Method for cultivating heterosis litchi resources by using male sterile litchis

Abstract

The invention discloses a method for cultivating heterosis litchi resources by using male sterile litchis, relates to the technical field of fruit tree cultivation and breeding, and aims to solve the problems of unstable flowering phase overlapping degree of domestic litchi varieties and 'Kom', low pollination efficiency, low fruit retention rate and the like. The invention provides a method for cultivating heterosis litchi resources by using male sterile litchis, which comprises the following steps: selecting 'Kom' as a female parent, respectively grafting the 'Kom' and an extremely early male parent 'Sanyuhong' to litchi seedling stocks, unifying the growth environment and synchronizing the flowering phase. Secondly, compound fertilizer is applied and leaflets are removed when the spica is extracted, so that the quality of the spica is optimized, and the pollination efficiency is improved. Then, closed girdling is conducted on the bases of the fruit bearing branches to protect fruits, nutrients are regulated, fruit dropping is reduced, and it is ensured that the fruits grow to be mature. And finally, collecting mature fruits, sowing to obtain F1-generation plants, performing heterosis evaluation, and screening early-maturing and high-quality new varieties.

Description

Technical Field

[0001] The invention relates to the technical field of fruit tree breeding and cultivation, and in particular to a method for cultivating heterotic litchi resources by utilizing male sterile litchi. Background Art

[0002] The discovery and application of male sterile resources is a major breakthrough in improving litchi breeding efficiency. Male sterility refers to the genetic trait in which the female reproductive organs of a plant function normally, while the male reproductive organs lose their fertility. In hybrid breeding, the use of male sterile materials has significant advantages: on the one hand, it can eliminate the tedious manual detasseling operation and simplify the breeding process; on the other hand, by controlling pollination, it can ensure the genetic purity of the offspring germplasm, thus showing important value in utilizing hybrid vigor (heterosis). Hybrid vigor is manifested as hybrid offspring being superior to their parents in terms of fruit quality, early maturity, yield or stress resistance, providing an effective way to cultivate high-quality litchi varieties.

[0003] In recent years, the imported litchi cultivar 'Kom' has demonstrated pollen-free male sterility under domestic cultivation conditions and has been designated litchi male sterile line MS1. This cultivar boasts easy and early flowering and parthenocarpy, making it the only male sterile litchi line reported in the literature and possessing significant research and application potential. However, 'Kom''s extremely early flowering period prevents it from overlapping with the flowering period of most domestic litchi cultivars. Furthermore, its complete male sterility prevents effective fruit set without suitable pollinating species, severely restricting its application in hybrid breeding and research on the genetics of male sterility.

[0004] According to local documentation, the optimal pollinator for 'Kom' is 'Thai,' but this variety has not yet been introduced into China. Years of field observation have revealed that very early-maturing domestic lychee varieties, such as '9918,' '9919,' 'D11,' 'D13,' and 'Sanyuehong,' share similar phenological periods with 'Kom,' with flowering periods partially or completely overlapping. Combined with appropriate cultivation and management measures, such as adjusting planting layouts and optimizing flowering management, these very early-maturing varieties can serve as pollinators for 'Kom, effectively achieving cross-pollination and producing hybrid offspring. This not only opens up opportunities for studying the genetic mechanisms of male sterility in lychees but also lays the foundation for developing early-maturing, high-quality lychee breeding resources with hybrid vigor.

[0005] However, existing litchi hybrid breeding technology still has significant defects when utilizing the male sterility characteristics of 'Kom'. First, precise control of flowering synchronization is difficult. Affected by factors such as climate, soil and cultivation management, the degree of overlap between the flowering periods of domestic early-maturing varieties and 'Kom' is unstable, and the pollination success rate is low. Secondly, pollination efficiency is limited by the distance of insect pollination and the quality of the flower spike. The lack of a systematic planting layout and flowering management plan leads to insufficient hybrid fruit yield. In addition, 'Kom' fruits are prone to physiological fruit drop in the early stages due to nutrient competition or environmental stress. Existing fruit preservation measures (such as conventional fertilization or spraying of growth regulators) have limited effects and it is difficult to stably increase the fruit retention rate. These defects jointly hinder the full application of the male sterility characteristics of 'Kom' in efficient breeding and limit the efficiency of creating hybrid vigor litchi resources. Summary of the Invention

[0006] In response to the above-mentioned problems of unstable overlap in flowering period between domestic extra-early maturing varieties and 'Kom', low pollination efficiency, and low fruit retention rate, the present invention aims to provide a method for cultivating hybrid vigorous litchi resources using male sterile litchi. By integrating a systematic breeding technology of male parent selection, grafting cultivation, flowering period management, fruit preservation treatment and hybrid offspring screening, precise synchronization of flowering period, efficient pollination and significant improvement of fruit retention rate can be achieved, thereby efficiently creating early-maturing, high-quality hybrid vigorous litchi resources.

[0007] The main ideas of the technical solution adopted in the present invention are as follows: First, 'Kom' is selected as the female parent, and it is grafted onto the litchi seedling rootstock separately with the extra early-maturing male parent 'Sanyuehong' to unify the growth environment and synchronize the flowering period. Secondly, compound fertilizer is applied and the leaflets are removed when the flower spike emerges to optimize the quality of the flower spike and improve the pollination efficiency. Then, the fruit is protected by closed ring cutting at the base of the fruit-bearing branches, nutrients are regulated, fruit drop is reduced, and the fruit is ensured to mature. Finally, the mature fruits are collected, sown to obtain the F1 generation plants, and hybrid vigor is evaluated to screen early-maturing, high-quality new varieties. This scheme fully utilizes the male sterility characteristics of 'Kom' through a systematic combination of grafting, fertilization, fruit protection and screening to achieve efficient hybrid breeding.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] A method for cultivating heterotic litchi resources using male sterile litchi comprises:

[0010] 1) Using the male sterile litchi variety 'Kom' as the female parent and an early-maturing litchi variety with the same flowering period as the male parent, the female and male parents were grafted onto rootstocks separately;

[0011] 2) After the grafted mother and father plants have survived and entered the flowering period, apply compound fertilizer when the mother plant's flower spike has grown to 10-15 cm to supplement the nutrients needed for flowering;

[0012] 3) After the mother plant has finished flowering, the fruit-bearing branches are treated to promote fruit development and maturity;

[0013] 4) Collect mature fruits from the female parent, sow seeds, obtain F1 generation plants, and conduct heterosis evaluation after the F1 generation plants bear fruit to screen litchi resources with heterosis.

[0014] Through the above technical solution, further: in step (1), the early-maturing litchi variety is 'Sanyuehong';

[0015] Among them, the flowering period overlap means that under the same cultivation conditions, the flowering period of the male flowers of the male plant overlaps with the flowering period of the female flowers of the female plant for at least 3-5 days.

[0016] Through the above technical solution, further: the male parent 'Sanyuehong' is male fertile and provides fertile pollen for the female parent.

[0017] Through the above technical solution, further: the number of male litchi plants configured in step (1) is not less than 1, and increasing the number of male plants helps to increase the probability of successful pollination during the opening period of the female flowers of the female plant.

[0018] Through the above technical solution, further: the rootstock described in step (1) is a 'Huaizhi' litchi seedling that is more than 5 years old, and the grafting method includes cutting grafting and bark grafting, ensuring that the cambium of the rootstock and scion are aligned and the rootstock and scion are compatible after grafting.

[0019] Through the above technical solution, further: in step (1), the cultivation distance between the grafted rootstocks of the female parent and the male parent is limited to within 50 meters, and during the blooming period of the female flowers of the female parent, it is ensured that no male flowers of other litchi varieties bloom within the range to prevent pollen contamination.

[0020] Through the above technical solution, further: in step (2), when the length of the female parent flower spike reaches 10 cm, apply compound fertilizer with an NPK ratio of 15%-15%-15%, and the amount of fertilizer applied per plant is 2 kg.

[0021] Through the above technical solution, further: after the inflorescence of the male parent or the female parent is extracted in step (2), if there are leaflets on the inflorescence, the leaflets are removed, and fertilizer and water management is strengthened to promote the healthy development of the inflorescence.

[0022] Through the above technical solution, further: in the fruit preservation treatment in step (3), the base of the fruit-bearing branch is closed-ring cut, and the ring cutting depth reaches the xylem to promote fruit retention and development.

[0023] Through the above technical solution, further: the hybrid vigor evaluation in step (3) includes one or more indicators of fruit weight, medium parent value, high parent value, medium parent vigor, medium parent vigor rate, super high parent vigor, and super high parent vigor rate.

[0024] The beneficial effects of the present invention are:

[0025] 1. The present invention selects the very early-maturing litchi variety 'Sanyuehong' with a similar phenological period as the male parent, and grafts it onto the litchi seedling rootstock with the male sterile litchi 'Kom', respectively, thereby significantly increasing the probability of overlapping flowering periods of the male and female parents. The grafting technology unifies the growth environment, and combined with close-range cultivation (within 50 meters), it effectively promotes the efficiency of insect pollination and increases the number of fruits per ear on the fruit-bearing branches of 'Kom'. Compared with traditional breeding methods, the present invention overcomes the problem of the misalignment between the very early flowering period of 'Kom' and the flowering period of domestic varieties, improves the pollination rate, and provides sufficient materials for subsequent hybrid fruit and seed acquisition. This systematic flowering period synchronization scheme not only simplifies the breeding process, but also lays the foundation for studying the genetic laws of male sterility of 'Kom'. It has significant practical value and promotion potential, and is also applicable to the breeding of other male sterile fruit trees;

[0026] 2. The present invention greatly improves the retention rate and development quality of 'Kom' fruits through integrated flowering management and fruit preservation technology. During the flower spike extraction stage, NPK compound fertilizer is applied and the leaflets are wiped off to optimize the nutrient distribution of the flower spike and improve the activity of the female flowers; after the flowers have faded, closed ring cutting is performed at the base of the fruit-bearing branches, with a depth reaching the xylem, to regulate the flow of nutrients and reduce the fruit drop rate. Compared with conventional fruit preservation measures, the present invention improves the retention rate of 'Kom' fruits, makes the fruit development more uniform, and improves the seed quality. This precise fruit preservation strategy effectively solves the problem of easy fruit drop in 'Kom', ensures the high yield and high quality of hybrid offspring seeds, provides reliable protection for the cultivation of F1 generation plants, and significantly improves breeding efficiency;

[0027] 3. This study successfully screened litchi varieties with significant heterosis by evaluating the fruit of F1 plants. The results showed that some F1 plants exhibited fruit size, weight, and yield superior to both the male and female parents, with particularly strong mid-parent and high-parent heterosis indicators, with some exhibiting high-parent heterosis rates exceeding 30%. These new germplasm varieties enrich the litchi variety resource base, providing the market with high-value, original germplasm with broad application prospects and industrial potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The female parent is a pollen-free male sterile litchi 'Kom' plant of the present invention;

[0029] Figure 2 This is a cross-section of the male flower of the pollen-free male sterile litchi 'Kom' of the present invention;

[0030] Figure 3 The male parent is the fertile litchi plant 'Sanyuehong' of the present invention;

[0031] Figure 4 This is a cross-section of a male flower of the male fertile litchi 'Sanyuehong' of the present invention;

[0032] Figure 5 This is a schematic diagram of the planting of male and female plants of the present invention;

[0033] Figure 6 The pollen-free male sterile litchi 'Kom' fruit clusters are matched with male parent pollination trees within the cultivation distance (50m) required by the present invention;

[0034] Figure 7 The pollen-free male sterile litchi 'Kom' fruit clusters are grown within the cultivation distance (50m) required by the present invention without a male parent pollination tree;

[0035] Figure 8 This is a comparison of the appearance of the fruits of the first generation seedlings of 'Kom' F1-6, the female parent 'Kom', and the male parent 'Sanyuehong'. DETAILED DESCRIPTION

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Generally, the components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0037] Example 1

[0038] The present invention discloses a method for cultivating heterotic litchi resources by utilizing male sterile litchi, comprising the following steps:

[0039] Preferably, within 50 meters, use robust 'Huaizhi' litchi seedlings, aged five years or older, as rootstocks, 'Kom' litchi scion, and 'Sanyuehong' litchi scion as male scion. Graft the male and female scions onto the rootstocks, ensuring that the number of male scions is at least one. A greater number of male scions increases the probability of successful pollen reception when the female flowers of the female plant open. Grafting is performed by cut grafting or bark grafting, with the cambium layers aligned and the rootstock and scion compatible after grafting.

[0040] Preferably, about 2 years after the grafting is successful, after the male and female plants have flowered in large quantities, when the female male sterile litchi 'Kom' flower spike is about 10-15 cm tall, about 2 kg of compound fertilizer with an NPK ratio of 15%-15%-15% is applied to each tree.

[0041] Preferably, after the flower spike of the plant emerges, the leaflets on the flower spike (if any) are promptly removed, fertilizer and water management is strengthened, and a strong flower spike is cultivated.

[0042] Preferably, after the female male sterile litchi 'Kom' flower has faded, closed girdling is performed at the base of the fruiting branches, reaching a depth of xylem, to preserve the fruit. After the female fruit matures, the fruit is harvested and seeds are sown to produce F1 generation plants. After the F1 plants have completed their juvenile stage and set fruit, heterosis evaluation is performed on the F1 plants, revealing that the fruit of some plants in this population exhibits significant heterosis.

[0043] As shown in Table 1, after the fruits of the female parent matured, they were collected and counted, yielding an average of 3.75 fruits per ear. After harvest, seeds were sown to produce F1 plants. Hybrid vigor evaluation of some of the fruit-bearing F1 plants revealed significant heterosis compared to both the male and female parent varieties (Table 2).

[0044] Table 1 Statistics of the number of fruits per ear of the female parent 'Kom' under different cultivation and management measures

[0045]

[0046] Table 2 Heterosis indices of fruits of some hybrid offspring lines of 'Kom' and 'Sanyuehong'

[0047]

[0048] As shown in Table 2, some litchi seedling offspring lines hybridized with 'Kom' as the female parent and 'Sanyuehong' as the male parent showed outstanding performance in heterosis indicators. Taking the F1-6 line as an example, its average fruit weight was 28.63g, which was 11.81g heavier than the average weight of the parents, with a weight gain rate of 70.21%. It was 7.12g heavier than the average of the higher value of the parents, with a weight gain rate of 33.1%.

[0049] Example 2

[0050] In the breeding practice of this invention, to verify the importance of synchronized flowering between the early-maturing male and female 'Kom' varieties and close cultivation for pollination efficiency, a set of comparative examples was developed to highlight the superiority of the present invention's technical solution. Unlike the present invention's method of creating heterotic lychee resources using male-sterile lychees, this comparative example does not utilize male varieties with similar phenological periods for close grafting. Instead, the male and female plants are planted at a greater distance to simulate the misaligned flowering periods and low pollination efficiency seen in traditional breeding. The following describes the specific procedures of this comparative example:

[0051] Preferably, a robust 'Huaizhi' litchi seedling, at least five years old, is used as the rootstock, with a 'Kom' scion grafted onto the rootstock. Grafting is done by cut grafting or bark grafting, with the cambium layers aligned and the scion and rootstock in close proximity after grafting. Avoid grafting within 50 meters of the 'Sanyuehong' cultivar, which has a similar flowering period to the 'Kom' cultivar (the parent and parent plants should be approximately 300 meters apart).

[0052] When the female male sterile litchi 'Kom' flower spikes are about 10-15 cm tall, apply about 2 kg of compound fertilizer with an NPK ratio of 15%-15%-15% to each tree.

[0053] Furthermore, after the flower spikes of the 'Kom' plant emerge, the leaflets on the flower spikes (if any) should be promptly removed, and fertilizer and water management should be strengthened to cultivate strong flower spikes.

[0054] Furthermore, after the female male sterile litchi 'Kom' flowered, closed ring cutting was performed at the base of the fruiting branches, reaching the xylem depth, to preserve the fruit. After the female fruit matured, the fruits were collected and statistically analyzed, with an average of only 0.6 fruits per ear (see Table 1).

[0055] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for cultivating heterotic litchi resources using male sterile litchi, characterized in that: include: 1) Using the male sterile litchi variety 'Kom' as the female parent and an early-maturing litchi variety with the same flowering period as the male parent, the female and male parents were grafted onto rootstocks separately; 2) After the grafted mother and father plants have survived and entered the flowering period, apply compound fertilizer when the mother plant's flower spike has grown to 10-15 cm to supplement the nutrients needed for flowering; 3) After the mother plant has finished flowering, the fruit-bearing branches are treated to promote fruit development and maturity; 4) Collect mature fruits from the female parent, sow seeds, obtain F1 generation plants, and conduct heterosis evaluation after the F1 generation plants bear fruit to screen litchi resources with heterosis.

2. The method for cultivating heterotic litchi resources using male sterile litchi according to claim 1, wherein: The early-maturing litchi variety in step (1) is 'Sanyuehong'; Among them, the flowering period overlap means that under the same cultivation conditions, the flowering period of the male flowers of the male plant overlaps with the flowering period of the female flowers of the female plant for at least 3-5 days.

3. The method for cultivating heterotic litchi resources using male sterile litchi according to claim 2, wherein: The male parent 'Sanyuehong' is male fertile and provides fertile pollen for the female parent.

4. The method for cultivating heterotic litchi resources using male sterile litchi according to claim 1, wherein: The number of male litchi plants configured in step (1) is not less than one, and increasing the number of male plants helps to increase the probability of successful pollination during the opening period of the female flowers of the female plant.

5. The method for cultivating heterotic litchi resources by utilizing male sterile litchi according to claim 1, characterized in that: The rootstock described in step (1) is a 'Huaizhi' litchi seedling that is more than 5 years old.

6. The method for cultivating heterotic litchi resources using male sterile litchi according to claim 5, characterized in that: In step (1), the cultivation distance between the grafted rootstocks of the female parent and the male parent is limited to within 50 meters, and during the blooming period of the female flowers of the female parent, it is ensured that no male flowers of other litchi varieties bloom within the cultivation distance of the rootstock to prevent pollen contamination.

7. The method for cultivating heterotic litchi resources using male sterile litchi according to claim 1, wherein: The NPK ratio of the compound fertilizer applied in step (2) is 15%-15%-15%, and the amount of fertilizer applied per plant is 2 kilograms.

8. The method for cultivating heterotic litchi resources using male sterile litchi according to claim 1, wherein: After the inflorescence of the male parent or female parent is extracted in step (2), if there are leaflets on the inflorescence, the leaflets should be removed and fertilizer and water management should be strengthened.

9. The method for cultivating heterotic litchi resources using male sterile litchi according to claim 1, wherein: In the fruit preservation treatment of step (3), the base of the fruit-bearing branch is closed-ring cut, and the ring cutting depth reaches the xylem to promote fruit retention and development.

10. The method for cultivating heterotic litchi resources using male sterile litchi according to claim 1, characterized in that: The heterosis evaluation in step (3) includes one or more indicators of fruit weight, medium parent value, high parent value, medium parent vigor, medium parent vigor rate, super high parent vigor, and super high parent vigor rate.

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