Propagation Through Seed
Use of quality seed plays an important role in establishing a productive plantation. Hence, it is always advisable to procure authentic seed material from coffee Board Research department. Preparation of quality seed requires careful monitoring at all levels such as establishment of genetically pure seed blocks, removal of off-types, forcing the blocks, removal of off-types, forcing the blossom in advance to ensure isolation and following strict seed preparation protocol that include harvesting of the ripe fruits at right stage to shade drying to the required moisture levels.
Seed Plots and Seed Preparation Protocol
The seed plots established at CCRI, regional coffee research stations and also some of the technology evaluation centers of the board by using the nucleus seed material of a particular variety become the source for collection of seed. All the seed plots are regularly maintained by removing the off-types, if any. For ensuring controlled pollination, the seed plots are irrigated before the receipt of blossom showers. At the time of harvest, mature berries at correct stage of ripening and not over ripened once, are collected and are carefully pulped on the same day of harvest by using hand pulpier without damaging beans. These freshly pulped beans are stirred in a container of clean water to remove floats or lights. The beans are then mixed with finely sieved wood-ash, evenly spread out to a thickness of about 5 cm and dried in shade. They are stirred thrice a day to facilitate uniform drying and for removal of excess ash while drying. After the drying, the seed is garbled thoroughly to remove the excess ash and also the mutilated, triangular and elephant beans. The seed coffee is supplied to the indented growers through extension network of the board. Before packing, the seed is treated with fungicide (Bavistin 50 WP) 1g kg-1 to protect from any fungal infection occurring during transit or germination. In berry borer infested areas, the seed should be subjected to fumigation with aluminum phosphide (celphos) to kill live stages of berry borer. Seeds do not exhibit any dormancy and under natural conditions viability is also short.
Vegetative Propagation Techniques
Vegetative reproduction, which is a form of asexual reproduction using the vegetative parts such as shoots, leaves, ensures that the plant’s unique features are retained. Coffee can be propagated successfully by using conventional vegetative propagation techniques.
Propagation by Cutting
In coffee, two types of shoots viz., horizontal (plagiotropic) and vertical (orthotropic) shoots are produced. Orthotropic shoots (suckers) are suitable for vegetative propagation. The plagiotropic shoots are not suitable as they maintain only lateral growth. Selection of mother plants having superior characteristics like high yield potential, disease/pest resistance and good quality (beans) is very important for initiating propagation through cuttings. Three types of cuttings can be obtained from orthotropic shoots viz., single node cuttings, terminal cuttings and mallet cuttings. The method of preparing different types of cuttings is described below:
Single Node Cuttings
The technique is simple and easy to adopt at the estate level. The important steps include collection of orthotropic shoots (suckers), preparation of single node cuttings, chemical treatment, planting and after care
The monsoon (June to Aug) is an appropriate time for achieving maximum rooting success (~80%). Orthotropic shoots (suckers) of pencil thickness (semi-hard) that have sprouted after the summer showers are ideal for clonal propagation. Care should be taken to collect the material from a group of elite plants
2. Preparation of Cuttings:
From the collected suckers, single node cuttings of above 10cm length with a pair of leaves have to be prepared with a slant cut at the base and an horizontal cut at the top. Both leaves at the node should be cut to half of their size
3. Chemical Treatment:
The single node cuttings have to be immersed in a bucket containing Bavistin 50 WP solution (4 gm of Bavistin in 1 lt of water) for 5 min to avoid any fungal infection. Then, the basal portion of the cuttings (slant cut) have to be dipped for 5 to 10s in 5000 ppm IBA (Indole butyric acid- dissolve 500mg of IBA in 50 ml of alcohol and make up to 100 ml with water).
4. Planting of the Cuttings:
After the IBA treatment, the cuttings have to be planted upright in 22.5 cm x 15 cm (9”x 6”) size nursery bags, tightly filled with soil mixture (jungle soil, sand, farm yard manure in 5:3:2 ratio). These bags are kept arranged in trenches of 6m x 1mx 0.5m (length x breadth x depth). About 500 bags can be accommodated in each trench. Cover the trench with a polythene sheet (500 gauges) over the bamboo/iron frame. Proper drainage channels have to be made around the trenches to drain off rain water. Overhead shade has to be provided to the trenches.
5. Aftercare of Clonal Nursery:
The cuttings in the trenches have to be watered during the morning hours depending on the requirement. But, care must be taken to avoid excess watering. Normally in trench conditions, the water requirement is very low. The trenches must be covered with polythene sheet immediately after watering the cuttings in order to maintain the humidity in the trenches. The cuttings have to be monitored regularly and the rotten cuttings. If any, should be replaced with new cuttings.
6. Hardening of Rooted Cuttings:
Sprouting of shoots from nodal portion is seen within a month, but for the development sufficient roots it takes about 3 to 4 months. When the newly sprouted shoots attain 2 to 3 pairs of leaves, the bags with cuttings have to be observed for root development and then taken out from the trenches. The rooted cuttings have to be arranged in nursery beds under pendal shade and to be hardened. After hardening for two to three months, they can be planted in the field.
After preparing single node soft wood cuttings, the terminal portion of the orthotropic shoots can be made use of planting as terminal cuttings. Provide a slant cut at the base and treat with 0.2% Bavistin solution and later with 1000 ppm IBA solution (100 mg in 50 ml alcohol made up to 100ml by adding water) before planting.
A mallet cutting is nothing but a young sucker (45 to 65 day old), which is detached from the main stem with a piece of woody bark. Collect the millet cuttings from elite plants with a portion of wood using a sharp knife. Dip the basal portion in 0.2% Bavistin and then in 1000 ppm IBA solution for 5 to 10 s before planting.
Successful rooting (of the cuttings)is also dependent on the season in which the planting material is collected. According to empirical data, the best season for planting is during June-August which is the monsoon season. This ensures above 80% success rate. For a Robusta clonal plot, rooted cuttings of different elite mother plants should be mixed and planted, because of the cross pollinating nature of this species.
Wedge-cleft method of grafting is used in coffee and the grafting can be done at two stages i.e. seedling stage in nursery and mature plants in field. Seedling grafting is useful in overcoming the problems of nematodes, soil borne root diseases and drought conditions. The grafting in mature plants is followed for the conversion of old, unproductive, disease-susceptible and off-type plants into productive ones and this technique is popularly called ‘top working’.
1. Seedling grafting
Seeds of selected rootstock (having tolerance to nematodes, root diseases, drought i.e. Robusta or tree coffee) and scion (high yielding, disease tolerant i.e., usually Arabica) are sown in the nursery for germination. The time of sowing of both the rootstock and scion seed material should be adjusted appropriately so as to obtain seedlings of ‘topee stage’ at the same time. At ‘topee stage’, seedling of both stock and scion are uprooted carefully without injuring the root system and are immersed in water to which a pinch of urea is added. The topee end of the rootstock seedling is cutoff with a sharp nlade and a vertical slit (cleft) of 1.5 to 2cm is made. Likewise, the root portion of the scion seedling is cut off and to be removed. The cut end of scion is fashioned into a ‘wedge’ or ‘V’ shape (1 to 2cm length). The wedge of the scion is inserted into the cleft made in root stock seedling and the joint is tied firmly with a polythene strip. These grafted seedlings are planted in the nursery baskets and kept under pendal shade. The polythene strips are removed after the union takes place (4 to 5 weeks). These grafted plants should be maintained in the nursery till the filed planting
2 Field grafting or top working
The process of uprooting ‘off-type passenger plants’ by conventional methods and filling those gap with young seedling is a cumbersome and time consuming process. Moreover, such replanting usually starts yielding only after 4 or 5 years. To avoid these difficulties, rejuvenation of off-type plants through top working is practiced.
In this technique, the off-type plants are collar pruned at a height of about 30 to 45 cm in March-April, soon after summer showers. The stumps start sprouting and produce many vertical shoots (suckers) in about 30 to 45 days. However, there is a 20 to 30% chance that sucker production fails in old Robusta plants. To induce sucker production a spray of IAA 200 ppm in combination with 1%DMSO (200 mg of Indole acetic acid and 10ml Dimethyl Sulfoxide in 11 of water) could be applied on the collar-pruned stumps. 2 or 3 healthy suckers that arise from just below the cut ends are retained and the remaining suckers are removed at the time of grafting. During the monsoon season, suckers of the same age and thickness are collected from elite desirable plants. Single node scions are prepared and grafted by cleft method on to the suckers arising from the collar pruned ‘off type’ plants. The preparation of wedge and cleft is same as described in the case of seedling grafting. The graft portion is either sealed with grafting wax or tied with a polythene strip. The grafts are covered with polythene bags to protect them from rotting during heavy monsoon. Union takes place within 1 or 2 months depending upon weather conditions. The polythene strips are then removed to facilitate normal growth of the grafts. Around 65 to 70% success can be achieved using compatible scions. Hence, it is advisable to graft 2 to 3 suckers in each stump. The scion starts growing vigorously by drawing nutrients from the already established root system of the stock (off-type plant) and starts yielding within 2 or 3 years of grafting. Thus there is a saving of about 2 to 3 years times towards the first crop when compared to the conventional method of planting new seedlings. Besides, yields from top-worked plants are assured as the scion material is collected from superior mother plants. This system could also be practiced to grow Arabica types on Robusta stocks.