QUEENSLAND ARROWROOT, Australian arrowroot, Edible canna.
Canna indica L. syn. C. edulis Ker-Gawl.
Achera (Arg.); Achira (Bol., Col., Peru); Araruta bastarda, Bandera de Uribe (Col.); Berg, Bir manso (Braz.); Capacho (Venez.); Chisgua (Col.); Imbirg (Braz.); Purple arrowroot; Sembu (Philipp.); Sug (Col.); Tous les mods (W.I.); Zembu (Philipp.).
A perennial, herbaceous monocotyledon, rather variable in many characteristics such as colour of foliage, height, size, shape and composition of the rhizomes. The stems are usually purple, normally 0.9-1.8 m in height, but can reach 3 m or even higher and are fleshy and arise in clumps. The large, broad, pointed leaves are entire, normally 30 cm long and about 12.5 cm wide with a marked, thick midrib; they are often purplish beneath. The unisexual flowers have orange-red petals about 5 cm long and 3 petal-like staminodes. The fruit is a 3-celled capsule with round black seeds. The rhizomes have fleshy segments resembling corms, and are borne in clumps which can reach 60 cm in length. In the Andes two clones are recognised: 'Verdes' with gray-white corms and bright green foliage, and 'Morados' with corms covered with violet-coloured scales.
Origin and distribution
Canna edulis appears to have originated in the Andean region of South America; there is evidence of its cultivation on the Peruvian coast about 2500 BC (earlier than maize and cassava). In South America it now extends from the north, throughout the Amazon basin and as far south as northern Chile; in Central America and the West Indies it has become naturalised as a weed (occasionally cultivated), and it has been spread to parts of Australia, Polynesia and Africa.
The plant is not exacting in its climatic requirements, except that it cannot withstand prolonged exposure to strong winds and in exposed locations must be protected by shelter belts.
Temperature - although best suited to tropical temperatures, Queensland arrowroot can be grown outside the tropics in most areas which have a frost-free period sufficiently long for the tubers to mature. In Hawaii, maximum yields are obtained in areas where both days and nights are relatively warm, and there is little seasonal variation in temperature, yet it is grown extensively in the Aparimac Gorge in Peru, where the days are as warm as 32°C and the nights as cool as 7°C.
Rainfall - it does best with a moderate, evenly-distributed rainfall, although it can withstand periods of drought satisfactorily. Excessive moisture often promotes abnormal foliage growth, to the detriment of tuber development. In Hawaii, an annual rainfall of approximately 112 cm has been found satisfactory. Irrigation in dry areas may be used.
Soil - the plant can be grown on most types of soil, except heavy clays, provided there is adequate drainage, since it will not tolerate waterlogging. The best yields are obtained on deep sandy loams, rich in humus. It is a gross feeder and experiments in Hawaii have indicated that application of 280 kg/ha of each of ammonium sulphate, superphosphate and potassium sulphate results in higher yields.
Altitude - Queensland arrowroot can be grown at sea level, and in Hawaii produces its maximum yield at elevations below 450 m. Nevertheless it thrives in Peru at altitudes up to 2 500 m.
Material - normally propagated from the underground fleshy rhizomes; only those which have attained normal size and development and bear one or two healthy undamaged buds should be used for planting. As a precaution against rotting the rhizomes are sometimes dipped in a 10 per cent solution of copper sulphate before planting.
Method - Queensland arrowroot should be planted on land which has been thoroughly ploughed and cleaned of weeds. In areas where the temperature is fairly uniform it can be planted at any time except during drought. The rhizomes are planted 12.5-15 cm deep in furrows and kept free from weeds during the initial stages of growth by thorough inter-row cultivation.
Field spacing - on friable loam, spacing of 90 x 90 cm is recommended; on heavier soils, or where weed growth is likely to be a problem, 120x 120 cm is better or even 135 x 180 cm. In Peru the normal spacing used is 60-100 cm between the plants and 100-150 cm between the rows.
Seed rate - approximately 2.5 t rhizomes per hectare
Pests and diseases
Queensland arrowroot is relatively free from pests and diseases; grasshoppers and Japanese beetles are occasionally found feeding on the foliage in Hawaii, where cutworms (Agrotis spp.) are the most troublesome pest. In Peru, and certain other parts of South America, the crop is sometimes attacked by Calopodes ethlius and Quinta cannae. In addition, the following fungi are reported to affect the crop in Peru: Fusarium spp., Puccinia cannae and Rhizoctonia spp.
There is no definite period for maturing; the rhizomes are normally sufficiently mature for lifting 6-8 months after planting, but there is a considerable diversity of opinion as to the best time of harvesting. In Queensland, where growth is checked by cold weather and frosts, harvesting is normally 6-10 months after planting or when the rhizomes indicate they are mature by the triangular slit in the outer scale-leaf of the rhizome assuming a purple colour. In Hawaii, although the rhizomes are often harvested 8 months after planting, it has been suggested that for starch manufacture harvesting should take place when the plants are 17-19 months old, but there is evidence that it becomes increasingly difficult to prepare good quality starch as the rhizomes age.
Harvesting and handling
The stalks are usually cut by hand and the rhizomes which form a mass near the surface of the soil are either dug by hand or by a tractor with a tool bar fitted with three or four strong tines set at an angle. These break up each of the main clumps of rhizomes into three or four separate portions and also remove a good deal of the soil. The rhizomes are then scraped free from soil by hand and, if required for stock feed or planting, can be stored for several weeks without deterioration, provided they are kept cool and dry; in Japan they are stored over winter in field pits 30 cm deep. For starch manufacture they must be processed immediately.
Rhizomes - the starchy rhizomes vary from cylindrical to tapering and spherical to oval, usually ranging from 5 to 9 cm in diameter and from 10 to 15 cm in length. They are ringed by scale-scars and thick fibrous roots.
Yields vary considerably according to the length of the growing season, climatic and soil conditions. The following average yields have been reported: Hawaii (8 months) 45-50 t/ha, Queensland 25-37 t/ha, Zimbabwe 15-18 t/ha, Kenya (15-18 months) 50 t/ha.
Queensland arrowroot is cultivated for the starchy rhizomes which can be utilised as a source of edible starch, as in Queensland, or for animal feeding, as in several African countries. In Queensland approximately 80 per cent of the crop is used for the production of refined starch, I tonne of which is obtained from about 10 tonnes of rhizomes.
Because of the thickness of the fibres the rhizomes are not highly regarded for direct eating. In parts of South America the starch (which contains about 4 per cent sucrose) is often prepared as a dessert.
Secondary and waste products
Tops - the leaves and stalk are also used for animal feeding and are relished by pigs. The composition of the leaves is approximately: moisture 90.2 per cent; protein 1.1 per cent; fat 0.2 per cent; carbohydrate 7.1 per cent; ash 1.4 per cent; nutritive ratio 1:4.8.
Waste pulp - the pulp and fibrous tissues left after starch manufacture can be used to manure the crop or dried and bagged and used as an animal feedingstuff.
Analysis of the rhizomes has been given as: water 67-72 per cent; protein 1-1.7 per cent; fat 0.1 per cent; carbohydrate 24-30 per cent; fibre 0.6 per cent; ash 1.4 per cent; calcium 18 mg/100 g; phosphorus 63 mg/100 g; ascorbic acid 7 mg/100 g.
The percentage of starch varies with the age of the rhizomes and is usually at a maximum between 6 and 15 months, when the sucrose content is also high. The cysteine level in the protein is very low.
Queensland arrowroot starch is characterised by its exceptionally large granules, broadly oval, up to 145 microns in length, with a layered structure resembling a series of stacked plates. The starch gives a clear, transparent, firm gel at a concentration of 3.5 per cent and is easily digested so that it is often used for baby or invalid foods.
(i) The rhizomes are washed and the fibrous roots removed by hand. This step is difficult to mechanise because of the irregular size and shape of the rhizomes.
(ii) The washed rhizomes then pass to a rasping machine and a slurry is produced.
(iii) The slurry passes to a rotating drum and the fibrous tissue and impurities are deposited on a screen while the starch milk and water pass on to the settling tanks.
(iv) The starch quickly settles out; with starch milk of an initial solids content of approximately 5 per cent, precipitation is complete in about 20 minutes.
(v) The starch is then run off from the bottom of the settling tanks and thoroughly washed with water to eliminate any remaining impurities.
(vi) After repeated washing the pure starch is dried, sieved and packed ready for shipment.
Production and trade
Very little statistical information is available. Production in Queensland during the 1960s fell from a peak of 4 300 t in 1960/61 to 1 910 t in 1968/69. Current production is about 200 t, but it is reported that a small market for high quality Queensland arrowroot flour is again developing in Australia.
Queensland arrowroot has potential as a source of edible starch and as an animal feedingstuff. It grows rapidly and can be cultivated over a wide range of climatic and soil conditions in the tropics and subtropics. Under favourable conditions it produces good yields of starchy rhizomes, which can be harvested over a long period, and so the crop is capable of being produced on a continuous basis at minimum cost. Although the plant has been utilised for starch production in some countries for many years, world consumption is very low, due partly to the irregularity of supply and the low quality of many consignments, and to the rather heavy use of manual labour in the harvesting process.
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