Grafting and Seedling Cultivation Technique of Bitter Gourd for Disease Prevention in Hainan

Ziji LIU, Yu NIU, Renbo YU, Yan YANG

Tropical Crops Genetic Resources Institute, Chinese Academy of Tropical Agricultural Sciences, Haikou 571011, China

Abstract The paper had introduced the operation technical regulations of bitter gourd grafting and seedling cultivation, including all kinds of measures before, during and after grafting, in order to provide technical reference for efficient production of bitter gourd.

Key words Grafting; Seedling cultivation; Technical regulation

1 Introduction

Bitter gourd (MomordicacharantiaL.) is one of the main winter vegetable crops in Hainan Province, which is not only rich in nutrition, but also contains pharmacological active ingredients with anti-tumor[1], hypoglycemic[2-3], anti-inflammatory[4-5]and other effects. In recent years, with the continuous expansion of bitter gourd planting area, the wide application of protected area and facilities, and the expansion of continous planting area, a large number ofFusariumsp. has accumulated in soil, and the occurrence and damage ofFusariumwilt is increasingly severe. The incidence rate of bitter gourdFusariumwilt is as high as 60%-80%, which leads to a yield reduction of 50%-80% and even no harvest, seriously affecting the yield and quality of bitter gourd[6]. Using the characteristics of high disease resistance and strong root system of rootstocks, grafting technology could enhance resistance, prolong harvesting period and improve yield and quality by regulating the physiological function of plants[7], becoming one of the most economical and effective measures to preventFusariumwilt and to overcome continuous cropping obstacles. The operation processes of bitter gourd grafting and seedling cultivation in Hainan had been introduced in detail, in order to provide technical reference for efficient production of bitter gourd.

2 Technical regulations of grafting and seedling cultivation for disease prevention

2.1 Rootstock selectionThe rootstocks with strong affinity to scion, strong disease resistance and little influence on scion quality can be selected. The improper selection of rootstock will greatly affect the quality of bitter gourd. In production, cucurbita ficifolia and towel gourd are generally selected as rootstocks for bitter gourd grafting.

2.2 Selection and disinfection of seedling trayThe 50-well seedling tray is used for rootstock sowing and the 72-well seedling tray is used for scion sowing. The seedling tray is disinfected by soaking in 1 000 times potassium permanganate solution for 10 min.

2.3 Substrate preparation and tray loadingCommercial Bei-lei substrate is added with carbendazim at the dose of 0.2 kg/m3and added with water to keep humidity of about 50%. After mixed evenly, the substrate is loaded into seedling tray.

2.4 Timely sowingThe sowing time should be estimated accurately to avoid too much difference between scion and rootstock seedlings that will affect the quality of grafting. The bitter gourd seeds are sown about 15 d before grafting, and the rootstock varieties are sown about 18 d before grafting.

2.5 Soaking seed and accelerating germinationCucurbita ficifolia is generally used as the rootstock for bitter gourd grafting. The seeds are dried for 3-5 h before accelerating germination, then soaked in 25-30 ℃ warm water for 20 min and 55 ℃ hot water for 10 min, and continuously soaked in water for 4 h after the water temperature returning to normal temperature. Then, the seeds are wrapped with wet gauze and accelerated germination at 28-30 ℃ for 1-2 d, and sowing can be performed when 50%-70% seeds are germinated. The germ is downward in sowing, keeping the seed opening in the same direction. After sowing, the plot is covered with 1.0-1.5 cm of disinfection substrate and sprayed with enough water, and the seedling bed is covered with plastic film. The day temperature is kept at 28-32 ℃ and the night temperature is kept at 20-18 ℃. The mulching film is removed when 50%-70% seedlings are unearthed.

2.6 Preparation before graftingThe grafting tools such as blade, bamboo stick, alcohol,etc., are prepared. The tools and hands are disinfected with alcohol to keep the grafting site clean and tidy.

Preparation of shade shed: small arch shed is built in the nursery shed which is covered with film and sunshade net outside, and the nursery bed soil in the shed is fully moist.

2.7 Standard of rootstock and scion seedling ageFertilizer and water management should be strengthened at seedling stage, and seedlings should be exercised timely to prevent overgrowth, ensuring that rootstock seedlings and scion seedlings reach the standard of strong seedlings. The proper stage of grafting is when the rootstock cotyledons are fully spread, the first true leaf appears from beginning to half spread, and the scion cotyledons spread from beginning to full spread.

2.8 Grafting pretreatmentThe day before grafting, the rootstock and scion are watered adequately, and the leaves are sprayed with carbendazim fungicide on the surface.

2.9 Grafting timeGrafting of bitter gourd in Hainan should be done in a cloudy day or in the evening, and the temperature after grafting is cool, so as to avoid wilting of seedlings.

2.10 GraftingTop grafting method is commonly used in bitter gourd grafting. Top grafting method refers to perforation at the top of rootstock and wedge insertion of scion, without fixing materials. This method is featured by simple operation and high efficiency, which requires that the rootstock stem is slightly thicker than the scion and is not hollow, and is usually used for the grafting of cucurbit crops. The true leaves and growing points of the rootstock are removed, and a 30°-45° oblique puncture hole is formed from the base of one side of rootstock cotyledons to the hypocotyl of the other side of cotyledons with a bamboo stick, with a depth of about 0.5-0.8 cm. A 0.5-0.8 cm wedge face is cut diagonally at 1 cm below the scion cotyledon, which is equal to the depth of rootstock hole. Afterwards, the bamboo stick is pulled out from the rootstock, and the scion is immediately inserted into the rootstock hole, with wedge direction perpendicular to cotyledon direction. After insertion, the scion cotyledon and rootstock cotyledon are in the shape of a cross, and the grafting is completed.

2.11 Management of grafting seedlingsWithin 3 d after grafting, the sheds are strictly shading and airtight; the temperature is maintained at 24-26 ℃ during the day and 18-20 ℃ at night, and the relative humidity of the air is kept at 90%-95%. From the 4thto 6thday, the ventilation and light transmission time is gradually increased, and the sheds are shading at noon, maintaining 25-28 ℃ during the day and 18-20 ℃ at night. From the 7thto 10thday, the sunshade net is removed, and the ventilation volume is gradually increased and the air humidity is maintained at 50%-60%. After 10 d, the film of arch shed can be removed, and all seedlings are under routine seedling management.

2.12 Fertilizer and water managementWhen grafted seedlings are under routine seedling management, fertilizer water is sprayed once every 5-7 d. The high-quality foliar fertilizers, such as monopotassium phosphate and Kangpu can be chosen.

2.13 Management of grafted seedlings before transplanting

The light, temperature and humidity should be scientifically and reasonably controlled, to promote robust growth of seedlings. After grafting, the rootstock will still sprout side buds. It should be observed at any time to erase the side buds of the rootstock to prevent the growth of side buds that will affect the normal growth of scion. According to the healing quality and growth strength of grafted seedling interface, the seedlings are carried out grading management and transplanting in batches. Seedlings are exercised 3-5 d before transplanting. The main measures include: lowering temperature, reducing moisture, and increasing the duration and intensity of light. Fungicides are sprayed once before planting.

2.14 Prevention and control of diseases and pestsThe diseases of grafted seedlings in the seedbed mainly are damping off, sheath blight,etc., which can be controlled by propamocarb. The pests mainly include aphids, whitefly, leaf miner, mites and thrips,etc., which can be controlled by avermectin, imidacloprid, acetamiprid and so on.

3 Conclusions

With the continuous expansion of the planting area of bitter gourd, the occurrence and damage ofFusariumwilt is becoming more and more severe, which seriously affects the yield and quality of bitter gourd. Grafting is one of the most economical and effective measures to preventFusariumwilt and to overcome the obstacle of continuous cropping.