. The method for propagating sterile lines of introduced fast-growing mangrove species *Lagerstroemia indica* as described in claim 1, characterized in that... In step 5), the seedling base is selected as a white plastic film greenhouse or a glass greenhouse.

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