Method for cultivating citrus plants 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, where at least some of the Fe ions are Fe2+ ions, where the citrus plant is cultivated in an environment where Diaphorina citri inhabits.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for cultivating citrus plants and a 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 Summary of the Invention [Problem to be solved by the invention]

[0005] However, 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 are contained, and at least a part of the Fe ions is Fe 2+ applying a liquid composition comprising ions to said citrus plant; The method comprises cultivating the citrus plant in an environment inhabited by the citrus psyllid (Diaphorina citri). [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 infected with a pathogen causing brown rot disease. [6] The method according to any one of [1] to [5], wherein the liquid composition has a total Fe ion concentration of 100 mg / L to 1000 mg / L. [7] 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 [6], wherein the compound is an ion. [8] The method according to any one of [1] to [7], wherein the liquid composition is applied using an irrigation tube. [9] The method according to any one of [1] to [8], wherein the liquid composition is applied 2 to 8 times a year.

[10] The liquid composition is administered to one citrus tree per year for a period of about 10 days. 2+ The method according to any one of [1] to [9], wherein 0.27 g to 1.1 g of the compound is applied.

[11] Fe ions are contained, and at least a part of the Fe ions is Fe2+ The liquid composition for cultivating citrus plants grown in an environment inhabited by Asian citrus psyllids is an ion.

[12] The liquid composition of claim 11, for use on citrus plants grown in sandy soil.

[13] The liquid composition according to

[11] or

[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 any one of

[11] to

[13] , wherein the compound is an ion.

[15] The liquid composition according to any one of

[11] to

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

[16] The liquid composition according to any one of

[11] to

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

[17] The liquid composition according to any one of

[11] to

[16] , 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, HLB symptoms in citrus plants can be alleviated 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 the citrus plant with Fe ions, wherein at least a portion of the Fe ions is Fe 2+ applying an ionic liquid composition to said citrus plant, said citrus plant being grown in an environment inhabited by the Asian citrus psyllid.

[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 are 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.

[0014] Citrus plants may be grown in sandy soil, which is a general term for soil containing 50% or more coarse particles, including sandy soil with a particle size of 2.0 mm or less, as well as gravelly soil with a particle size of more than 2.0 mm.

[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 to be applied to the citrus plant contains Fe ions, 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+ Reduce all Fe ions 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] The liquid composition may contain, in addition to Fe ions, 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.

[0021] 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 the citrus plant, or irrigating the rhizosphere of the citrus plant with the liquid composition. The liquid composition is preferably irrigated into the rhizosphere of the 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.

[0022] The application frequency of the liquid composition can be 2 to 8 times a year. Alternatively, the application frequency of the liquid composition may 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 (citrus tree) 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

[0023] Fe 2+ Preparation of liquid compositions containing ions A liquid composition was prepared by diluting Tetsuriki Aqua (registered trademark of Japan) F10 (Aichi Steel Corporation) 100 times with 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 organic acid in the liquid composition was measured, the citric acid concentration was found to be 1.09 mg / L.

[0024] 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.

[0025] Evaluation items The evaluation items were root density, soil nutrients, soil pH, fruit yield, leaf composition analysis, pathogen quantification, canopy volume and canopy density.

[0026] result 1) Root density

[0027] [Table 1]

[0028] 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 both the first six months (summer to winter) and the second six months (winter to summer), Fe 2+ The root density of the Valencia oranges in the ion-treated plots increased. On the other hand, the root density of the Valencia oranges in the untreated plots decreased during the same period. The root density of the Hamlin oranges increased throughout the year in both experimental plots. However, the Fe concentration was higher than that of the untreated plots. 2+ In the ion application area, the root density increased more significantly. 2+ The increase in root density was most noticeable in the first six months after application. In trees infected with HLB pathogens, the root system, which cannot be seen above ground, is the most severely damaged by the pathogen. For this reason, Fe ions, which have the effect of increasing root density, were 2+ Ions are believed to contribute significantly to alleviating the symptoms of HLB.

[0029] [Table 2]

[0030] The table above shows the percentage change in root density from June 2020 to January 2021. No significant differences in root density were observed in any of the experimental plots.

[0031] 2) Soil nutrients

[0032] [Table 3]

[0033] The table above shows the amount of nutrients in the soil in June 2020. For Valencia oranges, Fe 2+ The soil in the ion-treated area had lower P, S, and Zn contents than the untreated soil. 2+ These results suggest that the Valencia oranges treated with ions absorbed more of these nutrients. 2+ No significant difference was observed between the soils in the ion-treated and control areas. 2+ It is possible that ion-treated trees utilize more S to reduce HLB and other stresses.

[0034] [Table 4]

[0035] The table above shows the percentage change in soil nutrients from June 2020 to January 2021. In Valencia oranges, Fe 2+ No significant difference was observed in the rate of change in soil nutrients between the ion-treated and untreated soils. 2+ There was a significant difference in the rate of change in Ca and CEC between the soils in the ion-treated and untreated plots.

[0036] 3) Soil pH

[0037] [Table 5]

[0038] The table above shows Fe 2+ The soil pH from the second to the 30th day after the start of ion application is shown. In all experimental plots, the soil pH on the 30th day was in the optimal range (5.8-6.5). 2+ The pH of the soil in the ion-treated area was lower than that in the untreated area, indicating that Fe 2+Fe ions 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-treated and untreated areas.

[0039] 4) Fruit yield

[0040] [Table 6]

[0041] The table above shows Fe 2+ The data on fruit yield in the first year after the start of ion application are shown below. 2+ The ion-treated area had a lower fruit drop rate and an increased yield compared to the untreated area. 2+ The fruit drop rate in the ion-treated area was more than 10% lower than that in the untreated area. 2+ The yield in the ion-treated area increased by about 17% compared to that in the untreated area. 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 application, there are already good signs of improved fruit yield.

[0042] [Table 7]

[0043] The table above shows Fe 2+ The data on fruit yield in the second year after the start of ion application are shown below. In the second year, due to the outbreak of brown rot, the fruit yield at harvest, estimated number of fruits on the tree, and fruit drop rate were all reduced by Fe application for both Hamlin oranges and Valencia oranges. 2+ No significant difference was observed between the ion-treated and control areas. However, before brown rot occurred (before fruit drop), the average yield of Valencia oranges was significantly higher in the Fe-treated area than in the control area. 2+The number of fruits was significantly higher in the ion application area. Also, the number of fruits increased compared to the first year. 2+ The ions were continuously applied, and in the first year, Fe 2+ ions were applied three times, whereas in the second year, Fe 2+ This may be due to the fact that ions were applied five times.

[0044] [Table 8]

[0045] 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-treated and untreated areas, and there was no difference in quality or size.

[0046] 5) Leaf component analysis

[0047] [Table 9]

[0048] The above table shows the rate of change in the components contained in the leaves of the trees from June 2019 (summer) to January 2020 (winter). In Valencia oranges, P and K increased in all experimental plots, while the other components decreased. In Hamlin oranges, only P increased in all experimental plots, while the other components decreased. In Valencia oranges, Fe 2+ The degree of decrease in Ca, S, B, Fe, and Cu in the ion-treated area was smaller than that in the untreated area. 2+ The degree of reduction in Fe in the ion-treated plot was less than half that in the untreated plot.

[0049] [Table 10]

[0050] 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 of 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, Zn, Mn, Fe, and Cu in the ion-treated area were smaller than those in the untreated area. In particular, S and Cu had negative values ​​and decreased from winter to summer. In Hamlin orange, Fe 2+ The increase rates of N, K, S, and B in the ion-treated area were smaller than those in the untreated area.

[0051] [Table 11]

[0052] The table above 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 and Hamlin oranges, most components tended to decrease in the untreated plots. In Valencia oranges, Fe 2+ The decrease in B and Fe was large in the ion application area. In Hamlin orange, Fe 2+ In the ion application area, Mg increased and Fe decreased.

[0053] Interestingly, Fe 2+ In the trees in the ion application area, differences were observed in the behavior of nutrient movement in the leaves. HLB is a disease in which the movement of nutrients within the tree is inhibited. For this reason, Fe 2+ It is possible that ion application may begin to normalize nutrient transport in order to resist HLB pathogens.

[0054] [Table 12]

[0055] The table above shows the percentage change in the components in the leaves of the trees from June 2020 (summer) to January 2021 (winter). For Valencia oranges, no significant differences were observed between any of the experimental plots. For Hamlin oranges, Fe 2+ The increase in B in the ion-treated area was larger than that in the untreated area, and a significant difference was observed. It is thought 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, resulting in a significant increase in B.

[0056] 6) Quantification of pathogens

[0057] [Table 13]

[0058] 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 do not kill the pathogen but induce gene expression that alleviates the symptoms of HLB. 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 trees are repeatedly infected with the pathogen before the HLB can be cured.

[0059] 7) Crown volume and crown density

[0060] [Table 14]

[0061] 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+ In the ion-treated area, the Valencia orange tree showed growth in both roots and crowns. In the untreated area, the Hamlin orange tree showed an increase in root density as mentioned above, but the crown volume decreased. 2+ The roots and crowns of the Hamlin orange trees in the ion application area grew.

[0062] [Table 15]

[0063] 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.

[0064] [Table 16]

[0065] 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: Fe ions are contained, and at least a part of the Fe ions is Fe ２＋ applying a liquid composition to said citrus plant, the citrus plant is a Hamlin orange or a Valencia orange; The citrus plant is grown 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 tree per year.

2. 10. The method of claim 1, wherein the citrus plants are 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. Fe ions are contained, and at least a part of the Fe ions is Fe ２＋ A liquid composition for alleviating symptoms of citrus greening disease in a citrus plant cultivated 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 tree per year.

8. 8. The liquid composition according to claim 7, for use on citrus plants grown in sandy soil.

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

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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