Saturday, December 26, 2009

The underground Treasure troves

Roots and tuber crops, due to their high calorific value and carbohydrate content occupy a remarkable position in the food security of the world, particularly in the developing nations. The economically and socially important tropical tuber crops are Cassava, Sweet potato, Yams, Dioscoreas, Aroids which include Elephant foot yam, Taro and Tannia (Amorphophallus, Colocasia or Taro, Xanthosoma or Tannia) and other minor tuber crops namely Chinese potato, Arrow root, Yam bean, Canna etc. In addition to the major tuber crops, there are many rhizomatous types and tuberising species which are grown and used in different parts of India. Some of them are already cultivated, but many others are grown wild as a neglected group. They are often used as food or serve as a source of raw material for the production of alcohol and animal feed.


The countries of Asia-Pacific region account for about 40% of world's total annual production of roots and tubers. Roots and tubers are a major staple in the Pacific islands, the Asian and African countries also use them as animal feed, and in starch-based industries. Increasing demands of cassava and sweet potato in non-food and organized market sectors are closely linked with increased production. There are considerable differences in the agro-climatic conditions suitable for the production for the different root and tuber crops. In fact, these crops remained neglected in terms of scientific input until the establishment of the International Center for Tropical Agriculture (CIAT) in Colombia, the International Institute for Tropical Agriculture (IITA) in Nigeria, and the International Potato Center (CIP) in Peru.

Consumption & Utilisation

In the developing countries (with the exception of China and Brazil), relatively small amounts (less than 20%) are fed to livestock and the rest is consumed as food. The consumption of root and tuber crops as food in developed countries is considerably smaller than it is in developing countries, but their use as animal feeds is relatively higher. They are staple foods in many parts of the tropics. These are also an important source of animal feed and industrial products. On a global basis, approximately 45% of root and tuber crop production is consumed as food, with the remainder used as animal feed or for industrial processing for products such as starch, distilled spirits, and a range of minor products.

In terms of contribution to calorie supply, the importance of root, tubers and derived products crops (all production included and converted into primary product equivalent) is small, compared to the contribution of cereals. The contribution of root and tuber crops to the world supply of calories is only 5% compared to 48% for cereals and 46% for other food. In Africa, root and tuber crops contribute 14% to the calorie supply as compared to 51% for cereals and 37% for other food, while in South America roots and tubers contribute 5% and in Asia only 4% to the calorie supply. Many tropical tuber crops are used in the preparation of stimulants, tonics, carminatives and expectorants. The tuber crops are rich in dietary fibres and carotenoids viz. carotene and anthocyanin.

Importance of Root and Tuber Crops

Among the tuber crops, Cassava is the most important one in the tropics and it ranks fourth, after rice, sugarcane and maize, as a source of calories for human consumption. It is a major carbohydrate food for about 500 m people in the world, and in Africa, it is the most important source of calories in the human diet. Cassava is cultivated in 16mha, spread over the continents of South America, Africa and Asia, producing 158mt of tubers. The average productivity in the world is 10.88t/ha and that in India is 27.42t/ha from an area of 0.24mha. However in sweet potato, average productivity in India is only 8-9t/ha as against the world average of 16t/ha. Area under tuber crops in India is 4 lakh ha under cassava and sweet potato besides approximately 2 lakh ha under elephant foot yam, Colocasia, Xanthosoma etc.

Research & Development

The CGIAR Institutes, mainly IITA, Ibadan, CIAT and CIP, Peru has made stupendous accomplishments in root and tuber research. Of major concern is the scarcity of germplasm collections and the greater lack of breeding programs. In India also Central Tuber Crops Research Institute (CTRI), Thiruvananthapuram is striving to promote R&D in tuber crops. Some other institutes like, RAU, Bihar, OUAT, Bhubaneshawar and BCKV, Mohanpur has made considerable contribution towards the development of root and tuber crops.


The crop has gained importance as a cheap source of carbohydrate, mainly for human consumption. Its importance in tropical agriculture is due to its drought tolerance, wide flexibility to adverse soil, nutrient and management conditions including time of harvest. As cassava has no definite harvest time farmers can have a staggered harvest, which provides security against famine. Cassava can be profitably cultivated throughout the year. Cassava roots are perishable with a shelf life of only a few days. The presence of hydrocyanic glucosides (HCN) in all plant parts presents some problems in marketing cassava. Other postharvest problems with cassava include proper handling and storage of cuttings under frost-free conditions. Even though cassava flour can be used as a partial substitute for wheat flour in the production of bread, market economics restrict this process to countries where wheat is an import commodity. Apart from its role as a staple/subsidiary food, during the past few decades there has been growing recognition of the value of cassava roots as a low cost energy source for livestock and as a raw material for industrial starch and fuel alcohol.

Sweet Potato

The tuber is an important source of carbohydrate. The yellow flesh varieties are rich in carotene. Sweet potato is a short duration crop, adaptable to a wide range of growing conditions. It exhibits no strict seasonality making it suitable as a combination crop with other crops. The major sweet potato growing states in India are Orissa, Uttar Pradesh and Bihar. In China, where approximately 85% of global sweet potato production is grown, multiple uses of the crop (e.g., as animal feed as well as processing of the roots into starch, noodles, and alcohol), have helped to diversify markets for what was once mostly a directly-consumed food crop.


Yams are cultivated in every tropical country, but their large-scale cultivation is restricted mainly to West Africa, South-East Asia including China and Japan. Yams are eaten mostly as boiled, baked or fried. Yam production is also significantly influenced by day length. In India, traditionally yams are grown in homesteads. Yams are usually baked or boiled and mashed. Unless the production expenses are reduced, little potential exists for commercial processing of yams into items like that of potato chips or french fries.


Aroids comprise several species under the family Araceae that are cultivated for food in most of the tropical and subtropical parts of the world. Important aroids cultivated in India are taro, tannia, giant taro/ alocasia and elephant foot yam. Aroids are short-statured perennial plants, grown as annuals. They store starches in large corms at or below the sod surface. Corms which contain 25 to 35% starch, are plagued by the presence of an acrid factor, which causes itchiness and considerable inflammation of tissues. The potential for expansion of these markets is considered to be very limited, as the acceptability is poor among the masses. Colocasia tubers are also good source of protein, minerals like phosphorus and iron. Elephant foot yam is basically an underground stem tuber and is gaining popularity due to its yield potential and culinary properties. These are crops having high yield potential and starch value and they are yet to be properly explored.

Harvesting & Marketing

The production, harvest and marketing of root and tuber crops are generally labor intensive. The sheer bulk of root and tuber crops, compared to cereals, is an even bigger problem than is their underground harvest. The processing of traditional consumable products from these crops may also require high labor inputs. Root and tuber crops share some similarities from a market perspective at the farm level. For instance, much of root and tuber crop production is consumed on-the-farm, or at distances that are relatively closer to production.

Post harvest management

All of the root and tuber crops have the distinct disadvantage, following harvest, of limited storability, and are fairly perishable if the conditions are not suitable. This characteristic of root and tuber crops predetermines the need for post-harvest treatment of these crops to preclude very large post-harvest losses.

Export avenues

Trade enquiries show that there is considerable demand, of about a lakh tonnes of cassava chips, for exports to the South East Asian countries. There is a need for series of studies be initiated to assess afresh the export potential from traditional and non-traditional areas, export demand of tuber crop-based products, policy issues relating to growth of exports, extension of technologies to non -traditional areas and linkages with APEDA for expertise and training in the area of exports of tuber crops. The lack of a clear export policy had hampered Indian interests, outpricing its products from the global marketplace and the price factor had been playing a crucial role in the cassava chips export scenario.

Major roadblocks

One of the persisting problems with root and tuber crops is its unrealized yield potential that could only be attained through yet-to-be-developed technologies. In the case of root and tuber crops, the potential for yield is considerably higher than the actual yield. Both biophysical i.e., diseases, insect pests, low-yielding cultivars, poor crop husbandry and socio-economical; scarce land, shortage of labor, shift in food habit linked with urbanization constraints are adversely affecting production of root and tuber crops.

The way-ahead

The potential of the roots and tubers being processed into snack foods depends on economics and public acceptance. Unless the costs of production can be reduced dramatically through mechanization and selection of earlier maturing clones, the future is not bright. Both obstacles are not insurmountable. However, a decided commitment to research and development must be made for this to happen. Some of the indicated changes will likely be driven by consumption demands and production opportunities as a result of technology yet-to-be-developed for root and tuber crops. Some of these technologies will no doubt entail food processing technologies and expanded feed markets, as well as current and new industrial uses for the harvested products of root and tuber crops.

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