A method for shortening the growth cycle of lettuce

Abstract

The application provides a method for shortening the growth cycle of lettuce, and belongs to the technical field of lettuce breeding. The method for shortening the growth cycle of lettuce comprises the following steps: after planting the lettuce, high-temperature treatment is performed for 20-22 days, and the conditions of the high-temperature treatment are as follows: 30 DEG C for 4 hours during the day, 40 DEG C for 4 hours during the day, 30 DEG C for 8 hours during the day, and 25 DEG C for 8 hours at night. The application promotes the lettuce to enter the reproductive growth stage in advance through high-temperature stress, can significantly shorten the present budding time and the initial flowering time of the lettuce, and can shorten the present budding time and the initial flowering time of the lettuce and the lettuce by 4-6 weeks, so that the growth cycle of the lettuce is shortened. The method is simple and easy to operate, and can be popularized and planted on a large scale.

Description

Technical Field

[0001] This invention belongs to the field of lettuce breeding technology, and in particular relates to a method for shortening the growth cycle of lettuce. Background Technology

[0002] Lettuce (Lactuca sativa) is an annual or biennial plant belonging to the genus Lactuca in the family Asteraceae. Lettuce is divided into leaf lettuce and stem lettuce. Leaf lettuce, also known as romaine lettuce, includes butter lettuce, curly lettuce, head lettuce, romaine lettuce, Mondial lettuce, and Rosa lettuce, and is primarily consumed for its leaves. Stem lettuce, also known as celtuce, includes celtuce var. sarmentosum and celtuce var. sarmentosum, and is primarily consumed for its tender stems. Lettuce is rich in trace elements, has a crisp and refreshing taste, and is high in dietary fiber, meeting the public's demand for a green diet. Therefore, lettuce is loved by many consumers.

[0003] Lettuce is an obligate self-pollinating species, and traditional hybridization is the most common method in lettuce breeding. Lettuce has a relatively long growth cycle, requiring approximately 180–230 days to propagate one generation, and only one to two seed harvests can be obtained annually. Therefore, it generally takes about five years to develop a genetically stable lettuce variety. Shortening the lettuce growth cycle is of great significance for accelerating the breeding of new varieties and speeding up research in lettuce genetics. Summary of the Invention

[0004] Therefore, the purpose of this invention is to provide a method for shortening the growth cycle of lettuce, which can significantly shorten the budding time and flowering time of lettuce, thereby shortening the growth cycle of lettuce.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for shortening the growth cycle of lettuce, comprising the following steps:

[0007] After transplanting the lettuce, it is subjected to high-temperature treatment for 20 to 22 days. The conditions for high-temperature treatment are 30°C for 4 hours during the day, 40°C for 4 hours during the day, 30°C for 8 hours during the day, and 25°C for 8 hours at night.

[0008] Preferably, the method further includes the following step: after the high-temperature treatment, the lettuce is cultured and grown under light quality conditions of 160 μmol / m³. -2 s -1 Red light, 40 μmol m -2 s -1 Blue light and 40 μmol m -2 s -1 Far-red light.

[0009] Preferably, the photosynthetically active radiation of the cultured canopy is 200 μmol m. -2 s -1 The light period is 16 hours, the day and night temperatures are 25℃ and 20℃ respectively, and the humidity is 60-80%.

[0010] Preferably, the method further includes the following steps: before transplanting, germinating and sowing the lettuce seeds, wherein the sowing and seedling raising method includes covering the surface of the germinated lettuce seeds with a layer of seedling substrate and watering with lettuce-specific nutrient solution.

[0011] Preferably, the culture conditions are 200 μmol / m² photosynthetically active radiation from the canopy. -2 s -1 The white light period lasts for 16 hours, with day and night temperatures of 25°C and 20°C respectively, and humidity of 60-80%.

[0012] Preferably, the lettuce-specific nutrient solution comprises: 4 mM KNO3, 0.8 mM KH2PO4, 0.3 mM K2HPO4, 1.5 mM MgSO4, 3 mM Ca(NO3)2, 0.05 mM ferric sodium ethylenediaminetetraacetate, 60 μM M3BO3, 3 μM ZnSO4, 20 μM MnSO4, 0.4 μM CuSO4, and 0.03 μM (NH4)6Mo7O 24 .

[0013] Preferably, the thickness of the seedling substrate is 1-10 mm; the seedling substrate is a peat substrate.

[0014] Preferably, after transplanting, the plants are irrigated with mineral-derived fulvic acid and the aforementioned lettuce-specific nutrient solution.

[0015] Preferably, the number of times the mineral-derived fulvic acid is applied is 1 to 3 times, and the content of mineral-derived fulvic acid is 25 to 35 mg / plant each time; the number of times the lettuce-specific nutrient solution is applied is 2 to 4 times per week, with an EC value of 1.3 to 1.7 mS / cm each time, and the lettuce-specific nutrient solution is applied until the high-temperature treatment is completed.

[0016] Preferably, the lettuce is cultivated and grown until the budding stage, then irrigated with the above-mentioned lettuce-specific nutrient solution 2-4 times a week, with an EC value of 1.6-2.0 mS / cm each time; when the lettuce enters the budding stage and before flowering, it is irrigated with the above-mentioned lettuce-specific nutrient solution 1-3 times a week, with an EC value of 1.1-1.5 mS / cm each time; during the flowering period, it is irrigated with the above-mentioned lettuce-specific nutrient solution 1-3 times a week, with an EC value of 0.8-1.2 mS / cm each time.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] This invention provides a method for shortening the growth cycle of lettuce. By applying high-temperature stress, this method promotes lettuce to enter the reproductive growth stage earlier, significantly shortening the budding and flowering times. For both lettuce and romaine lettuce, the budding and flowering times are advanced by 4-6 weeks, thus shortening the lettuce growth cycle. This method is simple and easy to implement, and can be widely promoted and cultivated. Attached Figure Description

[0019] Figure 1 The following are examples of growth states of lettuce grown according to the method of the embodiment: A is seed germination; B is seedling raising in plug trays for Sanqing lettuce; C is a growth state diagram of Mondai lettuce (left) and Sanqing lettuce (right) under high temperature treatment; D is a growth state diagram of Mondai lettuce (left) and Sanqing lettuce (right) at the budding stage; E is a growth state diagram of Mondai lettuce (left) and Sanqing lettuce (right) at the flowering stage.

[0020] Figure 2 Schematic diagram of temperature treatment conditions for different groups;

[0021] Figure 3 The results show the effects of different temperature treatments on the budding time and flowering time of lettuce. The horizontal axis of the budding time in the second row has the same group and lettuce variety as the horizontal axis of the flowering time in the second row.

[0022] Figure 4 Spectra of different light quality treatments;

[0023] Figure 5 The results show the effects of different light quality treatments on the budding time and flowering time of lettuce. The horizontal axis of the budding time in the second row has the same group and lettuce variety as the horizontal axis of the flowering time shown in the second row. Detailed Implementation

[0024] This invention provides a method for shortening the growth cycle of lettuce, comprising the following steps:

[0025] After transplanting the lettuce, it is subjected to high-temperature treatment for 20 to 22 days. The conditions for high-temperature treatment are 30°C for 4 hours during the day, 40°C for 4 hours during the day, 30°C for 8 hours during the day, and 25°C for 8 hours at night.

[0026] This invention has found that high-temperature stress can significantly shorten the budding and flowering times of lettuce, thereby shortening the lettuce breeding cycle. The high-temperature treatment is further preferably 20, 21, and 22 days. The lettuce varieties include Mondelez romaine lettuce, Rosa lettuce, Erqing lettuce, and Sanqing lettuce. During the high-temperature treatment stage, after transplanting, the lettuce is irrigated with mineral-derived fulvic acid and the aforementioned lettuce-specific nutrient solution. As a preferred embodiment, the irrigation with mineral-derived fulvic acid is preferably 1 to 3 times, more preferably 2 times, i.e., irrigated on the 2nd and 7th day after transplanting. The content of mineral-derived fulvic acid in each irrigation is preferably 25 to 35 mg / plant, more preferably 28 to 33 mg / plant, and even more preferably 29, 30, and 31 mg / plant. The lettuce-specific nutrient solution is applied 2-4 times per week, preferably 3 times, such as on Mondays, Wednesdays, and Fridays. Each application has an EC value of 1.3-1.7 mS / cm. The application continues until the high-temperature treatment is complete. This invention adds a biostimulant, namely mineral-derived fulvic acid, during the high-temperature treatment stage to enhance the lettuce's resistance, and applies the lettuce-specific nutrient solution throughout the entire growth period to ensure healthy lettuce growth.

[0027] In this invention, the initial flowering time refers to the time when the first flower blooms.

[0028] In this invention, after high-temperature treatment, lettuce is cultured and grown under light conditions of 160 μmol / m³. -2 s -1 Red light, 40 μmol m -2 s -1 Blue light and 40 μmol m -2 s -1 Far-red light. The light quality conditions of this invention can further shorten the budding and flowering time of lettuce, and promote the reproductive growth of lettuce. The photosynthetically active radiation of the cultivated canopy is 200 μmol m. -2 s -1 The light period was 16 hours, the day and night temperatures were 25℃ and 20℃ respectively, and the humidity was 60-80%. This invention promotes lettuce to enter the reproductive growth stage earlier through high-temperature stress, and then returns it to normal temperature during the later stages of growth to ensure seed viability and improve seed germination rate. This invention's research found that improper high-temperature treatment conditions may lead to thin stems, fewer vegetative organs, almost no seed harvest, or a significantly reduced seed germination rate.

[0029] In this invention, before transplanting, lettuce seeds are germinated and sown for seedling cultivation. The sowing and seedling cultivation method includes covering the surface of the germinated lettuce seeds with a layer of seedling substrate and watering with a lettuce-specific nutrient solution. During seedling substrate cultivation, the cultivation conditions are a canopy photosynthetically active radiation of 200 μmol / m³. -2s -1 The light source is white light, with a photoperiod of 16 hours, day and night temperatures of 25°C and 20°C respectively, and humidity of 60-80%. The thickness of the seedling substrate is preferably 1-10 mm, more preferably 1.5-7 mm, and even more preferably 2 mm. The seedling substrate is a peat substrate, such as a peat substrate with a diameter of 1-10 μm. This invention does not have a specific limitation on the source of the seedling substrate; it can be prepared using methods known in the art or a commercially available product. When germinating the seeds, lettuce seeds should be soaked in clean water and left at 4°C for two days. Direct germination results in a germination rate of only about 10%, especially for newly harvested seeds.

[0030] In this invention, the lettuce-specific nutrient solution comprises: 4 mM KNO3, 0.8 mM KH2PO4, 0.3 mM K2HPO4, 1.5 mM MgSO4, 3 mM Ca(NO3)2, 0.05 mM ferric sodium ethylenediaminetetraacetate, 60 μM M3BO3, 3 μM ZnSO4, 20 μM MnSO4, 0.4 μM CuSO4, and 0.03 μM (NH4)6Mo7O 24 The pH of the lettuce-specific nutrient solution is adjusted to 5.6–6.0 with phosphoric acid, such as 5.7, 5.8, or 5.9.

[0031] In this invention, the lettuce is cultivated and grown until the budding stage, then irrigated with the above-mentioned lettuce-specific nutrient solution 2 to 4 times a week (e.g., 3 times), with an EC value of 1.6 to 2.0 mS / cm each time; when the lettuce enters the budding stage and before flowering, it is irrigated with the above-mentioned lettuce-specific nutrient solution 1 to 3 times a week (e.g., 2 times), with an EC value of 1.1 to 1.5 mS / cm each time; during the flowering period, it is irrigated with the above-mentioned lettuce-specific nutrient solution 1 to 3 times a week (e.g., 2 times), with an EC value of 0.8 to 1.2 mS / cm each time.

[0032] This invention involves irrigating lettuce with a special nutrient solution throughout its entire growth period, which effectively ensures the nutritional needs of lettuce and thus promotes its growth.

[0033] In this invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art.

[0034] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0035] In the following examples, Mondai lettuce was purchased from Rijkswyn, Mondai (83-40); Erqing lettuce was purchased from Sichuan Maidehao Agricultural Technology Co., Ltd., Xiangfeng; Sanqing lettuce was purchased from Sichuan Maidehao Agricultural Technology Co., Ltd., Sanqingguan; and Rosa lettuce was purchased from Rijkswyn, Locarno (85-81).

[0036] The lettuce-specific nutrient solution consists of: 4 mM KNO3, 0.8 mM KH2PO4, 0.3 mM K2HPO4, 1.5 mM MgSO4, 3 mM Ca(NO3)2, 0.05 mM ferric sodium ethylenediaminetetraacetate, 60 μM H3BO3, 3 μM ZnSO4, 20 μM MnSO4, 0.4 μM CuSO4, and 0.03 μM (NH4)6Mo7O 24 Adjust the pH to 5.8 using phosphoric acid.

[0037] Example 1

[0038] A method to shorten the growth cycle of lettuce, the steps are as follows:

[0039] (1) Germination: Line a petri dish with a layer of filter paper, and place the seeds of Mondella lettuce, Rosa lettuce, romaine lettuce, and romaine lettuce on the filter paper respectively. Add purified water and germinate in the dark. The romaine lettuce and romaine lettuce seeds are seeds that have been moistened with water and stored at 4°C for two days. The Mondella lettuce and Rosa lettuce seeds do not need to be stored at 4°C and can be germinated directly at room temperature.

[0040] After using the above germination methods, the germination rate of each seed can reach over 95%.

[0041] (2) Sowing and seedling raising: After the germinated seeds show white sprouts, sow one seed in each 50-cell tray. Cover the surface with a seedling substrate of about 0.2 cm (i.e., peat substrate with a diameter of 1-10 μm). Cultivate in an artificial light climate chamber for two weeks. Spray lettuce-specific nutrient solution on the surface of the seedling substrate every three days, adjusting the EC value of the nutrient solution to 1.3 mS / cm each time. The conditions of the artificial light climate chamber are: photosynthetically active radiation of the canopy 200 μmol m -2 s -1 The light period is 16 hours, the day and night temperatures are 25℃ and 20℃ respectively, and the humidity is 60-80%.

[0042] (3) Transplanting and High-Temperature Treatment: Two weeks after sowing, when four true leaves appear in the seedlings of Mondane, Rosa, Erqing, and Sanqing lettuce, and the roots have completely covered the substrate, they can be transplanted. The seedlings are then transplanted into 15cm diameter pots. A suitable transplanting medium (prepared by mixing peat moss substrate with a diameter of 1-10μm, peat moss substrate with a diameter of 10-30μm, and perlite in a volume ratio of 8:8:1) is selected, and the plants are transferred to an incubator for three weeks of high-temperature treatment. The high-temperature treatment conditions are: light period temperature: 30℃ for 4 hours, 40℃ for 4 hours, 30℃ for 8 hours; dark period temperature: 25℃ for 8 hours. On the 2nd and 7th day after transplanting, the plants are irrigated with 30mg / plant of mineral-derived fulvic acid. On the first day after transplanting, irrigate with the lettuce-specific nutrient solution, adjusting the EC value to 1.5 mS / cm each time, three times a week on Mondays, Wednesdays, and Fridays, for three weeks. After three weeks, the internode spacing of the lettuce will lengthen, with the first internode spacing of lettuce reaching 2-4 cm and that of celery reaching 3-4 cm, indicating that the high-temperature treatment is complete.

[0043] (4) Normal growth: The seedlings of Mondelez paniculata, Rosa rosa, romaine lettuce, and romaine lettuce were transferred to the culture room. The culture room conditions were: 200 μmol / m² photosynthetically active radiation (PAR) in the canopy. -2 s -1 The photoperiod lasts 16 hours, with day and night temperatures of 25°C and 20°C respectively, humidity of 60–80%, and light quality of 160 μmol / m². -2 s -1 Red light, 40 μmolm -2 s -1 Blue light and 40 μmol m -2 s -1 Far-red light. Continue to water with lettuce-specific nutrient solution before the budding stage, three times a week on Mondays, Wednesdays, and Fridays, with the EC value adjusted to 1.8 mS / cm each time.

[0044] (5) Daily management: Lettuce, especially romaine lettuce, has short internodes in the early stage, so the lower leaves need to be removed regularly to keep the bottom ventilated and avoid diseases such as downy mildew caused by high temperature and humidity.

[0045] (6) Budding stage: Lettuce enters the budding stage 6-7 weeks after sowing, and lettuce enters the budding stage 11-12 weeks after sowing. Before flowering, irrigate with lettuce-specific nutrient solution twice a week, on Monday and Thursday, and adjust the EC value of the lettuce-specific nutrient solution to 1.3mS / cm each time.

[0046] (7) Initial flowering period: The first flower of Erqing lettuce and Sanqing lettuce will open 9-10 weeks after sowing, marking the beginning of the flowering period. Mondai lettuce and Rosa lettuce will enter the initial flowering period 14-15 weeks after sowing. During this period, irrigate with lettuce-specific nutrient solution twice a week, with the EC value of the lettuce-specific nutrient solution adjusted to 1.0 mS / cm each time.

[0047] (8) Seed collection:

[0048] Seeds of Mondai lettuce, Rosa lettuce, Erqing lettuce, and Sanqing lettuce are collected 30-40 days after flowering. The above-ground parts of the plant with seeds are cut off, placed in an 80-mesh plastic mesh bag, and hung in a cool place to air dry. Once the tissue can be crushed, the seeds, inflorescences, and other impurities are separated using a sieve to obtain mature lettuce seeds.

[0049] (9) Seed vigor test. The procedure is the same as the germination procedure. Use about 100 seeds to conduct a germination test and test the seed vigor.

[0050] Seed germination rate (%) = Number of germinated seeds ÷ Total number of seeds initially added × 100.

[0051] The growth status diagram of lettuce grown using the method in this embodiment is shown below. Figure 1 .

[0052] Experimental Example 1

[0053] The effect of the method in Example 1 of this invention on the growth period of lettuce

[0054] Following the cultivation method of Example 1, Mondai lettuce, Rosa lettuce, Erqing lettuce and Sanqing lettuce were cultivated until the seeds were collected, and the time and seed germination rate at each stage of the breeding process were recorded.

[0055] Control Group 1: Mondelez romaine lettuce, Rosa lettuce, Erqing lettuce, and Sanqing lettuce were cultivated in a greenhouse of the Sichuan Academy of Agricultural Sciences in Jinjiang District, Chengdu. The greenhouse was a regular plastic film greenhouse with no heating in winter. The nutrient solution was a lettuce-specific nutrient solution with an EC value of 1.3 mS / cm. It was irrigated twice a day (once at 9:00 am and once at 5:00 pm) by drip irrigation for 5 minutes each time. The time and seed germination rate at each stage of the breeding process were recorded.

[0056] Control group 2: Mondelez romaine lettuce, Rosa lettuce, romaine lettuce, and romaine lettuce were cultivated in the plant factory of Chengdu Academy of Agricultural and Forestry Sciences in Wenjiang District, Chengdu. Compared with Example 1, the control group did not undergo high-temperature treatment, and the light source was 200 μmol / m². -2 s -1 White light, all other cultivation measures were exactly the same. Record the time and seed germination rate at each stage of the breeding process.

[0057] Table 1. Relevant information regarding the lettuce growth process.

[0058]

[0059]

[0060] As shown in Table 1, compared with the control group, the method of the present invention can shorten the growth cycle of lettuce, shorten the breeding time, and has no effect on the seed germination rate.

[0061] Experimental Example 2

[0062] (1) Effects of different temperature treatments on the budding time and flowering time of lettuce

[0063] The experiment consisted of eight groups: T1, T2, T3, T4, T5, T6, T7, and T8. The high-temperature treatment conditions for each group are detailed below. Figure 2 Specifically, the treatment regimens are as follows: T1: 16 hours at 25°C during the day, 8 hours at 20°C at night, for two weeks. T2: 16 hours at 30°C during the day, 8 hours at 25°C at night, for two weeks. T3: 4 hours at 30°C during the day, 2 hours at 40°C during the day, 10 hours at 30°C during the day, 8 hours at 25°C at night, for two weeks. T4: 4 hours at 30°C during the day, 4 hours at 40°C during the day, 8 hours at 30°C during the day, 8 hours at 25°C at night, for two weeks. T5: 16 hours at 30°C during the day, 8 hours at 30°C at night, for two weeks. T6: 16 hours at 30°C during the day, 8 hours at 25°C at night, for three weeks. T7: 4 hours at 30°C during the day, 2 hours at 40°C during the day, 10 hours at 30°C during the day, 8 hours at 25°C at night, for three weeks. T8: Daytime treatment at 30°C for 4 hours, daytime treatment at 40°C for 4 hours, daytime treatment at 30°C for 8 hours, nighttime treatment at 25°C for 8 hours, for three weeks (T8 is the high-temperature treatment described in Example 1).

[0064] In this experimental example, group T8 grew lettuce according to the method in Example 1. The difference between the lettuce growing methods of groups T1, T2, T3, T4, T5, T6, and T7 and those in Example 1 was that the high-temperature treatment conditions were performed according to the parameters shown in the treatment methods of the above groups, while the remaining steps were the same as in Example 1. The budding time and flowering time of lettuce and romaine lettuce were recorded and statistically analyzed.

[0065] Figure 3The results showed that, compared with groups T1, T2, T3, T4, T5, T6, and T7, group T8, i.e., the high-temperature treatment method of the present invention, could significantly shorten the budding time and flowering time of lettuce. Specifically, compared with group T1, the budding time of Erqing lettuce, Rosa lettuce, Mondai lettuce, and Sanqing lettuce grown in group T8, i.e., the high-temperature treatment method of the present invention, was shortened by 23 days, 16 days, 22 days, and 24 days, respectively, and the flowering time was shortened by 20 days, 26 days, 28 days, and 18 days, respectively.

[0066] (2) Effects of different light qualities on the budding time and flowering time of lettuce

[0067] The experiment consisted of four groups: L1, L2, L3, and L4. L1 used a white LED with a light intensity of 200 μmol m². -2 s -1 L2 is 200 μmol m -2 s -1 White light, 40 μmol m -2 s -1 Far-red light. L3 is 160 μmol m -2 s -1 Red light + 40 μmol m -2 s -1 Blue light. L4 is 160 μmol m -2 s -1 Red light, 40 μmol m -2 s -1 Blue light, 40 μmol m -2 s -1 Far-red light (L4 is the light quality described in Example 1). The spectral diagrams of the light quality treatments for L1, L2, L3, and L4 are shown below. Figure 4 .

[0068] The method in this experimental example differs from that in Example 1 in that the light quality conditions in step (4) are processed according to the parameters shown in groups L1, L2, L3, and L4 above, while the remaining steps are the same as in Example 1. The budding time and flowering time of lettuce and romaine lettuce were recorded and statistically analyzed.

[0069] Figure 5 The results showed that, compared with group L1, adding far-red light to group L2 had little effect on the budding time and the initial flowering time. Compared with group L3, adding far-red light to group L4 could shorten the initial flowering time by 3-6 days and the budding time by 7-9 days. In addition, compared with group L2, group L4 could shorten the budding time and the initial flowering time by 2-5 days and 2-10 days, respectively.

[0070] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for shortening the growth cycle of lettuce, characterized in that, Includes the following steps: After transplanting the lettuce, it is subjected to high-temperature treatment for 20 to 22 days. The conditions for high-temperature treatment are 30°C for 4 hours during the day, 40°C for 4 hours during the day, 30°C for 8 hours during the day, and 25°C for 8 hours at night. The method further includes the following steps: after the high-temperature treatment, the lettuce is cultured and grown under light quality conditions of 160 µmol / m³. -2 s -1 Red light, 40µmol m -2 s -1 Blue light and 40µmol m -2 s -1 Far-red light; The photosynthetically active radiation of the cultivated canopy was 200 µmol / m². -2 s -1 The light period is 16 hours, the day and night temperatures are 25℃ and 20℃ respectively, and the humidity is 60~80%. After transplanting, the plants were irrigated with mineral-derived fulvic acid and lettuce-specific nutrient solution, respectively. The number of times the mineral-derived fulvic acid is applied is 1 to 3 times, and the content of mineral-derived fulvic acid is 25 to 35 mg / plant each time; the number of times the lettuce-specific nutrient solution is applied is 2 to 4 times per week, and the EC value is 1.3 to 1.7 mS / cm each time. The lettuce-specific nutrient solution is applied until the high-temperature treatment is completed. Before the budding stage, cultivate lettuce and water it with lettuce-specific nutrient solution 2-4 times a week, with an EC value of 1.6-2.0 mS / cm each time. After the lettuce enters the budding stage and before flowering, water it with lettuce-specific nutrient solution 1-3 times a week, with an EC value of 1.1-1.5 mS / cm each time. During the flowering period, water it with lettuce-specific nutrient solution 1-3 times a week, with an EC value of 0.8-1.2 mS / cm each time. The lettuce-specific nutrient solution consists of: 4 mM KNO3, 0.8 mM KH2PO4, 0.3 mM K2HPO4, 1.5 mM MgSO4, 3 mM Ca(NO3)2, 0.05 mM ferric sodium ethylenediaminetetraacetate, 60 µM H3BO3, 3 µM ZnSO4, 20 µM MnSO4, 0.4 µM CuSO4, and 0.03 µM (NH4)6Mo7O 24 .

2. The method according to claim 1, characterized in that, The method further includes the following steps: before transplanting, the lettuce seeds are germinated and sown for seedling cultivation. The sowing and seedling cultivation method includes covering the surface of the germinated lettuce seeds with a layer of seedling substrate and watering with lettuce-specific nutrient solution.

3. The method according to claim 2, characterized in that, The cultivation conditions were 200 µmol / m² of photosynthetically active radiation from the canopy. -2 s -1 The white light period lasts for 16 hours, with day and night temperatures of 25°C and 20°C respectively, and humidity of 60-80%.

4. The method according to claim 2, characterized in that, The thickness of the seedling substrate is 1-10 mm; the seedling substrate is a peat substrate.

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