Detailed Guide to the Method of Cultivating Mango Grafting Rootstock Seedlings

In monoembryonic mango varieties, a single seed produces only one seedling, while polyembryonic varieties can germinate and grow into multiple seedlings. A monoembryonic seed has only one embryo (a sexual embryo); the embryo is large, and the single seedling it develops into is vigorous. A polyembryonic seed has multiple embryos; the embryos are smaller, and the multiple seedlings they develop into are weaker. Therefore, in the past, emphasis was placed on using monoembryonic varieties as rootstock. However, the uniformity of the rootstock is very important for improving mango yield and quality. Monoembryonic seedlings are sexual seedlings, and their growth performance varies greatly. The huge differences in growth and yield among different plants in an orchard are very likely caused by the rootstock. Therefore, after testing, seeds of polyembryonic varieties should be selected for cultivating rootstock seedlings. In the past, local mangoes with smaller fruit, less flesh, and poorer quality but plump, well-filled embryos were mostly recommended as rootstock. These local mangoes were mostly monoembryonic and grew vigorously, but for the above reasons they are not ideal as rootstock. As for polyembryonic varieties suitable for use as rootstock, further testing is still needed to determine grafting compatibility, adaptability, and high-quality, high-yield performance.

Seedlings grown from seed are mainly used as rootstock or for breeding trials. The seeds used to cultivate seedlings from seed should come from the same variety and be collected from ripe fruit. The seeds must be plump, disease-free, and insect-free. They should be extracted and sown as quickly as possible, because mango embryos are sensitive to water loss; once dried, their germination capacity decreases rapidly. The seeds should have the fibrous skin and membranous layer removed, be soaked in a 0.1% potassium permanganate solution for 1 minute, taken out and air-dried, and then sown. The sowing medium is best as medium-coarse river sand or vermiculite, with a sand bed thickness of 30 cm.

If the seedbed has already been used, it should be thoroughly sprayed with a 1% formalin aqueous solution, covered with plastic film for 24 hours for sterilization, and then aired for 24 hours until the odor has completely dissipated. The embryos can also be kept moist in the dark to allow the embryo buds to begin sprouting before sowing. When sowing, place the embryos flat; for monoembryonic seeds, orient the embryo buds in the same direction and arrange them closely, with a row spacing of 15 cm. After sowing, cover with a 2 cm thick layer of river sand or vermiculite. If plastic film is not used to retain moisture, then when temperatures are high and air humidity is low, water must be applied daily. If film is used to cover, shade, and retain moisture, watering once every 3-5 days is sufficient, as long as the medium does not dry out. In Guangzhou, when sown between June and October, seedlings can emerge in 15-20 days. Generally, they are transplanted to the nursery field when they have 3-5 red leaves. Each polyembryonic seed can be separated into 3-4 seedlings; large and small seedlings should be graded slightly, and weak seedlings should be discarded. Seedlings from monoembryonic seeds can be transplanted a little later.

To cultivate high-quality nursery stock, it is best to use nursery bags at least 30-40 cm long and holding more than 3 kg of soil to cultivate rootstock seedlings for grafting. Because mango has few fibrous roots, bag cultivation helps ensure survival after transplanting. For cultivation in the nursery field, choose relatively clayey soil so that a ball of soil is easily retained when the seedlings are lifted. At transplanting, part of the main root must be cut off, leaving about 10 cm, or the main root should be coiled, in order to promote the development of lateral roots. The soil in the nursery bags can be somewhat sandy, but because fertilizing is less convenient than in the field, a sufficient amount of decomposed organic fertilizer should be mixed in to ensure good root development. After transplanting, shading should continue until the leaves have fully turned and the branches have matured, after which full light can be given. Monoembryonic seeds can also be sown directly into nursery bags.