Detailed Explanation of the Latest Techniques for Grafting Propagation of Shatian Pomelo Seedlings

Shatian pomelo is a plant of the genus Citrus in the family Rutaceae. Seedling cultivation can be done by grafting, air layering (marcotting), and cuttings, but in production practice grafted seedlings are superior to layered and cutting-propagated seedlings, so grafting is mostly used to propagate pomelo seedlings in current production practice, while air layering and cuttings are gradually being phased out. Let us take a look at grafting propagation of Shatian pomelo seedlings together below!

Collection of Rootstock Seeds

The rootstock for Shatian pomelo should be selected from sour pomelo trees (either red-fleshed pomelo or white-fleshed pomelo is acceptable). By the Frost's Descent season the pomelo has already matured; after harvesting the fruit, take out the seeds and process them promptly to prevent piling up and molding, which would affect germination. First wash off the gelatinous substance on the outside of the seeds with wood ash water, then rinse them clean with clear water, and then place them in a dilution of 1 part formalin to 50 parts clear water (or 1 part copper sulfate to 160 parts clear water), soak and wash for ten minutes, take them out and leave them for five minutes, then immediately rinse them clean with clear water, dry them in the shade in a ventilated place, and they are ready for sowing.

Selection of Rootstock Nursery Site

Before autumn arrives, the nursery site should be selected in advance. The nursery land should be chosen facing south or southeast, with good ventilation and light transmission, a slope of less than 10 degrees, a relatively thick soil layer (over 20 cm), good water retention and drainage, convenient irrigation, medium fertility sandy loam or sandy yellow loam, few wind hazards, and no pests or diseases. Places that are too sticky and heavy, barren, dry, poorly drained, or have a high groundwater level (above 1 m) are all unsuitable as nursery land.

Preparation of Rootstock Nursery Site

Reasonable deep plowing and fine land preparation of the rootstock nursery can promote the growth of the seedling root system and increase the emergence rate per unit area and the quality of the seedlings. Before sowing, the nursery land should be deep plowed and the soil sun-dried so that the soil is fully weathered. Drainage ditches should be opened around the nursery to facilitate irrigation and drainage. The nursery beds should be arranged in an east-west direction, generally 1.2 m wide, 15-20 cm high, with ditches 40 cm wide; the length of the beds depends on the terrain, the bed surface should be level, and the soil clods should be fine and broken up. A few days before sowing, apply grass fertilizer (about 1800 kg of farmyard manure per mu, 150 kg of wood ash, mixed evenly with the topsoil), and then sow.

Sowing in the Rootstock Nursery

The seeds processed after harvest in late October should be sown immediately. When sowing, first open small horizontal furrows on the bed surface, with a row spacing of 10 cm. About 15-18 kg of seed is used per mu, which can produce about 60,000 seedlings. After sowing, cover with about 10 cm of fine soil, then cover the bed surface with bracken fern, rice straw, or other weeds, water to keep moist; where irrigation is convenient, one run of “horse-running water” may also be used to seep through and wet the ground. During drought, pay attention to watering (irrigation), always keep the nursery land moist to promote seed germination, and remove the covering grass after the seedlings emerge.

Management of the Rootstock Nursery

After the rootstock seedlings emerge, the seedbed should always be kept moist, but not waterlogged. When the seedlings grow two true leaves and the leaves turn dark green, begin fertilizing. In the early stage, apply thin fertilizer frequently, once every ten days to half a month, for six or seven consecutive applications; in the later stage, fertilize appropriately according to the growth of the seedlings. The fertilizer should be mainly nitrogen fertilizers such as human and animal manure or ammonium sulfate, with an appropriate application of some wood ash or superphosphate and other phosphorus and potassium fertilizers.

Grafting of Shatian Pomelo Seedlings

In order to accelerate the propagation of seedlings to meet the needs of developing Shatian pomelo production, grafting should be carried out on the smallest possible rootstock seedlings. The grafting methods include the small-bud cut grafting method, the branch cut grafting method, and the “T”-shaped budding method. The small-bud cut grafting method is more suitable for small rootstocks, allowing earlier grafting and earlier release from the nursery. The small-bud cut grafting method and the “T”-shaped budding method are best carried out from late March to late June (when the temperature is 15-20 degrees Celsius), when the survival rate of grafted seedlings is highest. Climate conditions differ among regions, and the timing of young bud sprouting on branches also differs, so this should be flexibly controlled according to phenological changes.