In Burkina Faso, the existence of different races of Striga gesnerioides (Willd.) Vatke, with apparent variable aggressiveness on cowpea (Vigna unguiculata (L.) Walp) renders the breeding task very complex. Therefore, a number of studies was carried out from 2006 to 2009 in field, pot and ‘’in-vitro’’ to identify new sources of resistance to three prevailing Striga races, SR 1, SR 5 and a newly occurring Striga race named SR Kp and to understand the genetic pattern of the underlying resistance of cowpea germplasm to Striga races found in Burkina Faso. To achieve these objectives, the following investigations were initiated: (i) a participatory rural appraisal (PRA), a participatory variety selection (PVS) and grain quality survey were implemented to identify cowpea breeding priorities for Burkina Faso Striga hot-spots; (ii) the identification of sources of resistance in Burkina Faso germplasm, using three prevailing Striga races of S. gesnerioides as sources of inoculum; (iii) the identification of the mechanisms of resistance underlying the resistance to Striga in such genotypes; (iv) a study of combining abilities of selected parents through a diallel cross; (v) a study of the segregation patterns in crosses involving resistant and susceptible sources and a study of the allelic relationships between different resistance sources. The participatory studies conducted in 2007 and 2008 over three districts in Striga hotspots; there was no effective control method against Striga at farmers’ level. These investigations highlighted the importance of cowpea across all sites. Rain decline over time, low input use coupled with a poor extension system were the major constraints mentioned by farmers. Differential reactions of genotype KVx61-1 for Striga resistance suggested that different Striga races were prevailing in different areas. Farmers’ preferred traits in cowpea genotypes were oriented towards grain quality such as big sized grain, white seed colour and rough texture of cowpea grain, except in Northern-Burkina Faso, where farmers preferred brown-coloured grain for food. Cowpea was also seen as an income generating crop. An evaluation of 108 genotypes was done in 2007 in the field (rainy season) and in pots (off-season) for Striga resistance assessments. The screening trials enabled the identification of sources of resistance to S. gesnerioides. Genotypes KVx771-10, IT93K- 693-2, KVx775-33-2, Melakh and IT81D-994 are potential sources of resistance to all three Striga races with acceptable yield. Landraces were susceptible and late-maturing whilst most wild species were resistant but with unwanted shattering traits. A combining ability study for Striga resistance parameters conducted in pots and a resistance mechanism study conducted ‘’in-vitro’’ were performed using F1 populations from a 10 x 10 diallel cross. The general combining ability (GCA) effects were significant for the resistance parameters Striga emergence date (DSE), Striga height above soil (SH), cowpea grain weight (CGW), hundred grain weight (HGW) for all Striga races involved and Striga vigour (SVIG) for SR 5 and SR Kp. The pot-screening showed that, regardless of the SR used as inoculum, the additive genes were important in conferring Striga resistance for parameters DSE, SH, CGW and HGW. The selection of parents could therefore result in breeding advance. Complete dominance, partial, over-dominance and non-allelic interactions (epistasis or failure of some assumptions) were present for some parameters. The ‘’in-vitro’’ screening showed that additive genes were important, with high narrow sense heritability values for the resistance mechanisms Striga seed germination frequency (GR) for SR 1 and SR Kp, the frequency of Striga radicle necrosis before the penetration in cowpea rootlet (NBP) for SR 5, the frequency of Striga radicle necrosis after the penetration in cowpea rootlet (NAP) for SR 1 and SR Kp and the susceptibility ‘’in-vitro’’ (SIV) for SR 5 and SR Kp. The selection of parents can be useful in accumulating the genes for Striga resistance mechanisms in progenies. The F2 populations derived from crosses between Striga-resistant x susceptible genotypes were evaluated in Striga infested benches in 2008 and 2009. The segregation patterns suggest that single dominant genes govern Striga resistance. The test for allelism showed that two non-allelic genes were responsible for the resistance to S. gesnerioides in cowpea. A new Striga resistance gene seems to be involved in genotype KVx771-10 resistance to S. gesnerioides, which confers resistance to all studied Striga races. Gene 994-Rsg in genotype IT81D-994 which confers Striga resistance to SR 1 and gene Rsg 3 also conferring Striga resistance to SR 1 segregated differently for the resistance to SR 5 suggesting that they were different but both confer resistance to SR 5.

Sorghum (Sorghum bicolor) is an important cereal crop in sub-Saharan Africa. The parasitic weed Striga hermonthica is a major biotic constraint to sorghum production. A novel technology where planting seeds are coated with herbicide to kill Striga that attach to the roots of the host has been shown to be effective in protecting the cereal crop from Striga damage. However, the host plant must have herbicide tolerance. This technology has not been tested in sorghum because there are no herbicide tolerant sorghum varieties available in Kenya and is, therefore, unavailable for subsistence farmers. One of the ways in which genetic variation can be enhanced and herbicide resistance developed is through chemical mutagenesis with ethyl methane sulfonate (EMS). The objectives of this project, therefore, were to: 1) identify sorghum production constraints through farmer PRA in order to determine breeding priorities.in two Striga endemic districts in western Kenya; 2) develop an EMS mutagenesis protocol for sorghum and to enhance the genetic variability of the crop using chemical mutagenesis; 3) evaluate EMS-derived sorghum mutants for improved agronomic performance; 4) develop acetolactate synthase (ALS) herbicide resistance in sorghum and to characterize the mode of inheritance of the trait; 5) determine the effect of herbicide coating of seed of herbicide tolerant sorghum on Striga infestation. In order to determine breeding priorities and constraints in sorghum production and the likelihood of adoption of herbicide seed coating technology, a survey involving 213 farmers was conducted in two Striga endemic rural districts of Nyanza province in Kenya. Results indicated that local landraces like Ochuti, and Nyakabala were grown by more farmers (> 60%) than the improved varieties like Seredo and Serena (48%). Popularity of the landraces was linked to Striga tolerance, resistance to drought, bird damage and storage pests, yield stability and high satiety value. Major constraints to sorghum production were drought, Striga weed, storage pests, bird damage and poverty among the rural farmers. Important characteristics farmers wanted in new varieties were Striga and drought resistance, earliness, resistance to bird and weevil damage and good taste. Striga infestations in sorghum fields were > 70%. Cultural Striga control options were considered inadequate while inorganic fertilization and chemical control were considered effective but unaffordable. Farmers’ willingness to pay a premium of over 30% for a Striga solution gave indication that herbicide seed coating if effective could be adopted by farmers. As a prerequisite to development of herbicide resistance, a comparative study was carried out to determine optimum conditions for mutagenesis and to induce genetic variation in the sorghum. Two sorghum varieties were mutagenized using varying concentrations (0.1 to 1.5% v/v) of EMS and two exposure times (6h and 12h). In laboratory and greenhouse experiments, severe reduction of sorghum root and shoot lengths indicated effective mutagenesis. The LD50 based on shoot length reduction was 0.35% and 0.4% EMS for 6h for Seredo and Kari/mtama-1, respectively. The highest mutation frequency based on chlorophyll abnormalities was 56% for 0.3% EMS for 6h. In the M2 generation, phenotypic variances for panicle characteristics were increased on treatment with EMS. However, significant effects of exposure time and variety indicated the necessity of genotype optimization for some traits. In order to determine the significance of mutation breeding in sorghum, 78 mutant lines derived from EMS mutagenesis, their wild type progenitor (Seredo) and two local checks (Kari/mtama-1 and Serena) were evaluated for agronomic performance in two locations in Kenya. There were significant (P = 0.05) effects among entries for grain yield, 1000-seed weight and visual scores for height uniformity, head exertion, head architecture and overall desirability. The highest yielding entry-mutant line “SB2M13” had a yield of 160% and 152% relative to the wild type (Seredo) and the best check Kari/mtama-1, respectively. Mutant line “tag27” had the highest 1000-seed weight which was 133% relative to the wild type. Seven mutant lines were rated superior to the wild type for panicle characteristics, head exertion and overall desirability. However, the majority of mutants were inferior to the wild type for most characteristics. Superior mutant lines may be developed into direct mutant varieties after multi-location trials or used as breeding material for sorghum improvement. In order to develop acetolactate synthase (ALS) herbicide resistance in sorghum, over 50,000 seeds of Seredo were mutagenized with 0.3% EMS. Over four million M2 plants were screened using 20g ha-1 of the ALS herbicide, sulfosulfuron. Five mutants (hb46 hb12, hb462, hb56 and hb8) survived the herbicide treatment and were confirmed to be tolerant. Mutant lines displayed differential herbicide tolerance, and the general order of tolerance after spray or seed coat application was hb46 > hb12 > hb462 ~ hb56 > hb8. The LD50 values for herbicide application as a spray, or seed coat, showed mutant lines to be up to 20 and 170 fold, respectively, more resistant than the wild type. Chi square analysis of data from herbicide screening of F2 generation of mutant X wild type crosses indicated no difference from the Mendelian segregation of 1:2:1 indicating the herbicide tolerance was inherited as a single semi-dominant gene. Mutant X mutant crosses did not show allelism indicating that the tolerance in all five mutants could be a result of the same gene mutation. To determine effect of herbicide seed coating on Striga infestation, the five herbicide tolerant mutant lines, hb46, hb12, hb462, hb56 and hb8 and the wild type progenitor Seredo were coated with varying concentrations (0.5-1.5% g ha-1) of sulfosulfuron and planted in a Striga endemic field. There were significant (P=0.05) effects of herbicide concentration on Striga density, Striga flowering and seed set, and sorghum plant stand and biomass. All treatments with herbicide coated on sorghum seeds had lower Striga emergence. Coating sorghum seed with 1g ha-1 sulfosulfuron reduced Striga infestation, Striga flowering and Striga seed set by 47%, 52% and 77%, respectively, and was considered the most effective rate as it did not result in sorghum biomass reduction. Mutants displayed differential herbicide tolerance and Striga resistance. Combining seed coating with high herbicide tolerance and inherent Striga resistance would be most effective for Striga control. Overall, the study showed that EMS mutagenesis is effective in inducing variation in sorghum for several traits including herbicide resistance. The mutants developed in this study will be important for sorghum breeding and for protection of sorghum against the Striga weed. / Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2009.

Finger millet (Eleusine coracana (L.) Gaertn. ssp. coracana) is an important food, food security and cash crop in eastern and southern Africa where small-scale farmers grow it in low input farming systems. The crop has food security, nutritional, cultural, medicinal, and economic value with high industrial potential. Little research and hardly any breeding have been done on the crop leading to low yields and low production. A project was therefore implemented in western Kenya during 2004-2007 seasons to investigate the possible breeding contributions to enhance productivity and production of the crop. The research comprised a social survey, germplasm evaluation, appraisal of ethrel as a chemical hybridising agent (CHA), genetic analysis of yield, and resistance to blast and Striga, and breeding progress in developing new finger millet varieties. A participatory rural appraisal (PRA) was conducted in three districts during 2006 to position finger millet (FM) in the farming systems, production constraints, and variety diversity and farmer preferences. The PRA established the high rating the peasant farmers gave to finger millet among crop enterprises, using it for food, cash, brewing, ceremonies and medicinal purposes. Farmers cultivated many varieties ranging from five to nine in a district, but each district had its own popular variety. Farmers used the following criteria to select new cultivars: high yield potential; early maturity; resistance to blast disease, Striga, birds, drought, and lodging; large head size, dark grain colour, and good taste. This probably indicated the willingness of farmers to adopt new varieties. Farmers identified constraints to production as blast disease, Striga, wild FM, birds, rats, termites, lack of market, labour shortage, and low yield. The farmers’ variety selection criteria and production constraints underscored the need to improve finger millet varieties. Evaluation of 310 accessions for trait variability and association conducted during 2005 long rain (LR) season at two sites revealed wide variation among the accessions for yield and secondary traits. The best accessions grain yield was above the yield potential of 5,000- 6,000kg ha-1 reported in other environments. Accessions KNE 072 (7,833kg ha-1), GBK 028463 (7,085kg ha-1), GBK 029661 (6,666kg ha-1) and FMBT ACC#42 (6,566kg ha-1) were outstanding. The data showed the opportunity to select for yield directly because of its wide variability but indirect selection could also be used to exploit seedling vigour as shown by its high correlation to yield and direct and indirect positive effects on yield through plant height and single plant yield in path analysis. The wide genetic variability among the genotypes for several traits indicated high potential to breed new and better finger millet varieties. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.