Bitter gourd is a major local melon variety. However, due to the long-term problem of continuous cropping, severe blight has caused a steady decline in yield. In 1999, anti-season grafting using loofah as the rootstock was introduced in Shange Town, Pinghe County, in this municipality. This method significantly reduced the occurrence of Fusarium wilt, with mortality rates kept between 1% and 3%, achieving satisfactory results. Despite this success, challenges remained: loofah’s well-developed root system absorbs large amounts of water, while the bitter gourd leaves have low transpiration, leading to excessive leaf moisture and an increased risk of downy mildew. Additionally, traditional grafting methods—such as connection or plugging techniques—were slow, difficult to perform, and not suitable for large-scale production. Grafted seedlings were also prone to false vitality.
To address these issues, in 2005 we began using black-skin squash as the rootstock and developed a new grafting technique. This involved removing one heart and one cotyledon from the rootstock, leaving only one cotyledon for grafting when the rootstock had two leaves and one heart. This method improved efficiency, allowing each person to graft up to 140 plants per hour, with a high survival rate suitable for industrial application.
**1. Cultivation of Grafted Seedlings**
**1.1 Seed Germination**
Bitter gourd seeds are sown in mid-November. Black-skin squash seeds are soaked for 4–6 hours before being germinated at 30–32°C in a constant temperature incubator for 3–5 days. Bitter gourd seeds are first exposed to sunlight for 2–3 hours, then soaked in warm water (55°C) and stirred to reduce heat. After soaking at room temperature for 5–12 hours, they are washed, wrapped in wet gauze, placed in a plastic bag, and kept in the incubator. The seeds are rinsed daily, and when the shoots reach 2–3 mm, they are sown. Germination continues until ready for planting.
**1.2 Sowing Rootstock and Scion Seeds**
Rootstock seeds are sown in 70 or 72-cell trays, while bitter gourd seeds are sown in 98-cell trays. The growing medium consists of peat soil mixed with perlite and superphosphate in a ratio of 5:1. The mixture is compacted to ensure strong root development. Before sowing, the substrate is watered and placed in a greenhouse maintained at 25–30°C to promote germination.
**1.3 Grafting and Post-Grafting Care**
Grafting occurs when the rootstock has two leaves and one heart, and the scion has one fully developed leaf. The day before grafting, both rootstock and scion are watered. Grafting is performed in a windless environment. Using a sharp blade, the rootstock’s extra cotyledon and heart are cut at a 0.5 cm angle. The scion is similarly cut at 0.4 cm from the hypocotyl. The incisions are aligned and secured with a grafting clip. After grafting, seedlings are placed in a dark, humid area with over 90% humidity for 3 days, then gradually exposed to light and lower humidity. After 7 days, normal care begins. By day 15, side buds on the rootstock are removed to prevent interference with the scion’s growth. When the grafted seedling reaches about 15 cm in height, it is ready for transplanting.
**2. Field Planting and Management**
**2.1 Planting**
Choose loam or sandy loam with good drainage and organic matter. Greenhouses are typically 60 meters long, 7–8 meters wide, and oriented north-south. Ten days before planting, the soil is tilled and sun-dried. Basal fertilization includes 1000 kg of pig manure, 40 kg of compound fertilizer, 20 kg of potassium chloride, and 10 kg of magnesium sulfate per 667 square meters. The soil is raised into ridges 25 cm high and 1.7 m wide. Two to three days before planting, the greenhouse is covered with plastic film and black mulch to raise the temperature. One day before transplanting, the grafted seedlings are watered. Plants are spaced 80–100 cm apart, and the grafting site should be kept above the ground level.
**2.2 Temperature and Humidity Control**
After planting, monitor greenhouse temperatures closely. When the temperature exceeds 28°C, vents are opened. If it goes above 32°C, side vents are rolled up. Even on rainy days, ventilation is necessary to reduce disease risk.
**2.3 Pruning and Maintenance**
When the plant reaches 30 cm, use a “human†frame to support growth. Retain the main vine and two strong side vines below 80 cm, removing all other branches. Regular pruning removes yellow, diseased, or weak leaves, ensuring proper air circulation and light penetration. Remove deformed fruit, excess male flowers, and tendrils to concentrate nutrients.
**2.4 Fertilization and Irrigation**
Black-skin squash has a strong root system but is sensitive to waterlogging. Keep the soil consistently moist but not saturated. Furrow irrigation is used when dry, with water levels kept 5–8 cm below the surface. After the first harvest, apply 15 kg of compound fertilizer per 667 square meters, followed by a second top dressing of 20 kg compound fertilizer and 10 kg potassium chloride every three weeks. When humidity is high, dissolve fertilizer in water and apply it to both sides of the ridge.
**2.5 Artificial Pollination**
Artificial pollination is crucial for off-season cultivation. Male flowers are collected in the morning and used to pollinate open female flowers. Each male flower can pollinate 2–3 female flowers.
**2.6 Pest and Disease Management**
Common diseases include powdery mildew and anthracnose. Use fungicides such as polysulfide suspension, triadimefon, or difenoconazole. For downy mildew, metalaxyl or DuPont products are effective. Rotate treatments to prevent resistance. Pests like aphids and melon flies can be controlled with phoxim or lanthanum. Always increase ventilation after pesticide application to reduce humidity.
**3. Harvesting**
Harvesting typically begins around 20 days after pollination. At this stage, the fruits are 25–30 cm long, with smooth, firm bases. Use scissors to cut the stems, leaving 1–2 cm of stalk attached.
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