JP7751265B2 - Cultivation method - Google Patents

Description

The present invention relates to a method and apparatus for cultivating plants of the Asteraceae or Solanaceae family that can reduce the incidence of viral diseases.

Viruses that cause necrotic symptoms in plants, such as Tomato Spotted Wilt Virus (TSWV) and Tomato Mosaic Virus (ToMV), are easily transmitted by tiny insects or infected plant sap. Therefore, these viruses are transmitted through the management practices or soil contamination of Asteraceae or Solanaceae plants, causing significant damage to the production of these plants. This damage is spreading throughout the world, including Japan, and is becoming a serious problem.

Patent Document 1 discloses a technology for inducing resistance in tomatoes and reducing infection and disease occurrence by irradiating tomato seedlings with deep ultraviolet light (UV-B) having a wavelength of 280 to 290 nm at an irradiation dose of 0.7 to 1.4 kJ/ ^m2 . Note that Non-Patent Document 1 indicates that the deep ultraviolet light irradiation experiment described in Patent Document 1 was conducted during the light period.

Furthermore, Patent Document 2 discloses a technology in which the above-mentioned deep ultraviolet light is irradiated on tomato seedlings at an irradiation dose of 0.3 to 0.4 kJ/ ^m2 per day during the dark period, thereby reducing UV damage and reducing ToMV infection and disease onset.

Japanese Patent Application Laid-Open No. 2016-7185 Japanese Patent Application Laid-Open No. 2019-162059

S Matsuura et. al., "Suppression of Tomato mosaic virus disease in tomato plants by deep ultraviolet irradiation using light-emitting diodes", Letters in Applied Microbiology 59, p457-463, 2014.

However, while the technologies described in Patent Documents 1 and 2 can reduce ToMV infection and disease in tomatoes, there is still room for improvement in terms of the occurrence of UV damage such as leaf browning and leaf curl. If the level of UV damage could be further reduced, adverse effects on crop quality could be avoided, and further improvements in commercial value could be expected. This is particularly important for ornamental plants such as chrysanthemums, whose leaves are also included in the commercial product. Furthermore, it is unclear whether the technologies described in Patent Documents 1 and 2 are effective on plants other than tomatoes.

One aspect of the present invention aims to realize a cultivation method that can sufficiently reduce the occurrence of UV damage while reducing the incidence of viral diseases in plants of the Asteraceae or Solanaceae family.

In order to solve the above-mentioned problems, a cultivation method according to one aspect of the present invention includes a step of irradiating a plant of the Asteraceae or Solanaceae family with light using an LED light source, in which the plant is irradiated with light having a peak wavelength in the range of 287 nm or more and 295 nm or less at an irradiation dose of 0.6 kJ/ ^m2 or more and less than 1.2 kJ/ ^m2 per day during the dark period.

In a cultivation method according to one aspect of the present invention, the light may have a half-width within a wavelength range of the peak wavelength ±6 nm.

In a cultivation method according to one aspect of the present invention, the dark period may be a period during which the ratio of the amount of visible light irradiation to the amount of light irradiation is 10% or less.

In order to solve the above-mentioned problems, a cultivation device according to one aspect of the present invention is provided with an LED light source capable of irradiating Asteraceae or Solanaceae plants with light having a peak wavelength in the range of 287 nm or more and 295 nm or less at an irradiation dose of 0.6 kJ/ ^m2 or more and less than 1.2 kJ/ ^m2 per day during the dark period.

One aspect of the present invention makes it possible to realize a cultivation method that can sufficiently reduce the occurrence of UV damage while preventing the onset of viral diseases in plants of the Asteraceae or Solanaceae family.

1 is a schematic diagram showing a general configuration of a plant cultivation device according to an embodiment; 1 is a graph showing the effect of light irradiation on the TSWV disease index of chrysanthemums. 1 is a graph showing the effect of light irradiation on the amount of TSWV accumulated in chrysanthemums. 1 is a graph showing the effect of light irradiation on the number of TSWV ring spot lesions on tobacco. FIG. 1 is a photograph showing the TSWV reduction effect of light irradiation on cigarettes. 1 is a graph showing the effect of light irradiation on the number of TSWV local lesions on tobacco. 1 is a graph showing the effect of light irradiation on the TSWV lesion area rate of tobacco. 1 is a graph showing the effect of light irradiation on the ToMV disease index of tomatoes. 1 is a graph showing the effect of light irradiation on the amount of ToMV accumulated in tomatoes. 1 is a graph showing the effect of light irradiation on the number of ToMV local lesions on tomatoes.

One embodiment of the present invention will be described below. Please note that the following description is intended to provide a better understanding of the spirit of the invention and does not limit the present invention unless otherwise specified. Furthermore, in this specification, "A to B" means greater than or equal to A and less than or equal to B, unless otherwise specified.

[Cultivation equipment]
Reference numeral 101 in Fig. 1 is a schematic diagram showing the general configuration of a plant cultivation device 10 according to one embodiment of the present invention. Reference numeral 102 in Fig. 1 is a schematic diagram showing the external configuration of a light irradiation module 1 provided in the cultivation device 10. As indicated by reference numeral 101 in Fig. 1, the cultivation device 10 includes the light irradiation module 1, a support rod 2, and an electric cord 3. The light irradiation module 1 is a module that can uniformly irradiate UV (ultraviolet rays) of a predetermined wavelength at a predetermined irradiation amount within a glass greenhouse or vinyl greenhouse. The UV irradiated by the light irradiation module 1 is an example of "light" as defined in the claims.

The support rods 2 are suspended from the ceiling via wires, and multiple light irradiation modules 1 are installed on each support rod 2. Note that the installation method for the support rods 2 is not limited to this; any installation method may be used as long as the UV from the light irradiation modules 1 can be irradiated onto the plants 4 without any problems and the installation position of the support rods 2 equipped with light irradiation modules 1 can be fixed.

Plant 4 is a plant whose infection with and disease onset by viruses that cause necrotic symptoms (hereinafter sometimes simply referred to as "viruses") can be reduced by irradiating it with UV light from light irradiation module 1. Examples of such viruses include TSWV, stem necrosis virus (CSNV), and ToMV. Plant 4 is a plant of the Asteraceae family or Solanaceae family. Examples of Asteraceae plants include chrysanthemums, gerberas, dahlias, marigolds, daisies, lettuce, and garland chrysanthemums. Examples of Solanaceae plants include tomatoes, tobacco, eggplants, potatoes, chili peppers, shishito peppers, bell peppers, and petunias. However, examples of plant 4 are not limited to these, and are not particularly limited as long as they are plants of the Asteraceae family or Solanaceae family.

As shown by reference numeral 102 in FIG. 1 , the light irradiation module 1 includes an LED (Light Emitting Diode) light source 1a and an electrical cord 3. The light irradiation module 1 is electrically connected to a power source (not shown) via the electrical cord 3. The light irradiation module 1 has an overall shape that is approximately rectangular. The LED light source 1a is provided near the center of the approximately rectangular bottom surface that forms one side of the approximately rectangular shape of the light irradiation module 1. In this embodiment, one LED light source 1a (mounted LED chip) is provided for one light irradiation module 1. However, two or more LED light sources 1a may be provided for one light irradiation module 1. The light irradiation module 1 may also be a type in which the LED chip is covered with quartz glass to protect against humidity.

The LED light source 1a is a light source capable of emitting UV light with a peak wavelength in the range of 287 nm to 295 nm. It is more preferable that the LED light source 1a be capable of emitting UV light with a peak wavelength in the range of 290 nm to 292 nm. The light irradiation module 1 irradiates UV light using the LED light source 1a.

It has previously been known that irradiating tomatoes with deep ultraviolet light with an effective wavelength range of 280 nm to 290 nm (hereinafter sometimes referred to as "conventional UV") can reduce ToMV infection and disease onset. This is thought to be due to the induction of gene expression that confers resistance to the virus, such as genes that encode infection-specific proteins (pathogenesis-related proteins), in tomatoes irradiated with conventional UV. As a result of this induction of gene expression, tomatoes irradiated with conventional UV are thought to acquire resistance to the virus, resulting in reduced viral infection and disease onset.

However, when plants such as tomatoes are irradiated with this type of conventional UV, UV damage occurs. UV damage refers to undesirable morphological changes that can occur in plants due to UV exposure. Examples of UV damage include changes in leaf color such as browning, changes in leaf shape such as leaf curling, and increased leaf gloss due to the development of the cuticle layer.

To date, attempts have been made to reduce UV damage in tomatoes by limiting the amount of conventional UV radiation. However, it was unclear what UV characteristics would be optimal for achieving both a reduction in virus infection in plants and a reduction in UV damage.

The inventors conducted UV irradiation experiments on plants 4 using multiple LED light sources that emit UV light at varying wavelengths. As a result, the inventors discovered that UV light with a peak wavelength in the range of 287 nm to 295 nm provides the optimal balance between the effect of inducing viral resistance in plants 4 and the effect of reducing UV damage. Therefore, they found that such UV light can reduce viral infection in plants 4 and the level of UV damage to a higher degree than ever before. In other words, through their diligent research, the inventors have, for the first time, identified the optimal UV characteristics for achieving both a reduction in viral infection in plants and a reduction in the level of UV damage.

In addition, UV rays with a peak wavelength in the range of 287 nm to 295 nm have a wavelength range shifted toward the longer wavelength side compared to conventional UV rays. Therefore, even if UV rays with a peak wavelength in the range of 287 nm to 295 nm are irradiated onto the human body, they are less toxic to the human body than conventional UV rays. In other words, the UV rays irradiated by the cultivation device 10 according to this embodiment are superior in terms of safety for the human body.

The UV that can be irradiated by the LED light source 1a is preferably light whose half-width falls within a wavelength range of the peak wavelength ±6 nm. Here, half-width refers to the full width at half maximum. With this configuration, the UV irradiated by the LED light source 1a contains almost no wavelength components that deviate significantly from the peak wavelength. Therefore, when irradiated onto a plant 4, the peak wavelength and wavelength components in its vicinity effectively induce resistance to viruses in the plant 4, while wavelength components shorter than the peak wavelength are minimized, minimizing UV damage.

Because the LED light source 1a has a sharp light directionality, it is preferable to arrange the light irradiation modules 1 at regular intervals in the cultivation device 10 in order to uniformly irradiate the plants with UV. Note that reference numeral 101 in Figure 1 shows two plants 4 corresponding to one light irradiation module 1. However, one plant 4 may be associated with one light irradiation module 1, or three or more plants 4 may be associated with one light irradiation module 1. Furthermore, the light irradiation modules 1 may be arranged in two parallel rows or two staggered rows. In short, it is desirable to arrange the light irradiation modules 1 so that a constant, uniform irradiation intensity is obtained over the plant canopy. Furthermore, such an arrangement method can be calculated using simple optical calculations.

The LED light source 1a is capable of irradiating UV at an irradiation dose of 0.6 kJ/ ^m2 or more and less than 1.2 kJ/ ^m2 per day during the dark period. The irradiation dose required to reduce viral diseases while mitigating UV damage in the plant 4 is 0.6 kJ/ ^m2 or more and less than 1.2 kJ/ ^m2 per day during the dark period. The "dark period" will be described later.

If the amount of UV radiation irradiated onto the plant 4 is 1.2 kJ/ ^m2 or more, even UV irradiated by the LED light source 1a may cause UV damage to the plant 4. In order to minimize UV damage to the plant 4, the amount of radiation irradiated per day by the LED light source 1a is set to less than 1.2 kJ/ ^m2 .

Furthermore, if the amount of UV irradiation applied to the plant 4 is less than 0.6 kJ/ ^m2 , there is a possibility that virus resistance will not be sufficiently induced in the plant 4. For this reason, the amount of irradiation per day by the LED light source 1a onto the plant 4 is set to 0.6 kJ/ ^m2 or more.

As described above, the LED light source 1a only needs to have an output capable of irradiating a plant 4 with an irradiation amount of 0.6 kJ/ ^m2 or more and less than 1.2 kJ/ ^m2 per day during the dark period. Note that, when the cultivation device 10 is configured to irradiate one plant 4 with multiple LED light sources 1a, the multiple LED light sources 1a only need to have an output capable of irradiating the plant 4 with the above-mentioned irradiation amount in total.

[Cultivation method]
The cultivation method according to this embodiment includes a step of irradiating the plant 4 with UV light using the LED light source 1a. In this step, the plant 4 is irradiated with UV light having a peak wavelength in the range of 287 nm to 295 nm at an irradiation dose of 0.6 kJ/ ^m2 or more and less than 1.2 kJ/ ^m2 per day during the dark period. The LED light source 1a used in the cultivation method according to this embodiment may be the LED light source included in the cultivation device 10 described above.

In the cultivation method according to this embodiment, UV light is irradiated during the dark period. Here, the dark period may be the period during which the ratio of the amount of visible light irradiated to the plant 4 by the LED light source 1a to the amount of UV irradiated is 10% or less. Visible light is light having a wavelength of 360 nm or more and 830 nm or less, and may include both natural light and artificial light.

The dark period may refer to any period from after sunset to before sunrise (including twilight, when there is no natural light or when there is some natural light). In other words, the dark period is a state in which it is mostly dark, but may also include twilight. Twilight may also refer to the period from approximately 30 minutes before sunrise to sunrise, or the period from sunset to approximately 30 minutes after sunset.

The UV that the LED light source 1a can irradiate is safer than conventional UV in the wavelength range of 280 nm to 290 nm, but it is still a wavelength that can be harmful to humans. Therefore, from the perspective of human safety, it is preferable to irradiate the plants 4 with UV during dark periods such as at night or before dawn, when humans are not working.

The dark period may also be a period in which the proportion of visible light received by the plant 4 is artificially reduced by limiting the amount of natural light entering the room or by controlling the light source inside the room. In this case, the dark period may be set at any time of the day.

In this way, by configuring UV irradiation to occur during the dark period, UV can be irradiated onto the plants 4 while minimizing the impact of visible light. Therefore, the wavelength of light irradiated onto the plants 4 can be easily controlled, making it easy to simultaneously reduce UV damage and the incidence of viral diseases in the plants 4. From this perspective, it is most preferable to perform UV irradiation during the dark period when it is completely dark.

Note that if UV irradiation of plants 4 is limited to dark periods (e.g., at night) as described above, it becomes possible to operate without using equipment such as report lights, which Patent Document 1 recommends installing to improve safety. Furthermore, since workers do not perform maintenance on plants 4 during the dark periods, there are several practical benefits, such as avoiding the risk of workers accidentally looking directly at UV light.

The light irradiation module 1 can be used in relatively small seedbeds in sunlight-utilizing glass greenhouses or vinyl greenhouses. The light irradiation module 1 can also be used in large-area main fields, in which case it may be possible to reduce the incidence of viral diseases in plants 4 over the long term.

The UV irradiation in the cultivation method according to this embodiment can replace at least part of existing measures to prevent viral infection. Plant viruses are known to be transmitted by insects and other vectors. For this reason, insecticides are sprayed on plants 4 as a measure to prevent viral infection. By irradiating plants 4 with UV light, the number of times insecticides are sprayed on plants 4 can be reduced. This can reduce the amount of pesticides used and the labor required to spray them.

Furthermore, during plant 4 maintenance work using maintenance tools such as scissors, viruses may be transmitted through sap that adheres to the maintenance tools. For this reason, it is preferable to frequently disinfect such maintenance tools. By irradiating the plants 4 with UV light, the number of times the maintenance tools are disinfected and the amount of disinfectant used may be reduced. This also leads to a reduction in the cost of plant 4 maintenance work.

1. Effects of UV irradiation on Asteraceae plants
In order to clarify the optimal UV wavelength and irradiation dose that reduces infection and disease caused by TSWV, which is a problem in the cultivation of Asteraceae plants, and that does not cause UV damage to Asteraceae plants, we conducted a UV irradiation experiment on chrysanthemum ('Jinba').

(method)
In November, chrysanthemums ('Jinba') were planted in a 1a (are) steel-frame greenhouse. The cultivation conditions were drain bed isolation, planted in four rows with 20cm spacing between plants, a night temperature of 18°C, interrupted lighting at night, and nutrient solution soil cultivation. In addition, three drain beds were divided into two, creating a total of five treatment areas: one unirradiated area (control) and four irradiated areas.

In each irradiation area, the characteristics of the UV irradiated by the light irradiation module and the set irradiation amount per day are as follows:
(1) Peak wavelength 285 nm (λp=285 nm, Δλ=10 nm), 600 J/m ² ,
(2) Peak wavelength 285 nm (λp=285 nm, Δλ=10 nm), 300 J/m ² ,
(3) Peak wavelength 291 nm (error ±1 nm, λp = 290 to 292 nm, Δλ = 11 to 12 nm), 1200 J/m ² ,
(4) Peak wavelength 291 nm (error ±1 nm, λp=290 to 292 nm, Δλ=11 to 12 nm), 600 J/m ² .

"λp" indicates the range of peak wavelengths, and "Δλ" indicates the half-width. In (1) and (2) above, an SMD-mounted light irradiation module (manufactured by Nikkiso Giken) with an optical output of 30 mW was used, while in (3) and (4) above, an SMD-mounted light irradiation module (manufactured by Dowa) with an optical output of 31-35 mW was used. The UV irradiation amount was measured by connecting a UV detector (UV-3719-4) to an X1-1 optometer to measure the irradiation intensity at the upper layers of the plant crown, and the daily irradiation amount was calculated.

The chrysanthemums were irradiated with the above-mentioned dose for 5 hours at night (1:00 AM to 6:00 AM) from November to December, starting two weeks after planting. The irradiance intensity on the upper layers of the plant crown was set to 1.7 μW/ ^cm2 when the daily dose was 300 J/m2, 3.3 μW/ ^cm2 when ^it was 600 J/ ^m2 , and 6.7 μW/ ^cm2 when it was 1200 J/ ^m2 .

Seven days after the start of irradiation, the virus was inoculated into three uppermost expanded leaves of eight plants in each plot using Carborundum (registered trademark) sap inoculation of the TSWV chrysanthemum isolate propagated in tobacco (Nicotiana rustica). Carborundum is silicon carbide powder. UV irradiation continued thereafter.

Eleven and 21 days after inoculation, the disease index of the eight strains designated for each plot was investigated. UV damage was observed visually. The disease index was evaluated according to the following criteria:
"0": No symptoms,
"1": Slight yellowing and necrotic spots are observed on the inoculated leaves.
"2": Clear yellow necrotic spots are observed on the inoculated leaves.
"3": Numerous yellowed necrotic spots are observed on the inoculated leaves.

Here, "slight" refers to the degree to which symptoms can be detected with careful observation. Statistical analysis of the disease index was performed using the Kruskal-Wallis test, n=8, with P<0.05 considered significant.

The degree of UV damage was evaluated according to the following criteria:
"-": no disability,
"±": slight browning, curling or curling of the inoculated leaves was observed;
"+": Obvious browning, curling or curling of the inoculated leaves was observed;
"++": More obvious browning, curling or curling of the leaves is observed in the inoculated leaves.

Here, "slight" means that it can be detected with careful observation. The evaluation criteria for UV damage are the same for other examples.

Due to the nature of the test virus, TSWV, which localizes to lesions, the above-mentioned method cannot detect TSWV in some samples. Therefore, a method was adopted to investigate the amount of virus accumulation by whole leaf extraction. Here, whole leaves of TSWV-inoculated samples were frozen and crushed using liquid nitrogen, and each sample was divided into three 1.5 mL tubes to extract RNA, which was then pooled and purified in one tube. The amount of TSWV virus accumulation in chrysanthemum leaves was then investigated by quantitative PCR analysis using the comparative Ct method, using the gene expression level of PGK protein as a normalizer.

(result)
Figure 2 shows the disease index for each sample 21 days after inoculation. Figure 3 shows the amount of TSWV accumulated in each sample. As shown in Figure 2, in the non-irradiated area, clear yellowed necrotic spots were observed on the inoculated leaves 21 days after inoculation, but in each of the irradiated areas, the disease index was significantly reduced.

As shown in Figures 2 and 3, among the irradiation areas, the area irradiated with a peak wavelength of 291 nm and 600 J/ ^m² exhibited the greatest effect in reducing TSWV disease incidence and caused the least amount of UV damage. On the other hand, the area irradiated with a peak wavelength of 291 nm and 1200 J/ ^m² caused UV damage almost equivalent to that of the area irradiated with a peak wavelength of 285 nm and 600 J/ ^m² . These results demonstrate that the appropriate daily exposure dose for UV with a peak wavelength of 291 nm is less than 1200 J/ ^m² .

As shown in Figure 3, the amount of TSWV accumulated in chrysanthemums was low at both 600 J/m ² and 1200 J/m ² at a peak wavelength of 291 nm, and no significant difference in the effect of reducing TSWV infection was observed compared to when the peak wavelength was 285 nm.

These results indicate that irradiation with 600 J/ ^m² of UV light with a peak wavelength of 291 nm per day at night effectively reduces the incidence of chrysanthemum necrosis disease caused by TSWV while almost completely avoiding UV damage. Furthermore, it was shown that UV damage can be avoided if the daily irradiation dose of UV light with a peak wavelength of 291 nm is less than 1200 J/ ^m² .

2. Effects of UV irradiation on Solanaceae plants
To clarify the optimal UV wavelength and dose for reducing infection and disease development by TSWV or ToMV, which are problematic in the cultivation of Solanaceae plants, and for preventing UV damage to Solanaceae plants, we conducted UV irradiation experiments on tobacco (Nicotinia rustica) and tomato ('Momotaro 8'). Tobacco is a representative model plant of the Solanaceae family.

2-1. Irradiation of tobacco at 600 J/ ^m²
(method)
Four light irradiation modules were installed in a 50 cm square steel-framed PO (polyolefin) film greenhouse, and pot-grown tobacco (Nicotinia rustica) at the 4.1 leaf stage was placed underneath. A total of four treatment areas were set up: one unirradiated area (control) and three irradiated areas.

In each irradiation area, the characteristics of the UV irradiated by the light irradiation module are as follows:
(1) Peak wavelength 284 nm (error ±1 nm, λp = 283 to 285 nm, Δλ = 11 to 12 nm),
(2) Peak wavelength 291 nm (error ±1 nm, λp = 290 to 292 nm, Δλ = 11 to 12 nm),
(3) Peak wavelength 297 nm (error ±1 nm, λp = 296 to 298 nm, Δλ = 11 to 12 nm).

The daily irradiation dose from the light irradiation module was 600 J/ ^m² . The light irradiation module used was an SMD substrate-mounted light irradiation module (manufactured by Dowa) with a light output of 30 mW and an operating voltage of 5.5 V. The UV irradiation dose was calculated by measuring the irradiation intensity at the upper layer of the plant crown using a UV detector (UV-3719-4).

The irradiating method was to irradiate the tobacco plants at the 4.1 leaf stage with the above-mentioned dose for 14 hours (17:00-7:00) every night starting in March, starting from the day the plants were left standing. The irradiating intensity on the upper layers of the plant crown was 1.2 μW/ ^cm2 . The temperature inside the greenhouse was 15°C at night and 30°C during the day.

Eight days after the start of irradiation, virus inoculation was performed by inoculating the fourth and fifth leaves of each group of tobacco plants with TSWV-infected leaves prepared in advance using carborundum. UV irradiation continued thereafter.

Ten days after inoculation, the number of ring spot lesions on the inoculated leaves was counted. UV damage was observed visually. Statistical analysis of the number of ring spot lesions was performed using Tukey's test with n = 5, with P < 0.05 indicating a significant difference.

(result)
Figure 4 shows the number of ring spot lesions on the inoculated leaves of each sample 10 days after inoculation. As shown in Figure 4, the number of ring spot lesions on the inoculated leaves was significantly lower in the groups irradiated with peak wavelengths of 284 nm and 291 nm, demonstrating the effectiveness of UV irradiation. In the group irradiated with a peak wavelength of 284 nm, UV damage such as leaf curling and leaf burn occurred. In the group irradiated with a peak wavelength of 291 nm, slight UV damage occurred, but not to a degree that was problematic. On the other hand, in the group irradiated with a peak wavelength of 297 nm, no UV damage occurred at all, but the number of ring spot lesions was not significantly different from the non-irradiated group, demonstrating no virus-reducing effect of irradiation.

From the above results, it was found that UV with a peak wavelength of 291 nm has the properties to reduce viral diseases while sufficiently avoiding UV damage by irradiating it at night at 600 J/ ^m2 per day.

2-2. Irradiation of tobacco at 1000 J/ ^m²
(method)
Tobacco (Nicotiana rustica) plants transplanted into 9 cm pots were placed in a 1 a (are) steel-frame greenhouse. The drainage bed was divided into three sections: a non-irradiated area (control), an area irradiated with 291 nm light, and an area irradiated with 285 nm light. Six tobacco plants were placed in each section.

In each irradiation area, the characteristics of the UV irradiated by the light irradiation module are as follows:
(1) Peak wavelength 285 nm (λp=285 nm, Δλ=10 nm),
(2) Peak wavelength 291 nm (error ±1 nm, λp = 290 to 292 nm, Δλ = 11 to 12 nm).

The daily irradiation dose by the light irradiation module was 1000 J/ ^m2 . In the (1) experiment, an SMD substrate-mounted light irradiation module (manufactured by Nikkiso Giken) with a light output of 30 mW was used, and in the (2) experiment, an SMD substrate-mounted light irradiation module (manufactured by Dowa) with a light output of 31 to 35 mW was used. The UV irradiation dose was calculated by measuring the irradiation intensity on the plant surface with a UV detector (UV-3719-4).

The irradiation method was such that the tobacco was irradiated with the above-mentioned amount of radiation every night in February for 5.5 hours (10:30 PM to 4:00 AM) so that the irradiation intensity on the plant surface was approximately 5 μW/cm ² .

Five days after the start of irradiation, virus inoculation was carried out by inoculating the sixth leaf of six tobacco plants in each plot with a previously prepared TSWV chrysanthemum isolate (grown in tobacco) using carborundum. UV irradiation continued thereafter.

Ten days after inoculation, the number of local lesions on the inoculated leaves was counted. UV damage was observed visually. Statistical analysis of the number of local lesions was performed using Tukey's test (n=6) with P<0.05 indicating a significant difference.

(result)
Figure 5 shows the appearance of the inoculated leaves of each sample 10 days after inoculation. Figure 6 shows the number of local lesions on the inoculated leaves of each sample 10 days after inoculation. As shown in Figures 5 and 6 , an average of 214 local lesions appeared on the inoculated leaves 10 days after inoculation in the non-irradiated area. Meanwhile, 15 local lesions appeared in the area irradiated with a peak wavelength of 285 nm, and 65 local lesions appeared in the area irradiated with a peak wavelength of 291 nm. This was a significant reduction of 6% in the area irradiated with a peak wavelength of 285 nm and 31% in the area irradiated with a peak wavelength of 291 nm compared to the non-irradiated area. In the area irradiated with a peak wavelength of 285 nm, UV damage such as severe leaf curl and leaf burn occurred, but in the area irradiated with a peak wavelength of 291 nm, only slight leaf curl was observed, and UV damage was hardly a problem. From the above, it was found that irradiation with UV rays with a peak wavelength of 291 nm at 1000 J/ ^m2 per day can effectively reduce TSWV infection while sufficiently avoiding UV damage.

[2-3. Irradiation of tobacco at 500 J/ ^m2 ]
(method)
Tobacco (Nicotiana rustica) plants transplanted into 9 cm pots were placed in a 1 a (are) steel frame greenhouse. The drainage bed was divided into three sections: unirradiated section 1 (control) and irradiated section 2. Six tobacco plants were placed in each section.

In each irradiation area, the characteristics of the UV irradiated by the light irradiation module are as follows:
(1) Peak wavelength 285 nm (λp=285 nm, Δλ=10 nm),
(2) Peak wavelength 291 nm (error ±1 nm, λp = 290 to 292 nm, Δλ = 11 to 12 nm).

The daily irradiation dose by the light irradiation module was 500 J/ ^m2 . In (1) above, an SMD substrate-mounted light irradiation module (manufactured by Nikkiso Giken) with a light output of 30 mW was used, and in (2) above, an SMD substrate-mounted light irradiation module (manufactured by Dowa) with a light output of 31 to 35 mW was used. The UV irradiation dose was calculated by measuring the irradiation intensity on the plant surface with a UV detector (UV-3719-4).

The irradiation method was such that the tobacco was irradiated with the above-mentioned amount of radiation for two hours at night (2:00 AM to 4:00 AM) every day from January to February, so that the irradiation intensity on the plant surface was 7 μW/cm ² .

Six days after the start of irradiation, virus inoculation was carried out by inoculating the fifth and sixth leaves of six tobacco plants in each plot with a previously prepared TSWV chrysanthemum isolate (grown in tobacco) using carborundum. UV irradiation continued thereafter.

Seven days after inoculation, the lesion area ratio (%) on the inoculated leaves was measured. UV damage was observed visually. Statistical analysis of the lesion area ratio was performed using Tukey's test with n = 4-6, with P < 0.05 indicating a significant difference.

(result)
Figure 7 shows the lesion area ratio (%) on inoculated leaves for each sample 7 days after inoculation. As shown in Figure 7, in the non-irradiated area, the lesion area ratio on inoculated leaves 7 days after inoculation was approximately 30%. On the other hand, the lesion area ratio was 12.5% in the area irradiated with a peak wavelength of 285 nm and 18.3% in the area irradiated with a peak wavelength of 291 nm, with no significant difference between the two, and both were found to have a reducing effect on lesion formation. However, there was no significant difference in lesion area ratio between the non-irradiated area and the area irradiated with a peak wavelength of 291 nm. In other words, it was found that an irradiation dose of more than 500 J/ ^m² per day was required to achieve a TSWV infection reduction effect at a peak wavelength of 291 nm. UV damage such as leaf curl occurred in the area irradiated with a peak wavelength of 285 nm, but no UV damage was observed in the area irradiated with a peak wavelength of 291 nm.

2-4. Effect of UV irradiation on tomato plants to reduce disease occurrence and prevent UV damage
(method)
Tomato plants ('Momotaro 8') transplanted into 9 cm pots were placed in a 1 a (are) steel-frame greenhouse. 'Momotaro 8' is a cultivar that is heterozygous for the ToMV resistance gene Tm- ^2a . The drainage bed was divided into two treatment zones: a non-irradiated zone (control) and an irradiated zone. Nine tomato plants were placed in each zone.

In the irradiation area, the characteristics of the UV irradiated by the light irradiation module are as follows: peak wavelength 291 nm (error ±1 nm, λp = 290-292 nm, Δλ = 11-12 nm).

The daily irradiation dose from the light irradiation module was 1170 J/ ^m² . The light irradiation module used was an SMD substrate-mounted light irradiation module (manufactured by Dowa) with a light output of 31 to 35 mW. The UV irradiation dose was calculated by measuring the irradiation intensity at the upper layer of the plant crown using a UV detector (UV-3719-4).

The irradiation method was as follows: from February to March, the tomatoes were irradiated with the above-mentioned amount of radiation for 6.5 hours at night (10:30 PM to 5:00 AM) every day, so that the irradiation intensity was approximately 5 μW/ ^cm2 in the upper layer of the plant crown.

For virus inoculation, 11 days after the start of irradiation, the ToMV strain (grown in tobacco) of the resistance gene Tm- ^2a- defeated line was inoculated into the first and second leaves of nine tomato plants in each plot at the two-leaf stage using carborundum. UV irradiation was then continued.

Eight days after inoculation, the disease index was investigated. UV damage was observed visually. The disease index was evaluated according to the following criteria:
"0": no disease,
"1": Slight yellowing and necrotic spots are observed on the inoculated leaves.
"2": Clear yellow necrotic spots are observed on the inoculated leaves.
"3": Numerous yellowed necrotic spots are observed on the inoculated leaves.
"4": Withering and death of inoculated leaves is observed.

Here, "slight" refers to the degree to which the disease can be detected with careful observation. Statistical analysis of the disease index was performed using the Mann-Whitney U test, n=9, with P<0.1 indicating a significant trend.

Furthermore, as in Example 1, the amount of virus accumulation in tomato leaves was investigated. Here, 0.15 to 0.2 g of the fourth and fifth leaves of the tomatoes used to investigate the disease index above were sampled eight days after inoculation and stored at -80°C to serve as the ToMV-inoculated sample. Total RNA was extracted and purified from this ToMV-inoculated sample using a commercially available kit. Subsequently, the amount of ToMV virus accumulation in tomato leaves was investigated by quantitative PCR analysis using the comparative Ct method, using the gene expression level of the tomato EF1a gene as a normalizer.

(result)
Figure 8 shows the disease index for each sample 8 days after inoculation. Figure 9 shows the ToMV accumulation for each sample. As shown in Figure 8, the disease index for the non-irradiated area 8 days after inoculation was approximately 2, while the index for the irradiated area was approximately 1.1. In other words, a tendency for UV irradiation to reduce ToMV disease incidence in tomatoes was observed. In addition, in the irradiated area, UV damage such as slight leaf gloss and leaf curl was observed, but this was extremely minor and had almost no effect on growth.

As shown in Figure 9, the amount of ToMV accumulated in the tomato plants in the irradiated area was approximately 64% of that in the unirradiated area, meaning that the amount was lower in the irradiated area. In other words, UV irradiation was observed to have a reducing effect on ToMV proliferation in tomato leaves.

From the above results, it was found that irradiation of UV with a peak wavelength of 291 nm at 1,170 J/ ^m² per day at night effectively reduced the incidence of ToMV disease in tomatoes while fully avoiding UV damage.

[2-5. Infection reduction effect of UV irradiation on tomatoes]
(method)
Tomato plants ('Momotaro 8') transplanted into 9 cm pots were placed in a 1 a (are) steel-frame greenhouse. The drainage bed was divided into two treatment areas: a non-irradiated area (control) and an irradiated area. Six tomato plants were placed in each area.

In the irradiation area, the characteristics of the UV irradiated by the light irradiation module are as follows: peak wavelength 291 nm (error ±1 nm, λp = 290-292 nm, Δλ = 11-12 nm).

The daily irradiation dose from the light irradiation module was 1170 J/ ^m² . The light irradiation module used was an SMD substrate-mounted light irradiation module (manufactured by Dowa) with a light output of 31 to 35 mW. The UV irradiation dose was calculated by measuring the irradiation intensity at the upper layer of the plant crown using a UV detector (UV-3719-4).

The irradiation method was as follows: every day in March, tomatoes were irradiated with the above-mentioned amount of radiation for 6.5 hours at night (10:30 PM to 5:00 AM) so that the radiation intensity was approximately 5 μW/cm ² at the upper layer of the plant crown.

For virus inoculation, three days after the start of irradiation, the ToMV strain (grown in tobacco) of the resistance gene Tm- ^2a- defeated line was inoculated into the fourth to fifth leaves of six tomato plants at the 5.5-leaf stage using carborundum. UV irradiation was then continued.

Seven days after inoculation, the number of local lesions on the inoculated leaves was counted. Statistical analysis of the number of local lesions was performed using a t-test with n = 6, with P < 0.01 indicating a significant difference.

(result)
Figure 10 shows the number of local lesions on the inoculated leaves of each sample 7 days after inoculation. As shown in Figure 10, in the non-irradiated group, an average of 79.5 local lesions appeared on the inoculated leaves 7 days after inoculation. On the other hand, in the irradiated group, 24.8 local lesions appeared, demonstrating that UV irradiation has a significant and clear effect in reducing ToMV infection in tomatoes.

From the above, it was found that ToMV infection in tomatoes can be effectively reduced by irradiating them with UV light with a peak wavelength of 291 nm at a dose of 1,170 J/ ^m² per day.

[About LED light sources]
Due to issues with the manufacturability and distribution of LED light sources, it is impossible to continuously test all peak wavelengths, and experimental data was accumulated using discontinuous peak wavelengths spaced approximately 5 nm apart, as in this experiment. However, this method is also considered to provide the necessary and sufficient accuracy for narrowing down the optimal wavelength. In other words, at the state of the art at the time of filing this application, the above-mentioned examples were conducted under conditions in which the UV peak wavelength was divided into the smallest possible range.

Assuming that the peak wavelength error of an LED light source is ±1 nm, the LED light source with a peak wavelength of 285 nm used in the above examples can also irradiate UV with a peak wavelength of 286 nm. Furthermore, an LED light source with a peak wavelength of 297 nm can also irradiate UV with a peak wavelength of 296 nm. Taking this into consideration, it can be said that the above examples demonstrate that UV with a peak wavelength in the range of 287 nm to 295 nm can most effectively reduce viral diseases in plants of the Asteraceae or Solanaceae family while avoiding UV damage.

[Additional Notes]
Furthermore, the present invention is not limited to the above-described embodiments or examples, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention.

REFERENCE SIGNS LIST 1 Light irradiation module 1a LED light source 2 Support rod 3 Electric cord 4 Plant 10 Cultivation device

Claims (3)

The method includes a step of irradiating a plant of the Asteraceae or Solanaceae family with light using an LED light source, in which the plant is irradiated with light having a peak wavelength in the range of 287 nm or more and 295 nm or less at an irradiation dose of 0.6 kJ/ ^m2 or more and less than 1.2 kJ/ ^m2 per day during a dark period ;
A cultivation method characterized in that the dark period is a predetermined period from after sunset to before sunrise . The cultivation method described in claim 1, wherein the light has a half-width within a wavelength range of the peak wavelength ±6 nm. The cultivation method according to claim 1 or 2, wherein the light has a peak wavelength in the range of 290 nm or more and 295 nm or less.