Participation of farmers in plant breeding programmes has been reported to increase breeding efficiency. Farmers’ participation bridges the gap between variety development and dissemination and provides an opportunity for farmers to select varieties they prefer. The breeders on the others hand learn more about the farmers’ preferences and the environment in which the new varieties will be grown. However, the advantages of participatory breeding can best be realized when farmers’ indigenous technical knowledge (ITK) and experience complement the breeder’s scientific knowledge and skills. Cassava (Manihot esculenta Crantz) is a clonally propagated crop grown in diverse environments by small scale farmers for subsistence. Information on the roles of farmers and breeders at various stages of breeding and their ability to effectively participate in breeding programmes is limited. The objectives of this study were to determine: (1) cassava farmers’ preferences, production constraints and systems; (2) farmers’ selection criteria of cassava varieties; (3) genetic inheritance of farmer preferred traits; (4) how farmers and breeders complement each other at all stages and activities of cassava breeding. Participatory rural appraisal was conducted in three purposefully sampled districts of western Kenya based on ethnicity and agro-ecology. The results reveal that cassava is predominantly grown by small scale farmers with mean land size of 1.6 ha mainly under mixed cropping system for subsistence. The storage roots are eaten either after boiling or processing to flour. The majority of farmers (over 60%) are aware of the improved varieties but adoption rate is low (18% in some districts). The effects of pests and diseases, and the lack of high yielding varieties, capital, land, and disease free planting material are the most important constraints to cassava production. Farmers prefer tall, high yielding varieties that are resistant to diseases and pests, early maturing and long underground storability of harvestable storage roots. The districts surveyed significantly differed in popularity of utilization methods, traits preferences and relative ranking of the production constraints indicative of differences in ethnicity and agro-ecology. Three farmer groups from the three districts selected in western Kenya were used to study farmers’ variety selection criteria based on their own indigenous technical knowledge (ITK). The groups evaluated 15 (10 landraces and five improved) popular cassava varieties with concealed identities on their farms. The results revealed that farmers have effective methods of selecting varieties for most of their preferred traits. However, ITK alone cannot be used to evaluate all the important traits, such as cyanide content. The genetic inheritance of farmer preferred traits was determined through a genetic study. Six landraces and four improved varieties popular in western Kenya were crossed using the North Carolina mating design II to generate 24 full-sib families. The 24 families, represented by 40 siblings each, were evaluated at two sites, Kakamega and Alupe research station farms, in a 24 x 40 a-lattice design. General combining ability (GCA) and specific combining ability (SCA) mean squares were significant (P<0.05) for all traits evaluated except dry matter content and cyanide content. However, non-additive gene action predominated over additive gene for cassava mosaic disease (CMD) resistance, height to first branching, total number of storage roots per plant and fresh storage root yield in all environments. The best crosses were not necessarily obtained from parents with high general combining ability confirming the presence of non-additive gene action. The best performing parents per se did not necessarily have high GCA effects implying that selection based on the per se performance of parents may not always lead to development of superior hybrids. The clonal evaluation trial (CET) was established at Alupe research station and evaluated by the breeder and farmers from two districts independently. Three selection criteria were tested to determine the most appropriate approach to selection of varieties that meet both farmers’ and breeder’s preferences. The selection criteria were; farmers’ independent selection index (SI) derived from farmers’ selection criteria from each district, breeder’s negative selection and independent SI, and a participatory SI which combines farmers’ and breeder’s selection criteria. There was 14% overlap among the top 100 varieties selected by farmers from all districts and the breeder when independent SI were used. However, there was 49% overlap among the top 100 varieties selected by farmers using participatory SI and the breeder’s SI. The farmers and the breeder have a role to play in the variety development process. Varieties with traits preferred by both the farmers and the breeder are likely to enhance breeding efficiency and effectiveness. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

Cassava (Manihot esculenta Crantz) is an important food security crop in the semi-arid areas of Eastern Kenya. It provides food for more days in a calendar year than any other crop grown. Kenya has relied on varieties bred in other countries and because of this, local breeding methodologies and expertise are lacking. Access to appropriate varieties and adequate planting materials are major limiting factors to cassava production. Farmers grow late bulking landraces that take up to 18 mo to harvest. Efforts to introduce early bulking genotypes from IITA failed because of poor end-use quality. Local cassava breeding is necessary to alleviate the production constraints. Before a local breeding program can be established, farmers' preferences and production constraints must be identified and methodology appropriate to the Kenyan environment must be developed. The aims of this study were to identify farmer production constraints and preferences, to develop methods appropriate for cassava breeding in the semi-arid areas of Kenya, develop a population segregating for bulking period to estimate genetic variances that would explain the gene effects controlling yield components, and through participatory selection identify varieties that combine early bulking and preferred end-user traits. PRA tools, focus groups and individual interviews were used to identify production constraints and farmer preferences for cassava varieties. The PRA found that farmers grow 13 landraces in the area and 11 production constraints were identified and prioritised. The four most limiting in the order of importance were drought, lack of planting material, pests and diseases. Crosses between cassava varieties often do not produce much seed and the seed produced does not germinate well. Germination studies were done with open pollinated seeds to identify conditions favourable for seed germination in Kenya. The highest germination of the seeds was at 36°C. The control seeds had a higher germination percent (77%) compared to the seeds which were pre-heated at 36°C (57%). Crosses were made between selected IITA and local Kenyan genotypes following the NC 11 mating design to develop new genotypes which combine early bulking along with other farmer/end-user preferred characteristics. The hybrid progenies were evaluated in a seedling trial and clone genotypes advanced to a clonal trial and performance trial. The clonal trial was destroyed by red spider mites and cassava green mites, and only the tolerant 225 genotypes were planted in a performance trial that was harvested at 6, 7 and 8 mo after planting. The SCA effects were estimated to be 57% to 75% for most of the traits, except root number, which was mainly controlled by GCA effects (55%). Participatory selection of genotypes that combined early bulking and end-user qualities at the 7 and 8 mo after planting was done by farmers. Thirty genotypes that combined early bulking and end-user qualities were identified and ranked according to their performance in both agronomic and end-use traits using a selection index. A number of selected genotypes yielded more than three times the yield of the best parents, showing strong progress in breeding. Combining the farmers' preference aggregate score and the selection index based on the agronomic data, assisted in the final identification of the best genotypes developed in the breeding process. These results clearly demonstrated that it is possible to breed early bulking varieties with good end-use quality in the semiarid areas. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.