Method of grass cultivation for preventing plant diseases

Abstract

To prevent the serious agricultural damage caused by root rot disease, methods such as spraying or irrigating expensive, specialized pesticides and physically eliminating the causative fungus using high-temperature water have been developed and put into practical use. However, these existing methods require a great deal of cost and labor to eradicate the root rot pathogenic fungus that survives in the soil. Furthermore, problems have been pointed out, such as changes in the physicochemical composition of the soil, making it unsuitable for agricultural use, and facilitating the proliferation of new plant pathogenic microorganisms. [Solution] By cultivating herbaceous plants while supplying them with silver ion water at a concentration of 0.030 mg / L to 0.600 mg / L, the roots of the herbaceous plants can reach a soil depth of about 40 cm or more, and the soil near the root zone of the cultivated plants can be made aerobic, enriching the soil bacterial flora, making it possible to eradicate white root rot fungus and purple root rot fungus, which are the causative fungi of root rot disease and live deep in cultivated soil, which was previously impossible.

Description

[Technical Field]

[0001] The present invention relates to a method for controlling root rot (including white root rot and purple root rot) that occurs during soil cultivation of plants such as fruit trees and root vegetables, by applying an aqueous solution containing silver ions at a concentration effective for activating the root elongation of herbaceous plants. [Background technology]

[0002] Root rot is a plant disease caused by the pathogenic fungi white root rot (teleomorphs belong to the genus Rosellinia) and purple root rot (teleomorphs belong to the genus Helicobasidium). It causes serious damage to fruit and vegetable cultivation, and its control is extremely important in many agricultural industrial sectors.

[0003] To prevent the serious agricultural damage caused by root rot disease, methods have been developed and put into practical use, such as spraying or irrigating expensive, special pesticides to eliminate the causative fungus, or using high-temperature water. However, these existing methods require a great deal of cost and labor to eradicate the root rot pathogenic fungus that lives in the soil. Furthermore, problems have been pointed out, such as changes in the physicochemical composition of agricultural soil and the simultaneous eradication of beneficial microorganisms in the soil, which can facilitate the proliferation of new plant pathogenic microorganisms and make the soil unsuitable for agriculture.

[0004] Furthermore, in orchards and the like, conventional sod cultivation methods using natural water or tap water have been used to suppress the growth of white root rot fungus and purple root rot fungus, thereby controlling cultivated plant diseases. However, because the root rot fungus can be eradicated only in the rhizosphere of herbaceous plants by sod cultivation of normal herbaceous plants, it has been difficult to prevent damage to fruit trees and the like caused by the root rot fungus, which lives in soil deeper than the depth of the rhizosphere formed by normal sod cultivation.

[0005] The applicant has discovered that by applying an aqueous solution containing silver ions at a concentration effective to cause the roots of herbaceous plants used in grass cultivation to grow deeper into the soil than they would normally reach, it is possible to eradicate the white root rot fungus and purple root rot fungus, which are the causative fungi of root rot disease and live deep in cultivated soil, something that was previously impossible.

[0006] In the research that led to the present invention, eight longhorn bush plants, each consisting of 10 seedlings, were transplanted at equal intervals in a horizontal circle 60-90 cm around the base center of two apple trees showing advanced purple root rot symptoms in an apple field affected by purple root rot disease. The plants were then cultivated as a grass for 80 days. The two longhorn bush cultivation test plots were: a silver ion solution sprayed plot, in which 18 L of a 0.1 mg / L silver ion solution was sprayed 2 days before transplanting and on days 21, 43, and 63 after transplanting; and a silver ion non-sprayed plot, in which 18 L of tap water was sprayed instead of the 0.1 mg / L silver ion solution on the same days. Eighty days after sowing, the soil around all eight longhorn bush plants in each test plot was dug up without damaging the roots, and the maximum soil depth reached by the roots was measured.

[0007] The results showed that the average depth reached by the roots of longhorn grass from the soil surface in the area where silver ion solution was not sprayed was 17 cm, while the average depth reached by the roots of longhorn grass in the area where silver ion solution was sprayed from the soil surface in the field was 46 cm, meaning that the roots of longhorn grass in the area where silver ion solution was sprayed reached an average of about 2.7 times deeper underground than the roots in the area where silver ion solution was not sprayed.

[0008] Separately, two other apple trees showing early signs of purple root rot were selected in the same apple cultivation field described in paragraph 0006, and after the snow had melted in the field, the soil within a 2 m radius of the tree trunks was plowed to a depth of 20 cm, leveled, and longhornbeam seeds were sown. These two longhornbeam cultivation test plots were divided into a silver ion solution sprayed plot, in which 160 L of a solution containing 0.1 mg / L of silver ions was sprayed two days before sowing and on the 21st, 43rd, and 63rd days after sowing, and a non-silver ion solution sprayed plot, in which 160 L of tap water was sprayed on the same days instead of the 0.1 mg / L solution.

[0009] Sixty days after flowering of the apple trees (see above, item 0008), soil core samples were collected from the soil surface to a depth of 80 cm at three locations 100 cm circumferentially from the base of the tree. Soil samples from the core samples at depths of 20 cm or greater were mixed in 10-cm increments. DNA was extracted from 10 g of each mixed soil (wet weight). The copy number of the 18S ribosomal RNA gene of the violet root rot fungus was measured by quantitative PCR (real-time PCR) using a specific DNA primer set targeting the 18S ribosomal RNA gene of the violet root rot fungus. The results are shown in Figure 1 as relative copy numbers, with the average copy number of the violet root rot fungus 18S ribosomal RNA gene per gram of soil sample at each soil depth being 1.

[0010] The results shown in Figure 1 indicate that the average copy number of the 18S ribosomal RNA gene of the purple root rot fungus per gram of soil sampled at a soil depth of 30 to 40 cm in the rhizosphere of apple trees in the silver ion solution-treated plot was reduced to approximately 1 / 7.4 of the average copy number of the 18S ribosomal RNA gene of the purple root rot fungus in the soil in the apple tree rhizosphere of apple trees in the non-silver ion solution-treated plot. Considering that the 18S ribosomal RNA gene (DNA) of the purple root rot fungus remains in the soil to some extent even after the fungus has died out, this result is thought to indicate that the purple root rot fungus as a surviving fungus in the apple tree rhizosphere in the silver ion solution-treated and grass-grown test plot was nearly eradicated.

[0011] Next, eight bundles of eight longhorn weed seedlings, each consisting of eight plants, were transplanted horizontally and evenly spaced in a 60-90 cm circumferential zone around the base of two pear trees affected by white root rot in a pear field. A 62-day cultivation experiment was conducted. These two longhorn weed cultivation test plots were designated as a silver ion treatment plot, in which 30 L of a 0.1 mg / L silver ion solution was sprayed 2 days before sowing and on days 14, 35, and 49 after sowing, respectively. Another test plot was a silver ion treatment plot, in which 30 L of tap water was sprayed instead of the 0.1 mg / L silver ion solution on the same days. On day 62 after sowing, the soil around all eight bundles of longhorn weed in each test plot was dug up carefully, taking care not to damage the roots, and the maximum depth to which the longhorn weed roots had reached was measured.

[0012] The results showed that the average depth reached by the roots of longhorn grass from the soil surface in the area where silver ion solution was not sprayed was 19 cm, while the average depth reached by the roots of longhorn grass in the area where silver ion solution was sprayed from the soil surface in the field was 43 cm, meaning that the roots of longhorn grass in the area where silver ion solution was sprayed reached a depth on average approximately 2.26 times deeper than the roots in the area where silver ion solution was not sprayed.

[0013] Furthermore, 62 days after flowering, soil core samples were collected from three locations 100 cm circumferentially from the base of affected pear trees, extending from the soil surface to a depth of 80 cm. Soil samples from the core samples extending 20 cm or deeper were mixed in 10-cm increments. DNA was extracted from 10 g of each wet mixed soil, and the copy number of the 18S ribosomal RNA gene of the white root rot fungus was measured by quantitative PCR (real-time PCR) using a specific DNA primer set targeting the 18S ribosomal RNA gene of the white root rot fungus. The results are shown in Figure 2 as relative copy numbers, with the number of copies of the 18S ribosomal RNA gene of the white root rot fungus per gram of soil sample at each soil depth set to 1.

[0014] The results shown in Figure 2 indicate that the number of copies of the 18S ribosomal RNA gene of the white root rot fungus per gram of soil sample taken from a soil depth of 30 to 40 cm in the rhizosphere of pear trees in the silver ion solution-treated area was reduced to approximately 1 / 8.2 of the number of copies of the 18S ribosomal RNA gene of the white root rot fungus in the soil in the rhizosphere of pear trees in the non-silver ion solution-treated area. Considering that the 18S ribosomal RNA gene (DNA) of the white root rot fungus remains to some extent even after the fungus has died out, this result is thought to indicate that the white root rot fungus as a surviving fungus in the rhizosphere of the pear trees in the silver ion solution-treated and grass-grown test area was nearly eradicated.

[0015] In addition to the above, three 4m x 4m rectangular soil plots were created in an area of the apple cultivation field described in paragraph 0006 where no fruit trees were planted, and the same amount of base fertilizer was applied to all three plots. One of these plots was sprayed with 80 L of a 0.1 mg / L silver ion solution, followed by sowing of longhorn grass seeds. Longhorn grass was then cultivated in this plot for 84 days, with 80 L of a 0.1 mg / L silver ion solution being sprayed every 21 days, regardless of whether the weather was sunny or rainy. One of the remaining two plots was sprayed with 80 L of tap water, followed by sowing of longhorn grass seeds. The 0.1 mg / L silver ion solution was then replaced with 80 L of tap water every 21 days, and longhorn grass was cultivated in this plot for 84 days. In another plot, no longhorn grass seeds were sown, and the soil was maintained bare by spraying 80 L of tap water every 21 days and weeding once every 14 days.

[0016] In the center of each of the plots described above (item 0014), one soil oxygen sensor was installed at depths of 20 cm, 40 cm, 60 cm, and 80 cm from the soil surface, so that the soil air oxygen concentration (%) at each soil depth could be measured. The results of measuring the soil air oxygen concentration at each cultivation time in each of the above plots using this oxygen sensor are shown in Figure 3.

[0017] The results shown in Figure 3 indicate that in the field plots where longhorn grass was cultivated while 120 L of a 0.1 mg / L silver ion solution was sprayed every 21 days, the soil pore oxygen concentration exceeded 8.0% at a soil depth of 40 cm and fell to below 6% at a soil depth of 60 cm. In contrast, in the field plots where longhorn grass was cultivated while 120 L of tap water was sprayed instead of the silver ion solution, the soil pore oxygen concentration averaged approximately 8.2% at a soil depth of 20 cm and approximately 5.4% at a soil depth of 40 cm. Furthermore, in the field plots where longhorn grass was not cultivated but was left bare, the soil pore oxygen concentration averaged approximately 6.7% at a soil depth of 20 cm and fell to an average of approximately 3.1% at a soil depth of 40 cm.

[0018] Furthermore, of the three plots set up in the apple field described above (section 0015), two plots were used to cultivate longhorn grass. 84 days after sowing, six longhorn grass plants, including their roots, were randomly selected from each plot, and the average root depth and average above-ground length of each longhorn grass plot were measured.

[0019] The results showed that the average depth of the longhorn grass roots from the soil surface in the area where silver ion solution was not sprayed was 16.5 cm, while the average depth of the longhorn grass roots from the soil surface in the area where silver ion solution was sprayed was 43 cm, meaning that the roots of the longhorn grass roots in the area where silver ion solution was sprayed reached an average depth of about 2.6 times that of the roots in the area where silver ion solution was not sprayed.

[0020] After 77 days of cultivation of longhorn grass in each plot shown above (section 0015), soil core samples were collected from the soil surface to a depth of 90 cm near the soil oxygen sensor installation, and DNA was extracted from 5 g of wet soil every 15 cm of soil depth. The copy number of the 16S ribosomal RNA gene of all eubacteria (prokaryotes excluding archaea) was measured using quantitative PCR (real-time PCR) with a universal eubacterial primer set.

[0021] The measurement results showed that the total number of copies of the 16S ribosomal RNA gene per gram of soil sample from a soil depth of 30 to 45 cm in the silver ion solution-sprayed area was approximately 8.2 times higher than the total number of copies of the 16S ribosomal RNA gene per gram of soil sample from a soil depth of 30 to 45 cm in the apple tree root zone in the non-silver ion solution-sprayed area.This result indicates that the abundance of eubacteria increased significantly in the sod-cultivation test area where silver ion solution was sprayed.

[0022] Next, using the DNA samples extracted from the soil described in Section 0020, the copy number of the 16S ribosomal RNA gene of Clostridium bacteria, a representative bacterium of anaerobic eubacteria, was measured by quantitative PCR (real-time PCR) using a 16S ribosomal RNA gene primer set specific to this bacterial genus.

[0023] The measurement results showed that the number of copies of the 16S ribosomal RNA gene of Clostridium bacteria per gram of soil sample from a soil depth of 30 to 45 cm in the silver ion solution-sprayed area was reduced to approximately 1 / 18.7 of the number of copies of the 16S ribosomal RNA gene of Clostridium bacteria in the soil of the apple tree rhizosphere in the non-silver ion solution-sprayed area.This result indicates that the abundance of anaerobic eubacteria was significantly reduced in the soil 30 cm or deeper in the sod-cultivation test area where silver ion solution was sprayed.

[0024] Considering these results, along with those shown above (paragraphs 0021 and 0023), it is clear that cultivating longhorn grass while spraying a silver ion solution enriches the bacterial flora in soil at depths of 30 cm or more. Furthermore, because the number of Clostridium bacteria, a representative genus of anaerobic bacteria, decreased in the soil at depths of 30 cm or more, it was presumed that this enrichment of the bacterial flora was brought about by a significant increase in aerobic bacteria. Furthermore, this significant increase in aerobic soil bacteria is thought to have had a positive effect on the eradication of the root rot pathogen, as shown in paragraph 0009.

[0025] Next, to determine the silver ion concentration in the silver ion solution that is effective in promoting root growth of longhorn grass as described above, 18 transparent PVC pipes with an inner diameter of 131 mm were cut to lengths of 1 m, and each PVC pipe was filled with commercially available potting soil (horticultural soil) to which base fertilizer had been added to a depth of 90 cm. Longhorn grass seeds were then sown and a cultivation experiment was carried out in a plant cultivation booth where the temperature was set at 22°C and fluorescent lights were used to illuminate the soil surface with 4000 Lux of light for 14 hours per day (10 hours per day in darkness).

[0026] The 18 PVC pipes in which the longhorn grass seeds were sown were divided into nine groups, A to I, each consisting of two pipes. Each pipe was supplied with 1 L of water every seven days. From the 14th day after sowing, tap water was used in place of tap water in the two pipes in group A, dechlorinated tap water in place of tap water in the two pipes in group B, a silver ion solution containing 0.015 mg / L prepared using dechlorinated tap water in place of tap water in the two pipes in group C, a silver ion solution containing 0.030 mg / L prepared using dechlorinated tap water in place of tap water in the two pipes in group D, a silver ion solution containing 0.075 mg / L prepared using dechlorinated tap water in place of tap water in the two pipes in group E, and a silver ion solution containing 0.075 mg / L prepared using dechlorinated tap water in place of tap water in the two pipes in group E. The plants were cultivated for 77 days while watering the pipes with an aqueous solution containing 0.150 mg / L of silver ions prepared using dechlorinated tap water, the two pipes in group F with an aqueous solution containing 0.300 mg / L of silver ions prepared using dechlorinated tap water, the two pipes in group G with an aqueous solution containing 0.600 mg / L of silver ions prepared using dechlorinated tap water, the two pipes in group H with an aqueous solution containing 0.900 mg / L of silver ions prepared using dechlorinated tap water, and the two pipes in group I with an aqueous solution containing 1.200 mg / L of silver ions prepared using dechlorinated tap water.

[0027] The root depth was measured visually on the 77th day after the start of the longhorn grass cultivation experiment described above (items 0025 and 0026). The results are shown in Figure 4 as the average value of two cultivations for each group.

[0028] The results shown in Figure 4 indicate that the average root depth of the longhorn grass plants in Group A, which were watered with tap water, was 19.4 cm, while the average root depth of the longhorn grass plants in Group B, which were watered with a solution containing 0.015 mg / L silver ions, was 23.3 cm. In contrast, the average root depth of the longhorn grass plants in Groups C to I, which were watered with solutions containing silver ions at concentrations of 0.030 mg / L or higher, all exceeded 40 cm, but the greatest root depth was 61.4 cm in Group G, which was watered with a solution containing 0.600 mg / L silver ions. Within the range of silver ion concentrations used in Groups C to G, the higher the silver ion concentration, the greater the root elongation. However, it was found that the average root depth of the longhorn grass in Group H, which was watered with a solution containing 0.900 mg / L of silver ions, was 52.3 cm, while the average root depth of the longhorn grass in Group I, which was watered with a solution containing 1.200 mg / L of silver ions, was 41.7 cm, indicating that the increase in silver ion concentration actually decreased the root depth.

[0029] On the 77th day after the start of the longhorn grass cultivation experiment described above (paragraphs 0025 and 0026), the PVC pipes were cut at a depth of 40 cm from the surface of the culture medium, and 5 g of wet soil samples were taken from each of the two pipes in groups A and I. This was then mixed for each group, and 10 g of soil was extracted from the resulting mixture. DNA was extracted from the resulting mixture and the total bacterial 16S ribosomal RNA gene copy number was measured by quantitative PCR using a universal eubacterial (EUB) primer set. The results are shown in Figure 5, where the relative copy number of the 16S ribosomal RNA gene per gram of soil sample from the pipe in group A, which received only tap water, is taken as 1.

[0030] The results shown in Figure 5 indicate that the density of eubacteria, measured as the copy number of the 16S ribosomal RNA gene, in the soil at a depth of 40 cm clearly increased with increasing silver ion concentration in groups C to H, where longhorn grass was grown using a solution containing silver ions at concentrations of 0.030 mg / L to 0.600 mg / L, compared with when longhorn grass was grown using tap water alone. However, in the soil at a depth of 40 cm in groups H and I, where longhorn grass was grown using a solution containing silver ions at concentrations of 0.900 mg / L to 1.200 mg / L, the density of total eubacteria decreased with increasing concentration of the applied silver ions.

[0031] Based on the results of measurements of root elongation of longhorn bushes and the number of purple root rot and white root rot fungi in the soil as shown in paragraphs 0006 to 0030 above, as well as observations of soil bacterial dynamics and soil pore oxygen concentration, it was found that growing longhorn bushes while watering them with an aqueous solution containing silver ions at concentrations of 0.030 mg / L to 0.600 mg / L increases the silver ion concentration, thereby causing root elongation to extend deeper. It was also found that this root elongation increases the soil pore oxygen concentration at depths of 30 cm or more in the plant cultivation soil, and that this increased soil pore oxygen concentration stimulates the growth of soil bacteria (especially aerobic bacteria) in the soil at depths of 30 cm or more. However, silver ions at concentrations exceeding 0.600 mg / L not only reduced root growth of longhorn grass, but also inhibited the growth of aerobic soil bacteria that are thought to suppress root rot fungus, thereby reducing the effectiveness of root rot fungus eradication.

[0032] Considering the results summarized above (item 0031), and as shown in items 0006 to 0010 and items 0020 to 0024, it appears that the reason why root rot was actually eradicated from soil about 45 cm deep in orchards where purple root rot fungus and white root rot fungus had occurred was because longhorn grass was cultivated while being irrigated with an aqueous solution containing silver ions at a concentration of 0.030 mg / L to 0.600 mg / L, which caused the roots of the longhorn grass to grow deep, thereby aerobicizing the soil to a depth of 30 cm or more and resulting in the vigorous proliferation of aerobic soil bacteria.

[0033] The effectiveness of the above-mentioned grass cultivation of longhornbeam in eradicating purple root rot and white root rot fungi is attributed to the fact that when longhornbeam is cultivated using conventional methods, it is not possible to sufficiently aerate the soil to a depth of 30 cm or more. This is thought to be the reason why the previous grass cultivation method has not been able to completely eradicate the purple root rot and white root rot fungi that inhabit soil to a depth of 30 cm or more.

[0034] As described above, the main background technology that led to the present invention is the discovery that, with the aim of eradicating purple root rot fungus and white root rot fungus that live in soil to a depth of 30 cm or more, the purpose can be achieved by growing plants in a grass-grown state while supplying them with silver ion water at a concentration of 0.030 mg / L to 0.600 mg / L, causing the roots of the plants to reach a soil depth of about 40 cm or more, thereby increasing the aerobicity of the soil near the rhizosphere of the plants in a grass-grown state and enriching the soil bacterial flora. [Prior art documents] [Patent documents]

[0035] [Patent Document 1] Patent Publication No. 2022-029587 [Patent Document 2] Patent Publication No. 2022-036484 Summary of the Invention [Problem to be solved by the invention]

[0036] The problem to be solved by the present invention is to improve the effectiveness of suppressing the growth of white root rot fungus and purple root rot fungus by grass cultivation, which is currently used in orchards and the like as a method of preventing agricultural damage caused by root rot disease, thereby providing a method of more effectively and economically preventing the severe damage caused by root rot disease in agriculture. [Means for solving the problem]

[0037] In order to solve the above-mentioned problem of eradicating the root rot fungus that inhabits cultivated soil at a depth of more than 30 cm, the present invention devised a method of promoting plant root elongation by applying an aqueous solution containing silver ions at a concentration of 0.030 mg / L to 0.600 mg / L as an embodiment of the conventional grass cultivation method.

[0038] First, in this invention, we discovered that the activity of microbial flora in the soil (particularly increasing the density and species diversity of aerobic bacteria in the soil) can be enhanced by creating an aerobic condition in which the oxygen concentration in the soil pore air at a depth of 30 cm is 8% or higher. This led to the idea of eradicating white root rot fungus and purple root rot fungus that live in the soil using this highly diverse microbial flora that reaches a soil depth of 40 cm or more.

[0039] Maintaining an aerobic state in deep soil by supplying air or oxygen to soil 30 cm or deeper using conventional mechanical methods requires special equipment and methods, which is not easy in terms of cost. In particular, it has been thought that it is economically difficult to achieve an air pore oxygen concentration of 8% or more in the entire soil 30 cm or deeper in large cultivated areas such as orchards and grain farms using existing mechanical methods.

[0040] The herbaceous cultivation method using herbaceous plants has been adopted for the purposes of improving agricultural soil, providing organic biomass for fertilizer, and eliminating soil pests. It is also expected to be used as a method for eliminating soil pathogens such as the root rot fungus. However, because the elimination of soil pathogens using herbaceous cultivation is only effective in the rhizosphere of herbaceous plants, the challenge has been how to increase the depth of the rhizosphere of plants cultivated in herbaceous cultivation. The rhizospheres of many herbaceous plants commonly used in herbaceous cultivation to date rarely exceed a soil depth of 30 cm, making it difficult to completely eliminate the root rot fungus in soil deeper than 30 cm using this method.

[0041] In the present invention, we have discovered that by cultivating herbaceous plants with water containing an aqueous solution containing silver ions at a concentration of 0.030 mg / L to 0.600 mg / L, the roots of the plants can be extended to a depth of approximately 30 cm or more. We have also discovered that this allows the soil deep in the field to be maintained in an aerobic state, and that the soil microbial flora (especially the aerobic bacterial flora) deep in the field can be diversified and densely populated.

[0042] Furthermore, it is known that as the soil microbial flora in the deeper parts of the field becomes more diverse and denser, it is possible to eradicate the purple root rot fungus and white root rot fungus that existed as pathogenic fungi in the field, as described in the above section. It has also been found that a method of growing grass while supplying water containing an aqueous solution containing silver ions at a concentration of 0.030 mg / L to 0.600 mg / L is an effective concrete method for solving the problem of preventing purple root rot and white root rot, which have been difficult to control using previous grass cultivation methods. [Effects of the Invention]

[0043] Although violet root rot and white root rot have been controlled using herbaceous plants in the past, the root rot control effect of herbaceous plants is exerted in the rhizosphere of the plants, and it has been practically difficult to eradicate the root rot-causing fungi that parasitize the roots of fruit trees and root vegetables at a soil depth of more than 30 cm using conventional herbaceous cultivation methods.

[0044] The effect of the present invention is that by carrying out grass cultivation while applying an aqueous solution containing silver ions at a concentration of 0.030 mg / L to 0.6 mg / L, the white root rot pathogenic fungi and purple root rot pathogenic fungi that live in agricultural soil at a depth of more than 30 cm, which has been difficult to eradicate using conventional grass cultivation methods, can be eradicated with less labor and at lower cost than labor-intensive methods using hot water or expensive pesticides such as chloropicrin and freoncide.

[0045] By cultivating longhorn bean as a herbivore using this method, which was invented based on the discovery described in the "Background Art" section above, it is possible to eradicate the white root rot pathogen that inhabits agricultural soil at a depth of 30 cm or more, which can be visually observed after the longhorn bean cultivation period has ended. This effect of eradicating the white root rot pathogen can also be achieved by cultivating other crops, such as barley, oats, orchard grass, timothy grass, pensacola, African sedge, fescue, eastern fescue, centipede grass, purple sedge, alsaique clover, milk vetch, and wisteria, by watering them with an aqueous solution containing 0.030 mg / L to 0.600 mg / L of silver ions in the same manner as for the longhorn bean.

[0046] Similarly, the effectiveness of controlling purple root rot obtained by cultivating longhorn grass as described above with watering it with an aqueous solution containing silver ions at a concentration of 0.030 mg / L to 0.6 mg / L was confirmed not only when longhorn grass was used, but also when other plants were used: Loose barley, oats, orchard grass, Timothy grass, Pensacola, African sedge, Tall fescue, Common sedge, Purple sedge, Alsike clover, Chinese milk vetch, Japanese wisteria, American sedge, sorghum, Sesbania, and Crotalaria. Therefore, the method of the present invention is effective in controlling purple root rot fungus that survives at a soil depth of 30 cm or more, regardless of whether any of the above herbaceous plants is used. [Brief explanation of the drawings]

[0047] [Figure 1] Depth-dependent changes in the mean relative copy number of the 18S ribosomal RNA gene of Violet Root Rot Fungus per gram of soil sample in an apple orchard [Figure 2] Changes in the relative mean copy number of 18S ribosomal RNA gene of white root rot fungus per gram of soil sample along soil depth in a pear orchard [Figure 3] Depth-wise changes in soil pore oxygen concentration in field plots cultivated with longhorn grass [Figure 4] Changes in mean root penetration depth of longgrass (Cervus longiflora) as a function of sprayed silver ion concentration in a transparent PVC pipe root elongation test. [Figure 5] Changes in relative copy numbers of 16S ribosomal RNA genes in soil at a depth of 40 cm in a root elongation test of longhorn grass using a transparent PVC pipe as a function of sprayed silver ion concentration DETAILED DESCRIPTION OF THE INVENTION

[0048] Hereinafter, embodiments of the present invention will be illustrated by Examples 1 to 8. [Example]

[0049] Example 1 In each orchard, where apple, pear, peach, and cherry trees of the Rosaceae family were planted and suffering from purple root rot disease, five 4-are plots were set up. Two of the five plots were seeded with longhorn grass, one with oats, one with timothy grass, and the remaining one with silvergrass, which were then cultivated as weeds. All but one of the five plots seeded with longhorn grass (the control plot) were sprayed with 240 L of a solution containing 0.05 mg / L of silver ions four times, three weeks apart after sowing. The purple root rot eradication test in each of these orchards was conducted over a three-year period. As a result, except for one plot where silver ion solution was not sprayed, all plots where 240 L of 0.05 mg / L silver ion solution was sprayed and longhorn grass, oats, timothy grass, and longhorn grass were grown in weed beds, showed that after two years, the above-ground disease caused by purple root rot fungus on apple, pear, peach, and cherry trees had disappeared, and all fruit trees had recovered their vigor. In each of these orchards, fruit weights of apple, pear, peach, and cherry trees were harvested that were 1.2 times higher than before the onset of purple root rot disease. In contrast, in one plot where only longhorn grass was grown in weed beds without silver ion solution spraying, all apple, pear, peach, and cherry trees had died from purple root rot after two years. In mid-June of the third year of the experiment, the soil was dug down to a depth of 50 cm at a position 1.5 m horizontally from the trunk of one cultivated fruit tree in each test plot, and the presence of the purple root rot pathogen in the rhizosphere was visually inspected. Large amounts of purple root rot fungus were confirmed in the rhizosphere at a depth of 40 cm in the test plot where longhorn grass was grown without spraying silver ion solution. However, no purple root rot fungus was confirmed in the rhizosphere at a depth of 40 cm in the test plots where longhorn grass was grown with silver ion solution spraying.

[0050] <Example 2> Two 1-are plots were set up in a grape cultivation field thought to be affected by white root rot fungus, and longhorn grass was sown in both plots and cultivated as a grass. After sowing longhorn grass in one of the two plots, 120 L of a solution containing 0.05 mg / L of silver ions was sprayed four times every three to four weeks. The remaining plot (control) was not sprayed with this silver ion solution. This experiment to eradicate white root rot fungus by grass cultivation in grape cultivation field was carried out over a two-year period. In mid-June of the second year of the experiment, soil core samples were collected 0.6 m horizontally from the base of one grapevine in each of the two test plots to a depth of 40 cm. Visual inspection of the rhizosphere soil for the presence of the pathogenic fungus causing purple root rot was performed. The presence of large amounts of white root rot fungus was confirmed in the rhizosphere of the grapevines at a depth of 30 cm in the test plot where longhorn grass was cultivated without silver ion application. However, white root rot fungus was not detected in the rhizosphere of the grapevines at a depth of 30 cm in the test plot where longhorn grass was cultivated with silver ion application. Furthermore, the grape yield in the test plot where longhorn grass was cultivated with silver ion application was nearly the same as the grape yield two years prior to the longhorn grass cultivation experiment. However, the grapevines in the test plot where longhorn grass was cultivated without silver ion application died by October of the second year of the experiment.

[0051] Example 3 Two 1-acre plots were set up in a kiwifruit farm suffering from white root rot fungus disease, and orchard grass was sown in both plots and cultivated as a grass cover. After the orchard grass was sown in one of the two plots, 120 L of an aqueous solution containing 0.05 mg / L of silver ions, as well as zinc ions, magnesium ions, and other inorganic ions at appropriate concentrations, was sprayed four times every three weeks. The remaining plot (control) was not sprayed with this silver ion solution. A test of white root rot fungus eradication by grass cover cultivation was conducted in this farm for three years. In mid-June of the second year of the experiment, soil core samples were taken to a depth of 40 cm from a horizontal position 1.0 m below the base of one kiwifruit tree in each of the two test plots. Visual inspection of the rhizosphere for the presence of the pathogenic purple root rot fungus was performed. The test plot where orchard grass was cultivated without silver ion application revealed a high concentration of white root rot fungus at a depth of 30 cm in the rhizosphere. However, the test plot where orchard grass was cultivated with silver ion application did not contain white root rot fungus at a depth of 30 cm in the rhizosphere. Kiwifruit yields in the third year of the orchard grass cultivation experiment were similar to those two years prior to the orchard grass cultivation experiment. However, the kiwifruit trees in the test plot where orchard grass was cultivated without silver ion application died by September of the third year of the experiment, resulting in no fruit harvest.

[0052] Example 4 Two 4-are plots were set up in an olive orchard suffering from white root rot disease, and both plots were seeded with orchard grass and cultivated as a grass cover. After seeding with orchard grass, one of the two plots was sprayed four times every three weeks with 80 L of an aqueous solution containing 0.10 mg / L of silver ions, as well as zinc ions, magnesium ions, and other inorganic ions at appropriate concentrations. The remaining plot (control) was not sprayed with this silver ion solution. A grass cover cultivation test to eradicate white root rot disease was conducted on this orchard for three years. In mid-June of the third year of the experiment, the soil was dug down to a depth of 45 cm at a horizontal position 1.0 m from the trunk of one olive tree in each of the two test plots, and visual inspection was performed to determine the presence of the white root rot pathogen in the rhizosphere. The test plot where sedge was cultivated without silver ion application revealed a high concentration of white root rot fungi at a depth of 40 cm in the rhizosphere. However, the test plot where sedge was cultivated with silver ion application but with silver ion application did not reveal any white root rot fungi at a depth of 40 cm in the rhizosphere. Olive fruit yields in the third year of the sedge cultivation experiment were nearly identical to those two years prior to the sedge cultivation experiment. Meanwhile, the olive trees in the test plot where sedge was cultivated without silver ion application died in the second year of the sedge cultivation experiment, resulting in no fruit harvest.

[0053] <Example 5> Two 1-acre plots were set up in a blueberry farm suffering from white root rot disease, and in both plots a mixture of Lolium multiflorum and Wisteria japonica was sown and cultivated as a grassland. After sowing Lolium multiflorum and Wisteria japonica in one of the two plots, 240 L of an aqueous solution containing 0.05 mg / L of silver ions, as well as zinc ions, magnesium ions, and other inorganic ions at appropriate concentrations, was sprayed three times every three weeks. The remaining plot (control) was not sprayed with this silver ion aqueous solution. A test of white root rot disease control using grassland cultivation in this farm was conducted over a two-year period. In mid-June of the second year of the experiment, soil core samples were collected 0.4 m horizontally from the base of one blueberry tree in each of the two test plots to a depth of 40 cm, and the rhizosphere soil was visually inspected for the presence of the white root rot pathogen. Large amounts of the white root rot pathogen were confirmed in the rhizosphere at a depth of 30 cm in the test plot where Lolium persica and Wisteria japonica were cultivated without the silver ion solution spray. However, no white root rot pathogen was detected in the rhizosphere at a depth of 30 cm in the test plot where Lolium persica and Wisteria japonica were cultivated with the silver ion solution spray. Furthermore, the blueberry yield in this test plot in the second year of the herbaceous cultivation experiment was nearly the same as the blueberry yield two years prior to the herbaceous cultivation experiment with Lolium persica and Wisteria japonica. On the other hand, the blueberry trees in the test plots where Lolium multiflorum and Wisteria japonica were grown in grass without spraying the silver ion solution died in June of the second year of the grass cultivation test, and no blueberries were harvested.

[0054] Example 6 Five 1-are plots were established in soybean fields that had been affected by white root rot fungus during the previous growing season. Two of the five plots were seeded with purple sedge, one with timothy grass, one with Japanese wisteria, and the remaining one with alsaike clover, all of which were then cultivated under sodded conditions. All but one of the plots seeded with purple sedge (control) were sprayed five times with 80 L of a 0.05 mg / L silver ion solution every 3-4 weeks after sodded. The plot seeded with purple sedge (control) was not sprayed with the silver ion solution. This soybean field control experiment for the eradication of white root rot fungus by sodded cultivation was conducted for only one growing season of these herbaceous plants. In mid-August, soil core samples were collected from the test plots to a depth of 40 cm and visually inspected for the presence of the white root rot fungus in the rhizosphere. No white root rot fungus was detected in the soil core samples collected from all test plots where soybeans were grown with silver ion solution sprayed. Furthermore, in all test plots, soybean yields were approximately 1.1 times higher than in the cultivation period two years earlier, when no white root rot fungus damage was observed. Meanwhile, in the test plot where purple sedge was grown without silver ion solution spraying, the presence of white root rot fungus was confirmed to a depth of 30 cm, and soybeans were almost completely harvested in this plot.

[0055] Example 7 Four 1-are plots were established in each sweet potato field affected by the purple root rot fungus. Two of the four plots were seeded with African sedge, one with pensacola, and the remaining with fescue, and then cultivated under a grass-covered condition. All but one of the plots seeded with African sedge (the control plot) were sprayed four times every three weeks after sowing with 80 L of a silver ion solution containing 0.05 mg / L of silver ion as well as appropriate concentrations of zinc ion, magnesium ion, and other inorganic ions. The remaining plot (the control plot) was not sprayed with the silver ion solution. This grass-covered condition experiment on the sweet potato field was repeated for two years. In mid-August, soil core samples were collected from each test plot to a depth of 40 cm and visually inspected for the presence of the purple root rot fungus in the rhizosphere. No purple root rot fungus was detected in the soil core samples collected from all test plots where sweet potatoes were grown with silver ion solution spraying. Furthermore, sweet potato yields were comparable to those obtained in the cultivation period two years prior, when no purple root rot fungus disease damage was observed. However, the presence of white root rot fungus was confirmed to a depth of 30 cm in the soil core sample from the test plot where African beard grass was grown without silver ion solution spraying, and sweet potato harvests were not possible in this plot in the second year of the test.

[0056] Example 8 Two 1-are plots were set up in an asparagus field affected by the purple root rot fungus. After harvesting asparagus spears, Timothy grass and Chinese milk vetch were mixed and sown in the two plots. One of the plots was sprayed four times every four weeks after sowing with 80 L of a solution containing 0.05 mg / L silver ions, as well as zinc ions, magnesium ions, and other inorganic ions at appropriate concentrations. The remaining plot (control) was not sprayed with the silver ion solution. Sod cultivation in this asparagus field was continued until two weeks before the start of asparagus spear harvest the following spring. In mid-April, four months after the start of the sod cultivation experiment, soil core samples were collected from both test plots to a depth of 40 cm and visually inspected for the presence of the purple root rot pathogen in the rhizosphere. No purple root rot pathogen was detected in the soil core sample from the test plot where asparagus was grown with silver ion solution sprayed. Furthermore, 1.22 times the weight of asparagus spears was harvested during this cultivation period compared to the cultivation period two years prior, when no purple root rot pathogen was observed. On the other hand, the presence of purple root rot pathogen was confirmed to a depth of 30 cm in the soil core sample from the test plot where timothy grass and Chinese milk vetch were grown without silver ion solution spraying. Furthermore, almost no asparagus spears were harvested in this plot. [Industrial Applicability]

[0057] Several methods have been developed to control root rot disease, which causes enormous losses in agriculture, but none of the conventional methods have been able to easily eradicate the root rot-causing fungi that parasitize the roots of cultivated plants in soil deeper than 30 cm.The method of the present invention utilizes sod cultivation while applying silver ions at a concentration of 0.030 mg / L to 0.6 mg / L, thereby enabling the eradication of the white root rot and purple root rot pathogenic fungi that live in agricultural soil at depths that have been difficult to eradicate using conventional sod cultivation methods, with less labor and at lower cost than labor-intensive physical root rot eradication methods such as irrigation with hot water or disinfection methods using expensive pesticides, thereby providing benefits to the agricultural sector.

[0058] The present invention relates to a method for controlling root rot disease, a disease caused by root rot, which is a root rot disease caused by root rot in a plant, and a method for controlling root rot in a plant.

Claims

1. A method for cultivating herbaceous plants that enables the eradication of pathogenic fungi that cause root rot disease of plants, comprising cultivating herbaceous plants by applying an aqueous solution containing silver ions at a concentration of 0.03 mg / L to 0.60 mg / L.

2. 2. The method for controlling plant diseases caused by root rot according to claim 1, characterized in that the herbaceous plants cultivated as weeds are one or more of the following: longgrass, woolly barley, oats, orchard grass, timothy grass, fescue, staghorn grass, pensacola, African sedge, purple horsetail, alcyone clover, milk vetch, wisteria japonica, sorghum, sesbania, and crotalaria.

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