Application method for using lanthanum as a passion fruit cadmium reducing agent and improving fruit quality

Abstract

The application discloses a method for applying lanthanum as a passion fruit cadmium reduction agent and improving fruit quality, which comprises the following steps: during the young fruit period to the mature period of the passion fruit, a compound regulation agent prepared from La(NO3)3 and water is sprayed on the leaves; the concentration of La(NO3)3 in the compound regulation agent is 40-53.3 mg / L in terms of La; the spraying is performed three times, and the first spraying is preferably performed during the young fruit formation period, the second spraying is performed during the initial swelling period, and the third spraying is performed during the early fruit filling period. Through scientific spraying of the lanthanum nitrate in the Cd-polluted soil, the passion fruit can be stably grown, the Cd accumulation amount of the fruit and the plant can be significantly reduced, the sugar and acid constitution, the vitamin C content and the antioxidant enzyme activity of the fruit can be improved, and the fruit quality and the stress resistance can be ensured.

Description

Technical Field

[0001] This invention relates to the fields of agricultural biotechnology and safe production of agricultural products, and in particular to a method for applying the rare earth element lanthanum (La) through foliar spraying to reduce cadmium (Cd) accumulation in passion fruit, enhance the antioxidant activity of the fruit, and improve the nutritional and flavor quality of the fruit. Background Technology

[0002] In recent years, soil heavy metal pollution has received increasing attention, with carbon monoxide (Cd) pollution posing a significant threat to agricultural product safety due to its high mobility and biotoxicity. Passion fruit, a popular tropical fruit, may face Cd contamination risks when grown in industrial and mining areas. Cd can be absorbed by the passion fruit plant through its roots and transported to the fruit; long-term consumption of agricultural products with excessive Cd levels can harm human health. Therefore, reducing the Cd content in passion fruit is crucial to ensuring its safety for consumption. However, passion fruit growth and development are easily affected by changes in environmental factors, which can reduce yield and fruit quality. Addressing this issue by adopting a rapid and effective integrated pest management (IPM) technology to reduce the Cd content in passion fruit juice, ensuring safe fruit production in my country and globally, is key to alleviating the current conflict between population and arable land resources, and has significant practical implications for safeguarding the fruit industry.

[0003] Lanthanum (La), a rare earth element, exhibits a "low-promoting, high-inhibiting" effect on plant growth and enhances plant resistance to biotic and abiotic stresses. La can regulate cell membrane permeability and influence enzyme activity, thereby inhibiting the absorption and translocation of cadmium (Cd). In existing technologies, La is primarily used to promote seed germination, increase crop yield, or alleviate aluminum toxicity. However, a systematic approach has not yet been publicly reported to achieve multiple objectives simultaneously, such as reducing Cd accumulation, enhancing antioxidant capacity, and optimizing sugar-acid composition and vitamin C content, through precise intervention via foliar spraying of specific forms of La during passion fruit fruit development. Summary of the Invention

[0004] The purpose of this invention is to creatively apply La (in the form of lanthanum nitrate (La(NO3)3)) through a specific foliar spraying scheme, providing a new use and specific application method for La in reducing Cd accumulation in passion fruit and improving fruit quality. This method, through the scientific application of La(NO3)3 spraying scheme in Cd-contaminated soil, can achieve stable growth of passion fruit, significantly reduce Cd accumulation in fruit and plant, and at the same time improve the sugar and acid composition, vitamin C content and antioxidant enzyme activity of fruit, thus ensuring fruit quality and stress resistance.

[0005] The technical solution adopted in this invention is as follows:

[0006] A method for using La as a Cd-reducing agent and improving fruit quality in passion fruit involves applying a compound regulator made of La(NO3)3 and water by foliar spraying during the young fruit stage to the ripening stage of passion fruit.

[0007] In the aforementioned composite regulator, the concentration of La(NO3)3, calculated as La, is 40-53.3 mg / L;

[0008] The foliar spraying is performed three times, with the first spraying preferably occurring during the young fruit formation period, the second during the early stage of fruit enlargement, and the third during the early stage of fruit filling.

[0009] The method of foliar spraying of La is as follows: first, dissolve La(NO3)3 in an appropriate amount of water to prepare a La aqueous solution for foliar spraying, and then spray the La aqueous solution onto the passion fruit leaves with a sprayer on a cloudy day.

[0010] When spraying La on the leaves, it is necessary to ensure that the droplets are evenly attached to both sides of the leaves, so that the leaves are moist but not dripping. The spraying time should be chosen on cloudy days or in the evening to avoid high temperature evaporation and photosynthesis.

[0011] To cultivate passion fruit using the above method, select a plot of land with a soil pH of 5.5-6.5, an organic matter content of ≥2%, and good drainage as the planting base. The soil Cd content in this plot should be 0.3-0.8 mg / kg. Deeply till the soil to a depth of 30-40 cm and evenly apply the Cd source to the soil to stabilize the soil Cd content at 0.6-0.8 mg / kg. Apply base fertilizer at a rate of 2000-3000 kg / mu, which is a mixture of well-rotted farmyard manure and compound fertilizer in a mass ratio of 3:1. After application, thoroughly mix the soil with the base fertilizer and Cd source. Then, dig planting pits with a row spacing of 2.5-3 m and a plant spacing of 1.5-2 m, with a pit diameter of 50-60 cm and a pit depth of 40-50 cm. Apply 5-10 kg of well-rotted organic fertilizer to each pit and mix it evenly with the soil in the pit before use.

[0012] Select healthy passion fruit seedlings that are free from pests and diseases and are 25-30cm tall. Plant them in the prepared planting pits, water them thoroughly after planting, and cover them with mulch to retain moisture.

[0013] When the passion fruit seedlings grow to the young fruit stage, spray the passion fruit leaves with 40-53.3 mg / L La for the first time; when the passion fruit grows from the young fruit stage to the swelling stage, spray the passion fruit leaves with 40-53.3 mg / L La for the second time; in the early stage of the filling stage, spray the passion fruit leaves with 40-53.3 mg / L La for the third time; after the passion fruit matures, harvest the passion fruit.

[0014] The foliar spraying rate of La is 800 mg / mu. The 800 mg of La refers to the amount of La element in La(NO3)3, not the amount of La(NO3)3.

[0015] After transplanting, water, weed, prune, and control pests and diseases regularly. Water according to the principle of "watering when dry" to avoid waterlogging, which can increase Cd activity. When the seedlings grow to 40-50cm, build a support to guide the vines to climb. When pruning, retain the main vine and remove overly dense lateral vines, diseased or weak vines, and ineffective branches.

[0016] Biological pesticides should be given priority in pest and disease control to avoid the synergistic harm caused by chemical pesticides and Cd.

[0017] This invention utilizes a pot experiment on passion fruit throughout its entire growth period. A low dose of cadmium (Cd) was applied to the existing soil, and further, foliar spraying of laitrate (La) was used to control Cd transport. After being absorbed into the passion fruit plant through the leaves, La produced several physiological effects: First, La inhibited Cd transport: La upregulated cell wall synthesis within the plant, fixing more Cd in the roots, stems, and leaves, significantly hindering the long-distance transport of Cd to the reproductive organs—the fruit. Second, it provided antioxidant protection: La activated the antioxidant enzyme system (such as SOD, POD, and PPO) in passion fruit leaves and fruit, reducing oxidative damage caused by Cd stress and maintaining normal physiological functions of fruit cells, thereby indirectly ensuring fruit quality and reducing Cd activity. Finally, it effectively improved the quality and taste of the juice: With La spraying, the foliar-absorbed La was more efficiently transported and accumulated in the fruit, increasing the sugar content, reducing acidity, and increasing vitamin C content of the juice.

[0018] Passion fruit produced using the above method showed that the application of La reduced the Cd content in the fruit by 40%-70% compared to the untreated control group, which is significantly lower than the national food safety limit standard (GB 2762-2022).

[0019] The beneficial effects of this invention are:

[0020] 1. Foliar application of La may significantly reduce the Cd content in mature fruit by retaining Cd in the leaves and reducing the transport of Cd to the fruit.

[0021] 2. Exogenous La can activate the antioxidant enzyme system of passion fruit, significantly increase the activity of superoxide dismutase (SOD), peroxidase (POD) and polyphenol oxidase (PPO), and improve the total antioxidant capacity of the fruit, effectively alleviate oxidative damage, and help maintain the freshness and nutritional value of the fruit after harvest.

[0022] 3. Significantly increases the content of vitamin C (ascorbic acid) in the fruit; promotes the accumulation of soluble sugars (total sugars) and regulates the metabolism of organic acids (mainly titratable acids), so that the content of titratable acids tends to be optimal, thereby significantly increasing the sugar-acid ratio and improving the sweetness and flavor harmony of the fruit.

[0023] 4. This invention employs foliar spraying, which is highly targeted and avoids direct interaction with the soil, thus reducing the environmental exposure of rare earth elements. Using La(NO3)3 as the La source, it exhibits good water solubility, making it easy to prepare and absorb. This method is simple to operate, low in cost, and easy to promote in large-scale planting, providing an effective technical means for achieving safe and high-quality passion fruit production. Attached Figure Description

[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0025] Figure 1 This invention investigates the effect of La spraying on the Cd content in passion fruit juice under Cd stress.

[0026] Figure 2 This is a graph showing the soluble sugar content of passion fruit juice after spraying with La under Cd stress, according to the present invention.

[0027] Figure 3 This is a graph showing the titratable acidity content of passion fruit juice after spraying with La under Cd stress, according to the present invention.

[0028] Figure 4 This is a graph showing the vitamin C content of passion fruit juice after spraying with La under Cd stress, according to the present invention.

[0029] Figure 5 This is a graph showing the superoxide dismutase content in passion fruit juice after spraying with La under Cd stress, according to the present invention.

[0030] Figure 6 This is a graph showing the peroxidase content in passion fruit juice after spraying with La under Cd stress, according to the present invention.

[0031] Figure 7 This is a graph showing the polyphenol oxidase content in passion fruit juice after spraying with La under Cd stress, according to the present invention.

[0032] In the figure, Cd represents Cd treatment alone; Cd + La represents the addition of La treatment under Cd stress. Detailed Implementation

[0033] The applicant will further illustrate the method of the present invention below with reference to specific embodiments. It should be understood that the following embodiments are only used to clearly illustrate the technical solution for which protection is claimed in the present invention, and should not be construed as limiting the scope of protection of the present invention. The present invention will be further described below with reference to the appendix and embodiments.

[0034] The passion fruit variety used in the following examples is "Qinmi No. 9", and the seeds were provided by the passion fruit base in Wangmo County, Guizhou Province.

[0035] Example 1: Effect of foliar spraying of La on Cd content in passion fruit juice under Cd stress

[0036] This embodiment provides a method for reducing Cd content in passion fruit leaves by foliar spraying with La. When the passion fruit reaches the young fruit stage, La is sprayed on the leaves to inhibit the translocation of Cd from the leaves to the passion fruit, thereby reducing the Cd content in the fruit.

[0037] At this experimental site, Cd-contaminated soil was prepared by adding Cd exogenously, and this Cd-contaminated soil was used as the test soil for passion fruit cultivation. Each experiment was repeated in triplicate.

[0038] Specific experimental steps:

[0039] (1) Take a portion (about 1000 kg of soil) from the greenhouse of the passion fruit experimental base as the test soil. The soil of the base has a pH value of 5.5-6.5, an organic matter content of 2.2%, and good drainage. The natural Cd content of the soil in this plot is 0.3 mg / kg. The soil is deeply plowed to a depth of 30 cm, and cadmium chloride is evenly applied to the soil to stabilize the soil Cd content at 0.6 mg / kg.

[0040] (2) Apply base fertilizer to the soil obtained in (1). The amount of base fertilizer is 1000 kg / mu. The base fertilizer is made by mixing well-rotted farmyard manure and compound fertilizer in a mass ratio of 3:1. After application, mix the soil with the base fertilizer and cadmium chloride thoroughly and let it stand for 7 days. Then dig planting pits with a row spacing of 2.5m and a plant spacing of 1.5m. The pit diameter is 50cm and the pit depth is 40cm. Apply 5kg of well-rotted organic fertilizer to each pit and mix it evenly with the soil in the pit for later use.

[0041] (3) Put 50 kg of soil obtained in (2) into a plastic pot, select healthy passion fruit seedlings that are free from pests and diseases and have a plant height of 25 cm, and plant them in the planting pit prepared in step (2). After planting, water thoroughly and cover with mulch to keep the soil moist.

[0042] (4) The samples obtained in (3) were cultivated in open greenhouse according to the conventional cultivation method of passion fruit. The first spraying was carried out when the passion fruit seedlings grew to the young fruit stage, and the passion fruit was sprayed with 53.3 mg / L La on the leaves. The second spraying was carried out when the passion fruit grew from the young fruit stage to the swelling stage, and the passion fruit was sprayed with 40 mg / L La on the leaves. The last spraying was carried out when the passion fruit was in the early stage of filling, and 40 mg / L La was sprayed on the leaves.

[0043] (5) After the passion fruit matures, harvest the passion fruit, wash the fruit sample with tap water, remove the seeds, separate the juice, place it in an oven, and dry it at 65°C until constant weight.

[0044] (6) Place the juice sample obtained in (5) into a beaker and add an appropriate amount of mixed digestion solution (nitric acid to perchloric acid volume ratio = 4:1) into the beaker and let it stand overnight.

[0045] (7) The sample obtained in (6) was placed on a hot plate for heating and digestion. After the volume was adjusted, the Cd content in the sample solution was determined by ICP-MS.

[0046] In this embodiment, passion fruit is foliar sprayed with La, as shown in the attached image. Figure 1 Compared with Cd treatment alone, the addition of La reduced the Cd content in the juice by 57.1%.

[0047] Example 2: Graph showing the soluble sugar content of passion fruit juice after spraying with La under Cd stress.

[0048] This example provides a method for inhibiting Cd transport and increasing the soluble sugar content of passion fruit juice by foliar spraying with La under Cd stress.

[0049] At this experimental site, Cd-contaminated soil was prepared by adding Cd exogenously, and this Cd-contaminated soil was used as the test soil for passion fruit cultivation. Each experiment was repeated in triplicate.

[0050] Specific experimental steps:

[0051] (1) Take a portion (about 1000 kg of soil) from the greenhouse of the passion fruit experimental base as the test soil. The soil of the base has a pH value of 5.5-6.5, an organic matter content of 2.2%, and good drainage. The natural Cd content of the soil in this plot is 0.3 mg / kg. The soil is deeply tilled to a depth of 30 cm, and cadmium chloride is evenly applied to the soil to stabilize the soil Cd content at 0.6 mg / kg.

[0052] (2) Apply base fertilizer to the soil obtained in (1). The amount of base fertilizer is 1000 kg / mu. The base fertilizer is made by mixing well-rotted farmyard manure and compound fertilizer in a mass ratio of 3:1. After application, mix the soil with the base fertilizer and cadmium chloride thoroughly and let it stand for 7 days. Then dig planting pits with a row spacing of 2.5m and a plant spacing of 1.5m. The pit diameter is 50cm and the pit depth is 40cm. Apply 5kg of well-rotted organic fertilizer to each pit and mix it evenly with the soil in the pit for later use.

[0053] (3) Put 50 kg of soil obtained in (2) into a plastic pot, select healthy passion fruit seedlings that are free from pests and diseases and have a plant height of 25 cm, and plant them in the planting pit prepared in step (2). After planting, water thoroughly and cover with mulch to keep the soil moist.

[0054] (4) The samples obtained in (3) were cultivated in open greenhouse according to the conventional cultivation method of passion fruit. The first spraying was carried out when the passion fruit seedlings grew to the young fruit stage, and the passion fruit was sprayed with 53.3 mg / L La on the leaves. The second spraying was carried out when the passion fruit grew from the young fruit stage to the swelling stage, and the passion fruit was sprayed with 40 mg / L La on the leaves. The last spraying was carried out when the passion fruit was in the early stage of filling, and 40 mg / L La was sprayed on the leaves.

[0055] (5) After the passion fruit is ripe, harvest the passion fruit, wash the fruit sample with tap water, remove the seeds from the passion fruit, and extract the juice into a beaker.

[0056] (6) Centrifuge the juice obtained in (5), and take 0.1 mL of the juice sample diluted 1000 times after centrifugation; weigh 0.1 g of anthrone, dissolve it in 80% sulfuric acid (slowly pour 80 mL of concentrated sulfuric acid into 20 mL of distilled water, cool it before use) and make up to 100 mL, and use it immediately; further weigh 100 mg of glucose dried to constant weight, dissolve it in distilled water and make up to 100 mL to obtain a 1 mg / mL stock solution; dilute it to a working solution of 0.1 mg / mL before use.

[0057] (7) Place the sample prepared in (6) into a stoppered test tube, and take 0.1 mL of the sample solution diluted 1000 times into each tube. Add distilled water to each tube to 1 mL (to ensure that the sample and standard solution volumes are consistent). Then, quickly add 4 mL of anthrone reagent to each test tube (add slowly along the tube wall to avoid splashing concentrated sulfuric acid). Shake gently and then place the tube in a 100°C constant temperature water bath and boil for 10 minutes. After that, remove the test tube and immediately place it in ice water to cool for 5 minutes (to terminate the reaction and prevent the blue-green complex from fading). After returning to room temperature, measure the absorbance of each concentration using a UV spectrophotometer at a wavelength of 620 nm.

[0058] (8) Substitute the absorbance A obtained in (7) into the regression equation to calculate the soluble sugar concentration in the sample solution to be tested (denoted as C, μg / mL), and then calculate the soluble sugar content in passion fruit juice (unit g / 100mL) according to the formula.

[0059] In this embodiment, passion fruit is foliar sprayed with La, as shown in the attached image. Figure 2 Compared with Cd treatment alone, the addition of La increased the soluble sugar content of the juice by 60.6%.

[0060] Example 3: Titrizable acidity content of passion fruit juice after spraying with La under Cd stress.

[0061] This example provides a method for inhibiting Cd transport and reducing juice acidity by foliar spraying with La under Cd stress.

[0062] At this experimental site, Cd-contaminated soil was prepared by adding Cd exogenously, and this Cd-contaminated soil was used as the test soil for passion fruit cultivation. Each experiment was repeated in triplicate.

[0063] Specific experimental steps:

[0064] (1) Take a portion (about 1000 kg of soil) from the greenhouse of the passion fruit experimental base as the test soil. The soil of the base has a pH value of 5.5-6.5, an organic matter content of 2.2%, and good drainage. The natural Cd content of the soil in this plot is 0.3 mg / kg. The soil is deeply tilled to a depth of 30 cm, and cadmium chloride is evenly applied to the soil to stabilize the soil Cd content at 0.6 mg / kg.

[0065] (2) Apply base fertilizer to the soil obtained in (1). The amount of base fertilizer is 1000 kg / mu. The base fertilizer is made by mixing well-rotted farmyard manure and compound fertilizer in a mass ratio of 3:1. After application, mix the soil with the base fertilizer and cadmium chloride thoroughly and let it stand for 7 days. Then dig planting pits with a row spacing of 2.5m and a plant spacing of 1.5m. The pit diameter is 50cm and the pit depth is 40cm. Apply 5kg of well-rotted organic fertilizer to each pit and mix it evenly with the soil in the pit for later use.

[0066] (3) Put 50 kg of soil obtained in (2) into a plastic pot, select healthy passion fruit seedlings that are free from pests and diseases and have a plant height of 25 cm, and plant them in the planting pit prepared in step (2). After planting, water thoroughly and cover with mulch to keep the soil moist.

[0067] (4) The samples obtained in (3) were cultivated in open greenhouse according to the conventional cultivation method of passion fruit. The first spraying was carried out when the passion fruit seedlings grew to the young fruit stage, and the passion fruit was sprayed with 53.3 mg / L La on the leaves. The second spraying was carried out when the passion fruit grew from the young fruit stage to the swelling stage, and the passion fruit was sprayed with 40 mg / L La on the leaves. The last spraying was carried out when the passion fruit was in the early stage of filling, and 40 mg / L La was sprayed on the leaves.

[0068] (5) After the passion fruit is ripe, harvest the passion fruit, wash the fruit sample with tap water, remove the seeds from the passion fruit, and extract the juice into a beaker.

[0069] (6) Centrifuge the juice obtained in (5), and take 10 mL of the juice sample diluted 10 times after centrifugation; weigh 2 g NaOH, dissolve it in distilled water and make up to 500 mL; further weigh 1 g phenolphthalein, dissolve it in 95% ethanol, add 60 mL of ethanol and 40 mL of water to make up to 100 mL; finally, prepare a 25 mL alkaline burette.

[0070] (7) Place the sample prepared in (6) in an Erlenmeyer flask, add 1 drop of 1% phenolphthalein indicator, and titrate with calibrated NaOH solution until the solution turns red within 30 seconds. Calculate the titratable acid content in the sample juice based on the volume of NaOH solution consumed. Before measurement, allow the juice sample to equilibrate at room temperature for 30 minutes. Perform three biological replicates for each treatment.

[0071] (8) When the organic acids in the juice in (7) are completely neutralized, the pH of the solution reaches 8.2 (the color change point of the phenolphthalein indicator). At this point, the indicator changes from colorless to light pink (and does not fade for 30 seconds), which is the titration endpoint. The titrable acidity can be calculated by combining the volume of NaOH consumed with its concentration and the molar mass of the organic acid.

[0072] In this embodiment, passion fruit is foliar sprayed with La, as shown in the attached image. Figure 3 Compared with Cd treatment alone, the titratable acidity of the juice decreased by 31.1% after the addition of La treatment.

[0073] Example 4: Vitamin C content in passion fruit juice after spraying with La under Cd stress (Figure)

[0074] This example provides a method for inhibiting Cd transport in passion fruit juice and increasing the vitamin C content in the juice by foliar spraying with La under Cd stress.

[0075] At this experimental site, Cd-contaminated soil was prepared by adding Cd exogenously, and this Cd-contaminated soil was used as the test soil for passion fruit cultivation. Each experiment was repeated in triplicate.

[0076] Specific experimental steps:

[0077] (1) Take a portion (about 1000 kg of soil) from the greenhouse of the passion fruit experimental base as the test soil. The soil of the base has a pH value of 5.5-6.5, an organic matter content of 2.2%, and good drainage. The natural Cd content of the soil in this plot is 0.3 mg / kg. The soil is deeply tilled to a depth of 30 cm, and cadmium chloride is evenly applied to the soil to stabilize the soil Cd content at 0.6 mg / kg.

[0078] (2) Apply base fertilizer to the soil obtained in (1). The amount of base fertilizer is 1000 kg / mu. The base fertilizer is made by mixing well-rotted farmyard manure and compound fertilizer in a mass ratio of 3:1. After application, mix the soil with the base fertilizer and cadmium chloride thoroughly and let it stand for 7 days. Then dig planting pits with a row spacing of 2.5m and a plant spacing of 1.5m. The pit diameter is 50cm and the pit depth is 40cm. Apply 5kg of well-rotted organic fertilizer to each pit and mix it evenly with the soil in the pit for later use.

[0079] (3) Put 50 kg of soil obtained in (2) into a plastic pot, select healthy passion fruit seedlings that are free from pests and diseases and have a plant height of 25 cm, and plant them in the planting pit prepared in step (2). After planting, water thoroughly and cover with mulch to keep the soil moist.

[0080] (4) The samples obtained in (3) were cultivated in open greenhouse according to the conventional cultivation method of passion fruit. The first spraying was carried out when the passion fruit seedlings grew to the young fruit stage, and the passion fruit was sprayed with 53.3 mg / L La on the leaves. The second spraying was carried out when the passion fruit grew from the young fruit stage to the swelling stage, and the passion fruit was sprayed with 40 mg / L La on the leaves. The last spraying was carried out when the passion fruit was in the early stage of filling, and 40 mg / L La was sprayed on the leaves.

[0081] (5) After the passion fruit is ripe, harvest the passion fruit, wash the fruit sample with tap water, remove the seeds from the passion fruit, and extract the juice into a beaker.

[0082] (6) Centrifuge the juice obtained in (5), and take 0.1 mL of the juice sample diluted 100 times after centrifugation; weigh 5 g of trichloroacetic acid, prepare a 5% trichloroacetic acid (TCA) solution, and store it at 4℃ (to precipitate protein); further prepare a 0.1 mol / L acetate-sodium acetate buffer solution with pH = 5.0; further, weigh 0.2703 g of FeCl3·6H2O, dissolve it in the buffer solution and make up to 100 mL to prepare a 10 mmol / L FeCl3 solution; further, weigh 0.1982 g of o-phenanthroline, dissolve it in a small amount of ethanol, and make up to 100 mL in the buffer solution to prepare a 10 mmol / L o-phenanthroline solution; further still, weigh 10 mg of VC powder, make up to 10 mL in deionized water to prepare a 1 mg / mL VC standard, store it in the dark, and obtain a 1 mg / mL stock solution.

[0083] (7) Place the sample prepared in (6) into a stoppered test tube, take 0.1 mL of the sample solution to be tested diluted 100 times, add 2.9 mL of acetate-sodium acetate buffer, 0.5 mL of FeCl3 solution and 0.5 mL of o-phenanthroline solution in sequence, and vortex to mix (total reaction volume 4 mL); further, place it in a constant temperature water bath at 30℃ for 20 minutes, take it out and cool it to room temperature, and use an ultraviolet spectrophotometer to measure the absorbance of each concentration at a wavelength of 510 nm.

[0084] (8) Plot a standard curve with the absorbance obtained in (7) as the abscissa and the average absorbance as the ordinate, fit the regression equation (requires R²≥0.995), calculate the vitamin C concentration in the sample solution to be tested (denoted as C, μg / mL), and then calculate the vitamin C content in passion fruit juice (unit mg / 100mL) according to the formula.

[0085] In this embodiment, passion fruit is foliar sprayed with La, as shown in the attached image. Figure 4 Compared with Cd treatment alone, the vitamin C content of the juice increased by 45.3% after the addition of La treatment.

[0086] Example 5: Superoxide dismutase (SOD) content in passion fruit juice after spraying with La under Cd stress.

[0087] This example provides a method for reducing Cd content in passion fruit juice and improving fruit quality by foliar spraying with La under Cd stress, thereby increasing its SOD content.

[0088] At this experimental site, Cd-contaminated soil was prepared by adding Cd exogenously, and this Cd-contaminated soil was used as the test soil for passion fruit cultivation. Each experiment was repeated in triplicate.

[0089] Specific experimental steps:

[0090] (1) Take a portion (about 1000 kg of soil) from the greenhouse of the passion fruit experimental base as the test soil. The soil of the base has a pH value of 5.5-6.5, an organic matter content of 2.2%, and good drainage. The natural Cd content of the soil in this plot is 0.3 mg / kg. The soil is deeply tilled to a depth of 30 cm, and cadmium chloride is evenly applied to the soil to stabilize the soil Cd content at 0.6 mg / kg.

[0091] (2) Apply base fertilizer to the soil obtained in (1). The amount of base fertilizer is 1000 kg / mu. The base fertilizer is made by mixing well-rotted farmyard manure and compound fertilizer in a mass ratio of 3:1. After application, mix the soil with the base fertilizer and cadmium chloride thoroughly and let it stand for 7 days. Then dig planting pits with a row spacing of 2.5m and a plant spacing of 1.5m. The pit diameter is 50cm and the pit depth is 40cm. Apply 5kg of well-rotted organic fertilizer to each pit and mix it evenly with the soil in the pit for later use.

[0092] (3) Put 50 kg of soil obtained in (2) into a plastic pot, select healthy passion fruit seedlings that are free from pests and diseases and have a plant height of 25 cm, and plant them in the planting pit prepared in step (2). After planting, water thoroughly and cover with mulch to keep the soil moist.

[0093] (4) The samples obtained in (3) were cultivated in open greenhouse according to the conventional cultivation method of passion fruit. The first spraying was carried out when the passion fruit seedlings grew to the young fruit stage, and the passion fruit was sprayed with 53.3 mg / L La on the leaves. The second spraying was carried out when the passion fruit grew from the young fruit stage to the swelling stage, and the passion fruit was sprayed with 40 mg / L La on the leaves. The last spraying was carried out when the passion fruit was in the early stage of filling, and 40 mg / L La was sprayed on the leaves.

[0094] (5) After the passion fruit is ripe, harvest the passion fruit, wash the fruit sample with tap water, remove the seeds from the passion fruit, and extract the juice into a beaker.

[0095] (6) Enzyme activity was determined by photochemical reduction of NBT. 0.1 mL of the juice sample was mixed with 1.7 mL of 0.05 M NaH2PO4 (pH=7.8), 0.3 mL of 100 μM EDTA, 0.3 mL of 130 mM methionine, 0.3 mL of 750 μM NBT and 0.3 mL of 20 μM riboflavin.

[0096] (7) The mixture of (6) was placed in a laminar flow hood for UV (ultraviolet) light exposure for 15 minutes and the absorbance was measured at 560 nm at 25°C using a double-beam UV-Vis spectrophotometer.

[0097] (8) Calculate the superoxide dismutase content (unit U / mL·min) in passion fruit juice using the absorbance A sample formula obtained in (7).

[0098] In this embodiment, passion fruit is foliar sprayed with La, as shown in the attached image. Figure 5 Compared with Cd treatment alone, the addition of La treatment increased the superoxide dismutase activity of the juice by 92.6%.

[0099] Example 6: Peroxide superoxide dismutase (POD) content in passion fruit juice after spraying with La under Cd stress.

[0100] This example provides a method for reducing Cd content in passion fruit juice and improving fruit quality by foliar spraying with La under Cd stress, thereby increasing its POD.

[0101] At this experimental site, Cd-contaminated soil was prepared by adding Cd exogenously, and this Cd-contaminated soil was used as the test soil for passion fruit cultivation. Each experiment was repeated in triplicate.

[0102] Specific experimental steps:

[0103] (1) Take a portion (about 1000 kg of soil) from the greenhouse of the passion fruit experimental base as the test soil. The soil of the base has a pH value of 5.5-6.5, an organic matter content of 2.2%, and good drainage. The natural Cd content of the soil in this plot is 0.3 mg / kg. The soil is deeply tilled to a depth of 30 cm, and cadmium chloride is evenly applied to the soil to stabilize the soil Cd content at 0.6 mg / kg.

[0104] (2) Apply base fertilizer to the soil obtained in (1). The amount of base fertilizer is 1000 kg / mu. The base fertilizer is made by mixing well-rotted farmyard manure and compound fertilizer in a mass ratio of 3:1. After application, mix the soil with the base fertilizer and cadmium chloride thoroughly and let it stand for 7 days. Then dig planting pits with a row spacing of 2.5m and a plant spacing of 1.5m. The pit diameter is 50cm and the pit depth is 40cm. Apply 5kg of well-rotted organic fertilizer to each pit and mix it evenly with the soil in the pit for later use.

[0105] (3) Put 50 kg of soil obtained in (2) into a plastic pot, select healthy passion fruit seedlings that are free from pests and diseases and have a plant height of 25 cm, and plant them in the planting pit prepared in step (2). After planting, water thoroughly and cover with mulch to keep the soil moist.

[0106] (4) The samples obtained in (3) were cultivated in open greenhouse according to the conventional cultivation method of passion fruit. The first spraying was carried out when the passion fruit seedlings grew to the young fruit stage, and the passion fruit was sprayed with 53.3 mg / L La on the leaves. The second spraying was carried out when the passion fruit grew from the young fruit stage to the swelling stage, and the passion fruit was sprayed with 40 mg / L La on the leaves. The last spraying was carried out when the passion fruit was in the early stage of filling, and 40 mg / L La was sprayed on the leaves.

[0107] (5) After the passion fruit is ripe, harvest the passion fruit, wash the fruit sample with tap water, remove the seeds from the passion fruit, and extract the juice into a beaker.

[0108] (6) Determine enzyme activity using the guaiacol method. Prepare 0.1 mL of juice sample, 2.5 mL of 0.05 M NaH2PO4 (pH=7.8), 0.2 mL of 1% guaiacol, and 0.2 mL of 1.5% H2O2 solution.

[0109] (7) According to the solution in (6), first add sodium phosphate buffer, guaiacol and hydrogen peroxide solution, and finally add fruit juice enzyme solution to react. The formation of colored oxidation product (2,3-diaminophenazine) in the reaction solution is immediately measured at 485 nm at 25 °C for 3 minutes by a double beam UV-Vis spectrophotometer.

[0110] (8) Calculate the peroxidase content (unit U / mL·min) in passion fruit juice using the absorbance A sample formula obtained in (7). One unit of enzyme activity is defined as the amount of POD that produces 1 μmol of reaction product in 1 minute under specific conditions.

[0111] In this embodiment, passion fruit is foliar sprayed with La, as shown in the attached image. Figure 6 Compared with Cd treatment alone, the addition of La treatment increased the superoxide dismutase activity of the juice by 183.7%.

[0112] Example 7: Graph of polyphenol oxidase (PPO) content in passion fruit juice after spraying with La under Cd stress.

[0113] This example provides a method for improving fruit quality by foliar spraying with La under Cd stress, which can reduce Cd content in passion fruit juice by increasing its PPO content.

[0114] At this experimental site, Cd-contaminated soil was prepared by adding Cd exogenously, and this Cd-contaminated soil was used as the test soil for passion fruit cultivation. Each experiment was repeated in triplicate.

[0115] Specific experimental steps:

[0116] (1) Take a portion (about 1000 kg of soil) from the greenhouse of the passion fruit experimental base as the test soil. The soil of the base has a pH value of 5.5-6.5, an organic matter content of 2.2%, and good drainage. The natural Cd content of the soil in this plot is 0.3 mg / kg. The soil is deeply tilled to a depth of 30 cm, and cadmium chloride is evenly applied to the soil to stabilize the soil Cd content at 0.6 mg / kg.

[0117] (2) Apply base fertilizer to the soil obtained in (1). The amount of base fertilizer is 1000 kg / mu. The base fertilizer is made by mixing well-rotted farmyard manure and compound fertilizer in a mass ratio of 3:1. After application, mix the soil with the base fertilizer and cadmium chloride thoroughly and let it stand for 7 days. Then dig planting pits with a row spacing of 2.5m and a plant spacing of 1.5m. The pit diameter is 50cm and the pit depth is 40cm. Apply 5kg of well-rotted organic fertilizer to each pit and mix it evenly with the soil in the pit for later use.

[0118] (3) Put 50 kg of soil obtained in (2) into a plastic pot, select healthy passion fruit seedlings that are free from pests and diseases and have a plant height of 25 cm, and plant them in the planting pit prepared in step (2). After planting, water thoroughly and cover with mulch to keep the soil moist.

[0119] (4) The samples obtained in (3) were cultivated in open greenhouse according to the conventional cultivation method of passion fruit. The first spraying was carried out when the passion fruit seedlings grew to the young fruit stage, and the passion fruit was sprayed with 53.3 mg / L La on the leaves. The second spraying was carried out when the passion fruit grew from the young fruit stage to the swelling stage, and the passion fruit was sprayed with 40 mg / L La on the leaves. The last spraying was carried out when the passion fruit was in the early stage of filling, and 40 mg / L La was sprayed on the leaves.

[0120] (5) After the passion fruit is ripe, harvest the passion fruit, wash the fruit sample with tap water, remove the seeds from the passion fruit, and extract the juice into a beaker.

[0121] (6) Determine enzyme activity using the catechin method. Prepare 0.1 mL of fruit juice sample, 2.4 mL of 0.2 M NaH2PO4 (pH 6.8), and 0.5 mL of 0.5 mol / L catechin solution.

[0122] (7) Based on the solution in (6), first add sodium phosphate buffer and catechol solution, and finally add fruit juice enzyme solution to react. The PPO activity is determined by measuring the absorbance of the reaction solution at 410 nm for 3 minutes at 25°C using a double-beam UV-Vis spectrophotometer.

[0123] (8) Calculate the polyphenol oxidase content (unit U / mL·min) in passion fruit juice using the absorbance A sample formula obtained in (7). One unit of enzyme activity is defined as the amount of PPO that produces 1 μmol of reaction product in 1 minute under specific conditions.

[0124] In this embodiment, passion fruit is foliar sprayed with La, as shown in the attached image. Figure 3 Compared with Cd treatment alone, the addition of La treatment increased the polyphenol oxidase activity of the juice by 15.7%.

Claims

1. A method for using La as a cadmium-reducing agent in passion fruit and improving fruit quality, characterized in that, During the young fruit stage to maturity of passion fruit, a compound regulator made of La(NO3)3 and water is applied by foliar spraying.

2. The method for using La as a cadmium reducer and improving fruit quality in passion fruit according to claim 1, characterized in that, In the composite regulator, the concentration of La(NO3)3, calculated as La, is 40-53.3 mg / L.

3. The method for using La as a cadmium reducer and improving fruit quality in passion fruit according to claim 1, characterized in that, The foliar spraying is performed three times, with the first spraying preferably occurring during the young fruit formation period, the second during the early stage of fruit enlargement, and the third during the early stage of fruit filling.

4. The method for using La as a cadmium reducer and improving fruit quality in passion fruit according to claim 1, characterized in that, The method of foliar spraying of La is as follows: first, dissolve La(NO3)3 in an appropriate amount of water to prepare a La aqueous solution for foliar spraying, and then spray the La aqueous solution onto the passion fruit leaves with a sprayer on a cloudy day.

5. The method for using La as a cadmium reducer and improving fruit quality in passion fruit according to claim 4, characterized in that, When spraying La on the leaves, it is necessary to ensure that the droplets are evenly attached to both sides of the leaves, so that the leaves are moist but not dripping. The spraying time should be chosen on cloudy days or in the evening to avoid high temperature evaporation and photosynthesis.

6. The method for cultivating passion fruit according to claim 1, characterized in that, Select a plot of land with a soil pH of 5.5-6.5, an organic matter content of ≥2%, and good drainage as the planting base. The soil Cd content in this plot should be 0.3-0.8 mg / kg. Deeply till the soil to a depth of 30-40 cm and evenly apply the Cd source to the soil to stabilize the soil Cd content at 0.6-0.8 mg / kg. Apply base fertilizer at a rate of 2000-3000 kg / mu, which is a mixture of well-rotted farmyard manure and compound fertilizer in a mass ratio of 3:

1. After application, thoroughly mix the soil with the base fertilizer and Cd source. Then, dig planting pits with a row spacing of 2.5-3 m and a plant spacing of 1.5-2 m, with a pit diameter of 50-60 cm and a pit depth of 40-50 cm. Apply 5-10 kg of well-rotted organic fertilizer to each pit and mix it evenly with the soil in the pit before use. Select healthy passion fruit seedlings that are free from pests and diseases and are 25-30cm tall. Plant them in the prepared planting pits, water them thoroughly after planting, and cover them with mulch to retain moisture. When the passion fruit seedlings grow to the young fruit stage, spray the passion fruit leaves with 40-53.3 mg / L La for the first time; when the passion fruit grows from the young fruit stage to the swelling stage, spray the passion fruit leaves with 40-53.3 mg / L La for the second time; in the early stage of the filling stage, spray the passion fruit leaves with 40-53.3 mg / L La for the third time; after the passion fruit matures, harvest the passion fruit.

7. The method for cultivating passion fruit according to claim 6, characterized in that, The application rate of La for foliar spraying is 800 mg / mu. The 800 mg of La refers to the amount of La element in La(NO3)3, not the amount of La(NO3)3.

8. The method for cultivating passion fruit according to claim 6, characterized in that, After transplanting, water, weed, prune, and control pests and diseases regularly. Water according to the "water when dry" principle to avoid waterlogging which can increase Cd activity. When the seedlings grow to 40-50cm, build a support to guide the vines to climb. When pruning, retain the main vine and remove overly dense lateral vines, diseased or weak vines, and ineffective branches.

9. The method for cultivating passion fruit according to claim 8, characterized in that, Biological pesticides should be given priority in pest and disease control to avoid the synergistic harm caused by chemical pesticides and Cd.

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