Chapter 2 The major tropical perishable staple foods

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Overall, in the less developed countries of the tropics, as in the temperate world, the most important staple foods, i.e. those which provide the carbohydrate or calorific basis of diets, are the grain crops, but the tropical world, in particular, includes a great variety of ecosystems, typified by widely differing food production systems. Especially in the humid and sub-humid tropics, a large proportion of the staple food is derived from crops other than grains. These non-grain, perishable staples are estimated to provide the dietary base for between 500-700 million people across the tropics. Recent FAO statistics indicate a higher relative importance of perishables in the tropics than in the temperate world (AGS Bulletin, No. 43, 1981; Coursey, 1982).

These perishable staple foods are very largely produced from small-scale subsistence level systems and the technologies employed in both production and utilization are usually simple and founded on long-established traditional practice. The most important are the root crops; cassava, yams, the various aroids, sweet potatoes and white potatoes (Coursey and Haynes, 1970), the total production of which is now around 185 million t/a; fruits such as cooking bananas, (plantains) and breadfruit are also important, still the former being a major food with a world production of over 20 million t/a, while a proportion of the dessert banana crop also is eaten as a staple, cooked while unripe (Burden and Coursey, 1977); there are also crop products derived from vegetative organs such as stem starches of palms and other types of plant.

The principal crops in this group are listed in Table 2.1, which also includes estimates of total production within the developing countries, derived as far as possible from FAO sources but supplemented from personal knowledge of one of the writers (D.G.C.). It should be noted that much larger quantities of white or Irish potato and of sweet potato are produced in temperate countries than in the developing countries. White potatoes, being familiar from the extensive literature of the temperate zone will not be considered in this report.

Under humid tropical ecosystems the perishable staple crops are often far more productive than grain crops, whether in terms of production of tonnage, economic return or available energy per hectare per year (de Vries et al., 1967) as is shown in Table 2.2, derived from Johnston (1958). Especially in the case of cassava and plantain, these crops require a lower labour input to provide a given amount of food than any other crops (Coursey and Haynes, 1970)- The labour input to sago-based food production systems also appears very low (Stanton and Flach, 1980). A schematic layout, originally due to Coursey and Booth ( 1977) of a system under which these staples can be classfied, is given in Table 2.3.

It is not proposed in this report to give full detailed accounts of the botany or agronomy of these crops; it is assumed that the reader will be familiar with them. Reference can be made to such general works as Purseglove (1968; 1972); Cobley (1976) or Leakey and Wills (1977), or for more detail to crop-orientated monographs such as Jones (1959); Montaldo (1979); Coursey (1967); Simmonds (1962; 1966); Edmond (1971); Yen (1974); Ruddle et al. (1978) and Stanton and Flach (1980) .

Although the perishable staple food crops are, as already indicated, essentially crops of the humid or sub-humid equatorial and tropical regions, their ecological requirements vary considerably. At one extreme, the Metroxylon sago palms and some cultivars of Colocasia flourish under swamp or even flooded conditions: other edible aroids, some yams, plantains and breadfruit and sweet potatoes are well adapted to semi-continuous production under conditions of high rainfall with only a minimal dry season: at the other extreme, other yam species are essentially seasonal crops of the derived savanna and require a pronounced dry season for full development of dormant and, therefore, long-storing tubers. Sweet potatoes and some aroids can also be produced in the savannas, either under irrigation or as rainy season crops, the former is also grown at relatively high altitudes. Cassava is the most ubiquitous and will grow almost anywhere where there are no severe frosts, a reasonable growing period above 20C, at least 800 mm of annual rainfall and an absence of waterlogging or extreme salinity. The relative ecologies of the main perishable staple food crops have been discussed by Flach (1979) and Wilson (1977). The different optimal ecologies for growth of a crop can affect the type of post-harvest technology most likely to be appropriate for its products.

TABLE 2.1: The Principle Perishable Staples of the Tropical World

Common Names Botanical Names Estimated Production In Developing Countries Megatonnes/a
Cassava (tapioca, manioc, mandioca or yuca) Manihot esculenta Crantz (often, incorrectly, M. utilissimma, Pohl.) 100-120
Yam (igname, name) Dioscorea rotundata Poir, D.cayenensis Lam., D. alata L., D. esculenta (Lour.) Burk. and many minor Dioscorea spp. 18-22
Sweet potato (batata) Ipomcea batatas (L.) Lam. 15-20
Potato Solanum tuberosum L. (and S. tuberosum X S. andigenum crosses) 25-30
The edibile aroids:
Taro, dasheen, eddoe, "old cocoyam" Colocasia esculenta (L.) Schott  
Tannia, ocumo, "new cocoyam" Xanthosoma sagittifolia (L.) Schott 4-6
Elephant yam Amorphophallus campanulatus (Roxb.) Blume  
Giant taro, swamp taro Cyrtosperma spp. Alocasia spp.  
Plantains and other cooking bananas Musa spp. (AAA, AAB and ABB cultivars 25-30
Breadfruit Artocarpus altilis (Park) Fosberg 1-2
Ensete Ensete ventricosa (Welw.) Cheasm. about 1
Sago Metroxylon sagu Rott., M. rumphii Mart. and several 1-2
Pandanus Pandanus odoratissimus L.f less than 1 and some other species  

TABLE 2.2 Relative Production Cost of Staple Crops in West Africa (after Johnston, 1958)

Ranking Per hectare Per ton Per 1 000 cal.
Cheapest Plantain Plantain Plantain
Millet Cassava Cassava
Maize Sweet Potato Sweet Potato
Sorghum Cocoyam Maize
Rice Yam Cocoyam
Cassava Maize Sorghum
Cocoyam Sorghum Millet
Sweet Potato Millet Rice
Costliest Yam Rice Yam

TABLE 2.3 Classification of Staples (after Coursey and Booth, 1977)

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STAPLE FOODS (i.e. predominantly carbohydrate)

GRAINS

PERISHABLE STAPLES

REPRODUCTIVE ORGANS

(e.g. fruits: plantains, cooking bananas, breadfruit)

VEGETATIVE ORGANS

STEMS

(reserves for flowering in mono carpic spp., e.g. sago, ensete)

ROOTS AND TUBERS

ORGANS OF DORMANCY (yams, potatoes, sweet potatoes, aroid root crops)

OTHER ROOTS

(cassava-tapioca)

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