materials Article
Development of Compact High-Voltage Power Supply for Stimulation to Promote Fruiting Body Formation in Mushroom Cultivation Katsuyuki Takahashi 1,2, * , Kai Miyamoto 1 , Koichi Takaki 1,2 and Kyusuke Takahashi 3 1 2 3
*
Faculty of Science and Engineering, Iwate University, Morioka, Iwate 020-8551, Japan;
[email protected] (K.M.);
[email protected] (K.T.) Agri-Innovation Center, Iwate University, Morioka, Iwate 020-8550, Japan Morioka Forest Association, Morioka, Iwate 028-4132 Japan;
[email protected] Correspondence:
[email protected]; Tel.: +81-19-621-6460
Received: 21 November 2018; Accepted: 1 December 2018; Published: 5 December 2018
Abstract: The compact high-voltage power supply is developed for stimulation to promote fruiting body formation in cultivating L. edodes and Lyophyllum deeastes Sing. mushrooms. A Cockcroft-Walton (C-W) circuit is employed to generate DC high-voltage from AC 100 V plug power for the compact, easy handling and high safety use in the hilly and mountainous area. The C-W circuit is connected to high-voltage coaxial cable which works for high-voltage transmission and for charging up as energy storage capacitor. The output voltage is around 50 kV with several microseconds pulse width. The dimension and weight of the developed power supply are 0.4 × 0.47 × 1 m3 and 8.1 kg, respectively. The effect of the high-voltage stimulation on enhancement of fruiting body formation is evaluated in cultivating L. edodes and Lyophyllum deeastes Sing. mushrooms using the developed compact high-voltage power supply. The conventional Marx generator is also used for comparison in effect of high-voltage stimulation for fruiting body formation. L. edodes is cultivated with hosting to natural logs and the pulsed high voltage is applied to the cultivated natural logs. The substrate for Lyophyllum deeastes Sing. cultivation consists of sawdust. The results show that the fruiting body formation of mushrooms of L. edodes for four cultivation seasons and that of Lyophyllum deeastes Sing. for two seasons both increase approximately 1.3 times higher than control group in terms of the total weight. Although the input energy per a pulse is difference with the generators, the improvement of the fruit body yield mainly depends on the total input energy into the log. The effect for promotion on fruiting body formation by the developed compact high-voltage power supply is almost same that by the conventional Marx generator. Keywords: pulse power; electrical stimulation; electric field; mushroom; L. edodes; Lyophyllum deeastes Sing
1. Introduction The application of a pulsed high voltage to improve the yield in edible mushroom cultivation has also been attempted by some research groups. The fruiting capacity of shiitake mushroom (L. edodes; L. edodes) was remarkably promoted by applying a pulsed high voltage to log wood [1–3]. This effect was also recognized in L. edodes fruiting on a mature sawdust-based substrate [4,5]. The fruit body (sporocarp) yield in the electrically stimulated substrate was observed to be 1.7 times more than that in the spontaneous fruiting substrate control [6]. This effect was also recognized in the sporocarp formation of edible mushrooms: Grifola frondosa, Pholiota nameko, Flammulina velutipes, Hypsizygus marmoreus, Pleurotus ostreatus, Pleurotus. eryngii and Agrocybe cylindraceas [7–9]. Sporocarp yield, that is, fruit body formation in the electrically stimulated substrate, was observed to be 130–180% greater than Materials 2018, 11, 2471; doi:10.3390/ma11122471
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that in the spontaneous fruiting substrate control [6]. The pulsed high-voltage stimulation technique was also applied to ectomycorrhizal fungi, which form associations with some types of wood, such as Laccaria laccata and Tricholoma matsutake [9,10]. Many types of electrical power supplies have been employed to provide electrical stimulation. A large-scale 1 MV high-voltage impulse generator was used to stimulate L. edodes log wood [1]. High-voltage AC was used to stimulate an L. edodes sawdust substrate [4]. Inductive energy storage (IES) pulsed power generators have favorable features for mushroom-cultivating applications, for example, they are compact, cost effective, light and have high voltage amplification compared with capacitive energy storage generators such as the impulse generator [9,10]. The yield of L. edodes fruiting bodies was improved with high-voltage stimulation generated by the IES pulsed power generators [2,3]. The effect of the pulsed voltage stimulation on some other types of mushroom such as P. nameko and Lyophyllum decastes (L. decastes) was also confirmed using an IES generator developed for the improvement of mushroom yield [6,7]. As a result of these studies, the total harvested weight from log wood and/or sawdust substrates for mushroom cultivation increased by applying a pulsed voltage as an electrical stimulation. The hilly and mountainous area is suitable for the farmland of mushroom production because of its abundant forest resources and the significant overnight temperature changes. The method of pulsed voltage stimulation has been attracting attention as a promising technology that replaces the conventional stimulation methods such as the immersing water and the beating mushroom logs and improve the working efficiency in the hill and mountains. On the other hands, the electrical power supplies for pulsed voltage stimulation, such as Marx and IES pulsed power generators, has a heavy weight, a large size and a low safety because of its high power, large charging energy and high voltage, which is the major obstacle in a practical use. In this study, a Cockcroft-Walton (C-W) circuit is developed and employed to generate DC high-voltage from AC 100 V plug power as a compact and easy-handling high-voltage power supply for pulsed voltage stimulation. The promotion of mushroom production is affected by electric parameters such as applied voltage, pulse width and input energy. In the present experiment, the influence of the electric parameters on the mushroom production is evaluated using two types of power supply, C-W circuit and a conventional Marx generator [11]. The experiments are conducted on the mushroom production using two different fruiting types, Shiitake (L. edodes) mushroom and Hatakeshimeji (Lyophyllum deeastes Sing.) mushroom. The mushrooms are cultivated at a farmland in the hilly and mountainous area. 2. Experimental Setup 2.1. Pulsed Power Generators Figure 1 shows circuit diagram and photograph of high voltage pulsed power supply based on Cockcroft-Walton circuit (Green techno, Kanagawa, Japan; GM100) [12,13]. The circuit is consisted of an AC/DC converter, a DC/AC converter, 12 stages of ceramic capacitors and diodes, a charging capacitor, a 100 MΩ charging resistor and a spark gap switch. The ceramic capacitors have a capacity of several hundred pF. The DC/AC converter consists of a high voltage transformer driven by a resonance circuit and its output voltage of DC/AC converter is 6.2 kV with frequency of 25 kHz. The charging capacitor consists of a 2.6 m coaxial cable with the capacitance of 130 pF (50 pF/m). The AC/DC and DC/AC converters, C-W circuit, the charging capacitor and the charging resistor are inside of the box as shown in Figure 1b, which is filled by a resin for insulation. Figure 2 shows the charging voltage to the charging capacitor. Although the charging time depends on number of the stages and the frequency, the capacitor is charged during approximately 230 ms after turning the spark gap switch on because the output current of the DC/AC converter is limited.
gap switch switch is is closed, closed, the the other other switches switches are are sequentially sequentially closed closed automatically automatically and and the the connection connection of of gap capacitors is is changed changed from from parallel parallel to to series. series. The The voltage voltage is is stepped stepped up up and and is is applied applied to to the the load. load. capacitors Although the sizes of the Marx generator (1.0 m × 0.45 m × 0.45 m) and C-W circuit (0.4 m 0.47 Although the sizes of the Marx generator (1.0 m × 0.45 m × 0.45 m) and C-W circuit (0.4 m ×× 0.47 m ×× 1.0 1.0 m) m) are are almost almost same; same; however, however, the the weights weights of of them them are are 39.4 39.4 kg kg and and 8.1 8.1 kg, kg, respectively. respectively. m Therefore, the handling of C-W circuit in the farmland in hilly and mountainous areas is much easier easier Therefore, of C-W circuit in the farmland in hilly and mountainous areas is much Materials 2018,the 11, handling 2471 3 of 12 than that of Marx generator. than that of Marx generator. Coaxial cable Coaxial cable 1000 mm 1000 mm Spark gap gap switch 100 MΩ Spark switch 100 MΩ
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Figure 1. Circuit diagram (a) and photograph (b) of C-W circuit. Figure 1. Circuit Circuit diagram (a) and photograph (b) of C-W circuit.
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Figure Waveforms of Figure 2. 2. Waveforms of output output voltage voltage of of C-W C-W circuit circuit during during charging charging without without load. load. Figure 2. Waveforms of output voltage of C-W circuit during charging without load.
Figure 3 shows the circuit diagram and photograph of pulsed power generator based on Marx generator [8,11]. The Marx generator consists of 4 energy storage 0.22 µF capacitors (Maxwell, 31160), charging resistors (1 and 5 MΩ) connected to the capacitors and the spark gap switches. The capacitors are charged up using a high voltage DC power supply (Gamma high voltage research, RR3-5R/100) up to 12.5 kV. The charging time is required for approximately 10 s because of the output current limit. After charging up the capacitors, a spark gap switch is manually closed. When a spark gap switch is closed, the other switches are sequentially closed automatically and the connection of capacitors is changed from parallel to series. The voltage is stepped up and is applied to the load. Although the sizes of the Marx generator (1.0 m × 0.45 m × 0.45 m) and C-W circuit (0.4 m × 0.47 m × 1.0 m) are almost same; however, the weights of them are 39.4 kg and 8.1 kg, respectively. Therefore, the handling of C-W circuit in the farmland in hilly and mountainous areas is much easier than that of Marx generator.
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Figure Figure 3. Circuit diagram (a) and photograph (b) of Marx Marx generator. generator. Figure3. 3.Circuit Circuitdiagram diagram(a) (a)and andphotograph photograph(b) (b)of
2.2. Electrical ElectricalStimulation Stimulationto toL. L.edodes edodes 2.2. 2.2. Electrical Stimulation to L. edodes Thecultivating cultivatingmushroom, mushroom, L. L. edodes, edodes,is isinoculated inoculatedon onnatural naturallogs logsof ofQuercus Quercus crispula crispula Blume Blume two two The The cultivating mushroom, L. edodes, is inoculated on natural logs of Quercus crispula Blume two years before before the experiment. The strain strain of of the the fruiting type is (Mori. Co. Ltd., Ltd., Gunma, Gunma, years Mori#290 years before the the experiment. experiment. The The strain of the fruiting fruiting type type is is Mori#290 Mori#290 (Mori. (Mori. Co. Co. Ltd., Gunma, Japan). The dimensions of shiitake mushroom logs with a length of 0.9 m and a diameter of about Japan). 0.1 Japan). The The dimensions dimensions of of shiitake shiitake mushroom mushroom logs logs with with aa length length of of 0.9 0.9 m m and and aa diameter diameter of of about about 0.1 0.1 m. The logs are covered with a blackout curtain to maintain the moisture content in the logs hosting m. m. The The logs logs are are covered covered with with aa blackout blackout curtain curtain to to maintain maintain the the moisture moisture content content in in the the logs logs hosting hosting themushroom mushroom hyphae. hyphae. After Aftertwo twoyears yearsincubation, incubation,the theblackout blackoutcurtain curtainis isunveiled unveiledand andthe thelogs logsare are the the mushroom hyphae. After two years incubation, the blackout curtain is unveiled and the logs are placed side by side under environment as shown in Figure 4. placed placed side side by by side side under under environment environment as as shown shown in in Figure Figure 4. 4. No.9 No.9 No.10 No.10
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Figure Figure4. Arrangement(a) (a)and andphotograph photograph(b) Figure 4. Arrangement Arrangement (a) and photograph (b) of of L. L. edodes edodes logs logs for for cultivation. cultivation.
Mushroom fruits fruits body body production production varies varies among amonglogs, logs, which whichmakes makesthe theevaluation evaluationdifficult. difficult. Mushroom Mushroom fruits body production varies among logs, which makes the evaluation difficult. Therefore, it is needed to reduce the influence of variation on the evaluation. In the experiments, Therefore, Therefore, itit is is needed needed to to reduce reduce the the influence influence of of variation variation on on the the evaluation. evaluation. In In the the experiments, experiments, the the total total 80 80 logs logs are are divided divided into into 44 pulsed pulsed voltage voltage stimulated stimulated groups groups and and aa control control group group without without pulsed pulsed
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the total 80 logs are divided into 4 pulsed voltage stimulated groups and a control group without voltagevoltage to make the average amount of mushroom production of each group almost same after 1st pulsed to make the average amount of mushroom production of each group almost same after flash. The number of of logs for 16 logs logs and and numbered numbered 1st flash. The number logs foreach eachstimulated stimulatedgroup groupand andaacontrol control group group is is 16 from 1 to 16. After the 1st flash, the logs are alternately rearranged as shown in Figure 4a to reduce from 1 to 16. After the 1st flash, the logs are alternately rearranged as shown in Figure 4a to reduce the the influence of arrangement positions. influence of arrangement positions. Thepulsed pulsed voltage voltage is is applied applied to The to the the logs logs 11 month monthbefore beforethe thedate datethat thatmushroom mushroomfruit fruitbody bodyis usually expressed. Since the impedance of the logs is affected by the moisture content of wood, the is usually expressed. Since the impedance of the logs is affected by the moisture content of wood, pulsed voltage is applied when that day and its previous day are not rained. The fruit body of the pulsed voltage is applied when that day and its previous day are not rained. The fruit body of mushroomscan canbe becropped croppedfrom fromthe thelogs logsin inevery everytwo twoseasons, seasons, spring spring and and autumn, autumn, over over two two years. years. mushrooms Therefore, the experiments are conducted for 4 seasons, from 15 May to 20 June in 2017 (1st flush), Therefore, the experiments are conducted for 4 seasons, from 15 May to 20 June in 2017 (1st flush), from22 22September September to to22 22November November in in 2017 2017 (2nd (2nd flush), flush), from from 44 April April to to 11 11 June June in in 2018 2018 (3rd (3rd flush) flush) from and from 17 September to 9 November in 2018 (4th flush). Figure 5 shows the experimental setup for and from 17 September to 9 November in 2018 (4th flush). Figure 5 shows the experimental setup for pulse application to the logs. To apply the pulse voltages to logs, the electrode plate was installed pulse application to the logs. To apply the pulse voltages to logs, the electrode plate was installed atat bothends endsof oflogs logsplaced placedon onan aninsulator insulatorof ofacrylic. acrylic.The Thepulsed pulsedvoltages voltagesare areapplied appliedto tothe thelogs logsat atthe the both first day of 2nd and 4th flush seasons using the C-W circuit and the Marx generator. The total input first day of 2nd and 4th flush seasons using the C-W circuit and the Marx generator. The total input energyinto intothe thelogs logsisiscontrolled controlledby bythe theamplitude amplitudeand andthe thenumber numberof ofthe theapplying. applying.Four Fourgroups groupsare are energy stimulated by the pulsed voltages with the different amplitudes, 30 kV and 50 kV, for each generator. stimulated by the pulsed voltages with the different amplitudes, 30 kV and 50 kV, for each generator. Thenumber numberof ofpulses pulsesisisfixed fixedat at500 500times timesin inthe thecase caseof ofC-W C-Wcircuit circuitand and55times timesin inthe thecase caseof ofMarx Marx The generator. Because the mechanical stress to the mushroom hypha could be affected to the mushroom generator. Because the mechanical stress to the mushroom hypha could be affected to the mushroom production,the thelogs logsin inthe thecontrol controlgroup groupare areset setthe the experimental experimental setup setup without without the the applying applying voltage. voltage. production, The fruit bodies of mushroom are cropped when their pileus is 80% opened, which is suitable to be The fruit bodies of mushroom are cropped when their pileus is 80% opened, which is suitable to be in in the market. the market.
HV probe
Oscilloscope
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Electrode plate Current probe
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Insulator Ground Figure Figure5.5.Experimental Experimentalsetup setupfor forpulsed pulsedvoltage voltagestimulation stimulationto tothe theL.L.edodes edodeslogs. logs.
2.3. Electrical Stimulation to Lyophyllum deeastes Sing 2.3. Electrical Stimulation to Lyophyllum deeastes Sing The substrate for Lyophyllum deeastes Sing. cultivation consists of sawdust from Cryptomeria The substrate for Lyophyllum deeastes Sing. cultivation consists of sawdust from Cryptomeria japonica produced by Kamiyotsuba agricultural cooperative (Kami, Miyagi, Japan). The strain of the japonica produced by Kamiyotsuba agricultural cooperative (Kami, Miyagi, Japan). The strain of the fruiting type is Miyagi LD-2 (Tsukidate bio service. Co. Ltd., Miyagi, Japan). The dimensions of the fruiting type is Miyagi LD-2 (Tsukidate bio service. Co. Ltd., Miyagi, Japan). The dimensions of the sawdust substrate are 0.12 m × 0.2 m × 0.1 m and it has a cuboid-block shape. The weight of the sawdust substrate are 0.12 m × 0.2 m × 0.1 m and it has a cuboid-block shape. The weight of the substrate was 2.5 kg ± 200 g. Lyophyllum deeastes Sing. fungus are inoculated on the block and the substrate was 2.5 kg ± 200 g. Lyophyllum deeastes Sing. fungus are inoculated on the block and the incubated for 50–60 days under the temperature of 22–23 deg-C with a relative humidity of 65–70%. incubated for 50–60 days under the temperature of 22–23 deg-C with a relative humidity of 65–70%. The blocks are stimulated by the pulsed voltage after the incubation. The pulsed voltage was applied The blocks are stimulated by the pulsed voltage after the incubation. The pulsed voltage was applied to a needle electrode with a 4 mm diameter driven into the block to a depth of 50 mm, as shown in to a needle electrode with a 4 mm diameter driven into the block to a depth of 50 mm, as shown in Figure 6, using C-W circuit. The total input energy into the blocks are controlled by the amplitude Figure 6, using C-W circuit. The total input energy into the blocks are controlled by the amplitude and number of the applying voltage. Four groups are stimulated by the pulsed voltages with the and number of the applying voltage. Four groups are stimulated by the pulsed voltages with the different amplitudes, 30 kV and 50 kV and the different numbers of pulses, 100 times and 500 times. different amplitudes, 30 kV and 50 kV and the different numbers of pulses, 100 times and 500 times. The number of blocks for each group is 16 and numbered from 1 to 16. The number of blocks for each group is 16 and numbered from 1 to 16.
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HV HVprobe probe
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Oscilloscope Oscilloscope Needleelectrode electrode Needle Current probe
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Insulator Insulator Ground Ground Figure 6. 6.Experimental setupforfor pulsed voltage stimulation to the Lyophyllum Figure Experimental setup pulsed voltage stimulation to the Lyophyllum deeastes Sing.deeastes sawdust Sing. Figure 6. Experimental setup for pulsed voltage stimulation to the Lyophyllum deeastes Sing. sawdust block. sawdust block. block. the stimulation, blocksare areburied buried under under the thethe unburied upper surface as as AfterAfter the stimulation, thethe blocks thesoil soilwith with unburied upper surface After the stimulation, the blocks are buried under the soil with the unburied upper surface as shown in Figure 7. The blocks are alternately arranged as shown in Figure 7a to reduce the influence shown in Figure 7. The blocks are alternately arranged as shown in Figure 7a to reduce the influence shown in Figure 7. The blocks are alternately arranged as shown in Figure 7a to reduce the influence ofarrangement the arrangement positions.The Thefruit fruitbodies bodies of mushroom are cropped when theirtheir pileus is 80% of the positions. are cropped when pileus 80% of opened, the arrangement positions. fruit bodies of of mushroom mushroom are cropped when their pileus is is 80% which is suitable to beThe in the market. opened, which is suitable totobebeininthe opened, which is suitable themarket. market. Control
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Figure 7. Arrangement (a) (a) and photograph (b) of the Lyophyllum deeastes Sing. (b) sawdust block for cultivation.
Figure Arrangement(a) (a)and andphotograph photograph (b) (b) of of the the Lyophyllum Lyophyllum deeastes Figure 7. 7. Arrangement deeastes Sing. Sing. sawdust sawdustblock blockforfor cultivation. cultivation. 3. Results
3. Results 3. 3.1. Results Electrical Stimulation to Logs and Cropping Fruits Body of L. edodes Figure 8a,b shows the typical waveforms of Body the applied voltage and output current to the 3.1.3.1. Electrical Stimulation totoLogs Fruits of Electrical Stimulation Logsand andCropping Cropping Fruits Body of L. L. edodes edodes shiitake mushroom logs using the C-W circuit and the Marx generator in 4th flush season. When the
Figure 8a,b8a,b the the typical waveforms of the applied and output current tolog theand shiitake typical waveforms ofcharged the applied voltage and output to the gapFigure switch ofshows theshows circuits is shortened, the voltage atvoltage the capacitors is applied tocurrent the mushroom logs using theusing C-W the circuit Marx incalculated 4thinflush season. When thethe gap shiitake mushroom logs C-Wand circuit and thegenerator Marx 4th flush season. When then the voltage exponentially decays. The the impedance of thegenerator log is from the waveforms and 2.67 standard deviation 0.64 kΩcharged in 2nd flush season and 5.29 kΩ with a standard gap switch ofkΩ thewith circuits is shortened, theofvoltage atcapacitors the capacitors is applied to the switch ofisthe circuits is ashortened, the voltage charged at the is applied to the loglog andand then deviation of 1.97 kΩ in decays. 4th flush season. The differences the impedance could be caused by the and the voltage exponentially decays. The impedance the is calculated from the waveforms thethen voltage exponentially The impedance of theofof log islog calculated from the waveforms moisture contents of the logs and a decay with a hypha filled in the log. The time constant in the cases and is kΩawith a standard deviation of 0.64 2ndflush flushseason seasonand and 5.29 5.29 kΩ is 2.67 kΩ2.67 with standard deviation of 0.64 kΩkΩ in in 2nd kΩwith witha astandard standard of C-W circuit and Marx generator in the case of 2nd flush season are approximately 1.2 μs with athe deviation 1.97 4thflush flushseason. season.The The differences differences of byby deviation of of 1.97 kΩkΩ inin4th of the the impedance impedancecould couldbebecaused caused the standard deviation of 0.28 μs and 190 μs with a standard deviation of 51 μs, respectively and those moisture contents of the logs and a decay with a hypha filled in the log. The time constant in the cases moisture contents of the logs and a decay with a hypha filled in the log. The time constant in the cases the circuit case of 4th flush are approximately μsflush with aseason standard deviation of 0.61 μs and 410 a of in C-W and Marxseason generator inthe thecase case of of150 2nd are 1.21.2 μsµswith of C-W circuit and Marx generator in 2nd flush seasonthe areapproximately approximately with a μs with a standard deviation of 0.41 ms, respectively. Although impedances and the time standard deviation of 0.28 μs and 190 μs with a standard deviation of 51 μs, respectively and those standard deviation of 0.28 µs and 190 µs with a standard deviation of 51 µs, respectively and those in in the case of 4th flush season are approximately 150 μs with a standard deviation of 0.61 μs and 410 the case of 4th flush season are approximately 150 µs with a standard deviation of 0.61 µs and 410 µs μs with a standard deviation of 0.41 ms, respectively. Although the impedances and the time with a standard deviation of 0.41 ms, respectively. Although the impedances and the time constants
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constants are difference, the total input energy into the logs are almost same in the two seasons. In are input energypulses into the logs are almost same of in 30 thekV two seasons. In Materials 2018, the 11, x total FOR PEER REVIEW 7 ofthe 12 case the difference, case of C-W circuit, high voltage with maximum voltage and 50 kV are applied of C-W circuit, high voltage pulses with maximum voltage of 30 kV and 50 kV are applied for 500 for 500 times and the total input energy are 60 J and 148 J, respectively. In the case of Marx generator, constants are difference, the total input energy into the logs are almost same in the two seasons. In times andvoltage the total inputwith energy are 60 J and 148 of J, respectively. theare case of Marx the high the high pulses maximum voltage 30 kV and 50InkV applied to generator, the cultivation log the case of C-W circuit, high voltage pulses with maximum voltage of 30 kV and 50 kV are applied voltage pulses with maximum voltage of 30 kV and 50 kV are applied to the cultivation log for 5 times for 5 times and the total input energy are 127 J and 345 J, respectively. Assuming that the electric field for 500 times and the total input energy are 60 J and 148 J, respectively. In the case of Marx generator, and thelog total input energy are 127 Jfield and inside 345 J, respectively. Assuming that the50electric field in 56 thekV/m, log is in the is voltage uniform, the electric log case 30are kV and 34 and the high pulses with maximum voltage of in 30 the kV and 50ofkV applied tokV the is cultivation log uniform, the electric field inside log in the case of 30 kV and 50 kV is 34 and 56 kV/m, respectively. respectively. for 5 times and the total input energy are 127 J and 345 J, respectively. Assuming that the electric field
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Time (a) [s]
(a) (b) Figure 8. Typical waveforms of applied voltage and current to the L. edodes logs using (a) C-W circuit Figure 8. Typical waveforms of applied voltage and current to the L. edodes logs using (a) C-W circuit generator. and (b) Marx generator. and (b) Marx generator.
Figure 9a–c shows the diurnal change of the accumulated weight of fruitbody of shiitake Figure 9a–c shows the diurnal change of the accumulated weight of fruitbody of shiitake mushroom in in three seasons, seasons, 2ndflush, flush, 3rdflush flushand and4th 4thflush. flush. In the 2nd flush (Figure flush (Figure 9a), 9a), the mushroom three in three seasons,2nd 2nd flush, 3rd 3rd flush and 4th flush. In In thethe 2nd2nd flush (Figure 9a), the the accumulated of fruit body in the case of applying voltage is higher than that in the control accumulated of fruit body in the case of applying voltage is higher than that in the control group with accumulated of fruit body in the case of applying voltage is higher than that in the control group with group the duration. harvest duration. The yield ofin fruit body in the cases of groups thegroups stimulate groups of 30 kV the harvest duration. The yield fruit body thecases casesof ofthe the stimulate 30 kV 50 and thewith harvest The yieldofof fruit body in the stimulate of 30ofkV and kV50 and 50 kV using the C-W circuit and 30 kV and 50 kV using the Marx generator are 1.15, 1.38, 1.49 and usingusing the C-W circuit and 3030 kV theMarx Marxgenerator generator 1.15, andtimes 1.66 times the C-W circuit and kV and50 50 kV using using the areare 1.15, 1.38,1.38, 1.491.49 and 1.66 1.66 times higher than the control the 3rd the pulsed are not applied to logs higher than control group.InIngroup. the3rd 3rdIn flush, the pulsed voltages arevoltages notnot applied to logs (Figure higher than the the control group. the flush, theflush, pulsed voltages are applied to logs (Figure 9b),9b), the the yield of fruit body doesnot not increase in stimulated groups ingroups comparison with with (Figure of fruit body does not increase in theofof cases of stimulated in comparison 9b), the yield ofyield fruit body does increase in the thecases cases stimulated groups in comparison 2nd yield fruit body the cases of groups of 30 and 50 theusing with 2ndflush. flush. The yield of fruit body incases the cases ofstimulated the stimulated groups 30and kVkV and 50 using kV 2nd flush. TheThe yield of of fruit body ininthe of the the stimulated groups of kV 30ofkV 50using kV the C-W circuit and 30 kV using the Marx generator are 1.04, 1.14 and 1.04 times higher than the control the circuit 30using kV using the Marx generator are1.14 1.04,and 1.14 and 1.04higher times than higher the C-WC-W circuit and and 30 kV the Marx generator are 1.04, 1.04 times thethan control group in the 3rd flush. The yield in the case of the stimulated group of 50 kV using the Marx generator control in flush. the 3rd flush. yield in of the case of the stimulated group of 50 the kV Marx usinggenerator the Marx group ingroup the 3rd The yieldThe in the case the stimulated group of 50 kV using is much lower than other groups. Generally, the yield depends on the yield in previous flush, which generator is much lower than other groups. Generally, the yield depends on the yieldflush, in previous is much lower other groups. the yield in previous could causethan the decrease of the Generally, yield. In thethe 4thyield flush,depends the fruit on bodies are cropped from only thewhich flush, which could cause the decrease of the yield. In the 4th flush, the fruit bodies are cropped couldstimulated cause the decrease of the yield. In the 4th flush, the fruit bodies are cropped from onlyfrom the groups of 30 kV using C-W circuit and 30 and 50 kV using the Marx generator. only the stimulated groups of 30 kV using C-W circuit and 30 and 50 kV using the Marx generator. stimulated groups of 30 kV using C-W circuit and 30 and 50 kV using the Marx generator.
(a)
(b)
Figure 9. Cont.
(a)
(b)
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(c) (c) Figure 9. 9. Diurnal Diurnal change change of of the the accumulated accumulated weight weight of of fruitbody fruitbody of of L. L. edodes edodes in in (a) (a) 2nd 2nd flush, flush, (b) (b) 3rd 3rd Figure flush and (c) 4th flush. flush and (c) 4th flush. flush.
Average cropped bodycropped fruitbody weightofoffruit Averageweight per log[g/log] peraalog[g/log]
Figure 10 shows the average weight ofof fruit body cropped perper log, cropped for 44for seasons. The Figure 10 shows showsthe theaverage averageweight weightof fruit body cropped a log, cropped 4 seasons. Figure fruit body cropped per aa log, cropped for seasons. The error bars represent the standard error. Since the logs are divided into 5 groups stimulated groups The error bars represent the standard error. Since the logs are divided into 5 groups groups error bars represent the standard error. Since the logs are divided into 5 groups stimulated groups after 1st 1stflash, flash,the theamount amountofof of the weight of fruit fruit body is almost almost same. The average average weight ofbody fruit after the weight of of fruit body is almost same. The The average weight of fruit after 1st flash, the amount the weight body is same. weight of fruit body is improved improved by applying applying pulse voltages voltages and increased increased with increasing increasing totalenergy input energy energy into is improved by applying pulse voltages and increased with increasing total input into theinto log. body is by pulse and with total input the log. The average weight of fruit body in the case of the Marx generator is approximately 1.3 times The average weight of fruit body in the case of the Marx generator is approximately 1.3 times higher the log. The average weight of fruit body in the case of the Marx generator is approximately 1.3 times higher than thatcontrol in the the control control group. The show resultsthat show that the improvement improvement of the the fruit body yield than that in the group. group. The results thethat improvement of the fruit body yield mainly higher than that in The results show the of fruit body yield mainly depends depends on the the total inputinto energy into the log. log. depends on the total input energy the into log. the mainly on total input energy 500 500 450 450 400 400 350 350 300 300 250 250 200 200 150 150 100 100 50 50 0 0
111% 111%
117% 117%
127% 127%
126% 126%
Control Control
C-W C-W Marx Marx C-W C-W Marx Marx 30kV 50kV 30kV 50kV 30kV 50kV 30kV 50kV 500times 500times 5times 5times 500times 500times 5times 5times 60 J 148 J 127 J 345 J 60 J 148 J 127 J 345 J 1st flush 2nd flush 3rd flush 4th flush 1st flush 2nd flush 3rd flush 4th flush
Figure 10. Average yield fruit Figure 10. 10. Average Average yield yield of of fruit fruit body body fruitbody fruitbody of of L. L. edodes edodesper peraaalog logfor for444flushes. flushes. Figure of body fruitbody of L. edodes per log for flushes.
3.2. Electrical Stimulation to Blocks and Cropping Fruits Body of Lyophyllum deeastes 3.2. Electrical Electrical Stimulation Stimulation to to Blocks Blocks and and Cropping Cropping Fruits Fruits Body Body of of Lyophyllum Lyophyllum deeastes deeastes 3.2. Figure 11 shows waveforms of applied voltage and output current to the Lyophyllum deeastes Figure 11 11 shows shows waveforms waveforms of of applied applied voltage and and output current current to the the Lyophyllum deeastes deeastes Figure mushroom block. The resistivity of the bed isvoltage 45 Ωm andoutput the impedanceto of the Lyophyllum block is calculated mushroom block. The resistivity of the bed is 45 Ωm and the impedance of the block is calculated mushroom block. Theand resistivity of with the bed is 45 Ωmdeviation and the 0.12 impedance of the the block is calculated from the waveforms is 0.35 kΩ a standard kΩ. Because coaxial cable in from the waveforms and is 0.35 kΩ with a standard deviation 0.12 kΩ. Because the coaxial cable in in from the circuit waveforms is 0.35 kΩ with standard deviation 0.12 kΩ. Because coaxial cable the C-W acts asand a transmission line,athe waveforms of applied voltage andthe output current are the C-W circuit acts as a transmission line, the waveforms of applied voltage and output current are the C-W circuit a transmission line, the waveforms of applied voltage and output current are distorted and doacts not as have an exponential shape by the forward and backward transmitted waves [14]. distorted and and do do not not have have an an exponential exponential shape shape by by the the forward forward and and backward backward transmitted transmitted waves waves distorted Figure 12 shows the electric field distribution analyzed by the finite element method (Ansoft Maxwell [14]. Figure Figure 12 12 shows shows the the electric electric field field distribution distribution analyzed analyzed by by the the finite element element method (Ansoft (Ansoft [14]. 2D). The analysis results show that the electric field inside of the block finite is concentratedmethod at the tip of the Maxwell 2D). The analysis results show that the electric field inside of the block is concentrated at the the Maxwell 2D). The analysis show thatwith the electric field voltage inside ofofthe is concentrated needle and is ranged from results 18 to 360 kV/m the applied 30 block kV. The input energyat per a tip of of the the needle needle and and is ranged ranged from from 18 18 to to 360 360 kV/m kV/m with with the applied applied voltage of of 30 30 kV. kV. The The input input tip pulse in the cases of 15isand 30 kV applied voltages are 54 mJthe and 27 mJ, voltage respectively. The total input energy per a pulse in the cases of 15 and 30 kV applied voltages are 54 mJ and 27 mJ, respectively. energy in per a case pulseofin15the 15100 andtimes 30 kV applied aretimes 54 mJpulses and 27 mJ, respectively. energy the kVcases is 5.4 of J for pulses andvoltages 27 J for 500 and that of 30 kV is The total total input input energy energy in in the the case case of of 15 15 kV kV is is 5.4 5.4 JJ for for 100 100 times times pulses pulses and and 27 27 JJ for for 500 500 times times pulses pulses The 27 J for 100 times pulses and 160 J for 500 times pulses. and that that of of 30 30 kV kV is is 27 27 JJ for for 100 100 times times pulses pulses and and 160 160 JJ for for 500 500 times times pulses. pulses. and
[A] [A] Current [A] Current Current
[kV][kV] Voltage [kV]Voltage Voltage
mushroom from 27 August to 25 change Octoberofinaccumulated 2017 and from 13–21ofJune in 2018.ofThe pulsed voltage Figure 13a–c shows diurnal weight fruitbody Lyophyllum deeastesis applied to the logs at the first dayOctober using the C-W and circuit. Figure shows the average weight of fruit mushroom from 27 August to 25 in 2017 from 13–2114 June in 2018. The pulsed voltage is body cropped aPEER block for two flush The error bars represent standard error. The Materials 2018, 11,logs xper FORat REVIEW of 12 applied to the the first day using theseasons. C-W circuit. Figure 14 shows the the average weight of9fruit average weightper of fruit body by applying pulsebars voltages and increased witherror. increasing body cropped a block forwas twoimproved flush seasons. The error represent the standard The Figure 13a–c shows diurnal change of accumulated weight of fruitbody of Lyophyllum deeastes total input energy intobody the block. average weight of fruit was improved by applying pulse voltages and increased with increasing Materials 2018, 11, 2471 9 of 12 mushroom from 27into August to 25 October in 2017 and from 13–21 June in 2018. The pulsed voltage is total input energy the block. applied to the logs at the first30 day using the C-W circuit. Figure 14 shows the average weight of fruit body cropped per a block for 30 two flush seasons. The error bars represent the standard error. The average weight of fruit body was improved by applying pulse voltages and increased with increasing 100 20 total input energy into the block. 100 Voltage 20 30 Voltage Current 50 10 Current 50 10 100 20 0 0 Voltage 0 0 0.5 10 Current Time [s] 10 0 0.5 150 Time [s] Figure 11. Waveforms of applied voltage and current to the Lyophyllum deeastes Sing. Sawdust block Figure 11. Waveforms of applied applied voltage voltage and and current current to to the the Lyophyllum Sing. Sawdust Sawdust block block using. 11. C-W circuit. Figure Waveforms of Lyophyllum deeastes deeastes Sing. 0 0 using. C-W circuit. using. C-W circuit.
0
0.5 Time [s]
E[V/m]
1
Needle electrode
E[V/m]3.6×105 5
Electrode
3.4×10 Figure 11. Waveforms of applied voltage and current to the Lyophyllum 3.2×10 plate deeastes Sing. Sawdust block 3.6×10 Needle electrode 3.0×10 Electrode 3.4×10 Block 2.8×10 using. C-W circuit. 3.2×10 100 mm plate 5
5 5
5 5
5
2.6×105 3.0×105 5 2.4×10 2.8×105 5 2.2×10 2.6×105 5 2.0×10 2.4×105 5 1.8×10 E[V/m] 2.2×105 5 1.7×10 2.0×105 5 1.5×10 55 1.8×10 5 3.6×10 1.3×10 55 1.7×10 5 3.4×10 1.1×10 55 1.5×10 4 3.2×10 9.4×10 5 1.3×10 5 4 3.0×10 7.5×10 55 1.1×10 4 2.8×10 5.6×10 45 9.4×10 4 2.6×10 3.7×10 45 7.5×10 4 2.4×10 1.8×10 4 5.6×10 2.2×10 0.0 45 3.7×10 2.0×105 4 1.8×10 1.8×105 0.0 1.7×105 1.5×105 1.3×105 1.1×105 9.4×104 7.5×104 5.6×104 3.7×104 1.8×104 0.0
Block 50 mm 150 mm 50 mm Needle electrode 150 mm Insulator Block Insulator
100 mm
Electrode plate 200 mm 100 mm
Ground 200 mm 50 mm Ground
mm of Lyophyllum deeastes Sing. Sawdust block for applied Figure 12. Electric field distribution 150 inside Figure of 12.30Electric field distributionInsulator inside of Lyophyllum deeastes Sing. Sawdust block for applied voltage kV. voltage of 30 kV. Figure 12. Electric field distribution inside of Lyophyllum deeastes Sing. Sawdust block for applied 200 mm
Figure of 13a–c shows diurnal change of accumulated weight of fruitbody of Lyophyllum deeastes voltage 30 kV.
Ground mushroom from 27 August to 25 October in 2017 and from 13–21 June in 2018. The pulsed voltage is applied to the logs at the first day using the C-W circuit. Figure 14 shows the average weight of fruit Figure body cropped per a block for two flushofseasons. The errorSing. bars Sawdust represent the for standard 12. Electric field distribution inside Lyophyllum deeastes block appliederror. The average weight of fruit body was improved by applying pulse voltages and increased with voltage of 30 kV. increasing total input energy into the block.
(a) (a)
(b) (b)
(a)
(b)
Figure 13. Diurnal change of the accumulated weight of fruitbody of Lyophyllum deeastes Sing in (a) 1st flush and (b) 2nd flush.
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Figure 13. Diurnal change of the accumulated weight of fruitbody of Lyophyllum deeastes Sing in (a) 10 of 12 1st flush and (b) 2nd flush.
Average weight of fruit body cropped per a log[g/log]
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500
400
119%
114%
121%
127%
15kV 100times
15kV 500times
30kV 100times
30kV 500times
5.4 J
27 J
32 J
160 J
300 200 100 0 Control
2017 autum
2018 spring
Figure 14. Average yield of fruit body fruitbody of Lyophyllum deeastes Sing per a log for 2 flush seasons. Figure 14. Average yield of fruit body fruitbody of Lyophyllum deeastes Sing per a log for 2 flush 4. Discussion seasons.
When the pulsed voltages are applied to the logs, the mushroom hyphae are subjected to an 4. Discussion electric field. When the frequency component of the applied pulse voltage is less than several MHz, the membrane the cell, rather than the inside of the cell,the is mainly subjected to the fieldto[15]. When the of pulsed voltages are applied to the logs, mushroom hyphae areelectric subjected an The hyphae accelerated and displaced according the electric by the electrostatic forceMHz, such electric field.are When the frequency component of the to applied pulsefield voltage is less than several as amembrane Coulomb force couldthe induce physical on the hyphae.toItthe haselectric been suggested the of the[16], cell, which rather than insidea of the cell,stress is mainly subjected field [15]. that hyphae some genes encoding enzymes such as laccase and protease could be upregulated the The are accelerated and displaced according to the electric[17–19] field by the electrostatic forcebysuch physical stress force [1,5] in thewhich same manner as other physical stress stresses scrapping of been surface hyphae, as a Coulomb [16], could induce a physical onsuch the as hyphae. It has suggested which induces fruit body formation theand physical stress relates to thebefruit body formation, that some genes encoding enzymes [16,20]. such as Since laccase protease [17–19] could upregulated by the the flush is accelerated and the amount of cropped fruitbody is increased in the seasons that the logs physical stress [1,5] in the same manner as other physical stresses such as scrapping of surface hyphae, are stimulated the voltage pulses as [16,20]. shown inSince Figure which inducesby fruit body formation the10.physical stress relates to the fruit body The total edodes mushroom and yieldthe cropped from the logs is improved approximately times formation, the L. flush is accelerated amount of cropped fruitbody is increased in the1.3 seasons fromthe thelogs control group by stimulating. The Lyophyllum deeastes Sing.10. mushroom cropped from the that are stimulated by the voltage pulses as shown in Figure logs The is also improved 1.2 times. has been reported Lyophyllum deeastes Sing.1.3 yield is total L. edodes about mushroom yield It cropped from the logsthat is improved approximately times improved as same level using Marx-IES circuit. These results show the effect for promotion on fruiting from the control group by stimulating. The Lyophyllum deeastes Sing. mushroom cropped from the bodyisformation by theabout developed compact high-voltage power is almost same thatyield by the logs also improved 1.2 times. It has been reported thatsupply Lyophyllum deeastes Sing. is conventional improved as Marx same generator. level using Marx-IES circuit. These results show the effect for promotion on In the economic aspect, the developed productioncompact improvement of 1.2 to power 1.3 times usingiselectric fruiting body formation by the high-voltage supply almoststimulation same that directly increases the farmer’s income. The electric power consumption of the high voltage pulsed by the conventional Marx generator. power based aspect, on C-Wthe circuit for the improvement operation of the electrical stimulation is measured using In supply the economic production of 1.2 to 1.3 times using electric stimulation an electric power monitor (SANWA SUPPLY, TAP-TST7) and is less than 40 shows that the directly increases the farmer’s income. The electric power consumption of W, thewhich high voltage pulsed energysupply cost is low enough to circuit be negligible. The time cost forelectrical the operation and the load using of the power based on C-W for the operation of the stimulation is work measured electrical could(SANWA be much SUPPLY, lower than the traditional such as a that beating an electricstimulation power monitor TAP-TST7) and isstimulation less than 40methods W, which shows the and a shaking. Furthermore, acceleration of time the flush as shown in Figures andwork 13 could energy cost is low enough to the be negligible. The cost for the operation and9 the loadreduce of the the total time cost forcould a cropping period, could enhance the workmethods efficiency. Therefore, the electrical stimulation be much lower which than the traditional stimulation such as a beating electrical stimulation has a high potential for the farmer’s management improvement. and a shaking. Furthermore, the acceleration of the flush as shown in Figures 9a and 13a could reduce the total time cost for a cropping period, which could enhance the work efficiency. Therefore, the 5. Conclusions electrical stimulation has a high potential for the farmer’s management improvement. The C-W circuit is developed and employed to generate DC high-voltage from AC 100 V plug 5. Conclusions power as a compact and easy-handling high-voltage power supply for pulsed voltage stimulation. The influence the electric parameters on the mushroom production is evaluated twoVtypes The C-W of circuit is developed and employed to generate DC high-voltage fromusing AC 100 plug of power supply, C-W circuit and a conventional Marx generator. The weight of the C-W circuit is power as a compact and easy-handling high-voltage power supply for pulsed voltage stimulation. approximately 5 times lower parameters than the Marx The handling of C-W circuit inusing the farmland in The influence of the electric on generator. the mushroom production is evaluated two types hilly and mountainous areas is much easier than that of Marx generator. The experiments are conducted of power supply, C-W circuit and a conventional Marx generator. The weight of the C-W circuit is on the mushroom production using two different fruiting types, Shiitake (L. edodes) mushroom and
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Hatakeshimeji (Lyophyllum deeastes Sing.) mushroom. The fruiting body formation of mushrooms of L. edodes for four cultivation seasons and that of Lyophyllum deeastes Sing. for two seasons both increase approximately 1.3 times higher than control group in terms of the total weight. Although the input energy per a pulse is difference with the generators, the improvement of the fruit body yield mainly depends on the total input energy into the log. The effect for promotion on fruiting body formation by the developed compact high-voltage power supply is almost same that by the conventional Marx generator. Author Contributions: Katsuyuki Takahashi (K.T.), K.M. and Koichi Takaki (K.T.) conceived and designed the experiments; K.M. and Kyusuke Takahashi (K.T.) performed the experiments; K.M. analyzed the data; Katsuyuki Takahashi (K.T.) and Koichi Takaki (K.T.) wrote the paper. Funding: This work was supported by a Grant-in-Aid for Scientific Research (A) from the Japan Society for the Promotion of Science, Grant Number 15H02231. Acknowledgments: The author would like to thank Yuichi Sakamoto at Iwate Biotechnology Research Center for his valuable comments and discussions. The author would also like to thank Yutaka Shida at the Iwate University technical staff. Conflicts of Interest: The authors declare no conflict of interest.
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