Soft wood grafting ideal for cocoa
By Our Agriculture Correspondent
The graft joint is firmly secured using a polythene tape.
SOFT WOOD grafting is the best method of propagation for production and multiplication of high yielding varieties of cocoa.
"Soft wood grafts as superior planting material is practised in almost all the cocoa producing countries by different sources and they performed better with 80 per cent survival rate," says Dr. S. Elain Apshara, Senior Scientist at the Central Plantation Crops Research Institute's (CPCRI) Regional Station at Vittal, Karnataka.
Cocoa seedlings showed high genetic variability or non-uniform performance in the field. For the grafting technique to be successful, stock and scion compatibility is very important, and it exists in cocoa. The rootstocks should be prepared from big, well-matured seed pods harvested from pest- and disease-free proven mother trees. The seedlings should be raised in polythene bags of 15 cm by 22.5 cm filled with suitable pot mixture.
Beans from the harvested ripe pods should be extracted, rubbed gently with sand, washed off the mucilage and dibbled in the polythene bags and just covered with sand.
They should be covered with shade net or coconut thatch to allow only 25 to 50 per cent sunlight. Seeds should be sown horizontally or vertically with hilum end down.
Watering should be done immediately after sowing and on alternate days to keep the soil moist. Seeds will sprout in 10 to 15 days.
The bags should be stacked leaving at least 10 cm between them. In three to four months, the seedlings will be ready for grafting, according to Dr Apshara.
For getting the scions, trees of stable high yields are to be selected. Scion sticks of 12 to 15 cm length with 2 to 3 buds should be collected from these proven trees. These sticks can be transported with ease over long distances. The scion sticks from chupons are preferred, as they will produce trees requiring little pruning and training in the first few years. Scion sticks from fan shoots will grow into bushes requiring considerable pruning in order to produce trees with manageable canopy.
Grafting can be done by cutting the top portion of the rootstock with a grafting knife and making a vertical slit of 2 to 3 cm down (cleft). Scion sticks shorn of leaves should be given a `V' shaped slanting cut of 2 to 3 cm length (wedge) at the bottom.
The rootstock and scion stick should be of the same thickness and physiological age. The wedge should be inserted into the cleft and firmly tied with a polythene tape. The joint should be covered suitably to prevent it from drying.
The joint will fuse in a month and the graft will be ready for planting in the field in 5 to 6 months. The emerging shoots from the rootstocks should be nipped off. The best season for planting the grafts is October to December.
This grafting technique can be used to propagate pest- and disease-resistant clones on susceptible rootstocks.
Old and unproductive trees can be rejuvenated using this technique for top working. It can be employed for conservation of germplasm of multiple trees in a single tree.
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