Detailed Explanation of Key Techniques for Macadamia Nut Propagation
Macadamia nuts are propagated by grafting and cuttings. (1) Grafting propagation 1. Seed selection The seeds used to grow rootstock seedlings should be taken from robustly growing, consistently high-yielding plants, preferably disease-free with good nut quality. Both smooth-shell and rough-shell types can be used; because rough-shell seeds germinate and grow quickly, are relatively disease-resistant and have softer wood, they are easier to graft, so some regions prefer to use them.
Macadamia nuts are propagated by grafting and cuttings.
(1) Grafting propagation
1.Seed selection
The seeds used to grow rootstock seedlings should be taken from robustly growing, consistently high-yielding plants, preferably disease-free with good nut quality. Both smooth-shell and rough-shell types can be used; because rough-shell seeds germinate and grow quickly, are relatively disease-resistant and have softer wood, they are easier to graft, so some regions prefer to use them. New Zealand and other places believe that using rough-shell types as rootstock can improve the cold resistance of macadamia nuts. Australia mainly uses the D4 variety.
2.Seed storage
Seeds can be stored at 5-10°C in shaded moist sand, or sealed in plastic bags and refrigerated in a refrigerator.
3. Rootstock cultivation
Nuts that mature in high-temperature seasons lose viability very quickly; counting the germination rate at harvest as 100%, it drops to 50% after 6 months of storage. Therefore, it is best to sow immediately after harvest, once the outer soft shell has been removed.
Seeds are sown with the hard shell on, suture line facing downward, covered with 2.5 cm of sand, then watered thoroughly and the seedbed kept moist. Germination begins in 3-4 weeks at 30-35°C; if below 24°C, the germination time is more than doubled. During rootstock cultivation, attention must be paid to preventing ant and rodent damage. After two pairs of leaves have matured, the seedlings should be moved into plastic bags or other containers, with 50% shade. Seedlings are very sensitive to moisture fluctuations, so they must be given sufficient irrigation. During the seedling stage, trace elements and slow-release, low-phosphorus fertilizers should be applied. Plants should be trained into a single-trunk form; after 12-15 months they can be used for grafting. The terminal bud of macadamia is easily damaged by high temperature or insect pests, which stimulates the lateral buds below it to sprout multiple side branches and affects the normal growth of the rootstock seedling. Therefore, care should be taken to prune off branches and maintain single-trunk extension growth.
The germination substrate for sowing should be clean, pest-free coarse river sand, at least 20 cm thick. The seedling soil is made by mixing sand, loam, moss and fully decomposed sawdust or mushroom residue mud evenly. Decomposed macadamia shells can also be used. The seedling soil pH is 5.5-6.5.
4. Grafting
In grafting macadamia nuts, besides mastering the basic grafting techniques, it is also required that the scion be fully mature and that a good grafting time be chosen. The low survival rate is to a large extent caused by improper scion selection. Therefore, abroad, grafting propagation is mainly carried out by skilled workers in large commercial nurseries.
(1) Grafting period: spring and autumn are better, especially late autumn and early spring.
(2) Grafting conditions: the scion and rootstock should be 1-1.3 cm thick, both fully mature, with branch bark light brown to gray and raised lenticels. If conditions permit, the scion should undergo girdling treatment 6-8 weeks before grafting. The specific method is: select a long branch of suitable thickness, girdle about 2.5 cm wide at the base, and scrape clean the cambium tissue. Its purpose is to increase the accumulation of photosynthetic products in the scion and improve the grafting survival rate. When grafting, it is best to select dense-node buds. Before grafting, water the rootstock seedlings thoroughly first.
(3) Grafting methods: branch grafting, cleft grafting, splice grafting and cut grafting are all acceptable. In cleft grafting, the lower part of the scion is cut into a long wedge shape, the top of the rootstock is split from the center, and after the scion cut is inserted into the slit, the cambium of the rootstock and scion are aligned, and the joint is tied tightly and sealed firmly. In China, this grafting method is considered the most successful. According to our experience, the key to success with splice grafting and cut grafting is that the joining surface should be longer, reaching 1-1.5 cm. A cut surface that is too short is not easy to heal. This may be related to the water transport of the rootstock and scion. Inlay bud grafting and patch bud grafting are also used; abroad, patch bud grafting is the most successful.
After grafting, shade to protect from sun and water frequently to keep the soil and air moist, and promptly remove rootstock sprouts. The scion can sprout 25-30 days after grafting; if there are many sprouts, keep only the one strong-growing among them and remove the rest. When the seedling reaches 70 cm tall, pinch off the top to promote side branches and cultivate high-quality seedlings with multiple branches.
(2) Cutting propagation
The cutting bed uses clean, well-drained medium-coarse river sand.
Cuttings are taken when the tree's carbohydrate accumulation level is at its highest. In South China, winter and spring are best; during this period the air temperature is low and the soil temperature is high, which is favorable for rooting. Summer cuttings root poorly. Cuttings are cut to about 15 cm long, with two whorls of leaves kept at the top and all lower leaves removed; the base is soaked for 30 seconds in a solution containing 300-2500 mg of indolebutyric acid (IBA) per liter of water, then inserted 8-10 cm deep into the seedbed after drying. After insertion, shade is required, constant temperature should be maintained, and mist conditions are best if available.
Cuttings should keep their leaves intact; partial leaf removal is unfavorable for survival and rooting. However, there are differences among varieties. Macadamia cuttings take a long time to root; root primordia can only be seen about 60 days after insertion. As long as the cuttings root, the root system is relatively well developed and grows rapidly. Rooted cuttings should be moved promptly into nutrient bags, with appropriate supplemental light and various nutrients needed for growth and development.
(1) Grafting propagation
1.Seed selection
The seeds used to grow rootstock seedlings should be taken from robustly growing, consistently high-yielding plants, preferably disease-free with good nut quality. Both smooth-shell and rough-shell types can be used; because rough-shell seeds germinate and grow quickly, are relatively disease-resistant and have softer wood, they are easier to graft, so some regions prefer to use them. New Zealand and other places believe that using rough-shell types as rootstock can improve the cold resistance of macadamia nuts. Australia mainly uses the D4 variety.
2.Seed storage
Seeds can be stored at 5-10°C in shaded moist sand, or sealed in plastic bags and refrigerated in a refrigerator.
3. Rootstock cultivation
Nuts that mature in high-temperature seasons lose viability very quickly; counting the germination rate at harvest as 100%, it drops to 50% after 6 months of storage. Therefore, it is best to sow immediately after harvest, once the outer soft shell has been removed.
Seeds are sown with the hard shell on, suture line facing downward, covered with 2.5 cm of sand, then watered thoroughly and the seedbed kept moist. Germination begins in 3-4 weeks at 30-35°C; if below 24°C, the germination time is more than doubled. During rootstock cultivation, attention must be paid to preventing ant and rodent damage. After two pairs of leaves have matured, the seedlings should be moved into plastic bags or other containers, with 50% shade. Seedlings are very sensitive to moisture fluctuations, so they must be given sufficient irrigation. During the seedling stage, trace elements and slow-release, low-phosphorus fertilizers should be applied. Plants should be trained into a single-trunk form; after 12-15 months they can be used for grafting. The terminal bud of macadamia is easily damaged by high temperature or insect pests, which stimulates the lateral buds below it to sprout multiple side branches and affects the normal growth of the rootstock seedling. Therefore, care should be taken to prune off branches and maintain single-trunk extension growth.
The germination substrate for sowing should be clean, pest-free coarse river sand, at least 20 cm thick. The seedling soil is made by mixing sand, loam, moss and fully decomposed sawdust or mushroom residue mud evenly. Decomposed macadamia shells can also be used. The seedling soil pH is 5.5-6.5.
4. Grafting
In grafting macadamia nuts, besides mastering the basic grafting techniques, it is also required that the scion be fully mature and that a good grafting time be chosen. The low survival rate is to a large extent caused by improper scion selection. Therefore, abroad, grafting propagation is mainly carried out by skilled workers in large commercial nurseries.
(1) Grafting period: spring and autumn are better, especially late autumn and early spring.
(2) Grafting conditions: the scion and rootstock should be 1-1.3 cm thick, both fully mature, with branch bark light brown to gray and raised lenticels. If conditions permit, the scion should undergo girdling treatment 6-8 weeks before grafting. The specific method is: select a long branch of suitable thickness, girdle about 2.5 cm wide at the base, and scrape clean the cambium tissue. Its purpose is to increase the accumulation of photosynthetic products in the scion and improve the grafting survival rate. When grafting, it is best to select dense-node buds. Before grafting, water the rootstock seedlings thoroughly first.
(3) Grafting methods: branch grafting, cleft grafting, splice grafting and cut grafting are all acceptable. In cleft grafting, the lower part of the scion is cut into a long wedge shape, the top of the rootstock is split from the center, and after the scion cut is inserted into the slit, the cambium of the rootstock and scion are aligned, and the joint is tied tightly and sealed firmly. In China, this grafting method is considered the most successful. According to our experience, the key to success with splice grafting and cut grafting is that the joining surface should be longer, reaching 1-1.5 cm. A cut surface that is too short is not easy to heal. This may be related to the water transport of the rootstock and scion. Inlay bud grafting and patch bud grafting are also used; abroad, patch bud grafting is the most successful.
After grafting, shade to protect from sun and water frequently to keep the soil and air moist, and promptly remove rootstock sprouts. The scion can sprout 25-30 days after grafting; if there are many sprouts, keep only the one strong-growing among them and remove the rest. When the seedling reaches 70 cm tall, pinch off the top to promote side branches and cultivate high-quality seedlings with multiple branches.
(2) Cutting propagation
The cutting bed uses clean, well-drained medium-coarse river sand.
Cuttings are taken when the tree's carbohydrate accumulation level is at its highest. In South China, winter and spring are best; during this period the air temperature is low and the soil temperature is high, which is favorable for rooting. Summer cuttings root poorly. Cuttings are cut to about 15 cm long, with two whorls of leaves kept at the top and all lower leaves removed; the base is soaked for 30 seconds in a solution containing 300-2500 mg of indolebutyric acid (IBA) per liter of water, then inserted 8-10 cm deep into the seedbed after drying. After insertion, shade is required, constant temperature should be maintained, and mist conditions are best if available.
Cuttings should keep their leaves intact; partial leaf removal is unfavorable for survival and rooting. However, there are differences among varieties. Macadamia cuttings take a long time to root; root primordia can only be seen about 60 days after insertion. As long as the cuttings root, the root system is relatively well developed and grows rapidly. Rooted cuttings should be moved promptly into nutrient bags, with appropriate supplemental light and various nutrients needed for growth and development.