Changes in the incidence and severity of Cassava mosaic virus disease, varietal diversity and cassava production in Uganda

A survey in 1994 assessed the incidence and severity of Cassava mosaic virus disease (CMD) in Uganda and the changes that had occurred since the previous survey in 1990–92. Three counties in each of 27 districts were selected and 15 fields were assessed per county. CMD occurred in each of the 1215 fields surveyed and the overall incidence within fields was 64% compared with 52% in the same districts in 1990–92. Mean incidence differed significantly between districts and between counties within some districts. The incidence and severity of CMD had increased in 20 and 23 of the 27 districts, respectively, compared with 1990–92, indicating the continued progress of the epidemic that was first reported in Uganda in 1988. In all but three districts, there had been a decrease in the total area of cassava. The number of different varieties that predominated in one or more fields had increased in 17 districts compared with 1990–92, although the total number of varieties encountered was little changed. Ebwanateraka was again the most widely grown variety but it was recorded less frequently and predominated or was co‐dominant in only two districts in 1994 compared with seven in 1990–92. The biggest decrease in the cultivation of Ebwanateraka had occurred in districts where there was a high incidence of CMD in 1990–92.     

Mechanisms Explaining Variety Naming by Farmers and Name Consistency of Rice Varieties in The Gambia

Mechanisms Explaining Variety Naming by Farmers and Name Consistency of Rice Varieties in The Gambia. Understanding variety naming by farmers is important for better understanding crop genetic diversity in farmer fields and its management by farmers. This paper describes variety naming of rice by farmers in The Gambia and presents mechanisms that explain naming diversity and consistency. Three types of variety names can be distinguished, referring to common old varieties, common new varieties, and uncommon varieties. Interview and plant data suggest that variety exchange affects variety naming within villages. As a result, variety names give information on the period of time a variety is used in a village, and on the flow of varieties between and within villages. Name consistency within and between villages results from and illuminates the dynamics of variety exchange within and between villages.     

Quantitative trait loci controlling cyanogenic glucoside and dry matter content in cassava (Manihot esculenta Crantz) roots

Cassava (Manihot esculenta Crantz) is a starchy root crop grown in the tropics mainly by small-scale farmers even though agro-industrial processing is rapidly increasing. For this processing market improved varieties with high dry matter root content (DMC) is required. Potentially toxic cyanogenic glucosides are synthesized in the leaves and translocated to the roots. Selection for varieties with low cyanogenic glucoside potential (CNP) and high DMC is among the principal objectives in cassava breeding programs. However, these traits are highly influenced by the environmental conditions and the genetic control of these traits is not well understood. An S(1) population derived from a cross between two bred cassava varieties (MCOL 1684 and Rayong 1) that differ in CNP and DMC was used to study the heritability and genetic basis of these traits. A broad-sense heritability of 0.43 and 0.42 was found for CNP and DMC, respectively. The moderate heritabilities for DMC and CNP indicate that the phenotypic variation of these traits is explained by a genetic component. We found two quantitative trait loci (QTL) on two different linkage groups controlling CNP and six QTL on four different linkage groups controlling DMC. One QTL for CNP and one QTL for DMC mapped near each other, suggesting pleiotrophy and/or linkage of QTL. The two QTL for CNP showed additive effects while the six QTL for DMC showed additive effect, dominance or overdominance. This study is a first step towards developing molecular marker tools for efficient breeding of CNP and DMC in cassava.     

Multi-trait evolution of farmer varieties of bread wheat after cultivation in contrasting organic farming systems in Europe

Because of the lack of varieties for organic agriculture, associations of organic farmers in several European countries have begun cultivating landraces and historic varieties, effectively practicing in situ conservation of agricultural biodiversity. To promote agrobiodiversity conservation, a special list for "conservation varieties" was implemented in 2008 by the EU because for any exchange and marketing of seeds in the EU, a variety must be registered in an official catalog. Our study aimed at improving knowledge on the phenotypic diversity and evolution of such varieties when cultivated on organic farms in Europe, in order to better define their specific characteristics and the implications for the registration process. We assessed multi-trait phenotypic evolution in eight European landraces and historic varieties of bread wheat and in two pureline variety checks, each grown by eight organic farmers over 2?years and then evaluated in a common garden experiment at an organic research farm. Measurements on each farmer's version of each variety included several standard evaluation criteria for assessing distinctness, uniformity and stability for variety registration. Significant phenotypic differentiation was found among farmers' versions of each variety. Some varieties showed considerable variation among versions while others showed fewer phenotypic changes, even in comparison to the two checks. Although farmers' variety would not satisfy uniformity or stability criteria as defined in the catalog evaluation requirements, each variety remained distinct when assessed using multivariate analysis. The amount of differentiation may be related to the initial genetic diversity within landraces and historic varieties.     

Current characteristics of cassava mosaic disease in postepidemic areas increase the range of possible management options

As a case study to document the current characteristics of cassava mosaic virus disease (CMD) in postepidemic areas, surveys were carried out, in 2003 and 2004, in Siaya District of western Kenya. This was an area affected by a severe CMD pandemic in the late 1990s. Data recorded on cassava varieties were CMD incidence, severity index and number of adult whiteflies. Farmers (174) were interviewed on their understanding of the disease and their knowledge and practice of management interventions. Cassava cultivation was being re‐established, but local landraces predominated. Resistant varieties were present 13% in 2003, and 4% in 2004, of the surveyed fields. Adhiambolera was the most common variety, occurring in 35% and 40% of fields in 2003 and 2004, respectively, and had an average CMD incidence of 82% in 2003 and 73% in 2004. By contrast, the CMD‐resistant variety Migyera had a low mean incidence (28% in 2003). The overall incidence for both years was 71%, consisting of 61% as a result of infection through planting diseased cuttings and 10% as a result of whitefly infection. In 2003, the total incidence was 72% and the average severity 2.7 (severity index), while in 2004 the incidence was 78% and the severity 2.6. There were significant severity variations in each division of the Siaya District during the 2 years except for Karemo and Ukwala. The abundance of whiteflies on the top five leaves of plants was low in 2003 but high in 2004, with means of 1 and 16, respectively, over the same seven divisions in both years, although this variation was thought to be because of seasonal factors. East African cassava mosaic virus‐Uganda was the predominant geminivirus present in every division. Phytosanitation by farmers was minimal, as evidenced by 29% of farmers using a selection of CMD‐free stems for planting and 15% using hand‐roguing for CMD management. Occurrence of more than 25% CMD‐free plants in 2004, moderate CMD severity and limited spread provide a conducive environment for the use of phytosanitation as a CMD control measure that can be immediately used by farmers growing their own cassava varieties.     

Can in vitro biology have farm-level impact for small-scale cassava farmers in Latin America?

Summary Cassava is uniquely suited for food security and economic development in unfavored areas of the tropics. Development research for cassava is an urgent need. In 1998, the Cassava Biotechnology Network (CBN) convened a workshop of cassava stakeholder groups in Latin America. After hearing an opening statement from representatives of small-scale cassava producers and processors, stakeholders formulated a consensus set of research and development (R&D) priorities. An adequate supply of good-quality planting material of desired varieties was clearly the most urgent, followed by R&D on market-value traits; yield losses due to pests, diseases, and drought; and cropping system flexibility. Two new projects are using in vitro techniques to address priorities of small-scale cassava farmers in Latin America. One project in Colombia combines a nongovernmental organization, a local farmers’ association, and the international research center, CIAT, to explore affordable micropropagation. Findings to date show that most culture medium components can be replaced with local products, and a rustic growth room permits good culture growth without electricity or air conditioning. Low-costs system(s) developed will be assessed as a local microenterprise. A second project, in Ecuador, couples local cassava germplasm (with oral histories and an in vitro back-up collection) and elite clones (introduced in vitro) with new concepts in agribusiness development, to restart local farmers’ cooperatives after the disastrous 1998–99 el Ni?o floods. The project was developed through group planning by the cooperatives, the local technical university, the national agricultural research program, and CIAT. Research to improve in vitro tools focuses on safe and stable conservation and exchange of cassava genetic resources, long-term, less expensive conservation, rapid clonal propagation, and ultimately, genetic transformation technologies to add desired traits to useful cassava varieties.     

Cassava Trait Preferences of Men and Women Farmers in Nigeria: Implications for Breeding

Nigeria is the world’s largest cassava producer, hosting a diverse array of cassava farmers and processors. Cassava breeding programs prioritize “common denominator” traits in setting breeding agendas, to impact the largest possible number of people through improved varieties. This approach has been successful, but cassava adoption rates are less than expected, with room for improvement by integrating traits in demand by farmers and processors. This paper aims to inform breeding priority setting, by examining trait and varietal preferences of men and women cassava farmer/processors. Men and women in eight communities in Southwest and Southeast Nigeria were consulted using mixed methods. Women and men had significantly different patterns of cassava use in the Southwest. Fifty-five variety names were recorded from the communities demonstrating high genetic diversity maintained by growers, especially in the Southeast. High yield, early maturity, and root size were most important traits across both regions, while traits women and men preferred followed gender roles: women prioritized product quality/cooking traits, while men placed higher priority on agronomic traits. Trait preference patterns differed significantly between the Southeast and Southwest, and showed differentiation based on gender. Patterns of access to stem sources were determined more by region and religion than gender.     

Traditional Maize Storage Methods of Mayan Farmers in Yucatan, Mexico: Implications for Seed Selection and Crop Diversity

For small-scale farmers who maintain genetically diverse crop populations, aspects of the storage of their seeds and harvest may be just as important for successful farming as those related to productivity. The community of Yaxcaba, Yucatan, Mexico was studied to understand how the conditions under which Maya farmers store their maize harvests influence their seed selection practices and the diversity of maize varieties grown. Most farmers select their maize seed based primarily on ear characteristics and secondarily on grain characters. Farmers incorporate storability concerns by selecting for an archetypal healthy ear and by conducting selection in several steps between harvest and planting of the subsequent crop generation. Most farmers store their maize harvest in the husk, initially in the field and then in rustic granaries constructed of logs and palm thatch, in which farmers conserve separately their different seed lots. All local landrace populations show morphological adaptation (principally husk characteristics) for local storage conditions, indicating that storability has been an important selection pressure on traditional maize. Storability also appears to be a key factor working against the straightforward adoption of improved maize seed in Yaxcaba. Local farmers value many qualities of improved maize varieties, but their principal complaint is that improved maize cannot be conserved reliably under local storage conditions. Nearly all farmers who utilize improved seed stock in Yaxcaba grow locally adapted or ‘creolized’ versions of improved varieties, displaying characteristics of local maize landraces that facilitate their storage.     

Factors Influencing Diversity of Farmers’ Varieties of Sweet Potato in Uganda: Implications for Conservation

Factors Influencing Diversity of Farmers’ Varieties of Sweet Potato in Uganda: Implications for Conservation. There is increasing concern that agricultural intensification is causing loss of crop biodiversity due to displacement of traditional farmers’ varieties by a small number of improved cultivars. Using ethnobotanical surveys, we assessed the implication of adoption of new sweet potato (Ipomoea batatas) cultivars on the maintenance of farmers’ varieties in Uganda. Other factors influencing varietal diversity were also assessed. A total of 102 farmer households distributed in the top three sweet potato production agro-ecological zones were interviewed. With the exception of released cultivars, very few varieties appeared in more than one region. The majority of the respondents indicated that they continue to plant some of the existing varieties when they adopt new cultivars. Loss of planting materials due to drought was a major constraint to maintaining varietal diversity for this vegetatively propagated crop. Limited land and lack of access to best management practices were also key constraints to maintenance of farmers’ varieties. The primary criteria for adopting new cultivars were higher yield, taste, and duration to maturity. Yield stability, tolerance to native biotic and abiotic stresses, and good taste were important for maintenance of currently grown varieties. Overall, criteria for variety selection varied with household characteristics including farmer age and gender, uses of the crop, micro-climatic conditions in the farmers’ fields, and level of access to agricultural extension. The observed heterogeneity in selection criteria, influence of social ties, and the role of environment in varietal maintenance have important implications for establishing breeding priorities and preservation of crop diversity.     

Disparity between Leaf and Root Symptoms and Crop Losses Associated with Cassava Brown Streak Disease in Four Countries in Eastern Africa

Cassava brown streak disease is endemic to the coastal regions of East Africa, and from around 2004, the disease resurged and became epidemic in the Great Lakes Region, where it continues to spread. In both these areas, cassava brown streak disease (CBSD) leaf symptoms occur at high incidences. However, it is the associated symptom of root rot (necrosis) in the starch‐bearing tissues that renders the root unfit for human consumption. Because the extent of root necrosis is not known until the crop is harvested and surveys require destructive sampling, root symptoms are much less frequently assessed than are the above‐ground symptoms on the leaves and stems. Surveys were undertaken in selected villages in Tanzania, Kenya, Uganda and Malawi to assess the incidence of CBSD leaf symptoms and the incidence and severity of root symptoms, to estimate the impact of the disease on household food security and on cassava processing. CBSD leaf symptoms were recorded at high incidences (40–90% in individual fields) in all fields visited throughout East Africa, but root necrosis incidence was lower than would be expected from the high incidence of leaf symptoms. Severe root necrosis at high incidence was found only on a few varieties, usually grown to a limited extent. It appears that varieties that are prone to root necrosis are being abandoned in favour of those with a lower propensity to develop root necrosis after infection by the virus.     

Thai elite cassava genetic diversity was fortuitously conserved through farming with different sets of varieties

Many in situ conservation programs have been developed to preserve plant landrace diversity and to promote its sustainable utilization, but little is known about the effectiveness of the developed programs in conserving plant genetic diversity. We investigated the effectiveness of an unregulated (i.e., unplanned or open) conservation system maintained by Thai farmers in conserving Thai elite cassava (Manihot esculenta Crantz) varieties. Specifically, we compared genetic diversity of 266 cassava clones that were collected from 80 farms in eight provinces with 16 cassava landraces and varieties released since the 1970s through genotyping with 35 informative simple sequence repeat (SSR) markers. The SSR analysis revealed a large regional heterogeneity in cassava diversity, with a strong genetic differentiation of the assayed clones among the 80 farms (19.8 %) and across the eight provinces (11.8 %). Significant associations were also found between SSR variation and farm agro-ecological factors or some farming practices. However, there was no significant genetic differentiation (0.9 %) between the 266 farm clones and 16 reference varieties. These findings suggest that the Thai elite cassava genetic diversity was fortuitously conserved by the farmers through farming with different sets of varieties. Implications of these findings are discussed with respect to on-farm conservation of plant genetic resources.     

Resource-Use Patterns in Swidden Farming Communities: Implications for the Resilience of Cassava Diversity

Resource-use patterns, especially through exchanges among farmers, may ultimately confer resilience to the local agrobiodiversity. We investigated the use of cassava ethnovarieties by swidden farming communities in Brazil, exploring the structure of networks depicting farmers and the varieties they cultivate. The emergent nested resource-use pattern indicated that all farmers shared a core of top-ranked ethnovarieties (most common/abundant) while some farmers also cultivate rarer varieties. This pattern may result of individual preferences. Due to the current loss of interest and cultivation area for traditional agriculture, we simulated the extinction of crop fields to evaluate whether nestedness conferred robustness to cassava diversity. The diversity of ethnovarieties of cassava tended to be conserved when farmers were randomly removed from the network than when we preferentially removed farmers with more diverse crop fields. Stem cuttings of ethnovarieties are commonly exchanged among farmers, thus the extinction of ethnovarieties within crop fields could be restored. Therefore, we suggest that the interplay between the farmer’s resource-use patterns and exchange system strengthens the resilience of cassava diversity, which is an important staple resource for such communities.     

Progress of cassava mosaic virus disease and whitefly vector populations in single and mixed stands of four cassava varieties grown under epidemic conditions in Uganda

Progress curves of cassava mosaic virus disease (CMD) and populations of the whitefly vector (Bemisia tabaci) were assessed using four cassava varieties grown alone and as a random mixture in two experiments established under epidemic conditions at a site near Kampala in southern Uganda. There were significant differences in final CMD incidence and in the areas under the disease progress curves between varieties when grown alone and as a mixture in both experiments. Variety Ebwanateraka had the highest incidence and SS4 the lowest, even though it supported the largest populations of adult whiteflies. The overall incidence of CMD in the mixture was similar to that in pure stands of the partially resistant Nase 2 and greater than in the resistant Migyera and SS4. Compared to pure stands, incidence of CMD in each component of the mixture was reduced significantly only in Ebwanateraka, whereas vector populations were less only in SS4 and Nase 2. On several observation dates the actual incidence of CMD and populations of adult whiteflies in the mixture were significantly less than expected values estimated from the results for the four varieties when each was grown alone. A highly significant positive relationship was established for each variety between peak populations of adult whitefly and leaf area index at the time. The implications of the findings and the scope for future research on the use of varietal mixtures for the management of CMD are discussed.     

Unmanaged sexual reproduction and the dynamics of genetic diversity of a vegetatively propagated crop plant, cassava (Manihot esculenta Crantz), in a traditional farming system

Occurrence of intervarietal or interspecific natural crosses has been reported for many crop plants in traditional farming systems, underlining the potential importance of this source of genetic exchange for the dynamics of genetic diversity of crop plants. In this study, we use microsatellite loci to investigate the role of volunteer seedlings (plants originating from unmanaged sexual reproduction) in the dynamics of genetic diversity of cassava (Manihot esculenta Crantz), a vegetatively propagated crop, in a traditional farming system in Guyana. A previous field study showed that farmers incorporate such plants into the germplasm for vegetative propagation, and that many of them are likely to be assigned by farmers to recognized varieties. Under strict vegetative propagation clonality of varieties is expected. The high proportion of polyclonal varieties observed suggests that incorporation of seedlings into the germplasm for propagation is a frequent event. The molecular variability assessed with microsatellite markers shows that there is high differentiation among heterozygous varieties, whereas populations of seedlings do not depart from the proportions expected under Hardy-Weinberg assumptions. Assignment of seedlings to a recognized variety on the basis of morphological similarity greatly increases genetic diversity within the variety. We argue that recombination and gene flow play a major role in the dynamics of genetic diversity of cassava in traditional farming systems. Documenting unmanaged sexual reproduction and its genetic consequences is a prerequisite for defining strategies of in situ conservation of crop plant genetic resources.     

Informal "seed" systems and the management of gene flow in traditional agroecosystems: the case of cassava in Cauca, Colombia

Our ability to manage gene flow within traditional agroecosystems and their repercussions requires understanding the biology of crops, including farming practices' role in crop ecology. That these practices' effects on crop population genetics have not been quantified bespeaks lack of an appropriate analytical framework. We use a model that construes seed-management practices as part of a crop's demography to describe the dynamics of cassava (Manihot esculenta Crantz) in Cauca, Colombia. We quantify several management practices for cassava--the first estimates of their kind for a vegetatively-propagated crop--describe their demographic repercussions, and compare them to those of maize, a sexually-reproduced grain crop. We discuss the implications for gene flow, the conservation of cassava diversity, and the biosafety of vegetatively-propagated crops in centers of diversity. Cassava populations are surprisingly open and dynamic: farmers exchange germplasm across localities, particularly improved varieties, and distribute it among neighbors at extremely high rates vis-à-vis maize. This implies that a large portion of cassava populations consists of non-local germplasm, often grown in mixed stands with local varieties. Gene flow from this germplasm into local seed banks and gene pools via pollen has been documented, but its extent remains uncertain. In sum, cassava's biology and vegetative propagation might facilitate pre-release confinement of genetically-modified varieties, as expected, but simultaneously contribute to their diffusion across traditional agroecosystems if released. Genetically-modified cassava is unlikely to displace landraces or compromise their diversity; but rapid diffusion of improved germplasm and subsequent incorporation into cassava landraces, seed banks or wild populations could obstruct the tracking and eradication of deleterious transgenes. Attempts to regulate traditional farming practices to reduce the risks could compromise cassava populations' adaptive potential and ultimately prove ineffectual.     

The VIRCA Project: virus resistant cassava for Africa

The VIRCA (Virus Resistant Cassava for Africa) project is a collaborative program between the Donald Danforth Plant Science Center, USA the National Crops Resources Research Institute, Uganda and the Kenya Agricultural Research Institute, Kenya. VIRCA is structured to include all aspects of the intellectual property, technology, regulatory, biosafety, quality control, communication and distribution components required for a GM crop development and delivery process. VIRCA's goal is to improve cassava for resistance to the viral diseases cassava brown streak disease (CBSD) and cassava mosaic disease (CMD) using pathogen-derived RNAi technology, and to field test, obtain regulatory approval for and deliver these products to small landholder farmers. During Phase I of the project, proof of concept was achieved by production and testing of virus resistant plants under greenhouse and confined field trials in East Africa. In VIRCA Phase II, two farmer-preferred varieties will be modified for resistance to CBSD and CMD, and lead events identified after molecular and field screening. In addition to delivery of royalty-free improved planting materials for farmers, VIRCA capacity building activities are enhancing indigenous capability for crop biotechnology in East Africa.     

Status and factors influencing on-farm conservation of Kam Sweet Rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) genetic resources in southeast Guizhou Province,China

Background

Kam Sweet Rice (KSR) is a special kind of rice landrace that has been cultivated for thousands of years in the borders of Guizhou, Hunan, and Guangxi Provinces of China, and is mainly distributed in southeast Guizhou Province of China currently. KSR has many unique qualities, including strong resistance to diseases, pests, and adverse abiotic conditions, difficulty of threshing, and well glutinous features. KSR germplasm resources are an indispensable material and cultural symbol in the production and daily life and customs of the Dong people. Related studies showed that numerous traditional KSR varieties and cultivation area of KSR decreased sharply from the Qing dynasty to 2015, but many KSR varieties are still conserved in Dong villages of southeast Guizhou Province compared to other areas. However, the number of KSR varieties that are conserved on farms in southeast Guizhou Province and factors influencing the erosion and conservation of KSR genetic resources is unclear. Therefore, this study was an on-farm conservation investigation of KSR genetic resource in China’s major KSR producing areas—Liping, Congjiang, and Rongjiang counties in Guizhou Province and influencing factors analysis of KSR abandonment and conservation.

Methods

The information of KSR conservation status and variety characteristics, typical villages, Dong’s cultural customs, and factors influencing KSR abandonment and conservation was obtained using ethno-biology methods, mainly through field research interviews, including participatory observation, semi-structured interviews, key informant interviews, focus group discussions, and cultural anthropology. The altitude, plant height, awn color and length, hull color, and rice color of 156 KSR accessions in 28 villages were recorded. The variety quantity and cultivation area of KSR were investigated in 33 ethnic villages. Questionnaire surveys were conducted in typical Dong villages to obtain local farmers’ attitudes toward cultivation and protection of KSR. We randomly selected 26 farmers from Sizhai village and 30 farmers from Huanggang village and chose 3 social characteristics including age, gender, and education levels of farmers, and adopted the method of face-to-face interviewing to complete the questionnaires. Then, we analyzed the correlation and determined the significance between farmers with different social characteristics and farmers’ attitudes to KSR development and protection using SPSS 17.0 software.

Results

(1) On-farm conservation status of KSR: a total of 156 KSR varieties were collected from 28 ethnic minority villages from 13 townships (accounting for 21% of three counties) in Liping, Congjiang, and Rongjiang counties. KSR accessions accounted for more than 90% of local rice varieties in each village. According to local farmers, although the quantity of KSR varieties decreased more than 50% in the investigated villages compared to the past 10–20 years, some Dong villages have still cultivated KSR, accounting for more than 50% of the rice field area in 10 villages. This result showed that many KSR varieties are still conserved by in Dong villages, and these KSR varieties have a high genetic diversity of phenotypes. (2) Typical villages investigation: the cultivation area of KSR in Congjiang was the highest, 6.7 times larger than Liping and eight times larger than Rongjiang. In addition, the cultivation area of KSR in Dong villages was larger than that in other ethnic villages, and villages that had a higher planting area of KSR had more KSR accessions. (3) Farmers’ attitude toward the development and conservation of KSR: Dong farmers hold the negative attitudes concerning the development of KSR resources, but they thought it is necessary to protect KSR landraces. Especially, a high level of education and female, young, and old farmers played more important roles in the cultivation and protection of KSR.

Conclusions

Until now, some Dong ethnic villages have still cultivated KSR for thousands of years in Qiandongnan area, although the number of varieties and the planting area of KSR have been greatly reduced. In addition, ethnic traditional culture and social customs were the main influencing factors of KSR conservation; economic, management, and policy factors were the main influencing factors of KSR abandonment. Through the analysis of the correlation between farmers with different social characteristics and their attitudes toward the cultivation, reasons for conservation and abandonment, development tendency, and protection of KSR, we found that a high level of education and female, young, and old farmers play more important role in the cultivation and protection of KSR. Therefore, in order to promote the protection and sustainable utilization of KSR, it is necessary to build on-farm conservation of KSR and improve the position of female farmers and the education level of young people, and encourage the old people to educate the middle-aged to conserve and protect KSR as well as Dong’s traditional culture and social customs. This study is of great significance to promote better protection and optimal utilization of KSR and enable the public, government, and related researchers pay more attention to conserving ethnic traditional cultures.

     

Role of seed flow on the pattern and dynamics of pearl millet (<Emphasis Type="Italic">Pennisetum glaucum</Emphasis> [L.] R. Br.) genetic diversity assessed by AFLP markers: a study in south-western Niger

We studied the regional genetic diversity and seed exchange dynamics of pearl millet landraces in south-western Niger. The genetic study was based on AFLP markers. We found significant genetic differentiation between landraces in different geographical areas of south-western Niger. However, the degree of differentiation was low insofar as only 1.9% of the total molecular diversity was due to regional differentiation, suggesting a relatively high gene flow. Anthropologic studies on farming practices have suggested that seed exchanges between farmers on a large geographical scale probably make a considerable contribution to this result. In order to test this hypothesis, the effects of seed exchange on the genetic diversity of landraces was analyzed on seed samples from two distant villages in contrasting areas of south-western Niger. Seeds imported by farmers into the southern village of Sina Koara did not differ significantly from locally grown landraces. By contrast, in the northern village of Alzou, several samples were genetically different from locally grown landraces and closer to southern accessions. These data suggest that the seed flow is preferentially from south to north, i.e. from an area with more favorable rainfall conditions. The potential consequences for the genetic diversity and adaptation of northern pearl millet landraces are discussed.     

Farmer Choice of Sorghum Varieties in Southern Mali

In southern Mali and throughout the semiarid tropics, small-scale family farmers are faced with the challenge of producing adequate harvests in difficult biophysical and socioeconomic environments. Professional plant breeders have had much difficulty developing modern varieties that outperform farmers’ traditional varieties in these environments, in part because of an incomplete understanding of why farmers choose the varieties they grow. Improved understanding of farmers’ varietal choices can contribute to collaboration between farmers and formal plant breeders. Based on a 15-month field study in Dissan, Mali, we examine farmer's choices among their traditional sorghum varieties in terms of one or more than one variety, and short-cycle or long-cycle varieties, and the interaction between these two choices. Results support our general hypothesis that farmers choose varieties to optimize outputs in the face of variation in the growing environment and in human managed inputs such as labor and tools.