A wearable microneedle sensor and non-destructive monitoring method for judging the healing state of grafted seedlings of melon vegetables

Abstract

The present application relates to a kind of judging melon vegetable grafting seedling healing state wearable microneedle sensor and nondestructive monitoring method, for judging melon vegetable grafting seedling healing state, comprising: electrode sensing module, by microneedle electrode array, respectively when detecting it is connected in stock and scion place;Signal acquisition and conversion module, after receiving excitation signal, excite the grafting seedling to be measured between two microneedle electrodes, obtain grafting junction part voltage signal, the real part and the imaginary part of output signal;Data processing and display module, the impedance of grafting seedling to be measured is calculated, after comparison, grafting healing result is shown by LED;Power module, signal acquisition and conversion module and data processing and display module are powered.The present application has no influence on grafting seedling healing growth, low in cost, can be in-depth grafting seedling stem tissue, using impedance change rule can detect the physiological change state of grafting seedling in healing period, realize real-time monitoring, obtain more reliable signal data.

Description

Technical Field

[0001] This invention belongs to the field of plant monitoring technology, specifically relating to a wearable microneedle sensor and monitoring method for determining the healing status of grafted seedlings of cucurbit vegetables. Background Technology

[0002] Under protected cultivation conditions, cucurbit vegetables often face problems such as various soil-borne diseases, low temperatures, salinization, and low fertilizer utilization efficiency. Rootstock grafting is an effective means to improve the resistance of cucurbit vegetables such as melons. The healing of the graft union is the key to judging graft compatibility. Traditional compatibility assessment involves manually judging the later growth of grafted seedlings, fruit yield, and quality. The entire process is time-consuming, resource-intensive, and costly. The testing mainly relies on manual or destructive methods, leading to inefficient selection of rootstocks and scions, a lack of high-quality rootstocks, and unstable seedling quality.

[0003] Currently, graft compatibility assessment can be categorized into four types: morphological observation, molecular marker analysis, physiological and biochemical index detection, and physical technique testing. Morphological observation is highly subjective and exhibits significant time lag. Molecular marker analysis and physiological and biochemical index detection require destructive sampling and only reflect instantaneous states. Physical technique testing has relatively large errors. The reconnection of vascular bundles between the scion and rootstock is a sign of successful healing between them and is also an important criterion for compatibility assessment. To quickly screen for compatible rootstocks, using fluorescent tracers to visualize the connectivity between the phloem and xylem of the scion and rootstock to identify grafting compatibility is an effective method, as illustrated by Chinese patents CN202110650781.9 ("Early Non-destructive Fluorescent Identification Method for Judging the Healing Status of Grafted Seedlings of Cucurbit Crops"), CN202211501191.0 ("A Method for Quantitatively Judging the Reconnection Efficiency of Phloem and Xylem during Grafting Healing"), and CN202111080828.9 ("A Method for Screening Grafting-Compatible Rootstocks Using Spectroscopy and Fluorescent Probes"). However, these methods suffer from dye toxicity that interferes with plant growth, high cost, and the need to select suitable fluorescent dyes for different species, which is challenging. Furthermore, they require destructive sampling followed by observation under a fluorescence microscope, making non-destructive, automated, and rapid detection impossible. Combining fluorescent tracer materials with hyperspectral imaging can also achieve early visualization and identification of grafting compatibility, but this method relies on fluorescent staining tracers and cannot avoid the drawbacks of the aforementioned fluorescent dye tracers. Hyperspectral imaging is also relatively expensive. Therefore, it is of great significance to study a method and device that is inexpensive and can continuously monitor the grafting healing status of grafted seedlings in real time and in situ, and to identify the compatibility of rootstocks with cucurbit vegetables. This will greatly promote the large-scale application of cucurbit vegetables in production and reduce production losses caused by graft incompatibility. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this application provides a wearable microneedle sensor for determining the healing status of grafted seedlings of cucurbit vegetables, comprising: The electrode sensing module consists of two microneedle electrodes, which are electrically connected to the output terminal VOUT and the input terminal VIN of the signal acquisition and processing module, respectively. The signal acquisition and conversion module uses the AD5933 impedance converter network analysis chip. After receiving the instruction signal from the data processing and display module, it sends an excitation signal to excite the grafted seedling under test between the two microneedle electrodes, processes the voltage signal generated at the grafting point, and outputs the real and imaginary parts of the voltage signal. The data processing and display module receives the real and imaginary values ​​input from the signal acquisition and conversion module, calculates the impedance of the grafted seedling to be tested, compares the impedance of the grafted seedling with the reference value through a comparator, and finally displays the grafting healing result through LEDs. The power supply module provides power to the signal acquisition and conversion module and the data processing and display module.

[0005] The microneedle electrode fabrication steps include: S1. After cleaning and drying the reverse structure microneedle mold, place it in a vacuum coating machine to vapor deposit an organic layer of parylene. The microneedle mold uses flexible PDMS material as the mold base. S2. Mix the main agent PDMS with the curing agent containing hydrogen silicone oil at a mass ratio of 10:1, stir at room temperature for 1-2 hours, fill the mixed PDMS into the mold base, and cure under vacuum heating; S3. After the microneedle material in S2 is demolded, it is placed in a vacuum coating machine to vapor-deposit an organic layer of parylene. S4. After vapor deposition in S3, a conductive layer is deposited on the surface of the microneedle, and a lead is soldered to the root to obtain the microneedle electrode.

[0006] A non-destructive monitoring method for determining the healing status of grafted seedlings of cucurbit vegetables using the wearable microneedle sensor includes the following steps: M1. A standard resistor is electrically connected between the two microneedle electrodes to calibrate the sensor and determine the gain coefficient G of the signal acquisition and conversion module; M2. Clamp the microneedle electrode with a grafting clip, ensuring that the two microneedle electrodes are inserted into the scion and rootstock of the grafted seedling to be tested, respectively, and that the two microneedle electrodes are close to the grafting surface of the grafted seedling. M3. The signal acquisition and conversion module outputs a sweep frequency signal to excite the grafted seedling under test, and acquires the voltage signal generated after the sweep frequency signal excites the grafted seedling under test; M4. The voltage signal undergoes gain adjustment, filtering, analog-to-digital conversion, and discrete Fourier transform to extract information about the grafted seedling under test, returning the real part value R and the imaginary part value I at each frequency point; M5. Calculate the amplitude A based on the real and imaginary values ​​of the grafted seedling to be tested, and calculate the impedance Z of the grafted seedling to be tested using the gain coefficient G in step M1. M6. Determine the operating frequency f as the frequency with the maximum impedance value; M7. Excite the grafted seedling under test with the working frequency f and monitor the impedance value in real time; M8. Compare the current impedance value with the reference impedance value to determine the healing status and compatibility of the grafted seedling. The determination result is displayed via LED. If ΔZ1(t)>0, the grafted seedling has not yet healed; if ΔZ1(t)<0, the grafted seedling is healing; when ΔZ1(t)<0 and ΔZ2(t) approaches 0, the grafted seedling has healed and the rootstock and scion are compatible; if ΔZ1(t) remains greater than 0, the graft is incompatible.

[0007] The method for calculating the gain coefficient G in step M1 is as follows: M11. The standard resistor R is excited by a sinusoidal signal with programmable frequency and amplitude output by the signal acquisition and processing module to obtain a standard voltage signal; M12. The standard voltage signal is amplified, filtered, converted from analog to digital and then subjected to discrete Fourier transform to extract information about the standard resistor and return the real part R and the imaginary part I at each frequency point. M13. Based on the real and imaginary parts of the standard resistor, calculate the amplitude A of the standard resistor, and further calculate the gain coefficient G, where, In step M2, the distance between the microneedle electrodes is no greater than the length of the grafting clip.

[0008] Step M2 includes: M21. Prepare the melon rootstock and melon scion for grafting; M22. Grafting should be performed when the first true leaf of the rootstock is fully expanded and the first true leaf of the scion is half-expanded. M23. Insert the sensor microneedle electrode close to the grafting point into the rootstock and scion.

[0009] Step M21 involves preparing the melon rootstock for grafting, including: disinfecting the melon rootstock seeds with a 0.1‰ potassium permanganate solution for 15 minutes, rinsing them three times with tap water, and soaking them at room temperature for 8-12 hours; then germinating the seeds at a constant temperature of 30℃ in the dark for 24-48 hours, and planting them in a sterilized 50-cell tray when the radicle emerges, one seed per cell, and grafting when the first true leaf is fully expanded.

[0010] Step M21 involves preparing the melon scions for grafting, including: disinfecting the melon scion seeds with a 0.1‰ potassium permanganate solution for 10 minutes, rinsing them three times with tap water, and soaking them at room temperature for 8-12 hours; then germinating the seeds in a constant temperature and dark environment at 30℃ for 24-48 hours, sowing them in a flat tray when the radicles show white, and grafting when the first true leaf is half-exposed.

[0011] Step M22 includes: Rootstock preparation includes: using a blade to cut off the true leaf, growing point, and one cotyledon at a 45° angle from the base of the cotyledon, leaving only one cotyledon. The cut should be 0.5 cm long and smooth. Scion treatment includes: making a 45° oblique cut upwards with a blade about 1.0 cm from the base of the cotyledons, keeping the cut surface 0.5-1.0 cm and smooth.

[0012] One day before grafting, thoroughly water the substrate and sterilize the grafting blade, grafting clip, and grafting healing environment with 75% medical alcohol beforehand, and let them air dry naturally before use.

[0013] This invention utilizes a grafting clip with microneedle electrodes for wearable measurement, which has no impact on the healing and growth of grafted seedlings, is low-cost, and can penetrate deep into the stem tissue of grafted seedlings for real-time monitoring, obtaining more reliable signal data. This establishes a data foundation for screening compatible rootstocks. A method for determining the compatibility of grafted seedlings of cucurbit vegetables using impedance data is proposed; the physiological changes in grafted seedlings during the healing period can be detected by utilizing impedance change patterns. It has the advantages of being wearable, portable, simple in structure, providing in-situ real-time monitoring, low cost, having no impact on the healing and growth of grafted seedlings, and enabling early detection. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of microneedle fabrication. Figure 2 Block diagram of a system for selecting graft compatibility rootstocks for melon grafting; Figure 3 A schematic diagram of grafting rootstock and scion; Figure 4 Flowchart for measuring grafted seedlings; Figure 5 This is a circuit diagram of the AD5933 impedance converter network analysis chip. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0016] Example 1 The method for selecting grafting compatibility rootstocks for melons includes the following steps: Step 1: Disinfect the seeds of melon rootstock and melon scion with 0.1% potassium permanganate solution for 15 minutes; wash them repeatedly until all impurities are removed, soak them at room temperature for 10 hours, and then rinse them with distilled water again. Step two: After soaking, germinate the muskmelon rootstock seeds at a constant temperature of 30℃ in the dark for 24-48 hours. When the radicles show white, plant one seed in each of the sterilized 50-cell trays. After soaking, germinate the muskmelon scion seeds at a constant temperature of 30℃ for 24 hours. When the radicles show white, sow them in a flat tray. Before grafting, disinfect the blades and grafting clips with 75% medical alcohol and let them air dry naturally. Water the substrate thoroughly one day before grafting.

[0017] Grafting should be performed using a monocotyledonous grafting method when the first true leaf of the rootstock is fully unfolded and the first true leaf of the scion is slightly exposed. Rootstock preparation: First, remove all true leaves from the rootstock, then use a blade to cut off one cotyledon at a 45° angle downwards from the base of the cotyledon, with a cut surface of about 0.5 cm. Scion treatment: Make an oblique cut at about 45° upwards with the grafting blade 0.5 cm-1 cm from the base of the cotyledons, with a cut surface of about 0.5 cm; Place the cut surfaces of the rootstock and scion tightly together and clamp them with a grafting clip.

[0018] Step 3: Management of the grafting healing period, including temperature, humidity, and light management, i.e., 28-25℃ during the day and 22-18℃ at night; maintain humidity above 95% for the first 3 days after grafting; ventilate for 4-6 days after grafting, ensuring the cotyledons of the scion do not wilt; remove the film after 7 days and enter normal management; keep the area in darkness for the first day after grafting, then maintain weak light (approximately 85 umol / m² s⁻¹), and then enter normal light management after 7 days (approximately 170 umol / m² s⁻¹).

[0019] Step four: Perform healing detection during the grafting healing period. Insert the two microneedle electrodes of the wearable sensor close to the grafting site into the rootstock and scion respectively. The distance between the two microneedle electrodes should not be greater than the length of the grafting clip. Use the grafting clip to clamp the microneedle electrodes at the grafting site.

[0020] Step 5, as Figure 2 and 3 As shown, the two microneedle electrodes are electrically connected to the output terminal VOUT and the input terminal VIN of the signal acquisition and processing module 2, respectively. The signal acquisition and processing module 2 generates an excitation signal and acquires the voltage signal generated after the excitation signal passes through the grafting point. The data processing and display module 3 reads the real and imaginary parts of the measurement signal processed by the signal acquisition and processing module 2 through the interface, calculates the grafting seedling impedance Z, compares the grafting seedling impedance Z with the reference value through a comparator, and finally displays the grafting healing result through an LED.

[0021] Based on the above structure, the wearable sensor includes two microneedle electrodes 1, a signal acquisition and processing module 2, a power supply module 4, and a data processing and display module 3; The microneedle electrode 1 is composed of a microneedle electrode array, with a diameter of 500 μm and a height of 750 μm. A detailed schematic diagram is shown below. Figure 1 As shown, the specific fabrication steps for the microneedle electrode are as follows: (1) High-precision, high-temperature resistant, transparent and flexible PDMS (polydimethylsiloxane) material is selected as the mold base, and its flexibility facilitates the subsequent demolding of microneedles; (2) Mold cleaning: ultrasonic cleaning with acetone and ethanol for 30 min, followed by nitrogen drying; (3) Vacuum coating organic layer filling mold: Place the PDMS microneedle mold (reverse structure) into the vacuum coating machine and evaporate a 30 nm organic layer Parylene (poly(p-xylene)) to facilitate subsequent microneedle demolding. (4) Flexible polydimethylsiloxane (PDMS) was selected as the microneedle material; the main agent PDMS and its curing agent (main component, containing hydrogen silicone oil) were mixed at a mass ratio of 10:1 and stirred at room temperature for 1 h to mix evenly; (5) Press the well-stirred PDMS into the PDMS microneedle template coated with organic layer in small amounts and multiple times. Vacuum at room temperature for 1 h with a vacuum degree of -0.1MPa. After removing air bubbles, cure at 90℃ on a heating table for 1 h. (6) Vacuum evaporation of organic layer for microneedles: After the PDMS microneedles have been cured, they are demolded and placed in a vacuum coating machine to evaporate a 30 nm organic layer of Parylene (poly(p-xylene)) to increase the adhesion between the metal layer and PDMS, so that the metal layer does not fall off when bent and the channel is still maintained. (7) Vacuum evaporation of micro-needle conductive layer: evaporation material is copper particles with a purity of 99.9% (Cu, 200nm) and a vacuum degree of (2×10-3Pa). (8) Using welding technology, silver wires are welded to the root of the microneedle as microneedle electrode leads, such as... Figure 3As shown, a silver wire is welded to each of the microneedles on the rootstock and the scion, and connected to the signal acquisition module to lead out the electrical signal for measurement, thereby realizing real-time signal monitoring.

[0022] The signal acquisition and processing module 2 consists of four parts: current excitation, current measurement, voltage measurement, and microcontroller. The current excitation, current measurement, and voltage measurement form an impedance converter. The signal acquisition and conversion module measures the complex impedance at the grafting point. It contains a signal generator that outputs a sinusoidal signal with programmable frequency and amplitude to excite the grafting point between the stem and rootstock. After being filtered by a low-pass filter, the signal is sampled by an analog-to-digital converter and then subjected to discrete Fourier transform by the internal digital processing module to extract the impedance information. It returns a real part value and an imaginary part value at each frequency point.

[0023] Preferably, in this embodiment, the signal acquisition and conversion module 2 uses an AD5933 impedance converter network analysis chip. The direct digital synthesizer (DDS) core inside the AD5933 impedance converter network analysis chip is used to generate a frequency-adjustable sine wave signal (also known as an excitation signal). The frequency of the sine wave signal can be configured through the I2C interface. The digital-to-analog converter (DAC) converts the digital signal generated by the DDS into an analog signal and outputs it to the output amplifier. The output amplifier amplifies the analog signal output by the DAC to the output terminal VOUT. After the output signal passes through the grafted seedling Z(ω), a voltage signal is generated and input to the amplifier VIN. The voltage signal passing through the grafted seedling is amplified, and the gain is adjusted by the gain amplifier. It is then filtered by the low-pass filter LPF. The analog-to-digital converter (ADC) converts the analog signal into a digital signal, and then performs a discrete Fourier transform through the internal digital processing module (1024-point DFT) to extract the information of the grafted seedling. At each frequency point, it returns a real part value R and an imaginary part value I.

[0024] Preferably, the direct digital synthesizer (DDS) core uses a sweep signal with a starting frequency of 5 kHz, a step size of 5 kHz, and a stop frequency of 100 kHz as the excitation signal.

[0025] Furthermore, the data processing and display module 3 connects to the signal acquisition and processing module 2 via I... 2 The C interface reads the values ​​of the real and imaginary registers, calculates the impedance of the grafted seedling to be tested, compares the impedance Z of the grafted seedling with the reference value through a comparator, and finally displays the grafting healing result through an LED.

[0026] Preferably, in this embodiment, the data processing and display module 3 uses an STM32F407 microcontroller and an LM358 dual operational amplifier circuit.

[0027] Furthermore, the power supply module provides power to the signal acquisition and conversion module and the data processing and display module. In this embodiment, the power supply module uses the TL5209 linear voltage regulator chip, which is a low-dropout regulator characterized by low power consumption and low noise.

[0028] The method for using the aforementioned wearable sensor to screen for compatible rootstocks for cucurbit vegetables includes the following steps: S1. The direct digital synthesizer (DDS) core of the signal acquisition and processing module 2 outputs a sinusoidal signal with programmable frequency and amplitude to excite the standard resistor R connected between the two microneedle electrodes 1, thereby obtaining a standard voltage signal passing through the standard resistor R. The standard resistor R has a resistance of 1K Ω and an accuracy of 1%. The direct digital synthesizer (DDS) core uses a sweep frequency signal with a starting frequency of 5 kHz, a step size of 5 kHz, and a termination frequency of 100 kHz as the excitation signal. S2. The standard voltage signal is adjusted by a gain amplifier, filtered by a low-pass filter, sampled by an analog-to-digital converter, and then subjected to discrete Fourier transform by an internal digital processing module to extract the information of the standard resistor, returning a real part value R and an imaginary part value I at each frequency point. S3. Calculate the amplitude A of the standard resistor based on its real and imaginary parts; Calculate the gain coefficient G of signal acquisition and processing module 2; S4. Use grafting clip 1 to hold the microneedle electrode 1 inserted into the interface between the scion and rootstock of the grafted seedling to be tested, ensuring that the two microneedle electrodes 1 are inserted into the scion stem and the rootstock stem respectively. S5. The data processing and display module 3 issues an instruction to the direct digital synthesizer (DDS core) of the signal acquisition and processing module 2 to output a sinusoidal signal with programmable frequency and amplitude to excite the grafted seedling to be tested connected between the two microneedle electrodes 1, thereby obtaining the grafted seedling voltage signal passing through the grafted seedling to be tested. The direct digital synthesizer (DDS core) uses a sweep frequency signal with a starting frequency of 5 kHz, a step size of 5 kHz, and an ending frequency of 100 kHz as the excitation signal. S6. The voltage signal of the grafted seedling is adjusted by the gain amplifier, filtered by the low-pass filter, sampled by the analog-to-digital converter, and then subjected to discrete Fourier transform by the internal digital processing module to extract the information of the grafted seedling under test. At each frequency point, a real part value R and an imaginary part value I are returned. S7. Based on the real and imaginary values ​​of the grafted seedling to be tested, calculate the amplitude A of the grafted seedling to be tested, and calculate the impedance Z of the grafted seedling to be tested at each frequency according to the gain coefficient G determined in step S3. S8. After the test is completed, determine the frequency with the largest impedance value within the sweep frequency range as the operating frequency f; S9. The data processing and display module 3 sends an instruction to the signal acquisition and processing module 2 to excite the grafted seedling under test at the working frequency f, monitor the impedance value in real time, and compare the impedance with the reference impedance once each time it works. S10. Compare the impedance value with the reference impedance; If ΔZ1(t)>0, it means that the resistance increases rapidly with the formation and thickening of the isolation layer, and the grafted seedling has not yet healed. If ΔZ1(t)<0, the rootstock and scion are connected by plasmodesmata. When cells are connected by plasmodesmata, the cellular resistance between the two cells decreases sharply, which means that the grafted seedling is healing. When ΔZ1(t)<0 and ΔZ2(t) approaches 0, it means that the grafted seedling has healed and the rootstock and scion are compatible. If ΔZ1(t) continues to be greater than 0, it means that intercellular communication cannot be established through the flow of water and minerals from the rootstock to the scion, and resistance will continue to increase, thus making the graft incompatible.

[0029] According to CN202110650781.9, the method for early non-destructive fluorescence identification of the healing status of grafted seedlings of cucurbit crops can obtain the grafting healing status of rootstock and scion after grafting. However, when it is determined that the rootstock and scion have healed, the impedance measured by steps S1 to S7 of this invention is used as the reference impedance.

[0030] S11. Display the judgment result on the LED. A red LED indicates that the graft has healed and the rootstock and scion are not compatible; a green LED indicates that the graft has not healed and the rootstock and scion are compatible. Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A wearable microneedle sensor for determining the healing status of grafted seedlings of cucurbit vegetables, characterized in that, include: The electrode sensing module consists of two microneedle electrodes, which are electrically connected to the output terminal VOUT and the input terminal VIN of the signal acquisition and processing module, respectively. The signal acquisition and conversion module uses the AD5933 impedance converter network analysis chip. After receiving the instruction signal from the data processing and display module, it sends an excitation signal to excite the grafted seedling under test between the two microneedle electrodes, processes the voltage signal generated at the grafting point, and outputs the real and imaginary parts of the voltage signal. The data processing and display module receives the real and imaginary values ​​input from the signal acquisition and conversion module, calculates the impedance of the grafted seedling to be tested, compares the impedance of the grafted seedling with the reference value through a comparator, and finally displays the grafting healing result through LEDs. The power supply module provides power to the signal acquisition and conversion module and the data processing and display module.

2. The wearable microneedle sensor according to claim 1, characterized in that, The microneedle electrode fabrication steps include: S1. After cleaning and drying the reverse structure microneedle mold, place it in a vacuum coating machine to vapor deposit an organic layer of parylene. The microneedle mold uses flexible PDMS material as the mold base. S2. Mix the main agent PDMS with the curing agent containing hydrogen silicone oil at a mass ratio of 10:1, stir at room temperature for 1-2 hours, fill the mixed PDMS into the mold base, and cure under vacuum heating; S3. After the microneedle material in S2 is demolded, it is placed in a vacuum coating machine to vapor-deposit an organic layer of parylene. S4. After vapor deposition in S3, a conductive layer is deposited on the surface of the microneedle, and a lead is soldered to the root to obtain the microneedle electrode.

3. A non-destructive monitoring method for determining the healing status of grafted seedlings of cucurbit vegetables using a wearable microneedle sensor as described in claim 1, characterized in that, Includes the following steps: M1. A standard resistor is electrically connected between the two microneedle electrodes to calibrate the sensor and determine the gain coefficient G of the signal acquisition and conversion module; M2. Clamp the microneedle electrode with a grafting clip, ensuring that the two microneedle electrodes are inserted into the scion and rootstock of the grafted seedling to be tested, respectively, and that the two microneedle electrodes are close to the grafting surface of the grafted seedling. M3. The signal acquisition and conversion module outputs a sweep frequency signal to excite the grafted seedling under test, and acquires the voltage signal generated after the sweep frequency signal excites the grafted seedling under test; M4. The voltage signal undergoes gain adjustment, filtering, analog-to-digital conversion, and discrete Fourier transform to extract information about the grafted seedling under test, returning the real part value R and the imaginary part value I at each frequency point; M5. Calculate the amplitude A based on the real and imaginary values ​​of the grafted seedling to be tested, and calculate the impedance Z of the grafted seedling to be tested using the gain coefficient G in step M1. M6. Determine the operating frequency f as the frequency with the maximum impedance value; M7. Excite the grafted seedling under test with the working frequency f and monitor the impedance value in real time; M8. Compare the current impedance value with the reference impedance value to determine the healing status and compatibility of the grafted seedling. The determination result is displayed via LED. If ΔZ1(t)>0, the grafted seedling has not yet healed; if ΔZ1(t)<0, the grafted seedling is healing; when ΔZ1(t)<0 and ΔZ2(t) approaches 0, the grafted seedling has healed and the rootstock and scion are compatible; if ΔZ1(t) remains greater than 0, the graft is incompatible.

4. The non-destructive testing method according to claim 3, characterized in that, The method for calculating the gain coefficient G in step M1 is as follows: M11. The standard resistor R is excited by a sinusoidal signal with programmable frequency and amplitude output by the signal acquisition and processing module to obtain a standard voltage signal; M12. The standard voltage signal is amplified, filtered, converted from analog to digital and then subjected to discrete Fourier transform to extract information about the standard resistor and return the real part R and the imaginary part I at each frequency point. S13. Based on the real and imaginary parts of the standard resistor, calculate the amplitude A of the standard resistor, and further calculate the gain coefficient G, where, 。 5. The non-destructive testing method according to claim 3, characterized in that, In step M2, the distance between the microneedle electrodes is no greater than the length of the grafting clip.

6. The non-destructive testing method according to claim 3, characterized in that, Step M2 includes: M21. Prepare the melon rootstock and melon scion for grafting; M22. Grafting should be performed when the first true leaf of the rootstock is fully expanded and the first true leaf of the scion is half-expanded. M23. Insert the sensor's microneedle electrode close to the grafting point into the rootstock and scion.

7. The non-destructive testing method according to claim 6, characterized in that, Step M21 involves preparing the melon rootstock for grafting, including: disinfecting the melon rootstock seeds with a 0.1‰ potassium permanganate solution for 15 minutes, rinsing them three times with tap water, and soaking them at room temperature for 8-12 hours; then germinating the seeds at a constant temperature of 30℃ in the dark for 24-48 hours, and planting them in a sterilized 50-cell tray when the radicle emerges, one seed per cell, and grafting when the first true leaf is fully expanded.

8. The non-destructive testing method according to claim 6, characterized in that, Step M21 involves preparing the melon scions for grafting, including: disinfecting the melon scion seeds with a 0.1‰ potassium permanganate solution for 10 minutes, rinsing them three times with tap water, and soaking them at room temperature for 8-12 hours; then germinating the seeds in a constant temperature and dark environment at 30℃ for 24-48 hours, sowing them in a flat tray when the radicles show white, and grafting when the first true leaf is half-exposed.

9. The non-destructive testing method according to claim 6, characterized in that, Step M22 includes: Rootstock preparation includes: using a blade to cut off the true leaf, growing point, and one cotyledon at a 45° angle from the base of the cotyledon, leaving only one cotyledon. The cut should be 0.5 cm long and smooth. Scion treatment includes: making a 45° upward cut with a blade about 1.0 cm from the base of the cotyledons, keeping the cut surface 0.5-1.0 cm and smooth.

10. The non-destructive testing method according to claim 5, characterized in that, One day before grafting, thoroughly water the substrate and sterilize the grafting blade, grafting clip, and grafting healing environment with 75% medical alcohol beforehand, and let them air dry naturally before use.

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