Method and liquid composition for cultivating citrus plants

Abstract

To provide a cultivation method capable of alleviating symptoms of HLB of a citrus plant even if the citrus plant is cultivated under a natural environment.SOLUTION: A method for cultivating a citrus plant comprises: applying to the citrus plant a liquid composition containing Fe ions and humus acid, where at least some of the Fe ions are Fe2+ ions.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method and liquid composition for cultivating citrus plants. [Background technology]

[0002] Citrus greening disease (also known as huanglongbing or HLB) is a disease of citrus plants. HLB is a plant disease caused by the infection of citrus plants with pathogenic bacteria such as Candidatus Liberibacterb. The pathogenic bacteria are transmitted by the Asian citrus psyllid. Citrus plants infected with HLB pathogenic bacteria exhibit the following symptoms: yellowing of some leaves, small size of mature fruit, most of the surface of mature fruit remaining green, and bitter taste of mature fruit. As HLB progresses, citrus plants gradually weaken and wither from the tips of the branches, and eventually die.

[0003] Patent Document 1 reports that Fe is secreted from the leaf surface, rhizosphere, or both of citrus plants infected with HLB pathogens. 2+ A method for treating citrus greening disease in citrus plants is disclosed that involves applying a liquid containing ions. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 8,945,631 [Patent Document 2] Patent No. 6231059 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 merely verifies the therapeutic effect of HLB under conditions in which citrus plants are grown using vegetable seedling soil. 2+ The ion-containing liquid is applied to citrus seedlings as frequently as once every five days.

[0006] An object of the present invention is to provide a cultivation method capable of alleviating HLB symptoms in citrus plants even when the plants are cultivated in a natural environment, and a liquid composition for use in such a cultivation method. [Means for solving the problem]

[0007] The present invention includes the following aspects. [1] A method for cultivating citrus plants, comprising: Fe ions and humic acid are contained, and at least a part of the Fe ions is Fe 2+ applying to said citrus plant a liquid composition which is an ion. [2] The method according to [1], wherein the citrus plant is grown in sandy soil. [3] The method according to [1] or [2], wherein the citrus plant is an orange, grapefruit or lemon. [4] The method according to any one of [1] to [3], wherein the citrus plant is infected with a pathogen of citrus greening disease. [5] The method according to any one of [1] to [4], wherein the citrus plant is cultivated in an environment inhabited by Diaphorina citri. [6] The method according to any one of [1] to [5], wherein the citrus plant is infected with a pathogen of brown rot disease. [7] The method according to any one of [1] to [6], wherein the liquid composition has a total Fe ion concentration of 100 mg / L to 1000 mg / L. [8] At least 18% by mass of the total Fe ions in the liquid composition is Fe 2+ The method according to any one of [1] to [7], wherein the compound is an ion. [9] The method according to any one of [1] to [8], wherein the liquid composition is applied using an irrigation tube.

[10] The method according to any one of [1] to [9], wherein the liquid composition is applied 2 to 8 times a year.

[11] The liquid composition is capable of producing about 100% Fe per citrus plant per year. 2+The method according to any one of [1] to

[10] , wherein 0.27 g to 1.1 g of the compound is applied.

[12] A method for preparing a soil containing Fe ions and humic acid, wherein at least a portion of the Fe ions is Fe 2+ A liquid composition that is an ion.

[13] The liquid composition according to

[12] , wherein the liquid composition has a total Fe ion concentration of 100 mg / L to 1000 mg / L.

[14] At least 18% by mass of the total Fe ions in the liquid composition is Fe 2+ The liquid composition according to

[12] or

[13] , wherein the compound is an ion.

[15] The liquid composition according to any one of

[12] to

[14] , which is for cultivating citrus plants.

[16] The liquid composition according to

[15] , which is for cultivating citrus plants grown in sandy soil.

[17] The liquid composition described in

[15] or

[16] , wherein the citrus plant is an orange, grapefruit or lemon.

[18] The liquid composition according to any one of

[15] to

[17] , which is for use on a citrus plant infected with a pathogen of citrus greening disease.

[19] The liquid composition according to any one of

[15] to

[18] , which is for use in citrus plants grown in an environment inhabited by Asian citrus psyllids.

[20] The liquid composition according to any one of

[15] to

[19] , which is for use on a citrus plant infected with a pathogen of brown rot disease. Effect of the Invention

[0008] According to the present invention, it is possible to alleviate HLB symptoms in citrus plants even when the citrus plants are cultivated in a natural environment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described in detail.

[0010] In one embodiment, the method for cultivating a citrus plant includes cultivating a citrus plant comprising cultivating a citrus plant comprising: 2+applying to said citrus plant a liquid composition which is an ion.

[0011] Citrus plants include, for example, citrus, oranges, lemons, pomelo, yuzu, and kumquats. Citrus plants include, for example, oranges (Citrus sinensis), grapefruits (Citrus paradisi), or lemons (Citrus limon). Oranges may be early-ripening varieties, such as Hamlin oranges, or late-ripening varieties, such as Valencia oranges.

[0012] The method for cultivating a citrus plant according to the present embodiment can be applied to a citrus plant infected with a pathogenic bacterium of HLB. Therefore, the method according to the present embodiment can alleviate the symptoms of HLB in the citrus plant. The method can also be applied to a citrus plant that is not infected with a pathogenic bacterium of HLB. After applying the method according to the present embodiment, even if the citrus plant is infected with a pathogenic bacterium of HLB, the symptoms can be alleviated.

[0013] Citrus plants can be grown in sandy soil, a general term for soil that contains 50% or more coarse particles, including sandy soil with a grain size of 2.0 mm or less, as well as gravelly soil with a grain size of more than 2.0 mm.

[0014] Citrus plants may be cultivated in an environment inhabited by the Asian citrus psyllid (Diaphorina citri). When citrus plants are cultivated in a natural environment inhabited by the Asian citrus psyllid, the Asian citrus psyllid transmits HLB pathogens. This makes the environment more susceptible to infection by HLB pathogens for citrus plants. Even in such an environment, citrus plants cultivated by the method according to the present embodiment are not infected by HLB pathogens, or even if infected by HLB pathogens, the symptoms are alleviated.

[0015] The method for cultivating a citrus plant according to the present embodiment can be applied to a citrus plant infected with a pathogen of brown rot. Brown rot is a disease caused by the infection of a citrus plant with a pathogen such as a fungus of the genus Phytophthora, which causes fruit drop. The citrus plant to which the method according to the present embodiment is applied maintains the quality of the fruit even when infected with a pathogen of brown rot.

[0016] The liquid composition for application to citrus plants contains Fe ions and humic acid, and at least a portion of the Fe ions are Fe 2+ ions. Such liquid compositions include, for example, Fe 2+ It can be obtained by dissolving iron compounds capable of supplying ions in water. 2+ The iron compounds that can supply ions include Fe 2+ As long as it can liberate ions, there is no particular limitation. For example, divalent iron compounds such as FeO and FeSO4 can be used as such iron compounds. In addition, even if the iron compound contains trivalent iron in the solid state, such as iron citrate, it is possible to obtain Fe in the aqueous solution. 2+ If it is possible to release ions, Fe 2+ The liquid composition may be an iron compound capable of supplying iron ions. In addition, the liquid composition may be a combination of a trivalent iron compound such as Fe2O3 or FeCl3 and a reducing agent, and may be a compound capable of supplying iron ions such as Fe2O3 or FeCl3. 3+ Fe ions 2+ ions, and Fe 2+ Ions may be provided.

[0017] The total Fe ion concentration in the liquid composition is preferably 100 mg / L to 1000 mg / L, more preferably 100 mg / L to 500 mg / L, and even more preferably 100 mg / L to 300 mg / L. By making the total Fe ion concentration equal to or higher than the lower limit, it becomes easier to exert the effect of alleviating HLB symptoms. On the other hand, by making the total Fe ion concentration equal to or lower than the upper limit, damage to citrus plants can be avoided.

[0018] "Total Fe ions" means Fe 2+ ions and Fe 3+The term "Fe ions" refers to all Fe ions, including Fe ions, in the liquid composition. 2+ The concentration of the ion can be measured by a conventional method using o-phenanthroline. 2+ It selectively forms a complex with the Fe ion. Therefore, by measuring the absorbance of this complex, it is possible to determine the Fe 2+ The total Fe ion concentration in the liquid composition can be determined by selectively quantifying the Fe ion in the liquid composition. 3+ The total Fe ions are reduced to Fe 2+ After conversion to ions, they can be quantified using the o-phenanthroline method.

[0019] At least 18% by weight of the total Fe ions in the liquid composition is Fe 2+ At least 18% by mass of the total Fe ions are preferably Fe 2+ The liquid composition is preferably composed of 100% by mass of Fe ions, and more preferably 100% by mass of Fe ions. 2+ It may be an ion.

[0020] Humic acid includes humic acid and humate salts. Examples of humic acid include natural humic acid that is naturally produced in peat and weathered coal, artificial humic acid that is artificially produced by nitric acid oxidation of lignite, and humate salts obtained by neutralizing natural humic acid and / or artificial humic acid with alkaline substances such as sodium, potassium, ammonia, calcium, and magnesium. Examples of humic acid include humic acid, nitrohumic acid, ammonium humate, calcium humate, magnesium humate, ammonium nitrohumate, calcium nitrohumate, and magnesium nitrohumate. The humic acid may be a humic acid extract. The humic acid extract refers to an extract obtained by extracting nitric acid oxide from young coal such as lignite and brown coal at a pH range of 5 to 8, preferably at a pH range of 5 to 7. The humic acid extract is obtained as a liquid by, for example, stirring a mixture of nitric acid oxide of young coal obtained by oxidatively decomposing young coal with nitric acid, an inorganic compound containing at least one monovalent or divalent alkali selected from potassium hydroxide, sodium hydroxide, ammonium hydroxide, magnesium hydroxide, and calcium hydroxide, and water at 40 to 90°C for 0.5 to 1 hour, and then performing a solid-liquid separation process. The inorganic compound is added to water so that the pH is in the range of 5 to 8. A method for producing a humic acid extract is described in Patent Document 2. The solid content concentration of humic acid in the liquid composition can be in the range of 0.01 to 0.1 mass%. If it is 0.01 mass% or more, the effect of alleviating the symptoms of HLB is sufficient, and if it is 0.1 mass% or less, the solid content does not settle and separate, and clogging does not occur in the equipment for applying the liquid composition.

[0021] The liquid composition may contain, in addition to Fe ions and humic acid, metal ions such as Ca ions, Mg ions, Al ions, Ba ions, Cr ions, K ions, Mn ions, and Na ions. 2+ In order to stably maintain the ions and to maintain the effect of alleviating the symptoms of HLB, an acid may be included. Examples of such acids include citric acid, malic acid, tartaric acid, oxalic acid, and ascorbic acid. Of these, citric acid is preferred. 2+From the viewpoint of stably maintaining ions, the concentration of the acid is preferably 100 mg / L to 10 g / L, and more preferably 500 mg / L to 2 g / L.

[0022] The means for applying the liquid composition to a citrus plant is not particularly limited. Examples of such means include spraying the liquid composition on the leaf surface of a citrus plant, or irrigating the rhizosphere of a citrus plant with the liquid composition. The liquid composition is preferably irrigated into the rhizosphere of a citrus plant. When the liquid composition is applied to the rhizosphere, the acid released from the roots of the citrus plant is converted into Fe. 3+ Reduce the ion to Fe 2+ By making it into an ion, it is expected that the alleviating effect on the symptoms of HLB will be sustained. From the viewpoint of convenience of application, the liquid composition is preferably irrigated using an irrigation tube.

[0023] The application frequency of the liquid composition can be 2 to 8 times a year. Alternatively, the application frequency of the liquid composition can be once every 45 to 180 days. The application amount of the liquid composition is 0.1 g to 3.0 g of Fe per citrus plant per year. 2+ , preferably 0.27g to 1.1g of Fe 2+ By setting the application frequency and application amount within this range, the effect of alleviating the symptoms of HLB can be easily achieved. EXAMPLES

[0024] Fe 2+ Preparation of a liquid composition containing ions and humic acid A liquid composition was prepared by diluting (100 times) 50 g of Tetsuryoku Aqua (registered trademark of Japan) F10 (Aichi Steel Corporation) and 50 g of Humusu Power (registered trademark of Japan) H5 (solid content concentration 5%; Denka Corporation) with 5 L of water. 2+ The concentrations of Fe ions were 150 mg / L and 27 mg / L, respectively. That is, 18 mass% of the total Fe ions were Fe 2+ Furthermore, when the concentration of the organic acid in the liquid composition was measured, the concentration of citric acid was 1.09 g / L.

[0025] citrus plant cultivation Valencia and Hamlin oranges were grown in sandy soils in Florida. 2+ In the ion application area, 5 L of the above liquid composition was applied to one citrus plant (hereinafter referred to as "tree") using an irrigation tube once every 45 days. In the non-treated area, 5 L of water was applied to one tree using an irrigation tube once every 45 days. Application began in June 2019, and the citrus plants were evaluated at each time point in June 2019, January 2020, June 2020, and January 2021. Note that almost all of the trees were infected with HLB pathogens and were cultivated in an environment where the citrus psyllid also lives.

[0026] Evaluation items The evaluation items were root density, soil nutrients, soil pH, fruit yield, leaf composition analysis, pathogen quantification, canopy volume and canopy density.

[0027] result 1) Root density

[0028] [Table 1]

[0029] The above table shows the root density from June 2019 to June 2020 and the rate of change in root density over a six-month or one-year period. In the first six months (from summer to winter), Fe 2+ The root density of Valencia oranges in the iron and humic acid fertilized plots increased, but decreased in the following six months (winter to summer). On the other hand, the root density of Valencia oranges in the untreated plots decreased in both periods. The root density of Hamlin oranges increased throughout the year in both experimental plots. However, Fe fertilized plots showed a higher root density than the untreated plots. 2+ The root density increased more significantly in the areas where iron and humic acid were applied. 2+ions and humic acid were effective in increasing root density. The increase in root density was remarkable in the first six months after application began. In trees infected with HLB pathogens, the root system, which cannot be seen from above ground, is the most severely damaged by the pathogen. For this reason, Fe, which has the effect of increasing root density, was 2+ Ions and humic acids are thought to contribute significantly to alleviating the symptoms of HLB.

[0030] [Table 2]

[0031] The table above shows the rate of change in root density from June 2020 to January 2021. No significant differences in root density were observed in any of the experimental plots.

[0032] 2) Soil nutrients

[0033] [Table 3]

[0034] The table above shows the amount of nutrients in the soil as of June 2020. For both varieties, Fe 2+ The soil in the ion-treated area had a lower S content than the untreated soil. This was due to the presence of Fe. 2+ This suggests that the trees treated with Fe and humic acid absorbed more of these nutrients. 2+ It is possible that trees treated with ions and humic acid may have more S available to reduce HLB and other stresses.

[0035] [Table 4]

[0036] The table above shows the percentage change in soil nutrients from June 2020 to January 2021. Both Valencia and Hamlin oranges had high Fe concentrations. 2+No significant difference was observed in the rate of change in soil nutrients between the ion- and humic acid-treated plots and the control plot.

[0037] 3) Soil pH

[0038] [Table 5]

[0039] The table above shows Fe 2+ The soil pH from the second to the 30th day after the start of application of ions and humic acid is shown. In all experimental plots, the soil pH on the 30th day was in the optimum range (5.8-6.5). 2+ The pH of the soil in the treated area was lower than that in the untreated area. 2+ Fe ions and humic acids have the effect of acidifying the soil. Soil acidification is an effective way for citrus plants to resist HLB pathogens, and from this perspective, Fe 2+ The soil pH as of January 2021 was 1.0, ... 2+ The optimum range (5.8-6.5) was observed in both the ion and humic acid treated plots and the untreated plot.

[0040] 4) Fruit yield

[0041] [Table 6]

[0042] The table above shows Fe 2+ The data on fruit yield in the first year after application of Fe and humic acid are shown below. 2+ The area treated with ions and humic acid had a lower fruit drop rate and an increased yield compared to the control area. 2+ The yield of fruits in the Fe and humic acid treated plots increased by about 9% compared to that in the untreated plots. The harvest season for Hamlin oranges is from late December to January. 2+ Although it has only been about six months since the start of ion and humic acid application, there are already signs of good fruit yield.

[0043] [Table 7]

[0044] The table above shows Fe 2+ The data on fruit yield in the second year after the start of application of ions and humic acid are shown below. In the second year, the fruit yield at harvest, the estimated number of fruits on the tree, and the fruit drop rate at harvest were all significantly lower for both Hamlin and Valencia oranges due to the outbreak of brown rot disease. 2+ No significant difference was observed between the Fe and humic acid treatments and the control. However, before brown rot occurred (before fruit drop), the average yield and fruit number of Hamlin oranges were higher in the Fe treatments than in the control. 2+ The number of fruits was significantly higher in the areas where ions and humic acid were applied. The number of fruits also increased compared to the first year. 2+ The first year was the application of Fe ions and humic acid. 2+ ions and humic acid were applied three times, whereas in the second year, Fe 2+ This may be due to the fact that ions and humic acid were applied five times.

[0045] [Table 8]

[0046] The table above shows the data on the quality of the fruit harvested in the second year. Both Hamlin and Valencia oranges had Fe 2+ No significant difference was observed between the ion and humic acid treated areas and the untreated area, and there was no difference in quality or size.

[0047] 5) Leaf component analysis

[0048] [Table 9]

[0049] The above table shows the percentage change in the elements contained in the leaves of the trees from June 2019 (summer) to January 2020 (winter). In Valencia oranges, P and K increased, while the other elements decreased. In Hamlin oranges, only P increased, while the other elements decreased. In Valencia oranges, Fe 2+ The degree of decrease in Mg, Ca, S, and B in the ion and humic acid treated areas was smaller than that in the untreated area, and the decrease in Mg was especially small. 2+ The increase in P was significant in the ion and humic acid treatment areas compared to the control area.

[0050] [Table 10]

[0051] The table above shows the percentage change in the elements contained in the leaves of the trees from January 2020 (winter) to June 2020 (summer). In Valencia oranges, the opposite phenomenon to the change from summer to winter was observed, that is, P and K decreased, while the other elements increased. In Valencia oranges, Fe 2+ The increase rates of Ca, S, B, Mn, and Cu in the ion and humic acid treated areas were smaller than those in the untreated area. 2+ The increase rates of N, K, S, and B in the ion and humic acid treated areas were smaller than those in the untreated area.

[0052] [Table 11]

[0053] The above table shows the rate of change in the components contained in the leaves of trees over the one-year period from June 2019 (summer) to June 2020 (summer). In both Valencia oranges and Hamlin oranges, most components tended to decrease in the untreated plots. In Valencia oranges, Fe 2+ In the ion and humic acid application areas, the decrease in Mg was small, while Fe increased. In the Hamlin orange, Fe2+ In the ion and humic acid application areas, Mg increased and Fe decreased.

[0054] Interestingly, Fe 2+ Differences in the behavior of nutrient movement in leaves were observed in trees treated with ions and humic acid. HLB is a disease in which the movement of nutrients within the tree is inhibited. 2+ It is possible that the application of ions and humic acid may have begun to normalize nutrient mobilization to resist HLB pathogens.

[0055] [Table 12]

[0056] The table above shows the percentage change in the components contained in the leaves of the trees from June 2020 (summer) to January 2021 (winter). For Valencia oranges, no significant differences were observed in any of the experimental plots. For Hamlin oranges, Fe 2+ The increase in B in the ion and humic acid treated plots was larger than that in the untreated plot, and a significant difference was observed. It is believed that the amount of B used in the leaves affected by HLB is high. However, Fe 2+ It is possible that B was actively taken up by the application of ions and humic acid, resulting in a significant increase in B.

[0057] 6) Quantification of pathogens

[0058] [Table 13]

[0059] The table above shows the semi-quantitative results (Ct value of real-time quantitative PCR) of Candidatus Liberibacter asiaticus (cLas). As is clear from this table, no significant difference was observed in the amount of pathogenic bacteria in any of the experimental groups. 2+It is possible that the ions and humic acid induce gene expression that alleviates the symptoms of HLB, rather than killing the pathogen. In addition, because the trees are grown in an actual orchard environment, the Asian citrus psyllids attack the trees one after another, so there is a possibility that the pathogen infects the trees repeatedly before the HLB has been cured.

[0060] 7) Crown volume and crown density

[0061] [Table 14]

[0062] The table above shows the canopy volume (m2) of trees in June 2019, January 2020, and June 2020. 3 ) and the amount of change in each period. It must be remembered that citrus trees have a tendency for the roots below ground to stop growing when the crown above ground is growing, and vice versa. As mentioned above, the root density of the Valencia oranges in the untreated plot decreased, which is thought to be due to the use of carbohydrates for the growth of the aboveground parts. Fe 2+ The Valencia orange trees in the Fe and humic acid treatment plots are thought to have used carbohydrates for root growth. In the untreated Hamlin orange trees, the root density increased as mentioned above, but the crown volume decreased. 2+ Hamlin orange trees in the ion and humic acid treatment plots maintained their canopy volume while their roots grew.

[0063] [Table 15]

[0064] The table above shows the rate of change in canopy volume from June 2020 to January 2021. No significant differences were observed in canopy volume in any of the experimental plots.

[0065] [Table 16]

[0066] The table above shows the canopy density of trees in June 2019 and June 2020, as well as the amount of change over the course of a year. No significant differences in canopy density were observed in any of the experimental plots.

Claims

1. 1. A method for ameliorating symptoms of citrus greening disease in a citrus plant, comprising: The present invention relates to a method for producing a humic acid-based ... ２＋ applying a liquid composition to said citrus plant, the citrus plant is a Hamlin orange or a Valencia orange; The citrus plant is cultivated in an environment inhabited by Diaphorina citri, The liquid composition has a total Fe ion concentration of 100 mg / L to 300 mg / L; The liquid composition is applied 2 to 8 times per year; The method, wherein the liquid composition is applied at 0.27 g to 1.1 g of Fe 2+ per citrus plant per year.

2. 10. The method of claim 1, wherein the citrus plant is grown in sandy soil.

3. The method according to claim 1 or 2, wherein the citrus plant is infected with a pathogen of citrus greening disease.

4. The method according to claim 1 or 2, wherein the citrus plant is infected with a pathogen of brown rot.

5. At least 18% by weight of the total Fe ions in the liquid composition is Fe ２＋ 3. The method according to claim 1 or 2, wherein the compound is an ion.

6. The method of claim 1 or 2, wherein the liquid composition is applied using an irrigation tube.

7. The present invention relates to a method for producing a humic acid-based ... ２＋ A liquid composition for alleviating symptoms of citrus greening disease in citrus plants grown in an environment inhabited by Asian citrus psyllids, comprising: the citrus plant is a Hamlin orange or a Valencia orange; The liquid composition has a total Fe ion concentration of 100 mg / L to 300 mg / L; The liquid composition is applied to the citrus plant 2 to 8 times per year, and the liquid composition is used to apply 0.27 g to 1.1 g of Fe 2+ per citrus plant per year.

8. At least 18% by weight of the total Fe ions in the liquid composition is Fe ２＋ The liquid composition of claim 7 which is an ion.

9. The liquid composition according to claim 7 or 8, which is for cultivating citrus plants grown in sandy soil.

10. The liquid composition according to claim 7 or 8, which is for use on citrus plants infected with a pathogen of citrus greening disease.

11. The liquid composition according to claim 7 or 8, which is for use on citrus plants infected with a pathogen of brown rot.

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