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Muraya M.M.,University of Hohenheim | Muraya M.M.,Leibniz Institute of Plant Genetics and Crop Plant Research | Sagnard F.,CIRAD UMR Developpement et Amelioration des Plantes | Sagnard F.,International Crops Research Institute for the Semi Arid Tropics ICRISAT Nairobi | Parzies H.K.,University of Hohenheim
Genetic Resources and Crop Evolution | Year: 2010

Identifying populations that have recently suffered a severe reduction in size is particularly important for their conservation as they are likely to suffer an increased risk of genetic erosion. We investigated the presence of recent bottlenecks in two wild sorghum populations from different eco-geographical conditions in Kenya employing 18 microsatellite markers. Microsatellite analysis showed high allelic diversity in the two populations, with a mean of 4.11 and 6.94 alleles per locus in the North-West wild sorghum population (NWWSP) and the South-East wild sorghum population (SEWSP), respectively. The mean observed heterozygosity was 0.34 and 0.56 in NWWSP and SEWSP, respectively. A large long-term effective populations size for both populations was observed assuming either an infinite allele model or a stepwise mutation model. There was no apparent loss of genetic variability for either of the populations. Test of heterozygosity excess indicated that a recent bottleneck in the two populations is highly unlikely. Furthermore, analysis of the allele frequency distribution revealed an L-shaped distribution which would not have been observed in case a recent bottleneck had reduced genetic variability in the two populations. The fact that most loci displayed a significant heterozygosity deficiency could be explained by population subdivision and the mixed mating system exhibited by wild sorghum populations. Furthermore, the possibility of a historical expansion of wild sorghum populations and presence of null alleles could not be ruled out. © 2010 Springer Science+Business Media B.V. Source

DeVilliers S.M.,International Crops Research Institute for the Semi Arid Tropics ICRISAT Nairobi | Hoisington D.A.,Indian International Crops Research Institute for the Semi Arid Tropics
African Journal of Biotechnology | Year: 2011

Biotech crops, including those that are genetically modified (GM) with Bacillus thuringiensis (Bt) endotoxins for insect resistance, have been cultivated commercially and adopted in steadily increasing numbers of countries over the past 14 years. This review discusses the current status of insect resistant transgenic crops and the often raised concern that its resilience is limited and that its efficacy will be compromised by insect resistance. We consider this trait as it is currently deployed in fields across the world as well as potential candidates that are at various stages of development along the pathway between the laboratory and deregulation. Future trends and prospects for biotechnological applications to mediate crop protection against insects are also considered. These include strategies employing stacked genes, modified Bt toxins, vegetative insecticidal proteins, lectins, endogenous resistance mechanisms as well as novel approaches. In addition, the benefits and risks associated with the adoption of GM insect resistant crops, especially for developing countries andresource-poor smallholder farmers are also discussed. © 2011 Academic Journals. Source

Muraya M.M.,University of Hohenheim | Muraya M.M.,Leibniz Institute of Plant Genetics and Crop Plant Research | Geiger H.H.,University of Hohenheim | Sagnard F.,CIRAD | And 6 more authors.
Genetic Resources and Crop Evolution | Year: 2012

Gene flow between cultivated and their wild relatives is one of the main ecological concerns associated with the introduction genetically modified (GM) cultivars. GM sorghum cultivar has been developed and its commercial production may be possible in the near future. The rate of gene flow depends on the fitness of wild × cultivated sorghum hybrids. The study aimed at estimating adaptive values of wild × cultivated sorghum hybrids in generations F 1, F 2, and F 3 compared to their parents. Artificial crosses of four wild sorghums, five cultivated sorghums, and two male sterile lines were made to produce the F 1 generation, which were advanced to F 2 and F 3. Each hybrid generation and their respective parents were evaluated for their adaptive value at two sites in a randomised complete block design with seven replicates. The resulting progenies did not show serious fitness penalties. Some hybrids were as fit as their respective wild parents and no consistent differences exist between the three generations studied. Thus, the resultant wild × cultivated hybrids may act as avenue for introgression. © 2011 Springer Science+Business Media B.V. Source

Mutegi E.,Kenya Agricultural Research Institute | Mutegi E.,International Crops Research Institute for the Semi Arid Tropics ICRISAT Nairobi | Mutegi E.,Ohio State University | Sagnard F.,International Crops Research Institute for the Semi Arid Tropics ICRISAT Nairobi | And 9 more authors.
Theoretical and Applied Genetics | Year: 2011

Understanding the extent and partitioning of diversity within and among crop landraces and their wild/weedy relatives constitutes the first step in conserving and unlocking their genetic potential. This study aimed to characterize the genetic structure and relationships within and between cultivated and wild sorghum at country scale in Kenya, and to elucidate some of the underlying evolutionary mechanisms. We analyzed at total of 439 individuals comprising 329 cultivated and 110 wild sorghums using 24 microsatellite markers. We observed a total of 295 alleles across all loci and individuals, with 257 different alleles being detected in the cultivated sorghum gene pool and 238 alleles in the wild sorghum gene pool. We found that the wild sorghum gene pool harbored significantly more genetic diversity than its domesticated counterpart, a reflection that domestication of sorghum was accompanied by a genetic bottleneck. Overall, our study found close genetic proximity between cultivated sorghum and its wild progenitor, with the extent of crop-wild divergence varying among cultivation regions. The observed genetic proximity may have arisen primarily due to historical and/or contemporary gene flow between the two congeners, with differences in farmers' practices explaining inter-regional gene flow differences. This suggests that deployment of transgenic sorghum in Kenya may lead to escape of transgenes into wild-weedy sorghum relatives. In both cultivated and wild sorghum, genetic diversity was found to be structured more along geographical level than agro-climatic level. This indicated that gene flow and genetic drift contributed to shaping the contemporary genetic structure in the two congeners. Spatial autocorrelation analysis revealed a strong spatial genetic structure in both cultivated and wild sorghums at the country scale, which could be explained by medium- to long-distance seed movement. © 2010 Springer-Verlag. Source

Muraya M.M.,Leibniz Institute of Plant Genetics and Crop Plant Research | Muraya M.M.,University of Hohenheim | Mutegi E.,International Crops Research Institute for the Semi Arid Tropics ICRISAT Nairobi | Mutegi E.,Kenya Agricultural Research Institute | And 7 more authors.
Theoretical and Applied Genetics | Year: 2011

Knowledge of mating systems is required in order to understand the genetic composition and evolutionary potential of plant populations. Outcrossing in a population may co-vary with the ecological and historical factors influencing it. However, literature on the outcrossing rate is limited in terms of wild sorghum species coverage and eco-geographic reference. This study investigated the outcrossing rates in wild sorghum populations from different ecological conditions of Kenya. Twelve wild sorghum populations were collected in four sorghum growing regions. Twenty-four individuals per population were genotyped using six polymorphic simple sequence repeat (SSR) markers to compute their indirect equilibrium estimates of outcrossing rate as well as population structure. In addition, the 12 populations were planted in a field in a randomised block design with five replications. Their progeny (250 individuals per population) were genotyped with the six SSR markers to estimate multi-locus outcrossing rates. Equilibrium estimates of outcrossing rates ranged from 7.0 to 75.0%, while multi-locus outcrossing rates (tm) ranged from 8.9 to 70.0% with a mean of 49.7%, indicating that wild sorghum exhibits a mixed mating system. The wide range of estimated outcrossing rates in wild sorghum populations indicate that environmental conditions may exist under which fitness is favoured by outcrossing and others under which selfing is more advantageous. The genetic structure of the populations studied is concordant with that expected for a species displaying mixed mating system. © 2011 Springer-Verlag. Source

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