Gigantochloa atroviolacea

Gigantochloa atroviolacea Widjaja

Reinwardtia 10(3): 323 (1987).
2n = 72 (hexaploid)

Origin and geographic distribution
G. atroviolacea is only known from cultivation and its origin is unknown. It is widely cultivated on a small scale in Central and West Java, and occasionally it has been introduced elsewhere in Indonesia (e.g. southern Sumatra). Outside Indonesia it is grown in botanical gardens (e.g. Calcutta, India and Peradeniya, Sri Lanka) and in the 1980s it was introduced into Thailand and the Philippines. For map click: Map518.TIF.

In the past G. atroviolacea culms were exclusively used in West Java to make the famous bamboo musical instruments (angklung, calung, gambang and celempung). Apparently its thin culm has specific features that make it suitable for such instruments. The peculiar blackish culms, however, have also caught the attention of the handicraft and furniture industries, so that at present most of the culms disappear into these industries, creating a shortage of material to make musical instruments.
The young shoots are edible, turning yellow-pinkish after cooking.

Production and international trade
In Java, the production of G. atroviolacea culms and derived products is considerable, but no statistics are available. Trade is mainly local, but some export of furniture occurs.

The number of vascular bundles in culms of G. atroviolacea ranges from 1.83-2.30/mm2. Average fibre dimensions are: length 3.6 mm, diameter 25.9 µm, lumen diameter 16.8 µm, wall thickness 4.5 µm.
The moisture content of green culms ranges from 120% (top) to 154% (bottom); on average it is 16.8% in air-dried culms. Specific gravity ranges from 0.37-0.48 for green, and is 0.65 for oven-dried material.

Loosely tufted, sympodial bamboo. Culm up to 12 m tall, 6-8 cm in diameter at the base, wall up to 8 mm thick, dark green when young, turning greenish to dark brownish-purple with age, with distinct pale or whitish rings at the nodes, covered by dark brown glabrescent hairs; internodes up to 40-50 cm long; lower nodes with aerial roots. Branches numerous from 2-3 m upward, usually one branch is dominant at each node. Culm sheath 16-20 cm long, lower ones slightly persistent, with dark brown appressed hairs on the back; blade ovate to oblong, 4-9 cm long, spreading to reflexed; ligule up to 2 mm long, irregularly denticulate; auricles small, rounded to slightly curved outward, not joined to the base of the blade, 3-5 mm long and up to 4 mm in lateral extent, provided with bristles up to 7 mm long. Young shoots slender, dark green-brown, sometimes with a light green flash on the tips of the blades. Leaf blade lanceolate, 20-28 cm x 2-5 cm, glabrous; sheath covered with whitish hairs when young; ligule up to 2 mm long, irregularly toothed; auricles small, rim-like, up to 1 mm long and joined to ligule. Inflorescence consisting of branches with groups of pseudospikelets (up to 18 in a cluster) 3-5 cm apart; spikelet ovoid-lanceolate, 8-11 mm x 3 mm, comprising 4 perfect florets and 1 imperfect terminal floret. Caryopsis unknown.

Growth and development
G. atroviolacea is a slow grower. Usually only 1-2 young shoots arise from the rhizome at the base of an old culm so that clumps are usually smaller than those of other bamboos. Yet it has been recorded that 2 years after planting 15 culms can be present. Culms reach their maximum length within 5 months. The average growth rate is about 9 cm per day. Culm size increases with the age of the clump; average height is 3 m in the first year after planting, 6.4 m in the 2nd and 9.3 m in the 3rd; average diameter increases from 2.2 cm in the first year, 5.5 cm in the 2nd, to 7.6 cm in the 3rd year after planting. Branching starts by the formation of some rudimentary branches at the first node from below. Then branching continues at about the 10th node from the top, followed by the next two nodes down, and then development continues both up and down the culm from this area until branches have been produced from all nodes situated higher than 2-3 m from the ground.

Other botanical information
G. atroviolacea is closely related to G. atter (Hassk.) Kurz but can be distinguished from it by its purplish culm, its rounded to curved culm sheath auricles and its narrow palea with acute tip. Moreover, cells of the culm epidermis of G. atroviolacea are longer and less wavy than those of G. atter.
Kurz considered G. atroviolacea to be a variety of G. atter and later authors (Flora of Java) followed this view but considered G. atter to be a part of G. verticillata. The latter, however, has lodicules which are absent inG. atroviolacea and G. atter.
Variability in G. atroviolacea is such that several forms can be distinguished as already practised by local growers in Java. Culms with large diameter and thick walls are more suitable for the furniture industry, while those with small diameter and thin walls are preferred for making musical instruments. The latter form occurs especially in West Java.

G. atroviolacea grows well in the perhumid lowland tropics, with annual rainfall of 1500-3700 mm, relative humidity of over 70% and average temperature of 20-32ºC. In Java it occurs mostly on red and reddish-brown latosols and lateritic soils, but it prefers drier limestone soils. In dry areas the purplish colour of the culms is more prominent.

Propagation and planting
G. atroviolacea is only propagated vegetatively by rhizome or culm cuttings. In an experiment in Indonesia, 1-noded, 20 cm long cuttings of one-year-old culms were used in a nursery protected against heavy rains. Survival rate was 60%. Transplanting to the field was carried out about one year later, when the plants were about 75 cm tall. Recommended planting distance in the field is 8 m x 7 m, giving about 200 clumps per ha.

To guarantee a satisfactory establishment of young plants, regular watering, weeding and loosening of the soil are necessary until 2-3 years after transplanting. Overcrowded clumps are thinned. Cleaning clumps of culm remnants and earthing up regularly stimulates the development of young shoots.

Diseases and pests
Witches' broom disease, caused by Epichloe bambusae, commonly attacks G. atroviolacea but causes no real damage. Young plants may be harmed by termites. Harvested culms and derived products are damaged by powder-post beetles (e.g. Dinoderus minutus and Chlorophorus annularis). The damage is more serious when the harvested culms are not quite mature.

Harvesting may start 4-5 years after planting. It is recommended to harvest only in the dry season.

In Java the average yield of mature G. atroviolacea clumps is estimated at 20 culms per 3 years (or with 200 clumps per ha, about 4000 culms per ha every 3 years).

Handling after harvest
Traditionally, harvested culms are immersed in running or stagnant water for 15-30 days and then air dried. Chemical preservation is possible by soaking the culms in a 5% borax solution for 3 days. Penetration in the walls of whole culms is about 50% for borax.

Genetic resources and breeding
There are no germplasm collections of G. atroviolacea, but some conservation is effected in botanical and experimental gardens. In Indonesia some material is present in Dramaga, Pasir Awi, and Oray Tapa. There are no breeding programmes.

The future is bright for this purplish-black bamboo because of the increasing interest of the furniture, handicraft and musical instrument industries. More research is needed regarding propagation, cultivation, and preservation, and plantations of suitable cultivars should be established for different purposes.

E.A. Widjaja

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