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|Title: ||Genetic diversity of common beans as impacted on by farmer variety selection for the management of bean root rots in South Western Uganda|
|Authors: ||Buah, Stephen|
Legumes as food
Genetically modified foods (GMOs)
|Issue Date: ||Sep-2010 |
|Abstract: ||Common bean (Phaseolus vulgaris L) is the world’s most important grain legume providing the major source of human dietary protein and animal feed. Uganda is the second largest bean consuming country after Rwanda in Eastern Africa where on average one person consumes 66 Kg of dry beans in a year. Many farmers also depend on this crop as a source of income because of its short maturity period, ease of handling and storage. However, common bean production in south western Uganda has been devastated in the recent past by epidemics of Pythium root rot disease that usually lead to total crop loss when susceptible varieties are cultivated during conditions that favour disease development.
Farmers, who traditionally use mixed varieties, have responded by making complex choices about seeds to include in their mixtures which do not solely represent their varietal preferences but an expression of agro-ecological dictation. Knowledge of patterns of genetic diversity among these landraces and their relationships is crucial for broadening the genetic base of the crop and maximising the use of available germplasm. The goal of this study was therefore to examine the role that both disease and farmer selection processes have had on the diversity of the crop in a major bean production area of Uganda.
Eighty mixed bean samples were collected from bean growers and traders from 11 sub-counties in Kabale and Kisoro districts. Farmer’s indigenous knowledge on the use of diversity to manage disease was examined using formal structured questionnaires. The mixtures were separated according to seed phenotypes and all were planted in the field for recording of agronomic characters in a non replicated experiment. Seed phenotypic and agronomic data was used to group the varieties into clusters from which a representative number was randomly sampled for further investigation using both morpho-agronomic characters and microsatellite markers.
The data show that up to 80% of seeds in the region is small-to-medium seeded and that farmers do mix more small seed varieties in their mixtures during the second rainy season (that is heavy and lasts longer) when root rot epidemics are more likely to occur. About 60% of the farmers agree that the number of varieties used now is greater than what they used 10 years ago. This was attributed to seed influx from the neighbouring Rwanda and Democratic Republic of Congo. Farmers are also aware of Pythium root rot and have used various means in an attempt to combat the disease. A pathological test using P. ultimum showed that only 16% of the landraces are resistant to Pythium and most of these were seeds collected from Kisoro district.
Cluster analysis based on morphological characters and simple sequence repeats (SSRs) revealed two distinct groups that correspond to the Andean and Mesoamerican gene pools with more genotypes falling in the Mesoamerican group. Six SSR primers generated 41 alleles with an average of 7.8 alleles per locus. A high allelic polymorphism of 71.7% was observed in the landraces with an average gene diversity of 29.9%. However, a lesser genetic diversity was found in Kisoro compared to Kabale district. Phaseolin analysis suggests introgression between the two gene pools which we attribute to genetic out-crossing in farmers’ fields. These inter-gene pool recombinants could be of interest to breeders and geneticists who may be interested in transferring useful gene between the two gene pools.
Overall, this study demonstrates the utilisation of genetic diversity of common bean by farmers to a greater extent to manage the disease indirectly through practices such as selection of small seeded varieties for the long and heavy rainy second season, mixing many more varieties, and replacing bush with climbing beans thus providing a selective advantage for Mesoamerican genotypes. This indigenous knowledge could accelerate breeding processes through collections and screening of specific farmer-selected varieties.|
|Description: ||A thesis submitted in partial fulfillment of the requirements for the award of the Masters of Science Degree in Molecular Biology and Biotechnology of Makerere University.|
|Appears in Collections:||Theses & Dissertations (Science)|
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