What is the next step needed to integrate farmer perspectives into priority setting of cassava biotechnology research? What cassava biotechnologies are ready for application to identified priorities? These were important themes at the Second International Scientific Meeting of the Cassava Biotechnology Network (CBN), held 22­26 August in Bogor, Indonesia.

The Cassava Biotechnology Network (CBN) attempts to provide information to biotechnologists on the needs of developing­country cassava users (i.e. producers, processors, marketers, and consumers). The main objective of CBN is to invest in research, but for a proper direction of research efforts a practical method of interaction with users is felt to be essential. In Latin America and in West Africa, the network has access to information of farmers and processors through participatory research conducted by the International Centre for Tropical Agriculture (CIAT), Colombia, and through the work of the International Institute for Tropical Agriculture (IITA), Nigeria. To broaden its geographical scope, CBN has recently collaborated in case studies in Tanzania and China (see box).

Case study implications
How should CBN deal with the information that is gathered in these case studies? This question could be best discussed by identifying two issues:
(a) How can user perspectives be aggregated to provide CBN with guidance for priority setting on a regional and global level? Although comparisons between Tanzania and China are an extreme case, cassava systems differ greatly even within regions. How should this diversity be sampled?
(b) What can biotechnology offer in the short term to solve the problems of cassava users? Research contributing to food security and rural income for cassava users cannot wait for perfect information. Given the limitations of our knowledge at this point, and realizing that priorities will change with more information and changing agro­economic circumstances, available biotechnology could already be applied to contribute to the solution of existing problems. A related question is, what do the case studies suggest about directions for longer­term cassava biotechnology research?

User perspectives in priority setting
The first issue raised in relation to the case studies, the use of user perspective in priority setting on a regional and global basis, is best understood by considering the components of priority setting:
(1) Identification of problems or opportunities. Priority­setting exercises often use expert opinion to define research issues. CBN feels it is essential that a perspective of the users influence the setting of research priorities. Therefore, case studies, and other sources of farmer perspective, are input to CBN.
(2) Solution definition. When a problem (or opportunity) identified by cassava farmers and processors can be "translated" into a technological problem, it must be further specified. For example, in both Tanzania and China, farmers reported declining yields and poor soils. The cause of this problem must be defined before biotechnology, or any other approach, can offer a solution. Is potassium limiting? Are mycorrhizal associations inadequate? Is the soil eroding? Are the components of low yield on poor soils the same in both places, or quite different?
Disciplinary scientists and cassava users work together to define a problem and to choose between possible solutions. There may be multiple avenues to a solution, with differences in cost, time frame, product, and application. For example, losses from rapid deterioration of harvested cassava roots could be prevented through genetic transformation to produce a cassava root with several months storage life, through plant breeding to produce a root with one or two weeks' storage life, or through immediate post­harvest processing methods to produce a storable processed product.
(3) Feasibility and ex­ante impact evaluation. The evaluation of potential effects of a technology requires estimates of expected changes at household, farming system, agro­ecosystem, and market levels, and of trade­offs between farmers, processors, and consumers. Estimation must involve cassava users, but cannot be handled by participatory research alone. Many areas of concern to CBN, such as cyanogenesis, delayed post­harvest deterioration, and starch quality, require data­intensive evaluation within complex higher­system levels, especially processing and market systems.
(4) Priority ranking. The first three stages constitute an information system that will aid in setting research goals, assessing research options, and rating the importance of problems. Most information is generated in the field but systematized within a data base, which in essence links the farmer to the laboratory. CBN is preparing a Geographic Information System (GIS) referenced database for cassava production distribution, agro­ecosystem zones, and cassava marketing and uses. This database, the first of its kind, will be used as the basis for overlay of micro­data from participatory surveys with cassava farmers and small­scale processors.

Role of biotechnology
The second issue related to the case studies, i.e. what can biotechnology offer to solve problems of cassava users, can be addressed for the short, medium and long term:

Short term. Micropropagation can dramatically speed up cassava variety multiplication. It has been used to rush plantlets of new varieties directly to farmers in South China. In Tanzania, where farmers' demand for planting material of desired varieties exceeds the supply, tissue culture could be considered for integration as a direct or intermediate step in variety multiplication. This may include research on adapting technologies to local conditions in order to reduce input requirements, such as electricity.
In the short term, microbial biotechnology can develop faster, safer, more nutritious cassava fermentation products. Superior microbe strains for starter cultures can be selected and tested with Tanzanian villagers. Microbial biotechnology could play a role in solving pollution from cassava starch extraction effluent in Asia.
Molecular markers and micropropagation are being used to optimize management of cassava germplasm collections that could be sources of cassava biodiversity for regions such as South China, where genetic uniformity poses potential risks. These techniques can help describe and efficiently conserve cassava diversity in, for example, Tanzania.
Molecular markers can be used to assess existing variability and heritability of user­preferred cassava characteristics such as early maturity, in­field storability, drought tolerance and cyanogen content. This information can be used to identify traits most amenable to improvement.

Medium term. Gene cloning and genetic transformation will be used to alter and study traits for which there is little or no genetic variation available in cassava. Examples are cyanogen metabolism and its relationship to cassava productivity, plant defense, and processing quality; post­harvest deterioration; starch metabolism and its implications for processing and new products; or root nutritional value.
Cassava genetic transformation is the bottleneck. Cassava transformation research is using all techniques available, with the ultimate goal of developing protocols for a broad range of genotypes. Improvements in the somatic embryogenesis system now permit far higher levels of cassava plant regeneration than a year ago, which are a necessary prerequisite for transformation. A new, highly regenerable embryogenic suspension system, possibly a breakthrough for cassava transformation, has been used to produce the first fully transgenic embryoids. Experimental cassava genotypes created through gene cloning and genetic transformation are expected to be ready for initial testing in 2 to 4 years, depending on funding level.

Long term. In the longer term (6­10 years), experience with genetically transformed cassava in basic biological research will identify which novel genotypes will be useful for breeding with locally­adapted varieties. Eventually, transformation methods effective with a broad range of genotypes may permit direct transformation of desired varieties.
The Tanzanian Lake Zone and South China were relatively free of cassava diseases when visited by CBN, thus biotechnology application for disease control are beyond the scope of this article. Worldwide however, cassava incurs major production losses due to diseases. African cassava mosaic virus (ACMV), Cassava bacterial blight (CBB) and cassava root rots are CBN priorities in this field.
A.M. Thro (CBN)/G. Henry (CIAT)/J.K. Lynam (Rockefeller Foundation)

User perspectives on cassava production in Tanzania and China  Recently two case studies were carried out under the aegis of CBN to gather information on practices, farmer perspectives and opinions related to cassava production, processing, use, and marketing in Tanzania and China. These two case studies are illustrative for the differences that exist in the production and use of cassava worldwide. The Rapid Rural Appraisal (RRA) approach was chosen for its fit to CBN's needs for a cost­effective and relatively quick method of gathering information. The approach includes the study of background information, on­site observation and discussion with cassava users by a multidisciplinary team, consisting of people both familiar and unfamiliar with the area. Tanzania Cassava is a central part of life in Lake Victoria Zone of North Tanzania, and a subject of considerable interest to villagers. They regularly collect cassava varieties on travels and compare them to local material. Major concerns are attacks by mealybug, drought, and the devastation when both occur together. In a village close to the Serengeti National Park, farmers said they did not have enough land to open new fields, resulting in declining cassava yields. According to these farmers, cassava yields are declining in this village as soil fertility decreased with continuous cropping. Lake Zone farmers grow many varieties to satisfy a range of needs: early maturity for food in a hurry; long­term in­ground storability for food security; suitability for processing into storable form vs. quick preparation; leaf production (cassava is an important green vegetable), and cooking fuel. Some varieties are grown for extreme "bitterness" to prevent damage by wild pigs and rats. Most villages grow two or three "bitter" varieties on most of their cassava area, and two to five or more "sweet" varieties. Both women and men frequently asked how the speed, safety, and nutritional value of their village's cassava processing methods could be improved. In the Lake Zone, cassava processing mainly includes dry­fermentation, sun­drying into the storage form "udaga", which is later pounded to flour to make "ugali" (a stiff porridge). Some is used in brewing beer. "Sweet" varieties are eaten boiled or raw. Some women had experimented (unsuccessfully) with mixtures of cassava and wheat flour, in an attempt to sustain their production of baked goods for sale in the local market during a shortage of imported wheat flour.  Any innovations affecting harvesting, processing, or small­scale sales will have specific effects on women. Men are traditionally responsible for most decisions in cassava production and processing, including decisions regarding large­scale sales to meet large cash needs such as school fees, food shortage, or other hardship. Comments by villagers suggested that decision­making involves consultation between men and women in a household. Women are responsible for most labour except land preparation. Excluding beer brewing, cassava processing is exclusively a women's activity in the Lake Zone, as are small­scale harvests to meet daily food needs, and small sales of cassava to purchase household necessities. China Cassava production and consumption in South China contrast with the above described practices in several ways. Only a decade ago, cassava in China was consumed on­farm by both family and pigs. Farmers now sell most of their cassava fresh or dried to starch factories. Farmers, especially women, complain about the amount of labour needed for chipping and drying cassava. Mostly hand­chipped with rudimentary tools, cassava chips are of low and varying quality resulting in a price discounts. Soil fertility problems resulting in declining yields are often mentioned as a major constraint. However, in most regions cassava is grown on the "waste lands", where few other crops could thrive. In contrast to cassava diversity in Tanzania, in South China there are at most two or three varieties found in a county. Although not noted by farmers, this includes a potential danger and urges the issue of biodiversity to be considered. Another potential problem is the waste disposal from cassava­starch processing. Although solid waste is turned into animal feed, the liquid and most toxic waste is often dumped in streams.

For further information:
Cassava Biotechnology Network (CBN)
c/o Centro International de Agricultura Tropical (CIAT)
AA 6713, Cali, Colombia
Fax +57 2 455 0237/6647243
E­mail a.thro@cgnet.com

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