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OVERVIEW OF ROOT AND TUBER CROPS


Commodity Perspectives:
Research Accomplishments:

Commodity Perspectives:

The commodities that make up root and tuber crops in the CG System are cassava (Manihot esculenta), potato (Solanum tuberosum), sweet potato (Ipomoea batatas), yam (Dioscorea spp.), edible aroids (Colocasia esculenta and Xanthosoma spp.), and Andean root and tuber crops (several genera).

Root and tuber crops provide a substantial part of the world's food supply, and 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.

The pattern of root and tuber crop utilization varies considerably among countries. In the developing countries (with the exception of China and Brazil), relatively small amounts (less than 20%) are fed to livestock. Most of the remainder is used locally as food. The relatively high cost of transportation, processing, and storage, as well as the considerable time needed in food preparation, frequently makes unprocessed root and tuber crops less attractive to urban consumers.

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. A very small proportion of root and tuber crop production (approximately 5%) is traded internationally. More than two-thirds (2/3) of those exports come from developing countries, with Thailand's cassava exports accounting for more than half (½) of the total. Apart from cassava, only potatoes are traded internationally in significant quantities - mainly among developed countries.

There are considerable differences in the agroclimatic conditions suitable for the production for the different root and tuber crops studied by the CG System. Cassava is grown across a broad range of agroclimatic conditions from sea level to 1,800 meters, and from areas with as little as 500 mm of rainfall, to tropical rain forest areas with more than 2,000 mm per year. Potatoes, on the other hand, are considered to be a high latitude/altitude crop, originating in the Andes, but now grown in a range of environmental conditions, from traditional ranges to warmer, drier areas, including irrigated production in Latin America, Asia, and portions of Africa.

Sweet potato is understood to have originated in the Americas (as did cassava and potato), and it too is grown over a considerable range of latitude and elevation (up to 2,500 meters). Conversely, yams have a relatively narrower range of production, being mainly confined to the tropical region throughout the world from sea level to 1,400 meters. The main production of yam is in the savannah region of West Africa, where more than 90% of the crop is grown. Unlike cassava, potato, and sweet potato, the white and yellow yam (Dioscorea rotundata and D. cayenensis [esculenta], respectively) are thought to be indigenous to West Africa, whereas the water yam (D. alata) is thought to have originated in Southeast Asia.

Most of the cultivated edible aroids are well adapted to high rainfall (and occasional flooding) and can be cultivated in temperatures ranging between 16° and 30° C, at elevations up to 1,600 meters.

The lesser-known Andean root and tuber crops, of which there are more than a dozen, vary considerably in their ranges of adaptation and tolerance to environmental conditions. They are primarily considered to be medium-to-higher elevation crops of moderate temperature regimes and water requirements, and have greater tolerance to frost than do other root and tuber crops.

According to the TAC Secretariat desk study3, annual production growth rates to the year 2010 for root and tuber crops are expected to be positive, with the exception of modest declines in cassava in Asia (including China; -0.4%) and sweet potato and yams in Northeast and North Africa (-1.0%). TAC also predicts a decline in area for potato, cassava, aroids, sweet potato and yam in Asia (including China) over the indicated period (potato, -4.9%; cassava, -1.3%; aroids, -1.1%; sweet potato and yam, -0.2%).

3 The panel cautions the reader that the Desk Study's projections are probably linear, and based on very poor data.

Indicated changes in yield in the TAC Secretariat report are all positive, with the minor exception of a decrease in yield in Northeast and North Africa for sweet potato and yam (-0.7%). Significant yield increases are anticipated for potato in sub-Saharan Africa and Asia (including China), cassava in sub-Saharan Africa, aroids in Asia (including China), and sweet potato and yam in sub-Saharan Africa as well as in Asia (including China).

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.

The TAC Secretariat desk study traces historical changes in food, feed, and industrial uses of root and tuber crops, by commodity and region. Patterns indicate significant change is apparently taking place in the utilization of root and tuber crops, particularly with cassava and sweet potato in Asia (both in China and elsewhere), and in Asia for potato as both food and feed crops. The latter trend is primarily in China.

Total root and tuber crop consumption increased for developing countries (1980-1992) while per capita consumption declined over the same period, primarily with the exceptions of potato (+0.9%) and yam (+5.5%). When these patterns are examined regionally by commodity, it is clearly evident that the total consumption of root and tuber crops is increasing in Africa with annual rates of change for potato and cassava of +0.32%, and of yam a surprising +8.5%. Despite these increases in total consumption, per capita consumption patterns in Africa are lagging, likely as a consequence of increased population. The striking exception to this pattern is for yam per capita consumption which in Africa increased +5.2% over the fourteen-year study period.

With a few notable exceptions, per capita consumption of root and tuber crops in South America and Asia declined over the period of the study, with some notable changes. Declining per capita consumption of sweet potato in South America (-2.7% per annum) was out-paced by the change in Asia (-5.2 %).

These patterns, derived from a TAC desk study, appear to be at odds with information provided by the relevant IARCs for their mandated root and tuber crop commodities. Consider the following points:

· For the past thirty years (from 1961-63 to 1991-93), potato production in developing countries grew rapidly. Annual growth was particularly strong in Asia (+3.9 % annually), and in Africa (+4.2%). Growth in production was combined with a continuing decline in the use of potato for animal feed in developed countries. Therefore, the share of global production in developing countries rose from 10% to 30%. By the early 1990s, developing countries accounted for 36% of the area planted in potato worldwide, up from 16% at the beginning of the thirty-year period. These patterns are expected to continue into the future at a projected rate of +2.7 % per annum in developing countries, reaching 105 million tons (for 34% of world production) by the year 2000.

· During the same thirty year period, world cassava production has experienced strong growth, with an annual rate of +2.7%, although this pace has declined during the past decade to +1.8% per annum (which does not keep pace with population growth). There are also differential patterns by region, but, for the most part, increased world production of cassava during the last decade has been mainly due to an area expansion (+1.7% annually) rather than increased yields. However, survey data gathered by the Collaborative Study of Cassava in Africa (COSCA) estimate cassava yields of 12 tons per hectare, as compared with FAO estimates of 8.5 tons. This difference indicates that yield increases may have been contributing more heavily to cassava production growth than other reports suggest.

· Processed cassava for human consumption is projected to play an important role in rural and lower- to medium- income urban populations' daily energy diets. This will be especially true in Africa, where cassava continues to play an important role in food security. Future cassava production levels are projected to be consistent with patterns of the past decade, which implies that the largest share of additional cassava supplies will continue to be derived from the African continent. Predicted patterns of cassava production in Latin America and Asia indicate continued growth of production at modest rates.

· The evolution of cassava from a basic world staple crop to a diversified end-use carbohydrate source has largely been completed in Asia, and is underway in Latin America. In Africa, while traditional processing techniques were integral to the adoption of the crop, agro-industrial transformation appears only to be in the beginning stages.

· Production growth rates of yams in West and Central Africa, where they are an important food staple, are surpassed only by rice. For example, yam production increased by seven million metric tons (20 to 27 million tons) between 1988 and 1993. The demand prospects for yams appear particularly positive, given expected economic growth and rising household incomes in the region4.

4 The panel notes that projections for rising incomes in West Africa are arguable.

· 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. In other regions, sweet potato use has declined or stagnated over the past thirty years. There are, however, some exceptions to this general trend. In sub-Saharan Africa, sweet potato production and area planted has not declined. Globally, in the poorest developing countries, and particularly in those areas affected by civil war, sweet potato production area has substantially expanded, a testament to its attributes as a human food during periods of famine and suffering.

There are, thus, discrepancies in not only the numerics of production and consumption of root and tuber crops, but also in the interpretation of exactly what the numbers mean, and how this information ought to be used to plan research strategies and set priorities for resource allocation. The panel took this divergence of opinion as an opportunity to reassess the strategies and priorities for roots and tubers from an inter-Centre perspective.

Research Accomplishments:

To set the stage for assessing strategies and priorities for root and tuber crops research, the standing panel inventoried CGIAR's accomplishments in root and tuber research. This provided some interesting background information that pointed out the very significant contributions that the CGIAR Centres have made to these crops.

Cassava (IITA)

· Collaborative studies, through a network (COSCA) in Africa, have examined varietal needs of farmers and the potentials for production, processing, and distribution. One anticipated outcome of the studies, namely to improve the relevance of research on cassava at national and international levels, was fully realized. For example, the description across several countries and socio-economic domains of preferred varietal characteristics at farmer, processor, and consumer levels has had a major input to priority setting in breeding programs.

· The characterization and integrated control of pests and diseases of root and tuber crops in Africa has led to a special focus on the biological control of cassava pests, including a remarkably successful Africa-wide biological control effort for the cassava mealybug.

· The genetic base of cassava has been expanded through varietal releases in a number of countries in sub-Saharan Africa. Most of these cultivars carry resistance to mosaic virus, mealybugs, cassava green mite, and cassava bacterial blight.

· Successful wide-crossing of cassava with its wild relatives has been accomplished to acquire genetic resistance to certain pests and diseases.

· Post-harvest research has solved, to a considerable extent, the riddle of cyanogenic glycosides in cassava, thus helping to reduce prussic acid problems in the leaves and roots.

· Assemblage and maintenance of a significant collection of cassava germplasm of more than 2,000 accessions, consisting mostly of African farmers' cultivars and some exotic materials from Latin America, including roughly 200 accessions of wild manihot species from Brazil.

· Diagnostic capability for reliable screening for African cassava mosaic virus (ACMV) has been developed. This has enabled routine indexing of elite materials for distribution to NARS, and has facilitated the international movement of elite ACMV resistant clones to Latin America.

· A better understanding of ACMV etiology and epidemiology has been achieved, enabling control strategies to be improved in West Africa.

Yam (IITA)

· The acquisition and maintenance of more than 2,800 accessions of yam comprising eight cultivated species and several wild relatives, with accompanying agrobotanical and biochemical characterization.

· The genetic improvement of yam became possible through the discovery of how to induce flowering, which - for the first time - permitted conventional plant breeding.

· The elaboration of a minisett technology appropriate for use by yam growers, which vastly improves the multiplication ratio, and therefore the supply, of vegetative planting materials. The technique has been adopted by seed yam producers in West Africa.

· Studies of little known viruses in Dioscorea spp. and the development of an indexing protocol for D. rotundata has enabled germplasm distribution regionally and internationally.

· The development of micropropagation techniques for producing virus-free minitubers which meet quarantine requirements and enable the routine transfer of elite materials to national programs.

Sweet Potato (IITA)

· From 1977 to 1988, when IITA passed responsibility for sweet potato improvement to CIP, a sizeable amount of breeding stock was developed and distributed as virus-free plantlets to national programs worldwide. By 1988, at least fifty improved clones, based on IITA germplasm, had been officially released.

Aroids (IITA)

· A treatment was identified and refined to induce flowering in the edible aroids, thus removing the bottleneck to selective hybridization and genetic improvement of this plant group.

General (IITA)

· Partner institutions have been strengthened for enhanced global and regional scientific participation, including helping to establish more than twenty national root and tuber crops research programs in Africa.

Cassava (CIAT)

· Development of cassava information services as resources for professional enrichment of cassava scientists.

· Assemblage and maintenance of a world germplasm collection, representing 80% of the total diversity of cassava, complemented with related wild species.

· Methods for the in vitro conservation of cassava germplasm.

· Morphological and biochemical characterization of collected cassava germplasm.

· Global germplasm conservation and distribution.

· Ecoregional approach to gene pool improvement in cassava.

· Broad-based and durable resistance to major insects, mites, and pathogens incorporated into cassava gene pools.

· Characterization of the mechanisms of drought tolerance in cassava.

· Understanding and describing the C3-C4 intermediate biochemical characteristics of cassava photosynthesis.

· Identification of several effective biological control agents for major pests of cassava.

· Characterization of the post-harvest physiology of cassava roots.

· Improvement and local adaptation of cassava selections for food and industrial processing.

· Co-development of cassava drying and processing plants in Central and South America.

· Research on cassava's best management practices led to an understanding of how to maintain long-term soil fertility.

Potato (CIP)

· Development of Integrated Pest Management (IPM) strategies based on biological control for the Andean potato weevil and the potato tuber moth.

· Diagnostic field kits for the serological and DNA-hybridization assay of potato tissue to determine virus status - especially useful in developing countries.

· Development of true potato seed technology, which is now deployed in a number of countries.

· Development of potato late blight resistant varieties that are being used in East Africa and portions of South America.

· Identification, cleanup and wide scale distribution of an Argentinean clone that is now grown on more than 150,000 ha. in China.

· Collaborative development of a highly saturated marker map of the potato genome and development of specific markers for virus and improved late blight resistance.

· Establishment of an R-gene-free population with durable late blight resistance.

· Development of an in vitro assay system for the conservation of potato germplasm.

· Completion of eight impact studies on CIP's work in varietal improvement, IPM, seed technologies, etc., identifying returns on investment ranging from 26-106% per annum.

· The acquisition and maintenance of an extensive collection of germplasm, comprising wild and weedy species, cultivars, improved varieties, and important breeding lines.

· Utilization of the "hairy potato" for resistance to potato insect pests.

· Bacterial wilt disease management strategy now being used in East Africa and Central America for effective disease control.

· Widespread utilization of CIP-released potato cultivars in Eastern Africa.

Sweet Potato (CIP)

· Production of improved sweet potato varieties now widely used in Peru.

· Development of an IPM system for sweet potato weevil that is now being used commercially in Cuba.

· An impact study of IPM of sweet potato.

· The collection and maintenance of a sweet potato germplasm bank (6,522 accessions).

· Development of methodologies to induce sweet potato flowering and seed set for germplasm conservation.

· Development of in vitro storage systems for sweet potato germplasm.

Lesser-known Andean Root and Tuber Species (CIP)

· Genetic conservation of nine Andean species of edible roots and tubers that are presently being evaluated for their agronomic characteristics, nutritional value, and potential for production and consumption.

The panel notes these achievements in root and tuber crops research with an appreciation of each individual Centre's success and with a view to the terms of reference of the Inter-Centre Review that asked for an evaluation of the opportunities and potential for inter-Centre collaboration. To undertake this evaluation, the panel gave focus to the similarities and dissimilarities of root and tuber crops in an attempt to find points-of-intersection that would permit synergies through inter-Centre collaboration.


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