Vegetative Propagation in Cashew
Authors: Ashok Yadav , Mocha Ajang , Madhumita Mallick, Nagaraja A and K.Usha
Division of fruits and Horticultural technology, IARI, New Delhi
Cashew (Anacardium occidentale) is cultivated widely throughout the tropics for its delicious kernels, often referred as "Goldmine of waste land". Maharashtra, Kerala and Karnataka are the primary producers of cashew along the western coast of the country, while Andhra Pradesh (AP), Odisha, Tamil Nadu (TN) and West Bengal (WB) are primary producers along the eastern coast. It is the third most important agro-commodity of India in terms of foreign exchange.
Cashew can be propagated by seed as well as vegetative means. Since, cashew is a highly cross pollinated crop, seedling progenies are highly variable in nature. Hence, various vegetative propagation methods have been standardized to obtain true-to-the-type progenies.
Vegetative Propagation method
Air layering is usually done during February-March, so that they will be ready for planting in June-July. A 9-12 month old pencil-thick terminal shoot is selected from which a ring of bark of 0.6 to 1.2 cm thickness is removed carefully by using a sharp knife without injuring the underlying wood. A string is tied around the cut area and covered with moist moss or wood shavings or sand and saw dust mixture or ordinary potting mixture. A polythene film of 150-200 gauge of 23 x 15 cm size is wrapped around it and the loose ends of film are tightly secured with a jute fibre. When roots emerge from the ringed portion in 40-60 days, a 'V' cut is then, given at the lower end of the shoot. After about 15 days, the cut is deepened slightly. About 7 days later, the rooted shoot is separated from the mother plant. Immediately after separation, the layer is potted into a container of 15 x 15 cm size with coconut husk as media and kept in shade. Excessive watering should be avoided. With the onset of southwest monsoon, the layer is planted along with the container in the prepared pit. Shade and mulch with dry leaves is to be provided to reduce sun-scorch in tender plants. It is advisable to defoliate the layers two weeks before separation from the mother plant.
Soft wood grafting
Selection of seed nuts
(1) Collect seed nuts during the peak period of harvest (February-March) and sun-dry them for 2-3 days.
(2) For quality seeds, immerse the nuts in water or 10% saline solution. Select seeds, which sink in water.
(3) Select medium sized nuts (7-9 g) to get vigorously growth in seedlings.
1) Use fresh seed nuts for raising rootstock. Avoid seed nuts stored for more than one year.
2) Soak seed nuts in water overnight before sowing.
3) Use polythene bags (size 25 cm x 15 cm and 300 gauge thickness) for filling potting mixture.
4) Make 16-20 holes on the polythene bags to ensure good drainage.
5) Prepare potting mixture (1:1:1 ratio of red soil, river sand and compost) mixed with rock phosphate @ 5 g per 2 kg potting mixture.
6) Fill the polythene bags up to the brim of the bag.
7) Sow the pre-soaked nuts in the centre of the bag with stalk end up, at a depth of 2.0-2.5 cm.
8) Immediately water the bags after sowing and daily thereafter. Avoid excess irrigation.
9) Nuts usually germinate within 15-20 days after sowing during monsoon and within 8-10 days during dry months.
10) Nuts should be sown at weekly intervals to get continuous supply of rootstocks.
11) Provide partial shade during summer to the seedlings till they change their bronze colour to green and then keep them in open.
12) The seedlings will be ready for grafting in 50-60 days after germination.
13) Germinating nuts should be protected from squirrels, birds etc.
14) During the rainy season, damping off of young seedlings is common. To control this disease, spraying/drenching Bordeaux mixture (1%) is effective.
Selection of rootstock
Select healthy seedlings of 50-60 day old as rootstock.
Selection of scions
1) Select a high yielding variety of cashew as a mother plant to collect adequate number of scions.
2) Select 3-5 month old non-flowering lateral shoots of current season's growth.
3) The selected scions should be 10-12 cm long, straight, uniformly round and pencil thick with brown colour having dormant plump terminal bud. The top 4-5 leaves should be dark green in colour indicating proper maturity of the scion.
Preparation of rootstock
1) Retain two pairs of bottom leaves on the selected seedlings and remove others using a sharp knife.
2) Give a transverse cut on the main stem, 15 cm above ground level.
3) Make a cleft of 4-5 cm deep in the middle of the decapitated stem of the seedling by giving a longitudinal cut.
Preparation of scion
1) Select a matching scion stick having same thickness as that of the rootstock.
2) Shape the cut end of the scion to a wedge of 4-5 cm long by chopping the bark and wood from two opposite sides.
1) Insert the wedge of the scion into the cleft of the rootstock, taking care to ensure that the cambium layers of stock and scion are in perfect contact with each other.
2) Secure firmly the graft joint using a polythene tape (1.5 cm wide and 30 cm long).
3) Cover the scion of the graft with a wet polythene cap (15 x 12.5 cm, 100 gauge thickness) and tie at the bottom to maintain humidity inside and to protect the apical bud from drying. The polythene cap should not touch the terminal bud.
4) Keep the grafted plants are under shade for 10-15 days to enable sprouting of the terminal buds.
5) Remove the polythene caps and shift the grafts to open place. The successful grafts will show signs of growth within 3-4 weeks after grafting.
6) The grafts will be ready for planting 5-6 months after grafting.
7) The success in softwood grafting is more during the period from March to September
Care in the nursery
1) Water the grafts regularly using a rose can or micro-sprinkler.
2) Remove new sprouts emerging from rootstock at frequent intervals.
3) Remove panicles, if produced by the grafts, as and when observed.
4) Shift the grafts frequently from one place to another to prevent them from striking roots into the ground.
5) Spray insecticide for controlling the infestation of sucking insects.
Graft production under polyhouse
Softwood grafts can be prepared almost throughout the year with a mean graft success of about 60-70%. Higher success is achieved during the monsoon season. For this, low cost polyhouses (prepared from casuarina / bamboo poles / areca reapers / GI pipes / PVC pipes and covered with high density polythene sheet of convenient dimensions, preferably 20 m long and 6 m wide may be utilized for graft production. The height of the polyhouse should be 2.5 m in the middle and 1.0 m on both sides. The plants may be watered using hose. Misting units can also be fitted at appropriate points and switched on for about 5-10 minutes at an interval of two hours from 10 a.m to 6 p.m during summer season. This reduces the temperature build up inside the polyhouse. Raising of rootstock seedlings, grafting of rootstocks and maintenance of grafts can be done inside the polyhouses. These polyhouses give protection to the seedlings and grafts during heavy rains and reduce the mortality. Again during summer months the seedlings / grafts can be maintained in these polyhouses by covering with HDPE shade nets (35-50% shade).
Planting and management of grafts
The softwood grafts will be ready for planting in 5-6 months after grafting. The pits are filled with topsoil and 5-10 kg of compost or dried cowdung / pit and the grafts are planted after carefully removing the polythene bags. Care should be taken while planting to see that the graft union is 2.5 cm above the ground level. The polythene tape is to be carefully cut and removed subsequently. Staking should be done immediately after planting to protect the grafts from damage.
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