Watermelon rootstock screening and high-efficiency grafting cultivation method with resistance to continuous cropping

Abstract

This invention discloses a method for selecting watermelon rootstocks and for efficient grafting cultivation to resist continuous cropping. Rootstock pools containing gourd, bottle gourd, pumpkin, and a dedicated F1 strain are constructed. Watermelon and gourd-specific Fusarium wilt pathogens are inoculated concurrently for initial screening (disease index ≤10, survival rate ≥90%) and secondary screening (disease index ≤5, survival rate ≥95%). Rootstocks are selected based on fruit setting verification at 15 / 10℃ (day / night) (fruit setting rate ≥80%) and quality evaluation (sugar content decrease ≤0.5°Brix, skin thickness increase ≤10%). Seedlings are raised using the grafting method (rootstocks are sown 6-8 days in advance; grafting is performed at the appropriate time; healing occurs at 25-28℃ for 5-7 days; rootstock buds are removed after 10 days). At field transplanting, biocontrol agents (≥1×10⁸ CFU / g, 2-3 kg / mu) are applied, EC ≤1.5 mS / cm is controlled, and 500-600 plants are planted per mu. Two-vine training is used, selecting the second female flower for fruit setting. To achieve synergistic effects of rootstock resistance spectrum and low-temperature fruit setting, reduce the risk of quality deterioration, quantify key parameters, reduce diseases, improve survival rate and uniformity in replanted fields, promote early maturity and increase yield, and facilitate large-scale promotion.

Description

Technical Field

[0001] This invention relates to the field of crop cultivation technology, specifically to a method for selecting watermelon rootstocks and for efficient grafting cultivation to resist continuous cropping. Background Technology

[0002] Watermelon is a high-value crop, but in many parts of my country, due to limited arable land resources and difficulties in implementing crop rotation systems, continuous cropping (repeated cropping) is a common problem. For dryland watermelon, a 6-7 year interval is needed for continuous cropping, and for water-dryland rotation, a 3-4 year interval is needed to effectively control soil-borne diseases. However, in actual production, limited by land area and market cycles, most production areas find it difficult to strictly adhere to these rotation intervals. Under continuous cropping conditions, large amounts of *Fusarium oxysporum* and *Fusarium wilt* specific pathogens of gourd accumulate in the soil, causing typical wilt disease, manifested as root browning, vascular bundle blockage, plant wilting, and even death. This disease can break out in the seedling stage, leading to missing seedlings and gaps in rows. In the fruiting stage, it causes premature aging of plants, sharp yield reduction, and even crop failure, becoming a core bottleneck restricting stable watermelon yields in continuously cropped fields. Furthermore, long-term continuous cropping is accompanied by the deterioration of soil physical and chemical properties (such as salt accumulation, decreased organic matter, and microbial community imbalance) and secondary salt damage, further exacerbating poor plant growth and the disease cycle.

[0003] Grafting is the most mature and effective method to overcome soil-borne diseases such as Fusarium wilt. By selecting disease-resistant rootstocks to replace infected primary roots, the infection pathway of pathogens is cut off. Currently, the rootstock types widely used in production mainly include gourd, bottle gourd, pumpkin, and some special hybrid F1 rootstocks. Among them, pumpkin rootstocks have strong synergistic resistance to both types of Fusarium wilt pathogens, but they generally suffer from fruit quality deterioration—such as thickened skin, fibrous flesh, decreased central sugar content, and bland flavor, affecting commercial value. Gourd and bottle gourd rootstocks have relatively less impact on quality, but they are usually only resistant to gourd-specific Fusarium wilt and lack sufficient resistance to watermelon-specific Fusarium wilt, limiting their universality in fields with continuous cropping. In addition, different rootstocks vary significantly in terms of low-temperature fruit setting, compatibility persistence, and growth vigor matching. Without systematic screening and quantitative evaluation standards, it is easy to lead to low grafting survival rates, uncoordinated later growth, or unstable fruit setting, affecting the stability of large-scale production. Therefore, it is urgent to establish a rootstock screening system that can simultaneously take into account high disease resistance, broad spectrum, excellent fruit quality, low-temperature fruit setting ability, and good compatibility.

[0004] In the grafting and seedling raising stage, techniques such as cleft grafting, approach grafting, and whip grafting are relatively mature. Key control points agreed upon by the industry include: difference in sowing time between rootstock and scion (rootstock 6-8 days earlier), matching seedling age (rootstock cotyledons fully expanded, first true leaf emerging, scion cotyledons turning green), constant temperature and humidity for healing after grafting (25-28℃, shading for 5-7 days), and timely removal of rootstock axillary buds and hardening off. However, these empirical parameters are mostly based on a single production area or a few varieties, lacking universal thresholds across ecological zones and multiple scion varieties. Especially for the unique adverse conditions of continuously cropped land (such as low temperature and low light, high pathogen pressure, and soil salinization), the existing process has failed to form a standardized cultivation plan linked to the rootstock selection results. In terms of field management, conventional practices focus on emergency pesticide application or simple crop rotation after disease occurrence, lacking a combined control strategy of pre-crop treatment—salt restriction and fertilizer control—microecological disease suppression—rhizosphere immune induction for continuously cropped soil, resulting in unstable resistance to continuous cropping. In view of this, this invention proposes an integrated technical route of "parallel screening of dual pathogens - verification of low-temperature fruit setting - quantification of affinity - standardization of grafted seedlings - field management against continuous cropping". For the first time, it seamlessly connects the comprehensive evaluation of multiple traits of rootstock with field stress-resistant cultivation, and clarifies the quantitative threshold of key process parameters to achieve high survival rate, low disease, early maturity and stable yield and quality maintenance of watermelons in continuous cropping fields, filling the gap in the existing technology in terms of systematization and replicability.

[0005] Therefore, we propose a method for selecting watermelon rootstocks and for efficient grafting cultivation that is resistant to continuous cropping. Summary of the Invention

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for screening watermelon rootstocks and for efficient grafting cultivation to resist continuous cropping, comprising the following steps:

[0007] S1: Construction of candidate rootstock pool: Select rootstock materials derived from gourd, bottle gourd, squash, or special hybrid F1;

[0008] S2: Parallel screening of dual pathogens: Potted plants were initially screened for watermelon-specific and gourd-specific Fusarium wilt pathogens, and diseased plants were screened for secondary screening of candidate rootstocks. The entry thresholds were: disease index ≤10 and survival rate ≥90% (initial screening) and disease index ≤5 and survival rate ≥95% (secondary screening).

[0009] S3: Low-temperature fruit setting verification: Artificial pollination was carried out under day / night conditions of 15 / 10℃, and rootstocks with a low-temperature fruit setting rate of ≥80% were selected;

[0010] S4: Compatibility and Quality Evaluation: Grafting is performed using the target scion to evaluate grafting compatibility and symbiotic compatibility, with the following limits: fruit center sugar content decrease ≤ 0.5°Brix and peel thickness increase ≤ 10%;

[0011] S5: Standardized grafting and seedling raising: The grafting method is adopted. The appropriate grafting time is when the cotyledons of the rootstock are fully expanded, the first true leaf appears (about 7-10 days), and the cotyledons of the scion turn from yellow to green. After grafting, the seedlings heal for 5-7 days under the conditions of 25-28℃, shade and moisture. Then, the seedlings are hardened off by ventilation. They can be transplanted in about 20 days.

[0012] S6: Field cultivation to resist continuous cropping: prioritize water-dry rotation in fields with continuous cropping; for fields where rotation is not possible, disinfect the soil before planting and control soil EC ≤ 1.5 mS / cm; apply biocontrol Bacillus preparations for rhizosphere colonization at planting time, and combine drip irrigation, fertigation and ventilation to reduce humidity for green control. The planting density is 500-600 plants per mu, with two vines per plant and the second female flower selected for fruit setting.

[0013] Preferably, in the parallel screening of dual pathogens, the concentration of the pathogen spore suspension is 1×10^6 spores / mL, and the inoculation method is root-dip or root-drenching, with 10 mL per plant.

[0014] Preferably, in the standardized grafting seedling raising, the bamboo stick is inserted to a depth of 0.5-1.0 cm into the hypocotyl of the rootstock during grafting, the length of the cut surface of the scion is 1.0-1.5 cm, and the axillary buds of the rootstock are removed 10 days after grafting.

[0015] Preferably, in the field replanting resistance cultivation, Bacillus subtilis / Bacillus amyloliquefaciens biocontrol agent is applied at the time of transplanting at a rate of 2-3 kg per mu, and the effective viable count of the agent is ≥1×10^8 CFU / g.

[0016] Preferably, in the field cultivation to resist continuous cropping, the continuous cropping period does not exceed 4 years throughout the entire growth period, and the soil EC is controlled at ≤1.5 mS / cm through water and fertilizer regulation and drip irrigation.

[0017] Preferably, the target scion is Zaojia 8424 or an early-maturing, high-quality watermelon variety of the same type.

[0018] Preferably, the rootstock is a special hybrid F1 or a specific gourd / cupberry variety, which simultaneously meets the following requirements in the re-screening and low-temperature fruit setting verification: disease index ≤5, survival rate ≥95%, low-temperature fruit setting rate ≥80%, and the impact on fruit quality meets the requirements of sugar content decrease ≤0.5°Brix and peel thickness increase ≤10%.

[0019] Preferably, in the field pruning and fruit setting management, after fruit setting, the topping and fruit thinning are carried out appropriately according to the growth to ensure the stability of single fruit weight and quality.

[0020] Preferably, the green control measures include yellow sticky traps, releasing natural enemies, and low-dose precision pesticide application, with a focus on controlling vine blight, blight, anthracnose, whiteflies, and aphids.

[0021] Preferably, the criteria for determining the appropriate grafting time for the standardized grafting seedling cultivation are: the cotyledons of the rootstock are fully expanded and the first true leaf has just appeared (about 7 to 10 days), the cotyledons of the scion have turned from yellow to green, and the age of the rootstock and scion seedlings are matched.

[0022] Compared with the prior art, the present invention provides a method for selecting watermelon rootstocks and for efficient grafting cultivation to resist continuous cropping, which has the following beneficial effects:

[0023] 1. This watermelon rootstock selection and high-efficiency grafting cultivation method for resistance to continuous cropping combines parallel screening of two pathogens with low-temperature fruit setting verification. It precisely selects materials from gourd, bottle gourd, pumpkin, and specialized hybrid F1 rootstocks that possess both watermelon-specific and gourd-specific wilt resistance and a low-temperature fruit setting rate ≥80%, fundamentally solving the problems of traditional rootstocks' "narrow resistance spectrum" or "poor quality." In applications in continuously cropped fields, the incidence of wilt in grafted seedlings can be reduced to below 5%, the disease index stabilizes at ≤5, and the survival rate is ≥95%, significantly better than the 30%–60% survival rate of conventional self-rooted seedlings and single-resistant rootstocks. Combined with a combined control measure of field pre-crop treatment—soil disinfection—salt restriction and fertilizer control—microecological disease suppression—rhizosphere immune induction, it can continuously suppress the accumulation of soil-borne pathogens and secondary salt damage under conditions where long-term crop rotation is not possible, ensuring robust plant growth throughout the entire growth period, achieving stable or even increased yields, and effectively overcoming the constraints of continuous cropping on the watermelon industry.

[0024] 2. This watermelon rootstock selection and high-efficiency grafting cultivation method for resistance to continuous cropping addresses the common problems of thickened rinds, fibrous flesh, decreased central sugar content, and bland flavor associated with traditional pumpkin rootstocks, which affect market prices and consumer acceptance. This invention introduces quality maintenance metrics (central sugar content decrease ≤0.5°Brix, rind thickness increase ≤10%, and no significant change in flesh firmness) during the selection stage. It prioritizes the retention of gourd / cup-shaped rootstocks or dedicated F1 rootstocks with minimal impact on quality, thus maintaining the inherent thin-skinned, juicy, high-sugar, and flavorful characteristics of the scion while achieving high disease resistance. Actual production shows that watermelons grafted using this method maintain a similar appearance and internal quality to the target scion even in continuously cropped fields, increasing the marketable fruit rate by more than 10%, significantly enhancing competitiveness and planting profits in the high-end market.

[0025] 3. This invention, concerning watermelon rootstock selection and efficient grafting cultivation for resistance to continuous cropping, not only clarifies key thresholds for rootstock selection such as disease index, survival rate, low-temperature fruit setting rate, sugar content, and peel thickness changes, but also provides precise operational parameters for the grafting method in the seedling stage (rootstock cotyledons fully expanded, first true leaf emerging, scion cotyledons turning from yellow to green; 25-28℃ shading for 5-7 days after grafting, removal of axillary buds after 10 days, and transplanting after 20 days). In field management, it provides quantifiable procedures for sowing date and density, water and fertilizer EC control, biocontrol agent dosage, and pruning and fruit setting strategies. This closed-loop standardized system, from laboratory selection to field implementation, significantly reduces farmers' reliance on empirical techniques and facilitates rapid replication and promotion in different ecological zones and large-scale bases. Meanwhile, due to the good fruit setting performance and coordinated growth vigor at low temperatures, the fruit development period is shortened, allowing for earlier market entry and seizing of high-price opportunities. Combined with high survival rates and low disease risks, yield per unit area and output value increase simultaneously, resulting in significantly better overall economic benefits than the traditional continuous cropping model. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example

[0028] An Example of a Method for Selecting Watermelon Rootstocks and Promoting High-Efficiency Grafting Cultivation to Resist Continuous Crop Damage

[0029] A method for selecting watermelon rootstocks and for efficient grafting cultivation to resist continuous cropping includes the following steps:

[0030] S1: Construction of candidate rootstock pool: Select rootstock materials derived from gourd, bottle gourd, squash, or special hybrid F1;

[0031] S2: Parallel screening of dual pathogens: Potted plants were initially screened for watermelon-specific and gourd-specific Fusarium wilt pathogens, and diseased plants were screened for secondary screening of candidate rootstocks. The entry thresholds were: disease index ≤10 and survival rate ≥90% (initial screening) and disease index ≤5 and survival rate ≥95% (secondary screening).

[0032] S3: Low-temperature fruit setting verification: Artificial pollination was carried out under day / night conditions of 15 / 10℃, and rootstocks with a low-temperature fruit setting rate of ≥80% were selected;

[0033] S4: Compatibility and Quality Evaluation: Grafting is performed using the target scion to evaluate grafting compatibility and symbiotic compatibility, with the following limits: fruit center sugar content decrease ≤ 0.5°Brix and peel thickness increase ≤ 10%;

[0034] S5: Standardized grafting and seedling raising: The grafting method is adopted. The appropriate grafting time is when the cotyledons of the rootstock are fully expanded, the first true leaf appears (about 7-10 days), and the cotyledons of the scion turn from yellow to green. After grafting, the seedlings heal for 5-7 days under the conditions of 25-28℃, shade and moisture. Then, the seedlings are hardened off by ventilation. They can be transplanted in about 20 days.

[0035] S6: Field cultivation to resist continuous cropping: prioritize water-dry rotation in fields with continuous cropping; for fields where rotation is not possible, disinfect the soil before planting and control soil EC ≤ 1.5 mS / cm; apply biocontrol Bacillus preparations for rhizosphere colonization at planting time, and combine drip irrigation, fertigation and ventilation to reduce humidity for green control. The planting density is 500-600 plants per mu, with two vines per plant and the second female flower selected for fruit setting.

[0036] Specifically, in the parallel screening of two pathogens, the concentration of pathogen spore suspension was 1×10^6 spores / mL, and inoculation was carried out by root dip or root irrigation method, with 10 mL per plant.

[0037] Specifically, in standardized grafting seedling cultivation, the bamboo stick is inserted to a depth of 0.5-1.0 cm into the hypocotyl of the rootstock during grafting, and the length of the cut surface of the scion is 1.0-1.5 cm. Ten days after grafting, the axillary buds of the rootstock should be removed promptly.

[0038] Specifically, in field cultivation to resist continuous cropping, apply Bacillus subtilis / Bacillus amyloliquefaciens biocontrol agent at the time of transplanting, at a rate of 2-3 kg per mu, with an effective live bacteria count ≥1×10^8 CFU / g.

[0039] Specifically, in field cultivation to resist continuous cropping, the continuous cropping period should not exceed 4 years throughout the entire growth period, and the soil EC should be controlled at ≤1.5 mS / cm through water and fertilizer regulation and drip irrigation.

[0040] Specifically, the target scion is Zaojia 8424 or a similar early-maturing, high-quality watermelon variety.

[0041] Specifically, the rootstock selection results are dedicated hybrid F1 or specific gourd / cupberry varieties, which simultaneously meet the following requirements in the re-screening and low-temperature fruit setting verification: disease index ≤5, survival rate ≥95%, low-temperature fruit setting rate ≥80%, and the impact on fruit quality meets the following requirements: sugar content decrease ≤0.5°Brix, and peel thickness increase ≤10%.

[0042] Specifically, in field pruning and fruit setting management, after fruit setting, the top should be appropriately pruned and the fruit thinned according to the growth to ensure the weight and quality of each fruit are stable.

[0043] Specifically, green control measures include yellow sticky traps, releasing natural enemies, and low-dose precision pesticide application, with a focus on controlling vine blight, blight, anthracnose, whiteflies, and aphids.

[0044] Specifically, the criteria for determining the appropriate grafting time for standardized grafting seedling cultivation are: the cotyledons of the rootstock are fully expanded and the first true leaf has just appeared (about 7 to 10 days), the cotyledons of the scion have turned from yellow to green, and the age of the rootstock and scion seedlings are matched.

[0045] Through the above technical solution, this invention combines parallel screening of two pathogens with low-temperature fruit setting verification to precisely select materials from gourd, bottle gourd, pumpkin, and special hybrid F1 rootstocks that possess both watermelon-specific and gourd-specific wilt resistance and a low-temperature fruit setting rate of ≥80%, fundamentally solving the problems of "narrow resistance spectrum" or "poor quality" of traditional rootstocks. In applications in replanted fields, the incidence of wilt in grafted seedlings can be reduced to below 5%, the disease index is stable at ≤5, and the survival rate is ≥95%, significantly better than the 30%–60% survival rate of conventional self-rooted seedlings and single resistant rootstocks. Combined with a combined control measure of field pre-crop treatment—soil disinfection—salt restriction and fertilizer control—microecological disease suppression—rhizosphere immune induction, it can continuously inhibit the accumulation of soil-borne pathogens and secondary salt damage under conditions where long-term crop rotation is not possible, ensuring robust growth of plants throughout their entire growth period, achieving stable or even increased yields, and effectively overcoming the constraints of replanting on the watermelon industry. While traditional pumpkin rootstocks offer broad-spectrum disease resistance, they commonly suffer from issues such as thickened rinds, fibrous flesh, decreased central sugar content, and diluted flavor, impacting market prices and consumer acceptance. This invention introduces quantifiable indicators for quality maintenance during the selection phase (central sugar content decrease ≤0.5°Brix, rind thickness increase ≤10%, and no significant change in flesh firmness). It prioritizes the retention of gourd / cup-shaped rootstocks or dedicated F1 rootstocks with minimal impact on quality, thereby achieving high disease resistance while maintaining the inherent characteristics of the scion: thin rind, abundant juice, high sugar content, and excellent flavor. Actual production shows that watermelons grafted using this method maintain a similar appearance and internal quality to the target scion even in continuously cropped fields, increasing the marketable fruit rate by over 10%, significantly enhancing competitiveness and planting profits in the high-end market. This invention not only clarifies key thresholds for rootstock selection, such as disease index, survival rate, low-temperature fruit setting rate, sugar content, and changes in peel thickness, but also provides precise operational parameters for grafting in the seedling stage (rootstock cotyledons fully expanded, first true leaf emerging, scion cotyledons turning from yellow to green; 25-28℃ shading for 5-7 days after grafting, removal of axillary buds after 10 days, and transplanting after 20 days). In field management, it provides quantifiable procedures for sowing date and density, water and fertilizer EC control, biocontrol agent dosage, and pruning and fruit setting strategies. This closed-loop standardized system, from laboratory selection to field implementation, significantly reduces farmers' reliance on empirical techniques and facilitates rapid replication and promotion in different ecological zones and large-scale bases. Simultaneously, due to good low-temperature fruit setting and coordinated growth vigor, the fruit development period is shortened, allowing for earlier market entry and capturing higher prices. Combined with high survival rates and low disease risk, yield and output value per unit area increase simultaneously, resulting in significantly better overall economic benefits than traditional continuous cropping models.

[0046] Example 1: Rootstock candidate pool and parallel screening of two pathogens

[0047] Candidate rootstocks: Select several commonly used gourd, bottle gourd, pumpkin, and special hybrid rootstock F1.

[0048] Pathogen preparation: Watermelon-specific and gourd-specific Fusarium wilt strains were isolated and preserved, and spore suspensions (1×10^6 spores / mL) were prepared.

[0049] Initial screening (greenhouse potted plants):

[0050] For seedling cultivation in plug trays, one seedling per hole, when the rootstock has grown to one true leaf, inoculate with pathogens using the root-dip or root-drenching method (10 mL of spore suspension per seedling).

[0051] Set up a control group without inoculation. Maintain the greenhouse temperature at 25-28℃, relative humidity at 80-90%, and 12 hours of light per day.

[0052] Observe for 7–14 days: use both the disease incidence index (DI) and survival rate as indicators for evaluation. If DI ≤ 10 and survival rate ≥ 90%, proceed to rescreening.

[0053] Secondary screening (net room / disease nursery):

[0054] Repeat the process 3 times, using either replanted soil or artificially inoculated diseased soil (each pot containing 200 g of pathogenic soil).

[0055] Record the incidence rate, disease index, growth (plant height / stem diameter), and survival rate of Fusarium wilt. Rootstocks with a DI ≤ 5 and a survival rate ≥ 95% are preferred for selection and compatibility evaluation.

[0056] Verification of low-temperature fruit setting (early spring conditions):

[0057] Artificial pollination was conducted under day / night temperatures of 15 / 10℃, and the fruit set rate, fruit set node position, and rate of deformed fruit were recorded. Rootstocks with a low-temperature fruit set rate ≥80% were preferred.

[0058] Affinity and quality evaluation:

[0059] Grafting was performed using target scions (such as Zaojia 8424, etc.) to evaluate grafting compatibility (survival rate) and symbiotic compatibility (growth vigor, fruit set, and fruit quality after survival).

[0060] Quality indicators: decrease in central sugar content (Brix) ≤ 0.5°Brix, increase in peel thickness ≤ 10%, and no significant change in flesh firmness (sensory evaluation and texture analyzer measurement).

[0061] Through the above process, rootstocks that are "highly resistant to two pathogens, have good fruit setting performance under low temperatures, and have minimal impact on quality" (such as a specific F1 variety or a particular gourd / cupberry strain) are selected and then enter the standardized seedling and cultivation stage.

[0062] Example 2: Standardized grafting seedling raising and healing management

[0063] Matching sowing date with seedling age:

[0064] Sow the rootstock 6-8 days earlier than the scion; the optimal time for grafting is when the cotyledons of the rootstock are fully expanded, the first true leaf appears (about 7-10 days), and the cotyledons of the scion turn from yellow to green.

[0065] Key points of the plug-in method:

[0066] Before grafting, water thoroughly and provide shade and moisture; remove the growing point of the rootstock and use a bamboo stick to make a hole at an angle 0.5-1.0 cm below the hypocotyl of the cotyledon; cut the scion into a wedge shape 1.0-1.5 cm below the cotyledon and quickly insert it so that the cotyledons of the rootstock and scion are in a "cross" shape.

[0067] Healing period management:

[0068] After grafting, cover with film to retain moisture, keep the temperature in the greenhouse at 25-28℃ and provide shade; do not ventilate or water for 5-7 days; then gradually ventilate and expose to weak light to harden the seedlings; remove the axillary buds of the rootstock in time after 10 days; transplant to the field in about 20 days.

[0069] Example 3: Field planting and high-efficiency cultivation resistant to continuous cropping

[0070] Site and soil treatment:

[0071] For fields that have been continuously cropped, priority should be given to implementing crop rotation between water and dry land; if crop rotation is not possible, high-temperature fumigation or soil disinfection (such as Weibaimu) should be carried out before planting, and residual branches, fallen leaves and diseased plant parts should be removed from the field.

[0072] Control soil salinity: EC ≤ 1.5 mS / cm throughout the entire growth period, and avoid continuous cropping for more than 4 years.

[0073] Planting and Density:

[0074] Use plastic film mulch + small greenhouse or multi-span greenhouse, with the beds facing north and south; plant 500-600 plants per mu, adjusting appropriately according to the variety and the growth of the rootstock.

[0075] Water and fertilizer and microecology for disease suppression:

[0076] Base fertilizer mainly consists of organic fertilizer and slow-release fertilizer, combined with drip irrigation and fertigation; nitrogen is controlled before fruit setting and potassium, calcium and magnesium are applied during the fruit expansion period.

[0077] Apply biocontrol agents such as Bacillus subtilis / Bacillus amyloliquefaciens (e.g., 10^8 CFU / g, 2-3 kg per acre) to the rhizosphere for colonization at the time of transplanting; foliar spray with alginic acid / amino acids during the flowering and fruiting period to induce resistance.

[0078] Pruning and fruit setting:

[0079] Leave two main vines on each plant and remove the rest of the side branches in a timely manner; select the second female flower for artificial pollination or bee pollination; after fruit set, prune the top and thin the fruit appropriately according to the growth to ensure the weight and quality of the single fruit.

[0080] Green prevention and control of diseases and pests:

[0081] The focus of monitoring is on diseases such as anthracnose, blight, and anthracnose, as well as pests such as whiteflies and aphids; the main methods are ventilation and humidity reduction, drip irrigation and water control, yellow sticky traps, release of natural enemies, and low-dose precision application of pesticides to reduce the risk of compounding obstacles from continuous cropping.

[0082] 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 method for selecting watermelon rootstocks and for efficient grafting cultivation to resist continuous cropping, characterized in that: Includes the following steps: S1: Construction of candidate rootstock pool: Select rootstock materials derived from gourd, bottle gourd, squash, or special hybrid F1; S2: Parallel screening of dual pathogens: Potted plants were initially screened for watermelon-specific and gourd-specific Fusarium wilt pathogens, and diseased plants were screened for secondary screening of candidate rootstocks. The entry thresholds were: disease index ≤10 and survival rate ≥90% (initial screening) and disease index ≤5 and survival rate ≥95% (secondary screening). S3: Low-temperature fruit setting verification: Artificial pollination was carried out under day / night conditions of 15 / 10℃, and rootstocks with a low-temperature fruit setting rate of ≥80% were selected; S4: Compatibility and Quality Evaluation: Grafting is performed using the target scion to evaluate grafting compatibility and symbiotic compatibility, with the following limits: fruit center sugar content decrease ≤ 0.5°Brix and peel thickness increase ≤ 10%; S5: Standardized grafting and seedling raising: The grafting method is adopted. The appropriate grafting time is when the cotyledons of the rootstock are fully expanded, the first true leaf appears (about 7-10 days), and the cotyledons of the scion turn from yellow to green. After grafting, the seedlings heal for 5-7 days under the conditions of 25-28℃, shade and moisture. Then, the seedlings are hardened off by ventilation. They can be transplanted in about 20 days. S6: Field cultivation to resist continuous cropping: prioritize water-dry rotation in fields with continuous cropping; for fields where rotation is not possible, disinfect the soil before planting and control soil EC ≤ 1.5 mS / cm; apply biocontrol Bacillus preparations for rhizosphere colonization at planting time, and combine drip irrigation, fertigation and ventilation to reduce humidity for green control. The planting density is 500-600 plants per mu, with two vines per plant and the second female flower selected for fruit setting.

2. The method for selecting watermelon rootstocks and cultivating them through efficient grafting to resist continuous cropping, as described in claim 1, is characterized in that: In the parallel screening of dual pathogens, the concentration of pathogen spore suspension was 1×10^6 spores / mL, and inoculation was carried out by root dip or root irrigation, with 10 mL per plant.

3. The method for selecting watermelon rootstocks and cultivating them through efficient grafting to resist continuous cropping, as described in claim 1, is characterized in that: In the standardized grafting and seedling raising process, the bamboo stick is inserted to a depth of 0.5–1.0 cm into the hypocotyl of the rootstock during grafting, and the length of the cut surface of the scion is 1.0–1.5 cm. The axillary buds of the rootstock are removed 10 days after grafting.

4. The method for selecting watermelon rootstocks and cultivating them through efficient grafting to resist continuous cropping, as described in claim 1, is characterized in that: In the field cultivation to resist continuous cropping, Bacillus subtilis / Bacillus amyloliquefaciens biocontrol agent is applied at the time of transplanting at a rate of 2-3 kg per mu, with an effective live bacteria count ≥1×10^8 CFU / g.

5. The method for selecting watermelon rootstocks and cultivating them through efficient grafting to resist continuous cropping, as described in claim 1, is characterized in that: In the field cultivation method for resisting continuous cropping, the continuous cropping period does not exceed 4 years throughout the entire growth period, and the soil EC is controlled at ≤1.5 mS / cm through water and fertilizer regulation and drip irrigation.

6. The method for screening watermelon rootstocks and for efficient grafting cultivation to resist continuous cropping, as described in claim 1, is characterized in that: The target scion is Zaojia 8424 or a similar early-maturing, high-quality watermelon variety.

7. The method for screening watermelon rootstocks and for efficient grafting cultivation to resist continuous cropping, as described in claim 1, is characterized in that: The rootstock selection results are specific hybrid F1 or specific gourd / cupberry varieties, which simultaneously meet the following requirements in the re-screening and low-temperature fruit setting verification: disease index ≤5, survival rate ≥95%, low-temperature fruit setting rate ≥80%, and the impact on fruit quality meets the following requirements: sugar content decrease ≤0.5°Brix, and peel thickness increase ≤10%.

8. The method for screening watermelon rootstocks and for efficient grafting cultivation to resist continuous cropping, as described in claim 1, is characterized in that: In the field pruning and fruit setting management, after fruit setting, the top should be appropriately pruned and the fruit thinned according to the growth to ensure the stability of single fruit weight and quality.

9. The method for selecting watermelon rootstocks and cultivating them through efficient grafting to resist continuous cropping, as described in claim 1, is characterized in that: The green control measures include yellow sticky traps, releasing natural enemies, and low-dose precision pesticide application, with a focus on controlling vine blight, blight, anthracnose, whiteflies, and aphids.

10. The method for screening watermelon rootstocks and for efficient grafting cultivation to resist continuous cropping, as described in claim 1, is characterized in that: The standard for determining the appropriate grafting time for standardized grafting seedling cultivation is as follows: the cotyledons of the rootstock are fully expanded and the first true leaf has just appeared (about 7 to 10 days), the cotyledons of the scion have turned from yellow to green, and the age of the rootstock and scion seedlings are matched.