Chapter 1
Introduction to Tropical Roots and Tubers

Harish K. Sharma and Pragati Kaushal

Department of Food Engineering and Technology, Sant Longowal Institute of Engineering and Technology, Sangrur, India

1.1 Introduction

Roots and tubers are considered as the most important food crops after cereals. About 200 million farmers in developing countries use roots and tubers for food security and income (Castillo, 2011). The roots and tubers contribute significantly to sustainable development, income generation and food security, especially in the tropical regions. The origin of tropical roots and tubers along with their edible parts is presented in Table 1.1.

Table 1.1 Origin of tropical roots and tubers

Individually, cassava, potato, sweet potato and yam are considered the most important roots and tubers world-wide in terms of annual production. Cassava, sweet potato and potato are among the top ten food crops, being produced in developing countries. Therefore, tropical roots and tubers play a critical role in the global food system, particularly in the developing world (Amankwaah, 2012). The leaders, policy-makers and technocrats have yet to completely recognize the importance of tropical tubers and other traditional crops. Therefore, there is a need to focus more on tropical roots and tubers to place them equally in the line of other cash crops.

Tropical root and tubers are the most important source of carbohydrates and are considered staple foods in different parts of the tropical areas of the world. The carbohydrates are mainly starches, concentrated in the roots, tubers, corms and rhizomes. The main tropical roots and tubers consumed in different parts of the world are taro (Colocasia esculenta), yam (Dioscorea spp.), potato (Solanum tuberosum L.), sweet potato (Ipomoea batatas), cassava (Manihot esculenta) and elephant foot yam (Amorphophallus paeoniifolius). Yams are of Asian or African origin, taro is from the Indo Malayan region, probably originating in eastern India and Bangladesh, while sweet potato and cassava are of American origin (Table 1.1). Naturally suited to tropical agro-climatic conditions, they grow in abundance with little or no artificial input. Indeed, these plants are so proficient in supplying essential calories that they are considered a "subsistence crop" (www.fao.org). Because of their flexibility in cultivation under a mixed farming system, tropical roots and tubers can contribute to diversification, creation of new openings in food-chain supply and to meet global food security needs.

The perishability and post-harvest losses of tropical roots and tubers are the major constraints in their utilization and availability. The various simple, low-cost traditional methods are followed by farmers in different parts of the world to store different tropical roots and tubers. The requirements of storage at different stages during the post-harvest handling of tropical roots and tubers are presented in Figure 1.1. The perishable nature of roots and tubers demands appropriate storage conditions at different stages, starting with the farmers to their final utilization (consumers). Therefore, an urgent requirement exists to modernize the traditional methods of storage at different levels, depending upon the requirements of keeping quality.

Figure 1.1 Post-harvest handling stages in the storage of tropical roots and tubers.

The various interactive steps involved in post-harvest management of any tropical root or tuber, if not controlled properly, may result in losses. To prevent these losses, several modern techniques such as cold storage, freezing, chemical treatments and irradiation may be widely adopted. Roots and tubers not only enrich the diet of the people but are also considered to possess medicinal properties to cure various ailments. So the role of roots and tubers in functional products can also be investigated in the light of medicinal properties. An immense scope exists for commercial exploitation in food, feed and industrial sectors. Since tropical roots and tubers crops are vegetatively propagated and certification is not common, the occurrence of systemic diseases is another problematic area. Some of these root and tuber crops remain under-exploited and deserve considerably more research input for their commercialization.

1.2 Roots and Tubers

1.2.1 Roots

The root is the part of a plant body that bears no leaves and therefore lacks nodes. It typically lies below the surface of the soil. Edible roots mainly include cassava, beet, carrot, turnip, radish and horseradish. Roots have low protein and dry matter compared to tubers. Moreover, the major portion of dry matter contains sugars. The major functions of roots include absorption of inorganic nutrients and water, anchoring the plant body to the ground and storage of food and nutrients.

1.2.2 Tubers

Tubers are underground stems that are capable of generating new plants and thereby storing energy for their parent plant. If the parent plant dies, then new plants are created by the underground tubers. Examples of tubers include potatoes, water chestnuts, yam, elephant foot yam and taro. Tubers contain starch as their main storage reserve and contain higher dry matter and lower fiber content compared to roots. Various tropical roots and tubers are presented in Figure 1.2.

Figure 1.2 Various tropical roots and tubers.

The production of roots and tubers can be grouped into annuals, biennials and perennials. The perennial plants under natural conditions live for several months to many growing seasons, as compared to annual or biennial. The main points of difference among annuals, perennials and biennials are presented in Table 1.2. The perennials generally contain a greater amount of starch as compared to biennials.

Table 1.2 Annual, biennial and perennial roots/tubers

1.3 Requirements for the Higher Productivity of Tropical Roots and Tubers

The factors that need to be focused upon to meet the objectives of food security, sustainable farming and livelihood development are farming systems, pest and pathogen control systems, genetic systems and strategies for improvement, together with marketing strategies and the properties of the products and constituents.

1.3.1 Farming Systems

Tropical roots and tubers are generally grown in humid and sub-humid tropics, which are not suited for cereal production. Significant differences exist in the farming system perspectives of tropical root and tuber crops, varying from complex systems of production to intercropping farming systems. These systems are important to consider when studying the variation of different crop farming systems. The increasing production in the Pacific region has depended largely on farming more land rather than increasing crop yields. This is contrary to the projections of FAO that the 70% growth in global agricultural production required to feed an additional 2.3 billion people by 2050 must be achieved by increasing the yields and cropping intensity on existing farmlands, rather than by increasing the amount of land brought under agricultural production (Hertel, 2010).

Farming systems need to be carefully looked after, by protecting and raising the production of tropical roots and tubers. For this purpose, various changes in attitudes and agricultural practices are desirable. Additional investments are required to reduce the impact of climate change and to overcome the disastrous effects of soil erosion. Diversity in the production of tropical roots and tubers and increasing production surface area may be adopted for higher productivity and better quality of tropical roots and...