Gigantochloa robusta

Gigantochloa robusta Kurz

Ind. For. 1: 344 (1876).
2n = 72 (hexaploid)
Origin and geographic distribution
The origin of G. robusta is unknown, but it is found growing wild in Java (Banten, West Java and Banyuwangi, East Java). It is mainly known from cultivation in Sumatra, Mentawai Islands, Java and Bali. For map click: Map405.TIF.

Culms of G. robusta are widely used for water pipes, floors and walls for houses, to make handicrafts and bamboo musical instruments. In West Java a typical water carrying vessel ('kele') is made from the culm by the Baduy. Young shoots are eaten as a vegetable.

Production and international trade
Locally, especially in Sumatra, G. robusta is important as a garden crop, but no statistics on production or trade are available. There is no large-scale cultivation. In Jakarta young shoots of G. robusta, originating from southern Banten, are sold in vegetable markets. It is possible that customers in Jakarta are deceived because the young shoots look rather similar to those of Dendrocalamus asper (Schultes f.) Backer ex Heyne, which are considered as the best.

In culms of G. robusta the average number of vascular bundles ranges from about 1.54/mm2 in the lower part, to 1.94/mm2 in the central part, and 2.32/mm2 in the upper part. Its fibre dimensions are: length 3.6 mm, diameter 30-32 µm. In the Indonesian wood criteria on pulp and paper, those fibres are classified as flexible and having medium strength (flexibility ratio is 0.64).
The moisture content of green culms averages 118% and increases from bottom to top. Specific gravity ranges from 0.38 to 0.62 (average 0.55). The average mechanical properties measured in Indonesia on split green bamboo parts (30 cm x 2 cm x 0.5-1 cm) are: modulus of elasticity 9829 N/mm2, modulus of rupture 136 N/mm2, compression strength parallel to grain 52 N/mm2, and tensile strength 191 N/mm2.

Densely tufted, sympodial bamboo. Culm up to 20 m tall, 7-9 cm in diameter, wall up to 18 mm thick, dirty yellow to light green with yellow stripes in lower 2 m; internodes up to 40 cm long, non-waxy, with scattered brownish hairs on upper parts; lowest nodes with aerial roots. Branches arising from almost all nodes from 2-3 m upwards, with one branch dominant at each node. Culm sheath deltoid but with truncate apex, 17-35 cm long, covered with dark brown hairs 2 mm long, deciduous with age but often long persistent on lower part of the culm; blade triangular, 10-14 cm x 3.5-5 cm, reflexed; ligule 5 mm long, irregularly incised and with 10 mm long bristles; auricles rounded, up to 7 mm long, well developed along the sheath apex, crisped and joined to the base of the blade, with bristles up to 5 mm long. Young shoots stubby and massive, brown-green, covered with dark brown hairs. Leaf blade lanceolate, 15-27 cm x 2.5-5 cm, hairy on the lower surface; ligule 1 mm long, denticulate, with fine hairs 3 mm long; auricles firm, 1 mm long, with bristles up to 5 mm long. Inflorescences borne on branches about 50 cm long, consisting of pseudospikelet groups 1-4 cm apart, each with up to 110 clustered pseudospikelets; spikelet flattened ovoid, 9-10 mm x 4 mm, slightly hairy on the tip, comprising 4 perfect and 1 imperfect florets. Caryopsis unknown.

Growth and development
After planting of a cutting, 1-5 culms develop in the first year, gradually increasing up to 11 culms in the next years. One year after planting, culm height averages 4.7 m and diameter 3.9 cm; these figures increase to 6.7 m and 5.4 cm in the 2nd year and to 12.3 m and 8.3 cm in the 3rd year, respectively.
Young shoots grow rapidly at first and culms attain their maximum height in 2-4 months. Branching begins when the lengthening phase of the culm is over, usually at 8-11 nodes from the top, followed by growth from 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 from 2-3 m upwards.
In Indonesia it is said that G. robusta clumps flower gregariously more than 50 years after planting. Flowers attract honey bees and other insects, but seed has never been observed.

Other botanical information
G. robusta, G. atter (Hassk.) Kurz, G. atroviolacea Widjaja and G. pseudoarundinacea (Steudel) Widjaja were formerly united into one complex species G. verticillata. Its yellow striped green-yellow culms and its characteristic sheath auricles make G. robusta distinctive. In herbarium specimens G. robusta looks similar to G. levis (Blanco) Merrill. It differs in having a non-waxy culm without brown hairy rings on internodes, slightly persistent culm sheaths, narrow and acuminate lemma apex and long hairs on the anther tips.

G. robusta can be found growing in the perhumid tropics from sea-level up to 1500 m altitude, in areas with average annual rainfall of 2350-4200 mm, temperatures of 20-32ºC, and relative humidity of over 70%. It normally grows on latosols.

Propagation and planting
G. robusta is only propagated vegetatively by rhizome or culm cuttings. Culm cuttings have a survival rate of nearly 100%. For large-scale planting, cuttings are raised in a nursery and transplanted to the field when the plants are about one year old. It is recommended to plant in holes of about 1 m x 1 m x 1 m to which compost or other organic fertilizer has been applied. Recommended planting distance is 8 m x 8 m (about 155 clumps per ha).

Weeding and watering (if rainfall is insufficient) is necessary during the first 2 years after planting. Mikania cordata (Burm.f.) B.L. Robinson, however, often occurs as a troublesome weed which can even kill young established bamboo clumps, and makes frequent weeding continuously necessary. Depending on soil fertility, chemical fertilizers are applied.
To promote young shoot production, mulching and thinning dense clumps until a few evenly spaced culms are left are recommended. Culm production benefits form removal of old culm remnants and regular earthing up.

Diseases and pests
Throughout its growing phase, no serious diseases and pests occur on G. robusta. Witches' broom caused by Epichloe bambusae often occurs but does not harm the culms. Harvested culms and derived products suffer seriously from powder-post beetles.

First harvesting may start 4-5 years after planting. It is recommended to harvest in the dry season by cutting mature culms just above the ground. A selective felling system in a 3-year cycle is recommended in Indonesia.

In Indonesia it is estimated that a mature clump produces yearly an average of 6 mature culms (about 900 culms per ha at planting distance of 8 m x 8 m).

Handling after harvest
Traditionally, culms are soaked in mud or running water for a few weeks and then air dried. G. robusta culms suffer heavily from borer attack; therefore, for large-scale production, chemical preservation treatment is necessary. Promising experimental results were obtained by soaking culms for 3-7 days in a solution of boron or wolmanit.

Genetic resources and breeding
Small germplasm collections of G. robusta are available in Indonesia in Lampung (Sumatra) and in Bogor (Java). Because this bamboo is rather variable, the existing variation should be properly conserved. There are no breeding programmes for G. robusta.

G. robusta is a promising bamboo, especially for its culms. More research is needed regarding other possible uses (e.g. edibility of young shoots), large-scale cultivation, and breeding of cultivars for culms resistant to borer attack after harvesting.

E.A. Widjaja

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