Propagation of Large cardamom is done through seeds, rhizomes (sucker multiplication) and tissue culture techniques. Cultivars suitable for specific areas, altitudes, agro-climatic conditions and mother plant/clump of known performance are selected for collection of seed, rhizome and vegetative bud.
Propagation through seeds
Healthy plantation, free from viral disease in particular, is selected for seed capsules. Gardens with productivity of 1000 kg/ha or more during the past 3 years are considered. Higher number of spike bearing (reproductive) tillers per plant (bush), higher number of spikes and capsules, bold capsules, higher number of seeds per capsule etc. are some of the criteria looked into for selecting a plot for collection of seed capsule.
Spikes are harvested at maturity and seed capsules are collected from the lowest two circles in the spike. After dehusking, the seeds are washed well with water to remove mucilage covering of seeds, mixed with wood ash and dried under shade.
The dried seeds are treated with 25 per cent nitric acid for 10 min for early and higher percentage of germination (). The acid-treated seeds are washed thoroughly in running water to remove the acid residue and are surface dried under shade. The seeds are sown immediately after acid treatment.
Nursery site selection
An open area with gentle slope and having facility for irrigation is selected for nursery establishment. Large cardamom nursery is raised in two stages viz., primary nursery and secondary nursery. Seedlings raised in primary nursery (by seeds) are transplanted to the secondary nursery beds or to polybags.
There are two seasons for sowing seeds: pre-winter (September–October and early November) and post-winter (late February–March). September sowing results in quicker and better germination (within 25–30 days), 30–40 per cent for acid-treated seeds ().
Seedbed is prepared in a well-drained area. The soil is cut to a depth of 30 cm and exposed to sun for a week. Bed of 15–25 cm height, 90 cm width and convenient length is prepared, incorporating well-decomposed compost/cattle manure. Seeds (acid treated) at the rate of 100 gm for a bed size of 1 X 3 m are sown in furrows along the width and they are covered with a thin layer of soil. The space between the furrows is maintained at 10 cm. After sowing, the beds are covered with thick mulch (with paddy straw or dry grass) and watered regularly to keep the bed moist.
The seedbeds are examined for germination between 25–30 days after sowing. Once the germination starts the following operations are made:
(a) Overhead shading of convenient height with Bamboo poles and agro-shade net/bamboo mat (50 per cent shade, black agro-shade net is found ideal).
(b) The mulch from the bed is removed and cut into small pieces and are spread over in between the seed rows.
(c) The beds are watered regularly to keep the bed moist and weeding is attended whenever necessary.
Once seedlings in the primary seed bed reach 3–4 leaf stage (in February/March if seeds are sown in September/October or April/May if the seeds are sown in February/March) they are transplanted either to polybags or into secondary nursery beds in February/March or April/May respectively ().
Topsoil in virgin land/forest area rich in leaf mold is collected and mixed with well-decomposed cattle manure to get good potting mixture. A potting mixture of 5:1, topsoil: cattle manure is prepared and filled in polybags of 8″ x 8″ size with perforations at the base for drainage. Polybags are arranged under overhead shaded shed. Primary seedlings are transplanted in polybag (one seedling per polybag) during February/March or April/May
Polybag seedlings are watered regularly with rose can to keep the soil moist. Care is taken to cover the collar region or exposed roots of seedlings with thin layer of topsoil, which help in better anchorage and tillering. Over watering should be avoided. Polybag seedlings attain a height of 30–40 cm with 2–4 tillers by July–August if transplanting is done in February/March. These seedlings are planted in the main plantation in July/August. The polybags are removed and seedlings with the soil ball intact are planted. Sometimes the seedlings are maintained in polybag till April next year and planted in May–June in the main field ().
Seedlings from primary nursery are sometimes transplanted in beds. Beds of the size and nature similar to that of primary beds are prepared; and seedlings at 3–4 leaf stages are transplanted in March/April/May, maintaining a spacing of 15 cm between the seedlings. A layer of well-decomposed cattle manure is applied and incorporated in the soil. Watering is given at regular intervals to keep the soil moist. The entire secondary nursery is maintained under overhead shade (preferably with black agro-shade net). Seedlings are maintained for 10–12 months. Expected growth of seedlings is about 45–60 cm heights with 5–10 tillers each. These seedlings are transplanted in June–July in the main field ().
Propagation through rhizome
High yielding, disease free planting materials are selected for multiplication. Trenches of two feet width, two feet depth and convenient length are made across the slopes. Trenches are filled with topsoil, leaf mold and decomposed leaf litter. Rhizomes with one mature tiller and two young shoots or vegetative buds are planted at a spacing of three feet in the trenches during June–July. Thick mulching with dry leaf/grass is applied at the base of the rhizome and watering if required, is done regularly to keep the soil moist.
Once fresh vegetative buds appear, well-decomposed cattle manure is applied one foot around the rhizome and incorporated to the soil. The rhizome multiplication plot is maintained with 50 per cent shade, either under shade trees or under agro shade-net. When the rhizomes are planted in June/July, about 15–20 tillers are produced from each of the rhizome within 6 to 10 months. Each such clump is split into units of two to three tillers and are used for planting in the main field during June/July or used for further multiplication ().
Large cardamom can be multiplied on a large scale through micropropagation. Protocols for micropropagation were developed at Indian Institute of Spices Research ().
Axillary buds of 0.5–2 cm lengths from promising, virus disease free mother plants are used as e xplants. The explants are thoroughly washed in clean running water and then in a detergent solution and treated in 0.15 per cent HgCl2 for 2 min, and then passed through absolute alcohol for 30 sec. These are cultured using the modified MS medium, solidified with agar and with the following adjuvant.
Step 1: For initial bud development and its growth in vitro (culture period 6–8 weeks): kinetin 3–5 mg/l + IBA 1–2 mg/l + sucrose 20 g/l
Step 2: For proliferation of the auxiliary bud rhizome (6–8 weeks): BAP 2 mg/l + NAA 3–5 mg/l + sucrose 20 g/l
Step 3: For rooting and establishment of plantlets (6–8 weeks): IBA 1–2 mg/l + KN 3–5 g/l + sucrose 20 g/l.
Nirmal Babu et al. () and Sajina et al. () accomplished both multiple shoots and rooting in the same medium, in MS basal + BAP (1 mg/l) and IBA (0.5 mg/l) with 3 per cent sucrose and gelled with 0.7 per cent agar at pH 5.8 and 12 h photoperiod at a light intensity of 2500 lux. This combination produced 8–12 shoots per culture and roots per shoots.
After the plantlets attain 4–5 leaf stage with good rooting, they are removed from culture flasks, thoroughly rinsed in distilled water and sprayed with Bavistin or Dithane M-45 (0.25 per cent) to check fungal infection, and planted in micropots (8 cm) filled with sterile peat moss and vermiculite (1:1 v/v) or 1:2:1 mixture of sterile sand, peat and perlite. Liquid fertilizer in very low concentration is given after 4–5 days and there after at 15 day intervals. Plantlets are maintained under shade (5000–8000 lux) and high humidity (>90 per cent RH at 25 °C). After about two months plantlets can be transferred to polybags filled with potting mixture or to secondary nursery beds and maintained under shade (10,000–15,000 lux).
Each axillary bud (explant) gives 12–18 plantlets in one subculture; 3–4 subcultures are possible with the initial explant to produce normal TC plantlets, which perform well under field condition. The in vitro method is also useful in the conservation of Large cardamom germplasm through slow growth. The protocol for the in vitro conservation developed at Indian Institute of Spices Research (IISR), Calicut consists of in vitro generated plantlets maintained in 1/2 MS +10 g/l sucrose +10 g/l mannitol ().
Selections from the book: “Cardamom. The genus Elettaria”. Edited by P.N. Ravindran and K.J. Madhusoodanan. Series: “Medicinal and Aromatic Plants — Industrial Profiles”. 2002.