rubber cultivation

Propagation of Rubber

In India, Hevea seeds normally ripen during July-September when the seeds are collected and seedlings raised. All earlier plantations were raised from unselected seeds. The yield potential of these having been low, the production of those plantations was poor. Selection work on Hevea with a view to improving the planting materials and the introduction of vegetative propagation by budding led, in course of time, to the establishment of numerous valuable clones.

Clonal Seeds

Seeds of clones are termed clonal seeds. There are different kinds of clonal seeds – monoclonal, polyclonal, legitimate and illegitimate. Monoclonal seeds of clone Tjir 1 which gave rise to seedlings superior to seedlings from ordinary, unselected seeds were once encouraged for planting extensively in our country. Evolution of newer, improved planting materials then progressively replaced Tjir 1 clonal seedlings. Hybrid polyclonal seeds collected from approved polyclonal seed gardens are the only seed material recommended for planting now. For production of good quality polyclonal seeds, gardens have been established in Kanyakumari district. Polyclonal garden seeds in the name Prang Besar Isolated Garden (PBIG) seeds from Malaysia used to find limited market in India until a few decades ago. Polyclonal seedlings: Seeds collected from clonal stands are known as clonal seeds.In olden days monoclonal seeds of single mother clones such as Tjir 1, not contaminated by crossing  with seedling rubber or undesirable  male parent clones,had been extensively used as improved planting materials.  Now only clonal seeds  of polyclonal origin which can be expected to possess significant hybrid vigour  are accepted.  Ployclonal seeds of good clones are planted in such seed gardens mixe as per specific designs.  For prevention of pollen contamination from rubber trees of neighbouring area, an isolation belt of 100 meters width is provided all around.  Polyclonal seeds give rise to seedling of good vigour and growth.  Compared to buddings, they are easier to establish and maintain.  The trunk of seedling is much larger than  those of budded trees. Owing to the inherent genetic variability, they are relatively  less suceptible to wind damange and disease.  However, the general yield  levels are far lower than selected modern clones.  The high tree to tree variability in growth and yield makes it necessary to adopt thorough selection of seedling for planting based on initial viour, high initial planting density in the main field  and subsequent  judicious thinning out of weakilings and poor yielders in a phased manner.  Still, the trees exhibit proneness to tapping panel dryness.  The average annual yield is 1200 to 1300 kg/ha/yr.  Nurseries Nurseries are required for raising seedlings, budded stumps and budwood. As far as possible open and level land should be selected for raising nursery. Water should be easily available for irrigation. The soil should be deep, well drained and fertile. The land should be dug to a depth of 75 cm and all stumps, roots, and stones should be removed. Nursery beds should be prepared with 60 to 120 cm width and convenient lengths and with pathways laid in between to facilitate manuring, watering, weeding etc. Planting distances should vary according to the type of planting materials to be raised in the nursery. The ideal spacing for seedlings is 30 cm X 30 cm. For budwood nurseries, the plants may be at distances of 60 X 90 cm or 60 X 120 cm or 90 X 90 cm Nursery management aims at the most rapid production of standard healthy planting materials. More intensive care can be exercised in a nursery than in a field. Plants which are obviously unsuitable can be eliminated at an early stage. Mainframe operations for nursery include weeding, mulching, irrigation during dry months, manuring and disease and pest control.  Budding The principle involved in budding is the replacement of the shoot system of a plant with that of another more desirable plant. In this process, a patch of bark of the seedling plant (stock) is replaced by a patch of bark with a dormant bud (bud patch) taken from the clone to be multiplied. The bud patch gets attached to the stock permanently and becomes a part of it. The stock is then cut off above the budded portion and the grafted bud develops into a shoot (scion) exhibiting the characters of the plant from which it was taken. The new tree thus formed is a two-part tree, comprising a root system belonging to the stock plant and a shoot system contributed by the donor of the bud. Depending on the colour and age of the buds as well as the age of the stock plants used, three types of buddings are mainly recognized. These are brown (conventional) budding, green budding and young budding. In the first method, older buds having brown colour are used while in the other two, green tender buds are utilised. Depending on the part of the stock where budding is carried out, buddings are classified into four types: base budding, crown budding, over budding and high budding. Base budding is carried out at the base of the stock plant and includes brown budding, green budding and young budding.  Brown Budding Brown budding is generally carried out by grafting brown coloured buds taken from budwood of about one year's growth onto stock plants of 10 months or more growth. Vigorously growing healthy stocks having a girth of 7.5 cm at the collar region are ideal for budding. Stocks should be budded when the bark peels off very easily. Peeling is usually good when the top whorl of leaves is well developed, but before further extension growth commences. Test peeling of a small patch of bark above 15 cm from the base is the sure method to assess the peeling quality of the bark. Since all stock plants may not attain this stage at the same time, more than one round of budding may be necessary to cover all the stocks. Green BuddingBoth the stock plant and budwood used for green budding are very young. Seedlings which are five to seven months old are used as stock. Buds are collected from six to eight weeks old budwood, also known as bud shoots or bud sticks. Buds found above the scale leaves of the shoots alone are used for budding. These buds are green in colour and hence the name green budding. Young, vigorous seedlings raised in nursery or in polythene bags are used as stock plants for green budding. Plants having a girth of about 2.5 cm at the base, with brown bark up to a height of about 15 cm, can be used for this purpose. The stock plants require about four to five months to attain this size. By proper care, this period could be further reduced. Green budwood  is obtained from budwood plants (source bushes) grown in nurseries for this purpose. They are collected when six to eight weeks old, when they have a length of 30 to 60 cm with a whorl of leaves at the top. The bud shoots are harvested by cutting at the base with a sharp knife. For proper peeling of the bud patch, harvesting should be done when the leaves are copper brown to dark green in colour. After harvesting, the leafy portion of the shoot is cut off. The non-leafy portion shows two to five scale leaves with axillary buds which are utilised for budding.  Advantages of Green Budding over Brown Budding It utilizes the growth of the stock more efficiently, i.e. when green budded plants are cut back, only a small    amount of stock growth is lost, Green budding is simpler and faster than brown budding and hence more number of plants can be budded reducing the labour cost per budding, It gives higher percentage of success during summer than brown budding, Opening of the budding and cutting back can be done simultaneously, thus saving labour cost, Yield of green buds from a unit area of nursery is two to three times that of brown buds, Since the polythene strip used for green budding is smaller, cost incurred for this material is reduced, After cutting back green buds develop earlier than brown buds, Green budding is more suitable for crown budding. Major Defects of Green Budding Technique Green bud shoots cannot be retained in the nursery for long after they become mature enough for harvesting, After harvesting, green sticks cannot be kept for long periods, unlike in the case of brown budwood Scion of green budding is less vigorous than that of brown budding and hence it requires very careful attention during the early period of growth, especially in the field.   Young BuddingThis is a kind of green budding carried out on very young plants less than two months old. Stocks are raised in small bags of lay flat size 33 x 15 cm. The plants are given intensive nursing such as foliar application of fertilisers and fungicides twice weekly and soil application of NPKMg mixture weekly. When seven to eight weeks old, they are green budded. Four weeks after budding, plants are cut back leaving a snag of 20 to 25 cm length. Buds on the snag are nicked or the shoots coming from then pruned off promptly. When the scion develops two or three whorls of leaves, the plants are transplanted to the field. This technique has got certain advantages over the normal green budding technique. By adopting this technique bag plants could be produced within seven months after the planting of germinated seeds in the bags, which is usually done in August/September. In our country, the time required for this is around nine months in the case of normal green budding. Since small bags are used for the production of plants transportation is easier. Crown Budding Replacing the undesirable crown of a high yielding clone with a desirable crown is of practical significance. In many of the modern clones, though the trunk possesses a capacity for high yield, the crown shows many undesirable characters like susceptibility to wind and diseases. An undesirable crown can be replaced by a desirable one through crown budding. The tree produced by crown budding is a three-part-tree comprising the root system of the stock plant, trunk of one clone and the crown of another clone. Thus the desirable characters of the trunk of one clone and crown of another clone are combined. Crown budding is ideally carried out when the scion of the budded plant has attained a height of 2.4 to 3 m. One to two years are usually required for the plants to attain such a growth. The height of the plant is more important than the age. Crown budding may be commenced when 50 to 60 per cent of the plants in the field are buddable. Budding is carried out at a height of 210 to 240 cm on the inter-whorl region below the top whorl of leaves. It should be done only when the top flush of leaves are fully expanded and hardened. Stem tissue should be green or dark green at the time of budding. This ensures maximum budding success.