A Detailed Explanation of the Latest Seedless Watermelon Cultivation Process
Seedless watermelons are grown from seeds, but these seeds are not the seeds found inside a seedless watermelon; rather, they are the seeds inside a triploid watermelon formed by crossing a natural diploid watermelon with a tetraploid produced through induced mutation. The cultivation techniques share similarities with those for ordinary watermelons, as well as some differences. Let us take a look together at the cultivation process of seedless watermelons!
The Cultivation Principle of Seedless Watermelons
Seedless watermelons are obtained by the method of artificially inducing polyploids. For example, treating the seeds or seedlings of diploid watermelons with colchicine (a plant alkaloid) blocks the formation of spindle fibers and the primary wall during the metaphase of cell division, so that the already replicated chromosome sets cannot separate toward the two poles and instead form a secondary wall in the middle. As a result, cells with doubled chromosome sets are formed, yielding tetraploid watermelon plants. These are then crossed with diploid watermelon plants (used as the male parent) to obtain triploid seeds. In triploid plants, due to disordered pairing of homologous chromosomes during meiosis, normal reproductive cells cannot be formed. The mature pollen of ordinary diploid watermelons is then used to stimulate the ovary of the triploid plant's flower to produce a triploid fruit, because its ovules cannot develop into seeds.
Seed Cultivation of Seedless Watermelons
1. Artificial induction: Seedless watermelons use the method of artificially inducing polyploids. Soak the seeds of diploid ordinary watermelons in a 0.2-0.4% colchicine (C22H26O6N) solution for 12-24 hours, or drip a 0.2-0.4% colchicine solution onto the growing point of the seedling stem tip every day between 6 and 7 p.m. for four consecutive days.
2. Careful management: After treatment, wash the seeds or seedlings clean with water. During treatment and the recovery period, place the plants under diffused light to avoid direct sunlight causing the decomposition and destruction of colchicine. At the same time, high temperatures must be strictly avoided, because under high temperatures the toxicity of colchicine to plants increases, easily causing seedling death. Before surviving, they should be given good cultivation conditions and careful management.
3. Bagging and pollination: Use tetraploid watermelons as the female parent and pollinate them with diploid pollen grains to produce triploid watermelon seeds. For small-scale seed production, follow the flowering habits of watermelons by bagging at the proper time each afternoon, then perform artificial pollination the next morning while attaching a marker. For large-scale seed production, partitioned isolation is required, planting the tetraploid female parent and diploid male parent plants in a certain ratio.
Seed Treatment of Seedless Watermelons
1. Seed selection and soaking: According to the traits of the variety, select seeds by seed shape, color, size and plumpness, pick out tetraploid and diploid watermelon seeds, and remove deformed seeds as well as hybrid and inferior seeds. Then, a few days before soaking, sun-dry the seeds for 1-2 days. Next, place the triploid seeds in warm water at 55°C and stir, then let the water cool naturally and soak the seeds for 6-8 hours.
2. Artificial shell cracking: The methods for cracking the shells of seedless watermelon seeds can be divided into two types: dry seed cracking and wet seed cracking. At present, wet seed cracking is mainly used. Dry seed cracking is highly efficient, but it easily damages the seed embryo, and the soaking time and soaking temperature are difficult to control, affecting the improvement of the germination rate. Wet seed cracking is slippery and less efficient, but the length of soaking time has little effect on the germination rate, it is easy to control, and the germination rate is higher and more stable.
3. Seed germination: Place the seeds that have been soaked and shell-cracked under a constant temperature of 33-35°C for germination, maintaining a certain humidity. After 24 hours, more than 90% of those with germination capacity will have germinated. Pick out those with sprouts 0.5 cm long and they can be sown, while the rest continue to germinate. After 36 hours, basically all normal seeds will have germinated. Seeds that still have not germinated after 48 hours have lost their viability and no longer need to be germinated.
4. Grafting and seedling raising: The low survival rate and slow healing speed of grafted seedless watermelon seedlings are problems commonly occurring in current production, restricting the development of seedless watermelon production and causing relatively large economic losses to melon farmers. To improve the survival rate of grafted seedless watermelon seedlings and cultivate robust grafted seedlings, grafting and seedling raising must be carried out according to the structural characteristics and growth characteristics of seedless watermelons.
Field Management of Seedless Watermelons
1. Land preparation and cultivation: Apply 3-5 cubic meters of high-quality farmyard manure, 20-30 kg of urea, 20-30 kg of diammonium phosphate, and 20 kg of potassium sulfate per mu, prepare the land finely, and make beds according to a row spacing of 1.7-2 m. For high-ridge cultivation, the high ridge is 60 cm wide and about 15 cm high, covered with 80-90 cm wide plastic film. Choose a windless sunny day for planting, with 500-700 plants per mu, watering as you plant. Implement three-vine pruning, and it is best to keep the 3rd female flower on the main vine for fruit set, avoiding fruit set at low nodes.
2. Fertilizer and water management: During the seedling stage of seedless watermelons (around the time of the rosette stage), apply 5 kg of urea per mu to promote seedling growth. During the flowering and fruit-setting stage, generally do not water or fertilize. When the watermelon is about the size of a duck egg, the fruit has basically set steadily; apply a fruit-swelling fertilizer once, with 15-20 kg of urea and 15 kg of potassium sulfate per mu. Spraying 0.2% potassium dihydrogen phosphate on the leaves in the later growth stage can increase yield and quality.
3. Artificial pollination: Seedless watermelons use artificial supplementary pollination, which is highly targeted, results in early and uniform fruit set, and makes the fruit mature relatively uniformly. At around 8 a.m., use the male flowers of the pollination variety that open on that day to pollinate the female flowers of seedless watermelons. The earlier the pollination after flowering, the better, and no later than 10 o'clock. One male flower can pollinate 3-4 female flowers. Pollination should be uniform and the movements gentle to avoid injuring the stigma.
4. Reasonable ripening: When seedless watermelons need to be marketed early, ethephon can be used for ripening treatment. When the fruit has reached full size but is not yet ripe, apply a 200 mg ethephon solution per kilogram of watermelon along the melon surface once in the evening. A small amount of neutral soap powder can be added to the solution to increase adhesion. Two days later, it can be harvested and marketed, allowing supply to the market 3-5 days earlier than naturally ripened ones.