Cassava (Manihot esculenta Crantz) is a staple food crop grown by smallholder farmers in the marg... more Cassava (Manihot esculenta Crantz) is a staple food crop grown by smallholder farmers in the marginal regions of western, coastal and eastern Kenya. The objective of this study was to evaluate popular cassava varieties for yield and cyanide content in the arid and semi-arid regions of Kenya. The study was carried out at five sites located in three sub-counties of Nakuru county in Kenya. Treatments included a collection of 27 sweet cassava varieties obtained from Western Kenya. Results revealed significant variations among varieties in all sites, for all parameters measured. The highest yields were obtained at Subukia, with the variety MM99/0067 yielding up to 200 t ha-1. Cyanide content varied significant among the varieties and sites; and was high in most of the cultivars, with highest levels recorded in variety Rao Onyoni (17.3 mg100 g-1) grown at the Lare site. The highest dry matter content was recorded in variety Selele rabuor (60.5%), at the Solai III site. Participating farme...
In Kenya, Russian wheat aphid (RWA) and stem rust race TTKS ("Ug99") are the most devastating pes... more In Kenya, Russian wheat aphid (RWA) and stem rust race TTKS ("Ug99") are the most devastating pests of wheat. Severe infestations by RWA result in yield losses of up to 90% while epidemics of "Ug99" can cause up to 100% loss. The two pests combined have seriously affected farmer incomes forcing them to rely heavily on pesticides and increasing the cost of production. This study sought to evaluate a wheat line that has been developed to be resistant to both RWA and "Ug99" by pyramiding two major resistance genes. Three varieties were used in this study: "Kwale", a Kenyan high yielding commercial variety but susceptible to both RWA and "Ug99"; "Cook", an Australian variety carrying stem rust resistance gene Sr36 conferring immunity to "Ug99"; and "KRWA9", a Kenyan line resistant to RWA but with poor agronomic attributes. The F 1 of the double cross (DC F 1) was obtained by crossing the F 1 of "Kwale × Cook" and the F 1 of "Kwale × KRWA9". The DC F 1 population was subjected to sequential screening for both RWA and "Ug99" resistance. The surviving DC F 1 progenies were left to self pollinate in the field to obtain the DC F 2. The DC F 2 progenies were sequentially screened against RWA and "Ug99" to obtain a resistant population to both RWA and "Ug99". The yield and yield components of the new resistant line were compared with the three parents. Results showed that the DC F 2:3 had higher yields than the three parents based on 1000 kernel weight, weight of kernel per spike, and the actual yield in tons/ha, indicating that the genes were successfully introgressed. It is concluded that though races with virulence for Sr36 have been reported, the gene provides immunity to race "Ug99" and can be used as a component for "Ug99" resistance breeding together with other Sr genes.
Insights of antibiosis resistance in various chickpea cultivars against pod borer Helicoverpa arm... more Insights of antibiosis resistance in various chickpea cultivars against pod borer Helicoverpa armigera (Hubner) under laboratory condtions. The present study was carried out in order to investigate the level of resistance against H. armigera on different cultivars by adopting detach leaf and pod assay. In leaf detach assay, pooled mean of 2012 and 2013, significantly lower and maximum weight gain and percent gain recorded was 101.9 mg (88.5%); 382.3mg (317.4%), respectively for ICCV 097105 and ICCV 07306. During podding stage, lowest pod damage (%) was recorded 55 % (ICCV 92944) and highest pod damage recorded by ICC 3137, LL 550 and ICCV07306 (95 %).Highest pupal weight of one day old pupae was recorded on LL 550 (405.2 mg) and lower pupal weight in ICCV 097105 (202.4 mg). The present result gave clue for future in depth studies on weeds for developing either specific pheromone compound or repellant compound for the eco- friendly management of H. armigera.
The establishment of grape vineyards in the Midwestern USA is greatly hampered by the use of the ... more The establishment of grape vineyards in the Midwestern USA is greatly hampered by the use of the herbicide 2,4-D in grain crop fields. The overall goal of this study was to transform 'Chancellor' with the plant expressible bacterial tfdA gene to make it tolerant to 2,4-D. Embryogenic callus was infected and cocultivated with an Agrobacterium construct (LBA4404: pAL4404::tfdA); transformed callus was selected with kanamycin; kanamycin resistant callus was bulked and transformed cell lines identified by PCR. Three PCRpositive embryogenic callus lines were used to regenerate transgenic plants. Analysis of the plant lines for the presence of the tfdA gene by PCR and southern hybridization confirmed its stable integration in their genomes. Transgenic 'Chancellor' grape plants regenerated from these calli proved to be resistant to up to 10 kg•ha-1 of a commercial ester-formulation of 2,4-D, indicating positive expression of the tfdA gene and affording them protection from 2,4-D injury.
Abundant embryogenic callus was obtained from leaf and floral explants of ʺChancellorʺ grape by c... more Abundant embryogenic callus was obtained from leaf and floral explants of ʺChancellorʺ grape by continuous culture for 12 weeks on Nitsch and Nitsch basal medium supplemented with 9 μM 2, 4-D + 17 μM IASP + either 1 μM BA or 1 μM TDZ (ECIM) in darkness. They were successfully maintained by a five to six week subculture interval on NN medium containing 2 μM 2, 4-D + 0.2 μM TDZ + 4 μM IASP (LTMM). Near synchronous embryo developed from embryogenic callus on medium containing 10 μM IASP + 8 μM NOA + 1 μM TDZ + 1 μM ABA + 2.5 g/l AC (EDMM). Individually separated somatic embryos were germinated on both NN and half strength of MS containing 0.5 μM BA + 0.025 μM NAA, respectively; normal plantlet conversion from embryos was low (35%). Whole fruiting plants were obtained. Aberrant embryo development was characterized by failure to form functional shoot meristems following the initial cotyledon expansion during germination. These observations indicate that the embryo conversion stage of the regeneration is difficult and remains a limiting factor requiring more empirical experimentation for improvement in grape tissue culture.
I. INTRODUCTION II. HISTORY III. BOTANY A. Taxonomy and Nomenclature B. Morphology C. Reproductiv... more I. INTRODUCTION II. HISTORY III. BOTANY A. Taxonomy and Nomenclature B. Morphology C. Reproductive Biology D. Genetic Structure E. Biochemistry IV. HORTICULTURE A. Production 1. Propagation 2. Field Establishment 3. Field Cultivation 4. Fertilization 5. Diseases, ...
Horseradish has been reported to be frequently sterile and therefore difficult to improve by trad... more Horseradish has been reported to be frequently sterile and therefore difficult to improve by traditional sexual crosses. In this paper we report a simple method to perform embryo rescues on Murashige and Skoog medium without growth regulators. We then demonstrate the usefulness of the method by making crosses and self-pollinated seeds of several horseradish lines, rescuing the embryos in vitro,
Chickpea (Cicer arietinum L.) is a good alternative food-security legume crop in semi-arid tropic... more Chickpea (Cicer arietinum L.) is a good alternative food-security legume crop in semi-arid tropics since it is more drought tolerant than other legumes currently grown. Chickpea yields have however remained stagnant for the past 2-3 decades due largely to biotic and abiotic stress factors during production (ICRISAT, 2007). Amongst biotic factors, flower and pod feeding Lepidopterans (Helicoverpa armigera, Maruca testulalis, Etiella zinckenella, and Lampides spp) account for up to 85% loss in grain yield in Eastern and Southern Africa (Minja, 2001). Helicoverpa armigera (pod borer) alone causes 25-40% loss amounting to $325 million annually (ICRISAT, 1992; Sharma et al., 2005). Widespread use of insecticides to control Helicoverpa armigera in the recent past has made the pest develop considerable levels of resistance (Kranthi et al., 2002) and is causing concern due to fears of increased environmental pollution.
A tissue culture and plant regeneration protocol for salt marsh bulrush, Scirpus robustus, was de... more A tissue culture and plant regeneration protocol for salt marsh bulrush, Scirpus robustus, was developed. Callus was induced from seedling mesocotyl on Murashige and Skoog (MS) medium plus 1mg/l 2,4-dichlorophenoxyacetic acid (2,4-D). Thirty-one percent of the calli became embryogenic upon transfer to MS medium supplemented with 0.25mg/l 2,4-D. Limited plant regeneration via somatic embryogenesis was obtained after transferring the embryogenic callus to MS medium without growth regulators (MS0). The addition of 6-benzylaminopurine (BA) to the medium effectively increased the number of regenerated shoots and more shoots were regenerated on 3mg/l BA medium (HBA) than on 0.1mg/l BA medium (LBA). Transfer of the plants regenerated from BA-supplemented medium to MS0 medium further enhanced the development of the plants, which subsequently grew vigorously in potting soil in the greenhouse. Having a tissue culture and regeneration protocol for S. robustus makes it possible to take advantage of somaclonal variation for selecting lines of this species with characteristics desirable for wetland creation and restoration.
Cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) are two important biotic con... more Cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) are two important biotic constraints affecting cassava (Manihot esculenta Crantz) production in sub-Saharan Africa, and the deployment of cassava varieties dually resistant to both diseases is the most effective and realistic way of reducing losses. Crosses were carried out between a Tanzanian local cassava cultivar (Namikonga) and a South American cassava genotype (AR37-80) to develop dual-resistant progenies, and they were evaluated for two seasons at Naliendele in Southern Tanzania, which is a CMD and CBSD hot spot area. The CMD-resistant progenies had low foliar severities (≤1.8), similar to the CMD-resistant parent. The CBSD-resistant progenies had minimal foliar (≤2.0) and root necrosis (≤1.2) severities, similar to the CBSD resistant parent, whereas CBSD-tolerant progenies had severe foliar severities up to 3.3 but minimal root necrosis severities (≤1.2). Traits with minimal environmental influence also had high heritability (≥0.65) and high selection accuracy (≥0.70), and they included CMD foliar symptoms, CBSD foliar symptoms at 6 mo after planting, root necrosis, root necrosis incidence, root weight, root number per plant, and harvest index. Correlation analysis showed that the presence of disease reduces usable roots, root weight, root number per plant, and harvest index. Dual resistance can improve yield as observed in Namar 050 and Namar 371, which had high root weights of 27.5 and 28.2 t ha −1 with high genetic gains of 56.1 and 58.5%, respectively. Dualresistant progenies identified were Namar 050, Namar 100, Namar 130, Namar 200, Namar 334, Namar 371, and Namar 479, as they had minimal CMD and CBSD symptom severities (≤2.0) and could be used for breeding cassava varieties with superior characteristics.
Cassava landraces were evaluated for resistance to cassava brown streak disease (CBSD) for two cr... more Cassava landraces were evaluated for resistance to cassava brown streak disease (CBSD) for two cropping seasons at a disease hotspot area in Naliendele, Tanzania. Based on reactions to CBSD, several landraces including Chimaje, Mfaransa and Supa B were considered to be resistant to the disease while Kikwada, Mbuyu, and Nyoka were tolerant. ANOVA revealed that the largest sum of squares (SS) (41.9-86.7%) was attributed to the genotype of the cassava landraces, while a smaller proportion of SS (8.1-38.2%) was due to genotype by environment interactions for all traits tested, which included disease symptoms, root weight, number of roots per plant and dry matter content. Environment accounted for the smallest effect (0.01-26.3%), however, the mean squares was nonetheless significant for a few genotypes, which indicated that their disease expression was indeed influenced by the environment. Increased CBSD severity was associated with low temperatures and rainfall. Increased rainfall towards harvesting led to higher root weight but lower dry matter content in the first cropping season. Correlation analysis showed that the presence of CBSD symptoms reduces the amount of usable roots, total root weight, and root dry matter content. Many resistant/tolerant landraces also had high root weight and dry matter content, and they can be used by farmers to reduce CBSD losses. The landraces described here form novel sources of CBSD resistance that can be used for breeding disease-resistant cassava varieties with superior agronomic characteristics.
The use of herbicides has revolutionized weed control in many crop production systems. However, w... more The use of herbicides has revolutionized weed control in many crop production systems. However, with the increasing development of weed resistances to many popular selective herbicides, the need has arisen to rethink the application of chemical weed control. Approaches to maintain the efficiency of chemical weed control include the discovery of new herbicide target sites in plants and the discovery/ synthesis of new, more potent herbicidal molecules. However, these approaches are expensive to execute, take considerably long times to succeed and may lead to increased chemical loads in the environment. Since many existing broad-spectrum herbicides are still effective, an alternative strategy adopted to ensure the safe use of broad-spectrum herbicides in a wide range of crops is the application of biotechnological techniques to engineer crop selectivity to these herbicides. In this review we summarize efforts being made to develop crop herbicide selectivity using biotechnology.
This is the peer reviewed version of the following article: Disparity between leaf and root sympt... more This is the peer reviewed version of the following article: Disparity between leaf and root symptoms and crop losses associated with cassava brown streak disease in four countries in eastern Africa, which has been published in final form at doi:10.1111/jph.12430. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. CBSD leaf and root symptoms Disparity between leaf and root symptoms and crop losses associated with cassava brown streak disease in four countries in eastern Africa.
In this study, we assessed the possible impacts of climate variability and change on growth and p... more In this study, we assessed the possible impacts of climate variability and change on growth and performance of maize using multi-climate, multi-crop model approaches built on Agricultural Model Intercomparison and Improvement Project (AgMIP) protocols in five different agro-ecological zones (AEZs) of Embu County in Kenya and under different management systems. Adaptation strategies were developed that are locally relevant by identifying a set of technologies that help to offset potential impacts of climate change on maize yields. Impacts and adaptation options were evaluated using projections by 20 Coupled Model Intercomparison Project—Phase 5 (CMIP5) climate models under two representative concentration pathways (RCPs) 4.5 and 8.5. Two widely used crop simulation models, Agricultural Production Systems Simulator (APSIM) and Decision Support System for Agrotechnology Transfer (DSSAT) was used to simulate the potential impacts of climate change on maize. Results showed that 20 CMIP5 ...
Wheat is the second most important cereal in Kenya. However, production is severely constrained b... more Wheat is the second most important cereal in Kenya. However, production is severely constrained by both abiotic and biotic stresses. Of the biotic stresses a devastating pest (Russian wheat aphid (RWA)) and a serious disease (stem rust race TTKS ("Ug99")) are currently the biggest problem for wheat producers in Kenya. Severe infestations by RWA may result in yield losses of up to 90% while "Ug99" infected fields may suffer 100% crop loss. The two pests combined are seriously affecting wheat farmers' incomes because of the heavy reliance on pesticides that increase the cost of production. This study attempted to develop and characterize wheat lines that are resistant to both RWA and "Ug99" by pyramiding two major resistance genes. Three wheat varieties: "Kwale", a Kenyan high yielding variety but susceptible to both RWA and "Ug99"; "Cook", an Australian variety carrying stem rust resistance gene Sr36 conferring immunity to "Ug99"; and "KRWA9", a Kenyan line with resistance to RWA but of poor agronomic attributes were used. A double cross F 1 (DC F 1) was obtained by crossing the F 1 of "Kwale × Cook" and the F 1 of "Kwale × KRWA9". The DC F 1 population was subjected to sequential screening for both RWA and "Ug99" resistance. Surviving DC F 1 progenies were left to self pollinate to obtain the F 2 of the double cross (DC F 2). The DC F 2 progenies were sequentially screened against RWA and "Ug99" to yield a population that was resistant to both RWA and "Ug99". Genotyping of the DC F 2:3 families were conducted to select homozygous resistant plants. Data indicated that the RWA and "Ug99" resistance genes were successfully pyramided. Though races with virulence for Sr36 have been reported, the gene provides immunity to race "Ug99" and can still be effectively used as a component for "Ug99" resistance breeding together with other Sr genes.
This paper examined the effect of variety attributes on adoption of improved sorghum varieties in... more This paper examined the effect of variety attributes on adoption of improved sorghum varieties in Kenya. Using data from a random sample of 140 farmers, a multivariate probit was used to identify variety-specific drivers of adoption. The results on the perception of farmers variety attributes showed that improved varieties had desirable production and marketing attributes while the local varieties were perceived to have the best consumption attributes. Evidence further indicated that the major sorghum variety attributes driving rapid adoption are taste, drought tolerance, yield, ease of cooking, and the variety's ability to fetch a price premium. Early maturity, a major focus of research was found to have no effect on the adoption decision. The findings of the study implied that, while developing improved seed varieties, breeders should also focus on non-yield attributes like taste and ease of cooking to increase adoption and satisfy the multiple needs of the farmers.
Cassava (Manihot esculenta Crantz) is a staple food crop grown by smallholder farmers in the marg... more Cassava (Manihot esculenta Crantz) is a staple food crop grown by smallholder farmers in the marginal regions of western, coastal and eastern Kenya. The objective of this study was to evaluate popular cassava varieties for yield and cyanide content in the arid and semi-arid regions of Kenya. The study was carried out at five sites located in three sub-counties of Nakuru county in Kenya. Treatments included a collection of 27 sweet cassava varieties obtained from Western Kenya. Results revealed significant variations among varieties in all sites, for all parameters measured. The highest yields were obtained at Subukia, with the variety MM99/0067 yielding up to 200 t ha-1. Cyanide content varied significant among the varieties and sites; and was high in most of the cultivars, with highest levels recorded in variety Rao Onyoni (17.3 mg100 g-1) grown at the Lare site. The highest dry matter content was recorded in variety Selele rabuor (60.5%), at the Solai III site. Participating farme...
In Kenya, Russian wheat aphid (RWA) and stem rust race TTKS ("Ug99") are the most devastating pes... more In Kenya, Russian wheat aphid (RWA) and stem rust race TTKS ("Ug99") are the most devastating pests of wheat. Severe infestations by RWA result in yield losses of up to 90% while epidemics of "Ug99" can cause up to 100% loss. The two pests combined have seriously affected farmer incomes forcing them to rely heavily on pesticides and increasing the cost of production. This study sought to evaluate a wheat line that has been developed to be resistant to both RWA and "Ug99" by pyramiding two major resistance genes. Three varieties were used in this study: "Kwale", a Kenyan high yielding commercial variety but susceptible to both RWA and "Ug99"; "Cook", an Australian variety carrying stem rust resistance gene Sr36 conferring immunity to "Ug99"; and "KRWA9", a Kenyan line resistant to RWA but with poor agronomic attributes. The F 1 of the double cross (DC F 1) was obtained by crossing the F 1 of "Kwale × Cook" and the F 1 of "Kwale × KRWA9". The DC F 1 population was subjected to sequential screening for both RWA and "Ug99" resistance. The surviving DC F 1 progenies were left to self pollinate in the field to obtain the DC F 2. The DC F 2 progenies were sequentially screened against RWA and "Ug99" to obtain a resistant population to both RWA and "Ug99". The yield and yield components of the new resistant line were compared with the three parents. Results showed that the DC F 2:3 had higher yields than the three parents based on 1000 kernel weight, weight of kernel per spike, and the actual yield in tons/ha, indicating that the genes were successfully introgressed. It is concluded that though races with virulence for Sr36 have been reported, the gene provides immunity to race "Ug99" and can be used as a component for "Ug99" resistance breeding together with other Sr genes.
Insights of antibiosis resistance in various chickpea cultivars against pod borer Helicoverpa arm... more Insights of antibiosis resistance in various chickpea cultivars against pod borer Helicoverpa armigera (Hubner) under laboratory condtions. The present study was carried out in order to investigate the level of resistance against H. armigera on different cultivars by adopting detach leaf and pod assay. In leaf detach assay, pooled mean of 2012 and 2013, significantly lower and maximum weight gain and percent gain recorded was 101.9 mg (88.5%); 382.3mg (317.4%), respectively for ICCV 097105 and ICCV 07306. During podding stage, lowest pod damage (%) was recorded 55 % (ICCV 92944) and highest pod damage recorded by ICC 3137, LL 550 and ICCV07306 (95 %).Highest pupal weight of one day old pupae was recorded on LL 550 (405.2 mg) and lower pupal weight in ICCV 097105 (202.4 mg). The present result gave clue for future in depth studies on weeds for developing either specific pheromone compound or repellant compound for the eco- friendly management of H. armigera.
The establishment of grape vineyards in the Midwestern USA is greatly hampered by the use of the ... more The establishment of grape vineyards in the Midwestern USA is greatly hampered by the use of the herbicide 2,4-D in grain crop fields. The overall goal of this study was to transform 'Chancellor' with the plant expressible bacterial tfdA gene to make it tolerant to 2,4-D. Embryogenic callus was infected and cocultivated with an Agrobacterium construct (LBA4404: pAL4404::tfdA); transformed callus was selected with kanamycin; kanamycin resistant callus was bulked and transformed cell lines identified by PCR. Three PCRpositive embryogenic callus lines were used to regenerate transgenic plants. Analysis of the plant lines for the presence of the tfdA gene by PCR and southern hybridization confirmed its stable integration in their genomes. Transgenic 'Chancellor' grape plants regenerated from these calli proved to be resistant to up to 10 kg•ha-1 of a commercial ester-formulation of 2,4-D, indicating positive expression of the tfdA gene and affording them protection from 2,4-D injury.
Abundant embryogenic callus was obtained from leaf and floral explants of ʺChancellorʺ grape by c... more Abundant embryogenic callus was obtained from leaf and floral explants of ʺChancellorʺ grape by continuous culture for 12 weeks on Nitsch and Nitsch basal medium supplemented with 9 μM 2, 4-D + 17 μM IASP + either 1 μM BA or 1 μM TDZ (ECIM) in darkness. They were successfully maintained by a five to six week subculture interval on NN medium containing 2 μM 2, 4-D + 0.2 μM TDZ + 4 μM IASP (LTMM). Near synchronous embryo developed from embryogenic callus on medium containing 10 μM IASP + 8 μM NOA + 1 μM TDZ + 1 μM ABA + 2.5 g/l AC (EDMM). Individually separated somatic embryos were germinated on both NN and half strength of MS containing 0.5 μM BA + 0.025 μM NAA, respectively; normal plantlet conversion from embryos was low (35%). Whole fruiting plants were obtained. Aberrant embryo development was characterized by failure to form functional shoot meristems following the initial cotyledon expansion during germination. These observations indicate that the embryo conversion stage of the regeneration is difficult and remains a limiting factor requiring more empirical experimentation for improvement in grape tissue culture.
I. INTRODUCTION II. HISTORY III. BOTANY A. Taxonomy and Nomenclature B. Morphology C. Reproductiv... more I. INTRODUCTION II. HISTORY III. BOTANY A. Taxonomy and Nomenclature B. Morphology C. Reproductive Biology D. Genetic Structure E. Biochemistry IV. HORTICULTURE A. Production 1. Propagation 2. Field Establishment 3. Field Cultivation 4. Fertilization 5. Diseases, ...
Horseradish has been reported to be frequently sterile and therefore difficult to improve by trad... more Horseradish has been reported to be frequently sterile and therefore difficult to improve by traditional sexual crosses. In this paper we report a simple method to perform embryo rescues on Murashige and Skoog medium without growth regulators. We then demonstrate the usefulness of the method by making crosses and self-pollinated seeds of several horseradish lines, rescuing the embryos in vitro,
Chickpea (Cicer arietinum L.) is a good alternative food-security legume crop in semi-arid tropic... more Chickpea (Cicer arietinum L.) is a good alternative food-security legume crop in semi-arid tropics since it is more drought tolerant than other legumes currently grown. Chickpea yields have however remained stagnant for the past 2-3 decades due largely to biotic and abiotic stress factors during production (ICRISAT, 2007). Amongst biotic factors, flower and pod feeding Lepidopterans (Helicoverpa armigera, Maruca testulalis, Etiella zinckenella, and Lampides spp) account for up to 85% loss in grain yield in Eastern and Southern Africa (Minja, 2001). Helicoverpa armigera (pod borer) alone causes 25-40% loss amounting to $325 million annually (ICRISAT, 1992; Sharma et al., 2005). Widespread use of insecticides to control Helicoverpa armigera in the recent past has made the pest develop considerable levels of resistance (Kranthi et al., 2002) and is causing concern due to fears of increased environmental pollution.
A tissue culture and plant regeneration protocol for salt marsh bulrush, Scirpus robustus, was de... more A tissue culture and plant regeneration protocol for salt marsh bulrush, Scirpus robustus, was developed. Callus was induced from seedling mesocotyl on Murashige and Skoog (MS) medium plus 1mg/l 2,4-dichlorophenoxyacetic acid (2,4-D). Thirty-one percent of the calli became embryogenic upon transfer to MS medium supplemented with 0.25mg/l 2,4-D. Limited plant regeneration via somatic embryogenesis was obtained after transferring the embryogenic callus to MS medium without growth regulators (MS0). The addition of 6-benzylaminopurine (BA) to the medium effectively increased the number of regenerated shoots and more shoots were regenerated on 3mg/l BA medium (HBA) than on 0.1mg/l BA medium (LBA). Transfer of the plants regenerated from BA-supplemented medium to MS0 medium further enhanced the development of the plants, which subsequently grew vigorously in potting soil in the greenhouse. Having a tissue culture and regeneration protocol for S. robustus makes it possible to take advantage of somaclonal variation for selecting lines of this species with characteristics desirable for wetland creation and restoration.
Cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) are two important biotic con... more Cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) are two important biotic constraints affecting cassava (Manihot esculenta Crantz) production in sub-Saharan Africa, and the deployment of cassava varieties dually resistant to both diseases is the most effective and realistic way of reducing losses. Crosses were carried out between a Tanzanian local cassava cultivar (Namikonga) and a South American cassava genotype (AR37-80) to develop dual-resistant progenies, and they were evaluated for two seasons at Naliendele in Southern Tanzania, which is a CMD and CBSD hot spot area. The CMD-resistant progenies had low foliar severities (≤1.8), similar to the CMD-resistant parent. The CBSD-resistant progenies had minimal foliar (≤2.0) and root necrosis (≤1.2) severities, similar to the CBSD resistant parent, whereas CBSD-tolerant progenies had severe foliar severities up to 3.3 but minimal root necrosis severities (≤1.2). Traits with minimal environmental influence also had high heritability (≥0.65) and high selection accuracy (≥0.70), and they included CMD foliar symptoms, CBSD foliar symptoms at 6 mo after planting, root necrosis, root necrosis incidence, root weight, root number per plant, and harvest index. Correlation analysis showed that the presence of disease reduces usable roots, root weight, root number per plant, and harvest index. Dual resistance can improve yield as observed in Namar 050 and Namar 371, which had high root weights of 27.5 and 28.2 t ha −1 with high genetic gains of 56.1 and 58.5%, respectively. Dualresistant progenies identified were Namar 050, Namar 100, Namar 130, Namar 200, Namar 334, Namar 371, and Namar 479, as they had minimal CMD and CBSD symptom severities (≤2.0) and could be used for breeding cassava varieties with superior characteristics.
Cassava landraces were evaluated for resistance to cassava brown streak disease (CBSD) for two cr... more Cassava landraces were evaluated for resistance to cassava brown streak disease (CBSD) for two cropping seasons at a disease hotspot area in Naliendele, Tanzania. Based on reactions to CBSD, several landraces including Chimaje, Mfaransa and Supa B were considered to be resistant to the disease while Kikwada, Mbuyu, and Nyoka were tolerant. ANOVA revealed that the largest sum of squares (SS) (41.9-86.7%) was attributed to the genotype of the cassava landraces, while a smaller proportion of SS (8.1-38.2%) was due to genotype by environment interactions for all traits tested, which included disease symptoms, root weight, number of roots per plant and dry matter content. Environment accounted for the smallest effect (0.01-26.3%), however, the mean squares was nonetheless significant for a few genotypes, which indicated that their disease expression was indeed influenced by the environment. Increased CBSD severity was associated with low temperatures and rainfall. Increased rainfall towards harvesting led to higher root weight but lower dry matter content in the first cropping season. Correlation analysis showed that the presence of CBSD symptoms reduces the amount of usable roots, total root weight, and root dry matter content. Many resistant/tolerant landraces also had high root weight and dry matter content, and they can be used by farmers to reduce CBSD losses. The landraces described here form novel sources of CBSD resistance that can be used for breeding disease-resistant cassava varieties with superior agronomic characteristics.
The use of herbicides has revolutionized weed control in many crop production systems. However, w... more The use of herbicides has revolutionized weed control in many crop production systems. However, with the increasing development of weed resistances to many popular selective herbicides, the need has arisen to rethink the application of chemical weed control. Approaches to maintain the efficiency of chemical weed control include the discovery of new herbicide target sites in plants and the discovery/ synthesis of new, more potent herbicidal molecules. However, these approaches are expensive to execute, take considerably long times to succeed and may lead to increased chemical loads in the environment. Since many existing broad-spectrum herbicides are still effective, an alternative strategy adopted to ensure the safe use of broad-spectrum herbicides in a wide range of crops is the application of biotechnological techniques to engineer crop selectivity to these herbicides. In this review we summarize efforts being made to develop crop herbicide selectivity using biotechnology.
This is the peer reviewed version of the following article: Disparity between leaf and root sympt... more This is the peer reviewed version of the following article: Disparity between leaf and root symptoms and crop losses associated with cassava brown streak disease in four countries in eastern Africa, which has been published in final form at doi:10.1111/jph.12430. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. CBSD leaf and root symptoms Disparity between leaf and root symptoms and crop losses associated with cassava brown streak disease in four countries in eastern Africa.
In this study, we assessed the possible impacts of climate variability and change on growth and p... more In this study, we assessed the possible impacts of climate variability and change on growth and performance of maize using multi-climate, multi-crop model approaches built on Agricultural Model Intercomparison and Improvement Project (AgMIP) protocols in five different agro-ecological zones (AEZs) of Embu County in Kenya and under different management systems. Adaptation strategies were developed that are locally relevant by identifying a set of technologies that help to offset potential impacts of climate change on maize yields. Impacts and adaptation options were evaluated using projections by 20 Coupled Model Intercomparison Project—Phase 5 (CMIP5) climate models under two representative concentration pathways (RCPs) 4.5 and 8.5. Two widely used crop simulation models, Agricultural Production Systems Simulator (APSIM) and Decision Support System for Agrotechnology Transfer (DSSAT) was used to simulate the potential impacts of climate change on maize. Results showed that 20 CMIP5 ...
Wheat is the second most important cereal in Kenya. However, production is severely constrained b... more Wheat is the second most important cereal in Kenya. However, production is severely constrained by both abiotic and biotic stresses. Of the biotic stresses a devastating pest (Russian wheat aphid (RWA)) and a serious disease (stem rust race TTKS ("Ug99")) are currently the biggest problem for wheat producers in Kenya. Severe infestations by RWA may result in yield losses of up to 90% while "Ug99" infected fields may suffer 100% crop loss. The two pests combined are seriously affecting wheat farmers' incomes because of the heavy reliance on pesticides that increase the cost of production. This study attempted to develop and characterize wheat lines that are resistant to both RWA and "Ug99" by pyramiding two major resistance genes. Three wheat varieties: "Kwale", a Kenyan high yielding variety but susceptible to both RWA and "Ug99"; "Cook", an Australian variety carrying stem rust resistance gene Sr36 conferring immunity to "Ug99"; and "KRWA9", a Kenyan line with resistance to RWA but of poor agronomic attributes were used. A double cross F 1 (DC F 1) was obtained by crossing the F 1 of "Kwale × Cook" and the F 1 of "Kwale × KRWA9". The DC F 1 population was subjected to sequential screening for both RWA and "Ug99" resistance. Surviving DC F 1 progenies were left to self pollinate to obtain the F 2 of the double cross (DC F 2). The DC F 2 progenies were sequentially screened against RWA and "Ug99" to yield a population that was resistant to both RWA and "Ug99". Genotyping of the DC F 2:3 families were conducted to select homozygous resistant plants. Data indicated that the RWA and "Ug99" resistance genes were successfully pyramided. Though races with virulence for Sr36 have been reported, the gene provides immunity to race "Ug99" and can still be effectively used as a component for "Ug99" resistance breeding together with other Sr genes.
This paper examined the effect of variety attributes on adoption of improved sorghum varieties in... more This paper examined the effect of variety attributes on adoption of improved sorghum varieties in Kenya. Using data from a random sample of 140 farmers, a multivariate probit was used to identify variety-specific drivers of adoption. The results on the perception of farmers variety attributes showed that improved varieties had desirable production and marketing attributes while the local varieties were perceived to have the best consumption attributes. Evidence further indicated that the major sorghum variety attributes driving rapid adoption are taste, drought tolerance, yield, ease of cooking, and the variety's ability to fetch a price premium. Early maturity, a major focus of research was found to have no effect on the adoption decision. The findings of the study implied that, while developing improved seed varieties, breeders should also focus on non-yield attributes like taste and ease of cooking to increase adoption and satisfy the multiple needs of the farmers.
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Papers by Richard Mulwa