Video Tutorial on Grafting Seedling Cultivation Techniques for Greenhouse Cucumbers
????1. Preparation Before Grafting
1.1 Selection of Cucumber Rootstock
There are many rootstocks suitable for grafting cucumbers, such as Chinese pumpkin, luffa, bottle gourd, etc., but most of them have a great impact on cucumber quality and poor compatibility, and the grafted cucumbers also taste poor. According to experience in recent years, black-seeded pumpkin is tolerant to low temperatures and has good compatibility with cucumbers, making it currently the most ideal rootstock for cucumber grafting.
1.2 Seed Selection
Black-seeded pumpkin seeds must be selected as dark-colored, mature and plump seeds. Since cucumber grafting mainly utilizes the rootstock's resistance to soil-borne diseases, while other diseases still depend on the resistance of the cucumber variety itself, and the traits of grafted cucumbers are also those of the cucumber itself, therefore, cucumber seeds must be selected from varieties with good compatibility.
1.3 Seed Treatment
Before sowing, sunning seeds for 2-3 d can eliminate bacteria and make germination uniform. Seed disinfection: ① High-temperature disinfection. Place seeds in 90-95 °C water for 5-7 s, which can kill or deactivate pathogenic bacteria or viruses. ② Warm water disinfection. Place seeds in 50-55 °C salt water with constant stirring, scald seeds for 15 min, then place in 25-50 °C warm water and soak for 4-6 h. ③ Potassium permanganate disinfection. Soak seeds in 0.1%-0.5% potassium permanganate solution for 3 h, then rinse clean with water. ④ Sodium phosphate disinfection. Place seeds in 0.1%-0.5% sodium phosphate solution, which can kill the mosaic virus on the seed surface.
1.4 Preparation of Grafting Tools
① Bamboo skewer. Prepare a bamboo skewer 5-6 cm long. Select the harder bamboo green part, sharpen the tip at 0.5 cm from the end into a wedge shape, with a flat top, about 3 mm wide, equivalent to the stem thickness of the cucumber. The tip of the skewer must be flat and smooth to facilitate graft survival. ② Blade. A razor blade can be split in half, removing one half, with the edge needing to be sharp; grafting-specific clips can use plastic wrap, cotton thread, or adhesive tape.
????2. Grafting Methods
2.1 Insertion Grafting Method
When using the insertion grafting method, first sow black-seeded pumpkin, then sow cucumber, with about 5 d difference between the two. When black-seeded pumpkin grows to 2 leaves and 1 heart, and cucumber grows to 2 leaves and 1 heart, grafting can be carried out. The specific operation is as follows: 1 d before grafting, water the black-seeded pumpkin's nutrient pot thoroughly to improve graft survival rate. First remove the terminal bud, i.e., the growing point, of the black-seeded pumpkin. Hold the bamboo skewer with the right hand, pinch the lower hypocotyl of the black-seeded pumpkin with the left thumb and index finger, so that the tip of the bamboo skewer is pressed close to the inner side of the base of the rootstock cotyledon and inserted obliquely toward the underside of the other cotyledon. The insertion depth is generally about 0.5 cm, and it must not pierce through the surface, to prevent the scion from producing adventitious roots; it also must not pass through to the hollow part inside the rootstock stem without reaching the inner side of the stem wall on the other side, to avoid forming small old seedlings. Then cut the cucumber scion. Select healthy cucumber seedlings, pinch the 2 cotyledons of the cucumber with the left thumb and ring finger, clamp the part of the cucumber near the root with the index and middle fingers, straighten the cucumber's hypocotyl. Pinch the blade with the right thumb and index finger, make the first cut from 0.4-0.5 cm below the cucumber cotyledons, and make one cut on each of the opposite sides. For the prepared scion, the length of the cut and the thickness of the scion should match the rootstock incision, and the cut should be smooth. The first cut can be longer, and the second cut is generally controlled at about 0.5 cm, shaping the cut into a wedge. After the scion is cut, immediately pull the bamboo skewer out of the rootstock, insert the scion and gently press so that the scion and rootstock fit fully without leaving gaps. The scion cotyledons and rootstock cotyledons form a "cross shape". The insertion depth of the scion is measured by having the scion cut surface flush with the rootstock. The entire process from cutting to inserting the scion must be steady, accurate, and fast. Immediately place the grafted cucumber seedlings in sequence into a pre-built arched shed. The ground inside the shed should be watered first to increase ground humidity and facilitate survival. After placing several rows, spray some water with a sprayer. Water droplets should not be too large, and do not spray on the graft union. After placing them, cover tightly with plastic film for moisture retention, heat preservation, and shading treatment.
2.2 Approach Grafting Method
When using the approach grafting method, cucumbers should be sown 5 d earlier. Both cucumbers and pumpkins are sown in seedling trays. When both stems are about 7 cm tall, grafting is optimal. The specific method is: first lift the rootstock seedlings and scion seedlings from the seedbed, use a sterilized blade or bamboo skewer to remove the growing point of the pumpkin seedlings, and at 0.5-1.0 cm below the cotyledons, on the side parallel to the cotyledon direction, make a downward cut at 45° with a blade, reaching 2/5-1/2 deep into the hypocotyl, about 1 cm long. Then take the scion, at 1.5 cm below the cotyledons, in the direction perpendicular to the cotyledons, make an upward diagonal cut at 30°, reaching 1/2-2/3 deep into the hypocotyl, with length equal to that of the rootstock. Fit the incisions of the rootstock and scion together, gently pinch the graft union by hand without loosening, to prevent the union from misaligning, then fix the union with a grafting clip, so that the cucumber cotyledons are higher than the pumpkin cotyledons in a "cross" shape. After approach grafting, immediately plant the seedlings into nutrient pots and place them in a pre-prepared arched shed. Note to gently hold the graft union area by hand when planting. To avoid the scion contacting the soil and producing adventitious roots, keep the stem-root distance at about 1 cm, and the graft union 3-4 cm from the nutrient soil. Before successful approach grafting, both the rootstock and scion each have their own roots. After 10-15 d when the graft has survived, promptly remove the wrapping material and use a blade to cut off the scion root system. After cutting the roots, lower the temperature for hardening seedlings and cultivate strong seedlings.
????3. Management of Grafted Seedlings
3.1 Temperature
Generally within 3-5 d after grafting, maintain 24-26 °C during the day, not exceeding 27 °C; 18-20 °C at night, not lower than 15 °C. After 3-5 d, begin ventilation and gradually lower the temperature. During the day it can be reduced to 22-24 °C. At night 12-15 °C.
3.2 Moisture Retention
Within 3-5 d after grafting, maintain the relative humidity in the arched shed between 85%-90%, but the soil moisture in the nutrient pots should not be too high, to avoid seedling rot.
3.3 Shading
Cover the small arched shed with thin straw mats or shade nets, and appropriately adjust temperature and humidity according to weather conditions. When temperatures are lower, uncover the straw mats to receive weak scattered light. Shade around noon, then gradually increase light exposure time, and stop shading after 1 week.
3.4 Ventilation
After 3-5 d of grafting, when the grafted seedlings begin to grow, ventilation can begin. Start with little ventilation, then gradually increase and gradually extend it. Generally, large ventilation is carried out at 9-10 d. After ventilation, observe the seedling condition carefully. If wilting is found, promptly supplement water and shade.
3.5 Cutting the Hypocotyl of the Approach-Grafted Scion
For approach-grafted seedlings, cut the cucumber hypocotyl at 10-12 d. The method is to make 1 cut at 1 cm below the graft union, then make another cut near the ground. The purpose of making 2 cuts is to prevent the hypocotyl from healing back together.