oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Genetic diversity among farmer-preferred cassava landraces in Uganda
LF Turyagyenda, EB Kizito, ME Ferguson, Y Baguma, JW Harvey, P Gibson, BW Wanjala, DSO Osiru
African Crop Science Journal , 2012,
Abstract: Understanding of genetic diversity among a breeding population is an important requirement for crop improvement as it allows for the selection of diverse parental combinations and formation of heterotic pools for genetic gain. This study was carried out to determine genetic diversity within and among 51 farmer-preferred cassava (Manihot esculenta) landraces and 15 elite accessions grown in Uganda. Twenty six simple sequence repeat (SSR) markers used for genetic diversity assessment in this study revealed a total of 154 alleles, of which 24% were unique alleles present only in landraces. The genetic diversity and observed herozygosity in landraces were slightly higher than in elite accessions. Elite accessions clustered with some of the landraces indicating that there were some alleles in common. However, 58.8% of the landraces fell into 3 different clusters independent of the elite accessions. Including these landraces with unique alleles in cassava breeding schemes will increase the chances of producing farmer preferred adapted elite cultivars. The study also revealed genetic differentiation among accessions from different regions providing an opportunity for establishment of heterotic pools within a breeding programme.
G×E interaction effects on yield and yield components of cassava (landraces and improved) genotypes in the savanna regions of Nigeria
OO Aina, AGO Dixon, I Paul, EA Akinrinde
African Journal of Biotechnology , 2009,
Abstract: Genetic enhancement of cassava aimed at increasing production and productivity through the provision of broad-based improved germplasm is a major goal for cassava breeders. At the International Institute of Tropical Agriculture (IITA), Nigeria, 18 varieties comprising 12 landraces and 6 broad-based and improved varieties were evaluated at 4 locations in 3 years in a randomized complete block design in 4 replicates to determine variability among cultivars for yield components and adaptation to different environments. Results showed fresh root yield was significantly correlated (P < 0.001) with number of roots, harvest index, shoot weight and number of stands harvested. AMMI analysis partitioned main effects into genotypes, environments and G × E with all the components showing highly significant effects (P < 0.001). Environment had the greatest effect (70.3%), G × E interaction (19.0%) and genotype (10.7%). AMMI1 and unadjusted means selected the same winner in 9 out of 12 environments (75%), but differently in 3 environments. The GGE biplot (E and GxE interaction) delineated environments into mega-environments. Cultivar 4(2)1425 (moderately yielding) was the most stable and specifically adapted to Zaria. ABBEY-IFE, ATU-IWO and 2ND-AGRIC though moderately yielding were highly tolerant to CMD, suggesting a rich resource within the germplasm that could be enhanced for further genetic improvement of the crop.
G×E interaction effects on yield and yield components of cassava (landraces and improved) genotypes in the savanna regions of Nigeria
OO Aina, AGO Dixon, I Paul, EA Akinrinde
African Journal of Biotechnology , 2009,
Abstract: Genetic enhancement of cassava aimed at increasing production and productivity through the provision of broad-based improved germplasm is a major goal for cassava breeders. At the International Institute of Tropical Agriculture (IITA), Nigeria, 18 varieties comprising 12 landraces and 6 broad-based and improved varieties were evaluated at 4 locations in 3 years in a randomized complete block design in 4 replicates to determine variability among cultivars for yield components and adaptation to different environments. Results showed fresh root yield was significantly correlated (P < 0.001) with number of roots, harvest index, shoot weight and number of stands harvested. AMMI analysis partitioned main effects into genotypes, environments and G × E with all the components showing highly significant effects (P < 0.001). Environment had the greatest effect (70.3%), G × E interaction (19.0%) and genotype (10.7%). AMMI1 and unadjusted means selected the same winner in 9 out of 12 environments (75%),but differently in 3 environments. The GGE biplot (E and GxE interaction) delineated environments into ega-environments. Cultivar 4(2)1425 (moderately yielding) was the most stable and specifically adapted to Zaria. ABBEY-IFE, ATU-IWO and 2ND-AGRIC though moderately yielding were highly tolerant to CMD, suggesting a rich resource within the germplasm that could be enhanced for further genetic improvement of the crop.
Botanical and molecular evidences of landraces from the germplasm exclusively collected from Baluchistan, a centre of diversity for Lens culinaris
T Sultana, A Ghafoor
African Journal of Biotechnology , 2009,
Abstract: Botanical descriptors, total seed proteins, isozymes and RAPD markers were applied to identify landraces from indigenous lentil germplasm exclusively collected from the province of Baluchistan, Pakistan. The Germplasm revealed the prevalence of landraces, especially on the basis of isozymes and RAPD markers. Dversity explored through various techniques revealed validity irrespective of the sample size from a particular district, RAPD being the best choice for investigating both inter and intraaccession variation that is needed to extend to more germplasm study along with botanical descriptors.
Ethnobotany, Morphology and Genotyping of Cassava Germplasm from Malawi  [PDF]
I.R.M. Benesi,M.T. Labuschagne,L. Herselman,N. Mahungu
Journal of Biological Sciences , 2010,
Abstract: The objectives of this study were to collect and characterise Malawian cassava germplasm using ethnobotany, morphological and Amplified Fragment Length Polymorphism (AFLP) markers. Exploration of accessions with the help of indigenous knowledge was done. Ninety three accessions collected from farmers fields and commercial programs were planted and morphologically characterised at Chitedze Agricultural Research Station (Malawi). A subsample of 28 accessions was used for DNA fingerprinting. Preferences of farmers for traits in cassava varieties were diverse according to use and areas. Ethnobotany revealed wide genetic diversity in the germplasm, as did morphological characterisation, but morphological characterisation failed to uniquely differentiate all analysed accessions. AFLP markers showed narrow genetic diversity but managed to distinguish all accessions. Hence, there is need to use all three techniques at different levels to identify genetic diversity.
Genetic variability of Brazilian rice landraces determined by SSR markers
Borba, Tereza Cristina de Oliveira;Mendes, Clistiane dos Anjos;Guimar?es, élcio Perpétuo;Brunes, Tuliana Oliveira;Fonseca, Jaime Roberto;Brondani, Rosana Vianello;Brondani, Claudio;
Pesquisa Agropecuária Brasileira , 2009, DOI: 10.1590/S0100-204X2009000700009
Abstract: the objective of this study was to evaluate the genetic variability of rice (oryza sativa) landraces collected in brazilian small farms. twelve simple sequence repeat (ssr) markers characterized 417 landraces collected in 1986, 1987 and 2003, in the state of goiás, brazil. the number of landraces with long and thin grain type increased in the evaluated period, probably due to market demand. based on the molecular data, the genetic variability increased during this period and, as per to the factorial correspondence analysis, most of the accessions were grouped according to the year of collection. the incorporation of modern rice cultivars in landrace cultivation areas and the selection carried out by small farmers are the most probable factors responsible for increasing landrace genetic variability, during the evaluated period. genotype exchange between farmers, selection practice and local environmental adaptation are able to generate novel adapted allele combinations, which can be used by breeding programs, to reinitiate the process.
Genetic differentiation and geographical Relationship of Asian barley landraces using SSRs
Naeem, Rehan;Dahleen, Lynn;Mirza, Bushra;
Genetics and Molecular Biology , 2011, DOI: 10.1590/S1415-47572011005000014
Abstract: genetic diversity in 403 morphologically distinct landraces of barley (hordeum vulgare l. subsp. vulgare) originating from seven geographical zones of asia was studied using simple sequence repeat (ssr) markers from regions of medium to high recombination in the barley genome. the seven polymorphic ssr markers representing each of the chromosomes chosen for the study revealed a high level of allelic diversity among the landraces. genetic richness was highest in those from india, followed by pakistan while it was lowest for uzbekistan and turkmenistan. out of the 50 alleles detected, 15 were unique to a geographic region. genetic diversity was highest for landraces from pakistan (0.70 ± 0.06) and lowest for those from uzbekistan (0.18 ± 0.17). likewise, polymorphic information content (pic) was highest for pakistan (0.67 ± 0.06) and lowest for uzbekistan (0.15 ± 0.17). diversity among groups was 40% compared to 60% within groups. principal component analysis clustered the barley landraces into three groups to predict their domestication patterns. in total 51.58% of the variation was explained by the first two principal components of the barley germplasm. pakistan landraces were clustered separately from those of india, iran, nepal and iraq, whereas those from turkmenistan and uzbekistan were clustered together into a separate group.
Assessment of genetic diversity of local varieties of cassava in tanzania using molecular markers
F Herzberg, NM Mahungu, J Mignouna, A Kullaya
African Crop Science Journal , 2004,
Abstract: Twenty four arbitrarily selected cassava (Manihot esculenta Crantz) landraces, supplied by the germplasm collections in Kibaha and Ukiriguru research stations of Tanzania, were analysed by two different molecular marker techniques. Genetic distances on the basis of RAPD (random amplified polymorphic DNA) revealed separate clustering of almost all coast region-derived varieties. Inter-sequence-tagged repeat (ISTR) analysis, the second method, reproduced the geographical segregation, though the effect was less pronounced. Two genotypes were found to be very similar with either method, indicating a possible double accession. There is high overall genetic variability of the cassava germplasm. However, the variability is non- homogenous; rather it represents varieties of the same geographical origin grouped together. These findings are useful in the rationalisation of sampling and management of germplasm collections.
Informal “Seed” Systems and the Management of Gene Flow in Traditional Agroecosystems: The Case of Cassava in Cauca, Colombia  [PDF]
George A. Dyer, Carolina González, Diana Carolina Lopera
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0029067
Abstract: Our ability to manage gene flow within traditional agroecosystems and their repercussions requires understanding the biology of crops, including farming practices' role in crop ecology. That these practices' effects on crop population genetics have not been quantified bespeaks lack of an appropriate analytical framework. We use a model that construes seed-management practices as part of a crop's demography to describe the dynamics of cassava (Manihot esculenta Crantz) in Cauca, Colombia. We quantify several management practices for cassava—the first estimates of their kind for a vegetatively-propagated crop—describe their demographic repercussions, and compare them to those of maize, a sexually-reproduced grain crop. We discuss the implications for gene flow, the conservation of cassava diversity, and the biosafety of vegetatively-propagated crops in centers of diversity. Cassava populations are surprisingly open and dynamic: farmers exchange germplasm across localities, particularly improved varieties, and distribute it among neighbors at extremely high rates vis-à-vis maize. This implies that a large portion of cassava populations consists of non-local germplasm, often grown in mixed stands with local varieties. Gene flow from this germplasm into local seed banks and gene pools via pollen has been documented, but its extent remains uncertain. In sum, cassava's biology and vegetative propagation might facilitate pre-release confinement of genetically-modified varieties, as expected, but simultaneously contribute to their diffusion across traditional agroecosystems if released. Genetically-modified cassava is unlikely to displace landraces or compromise their diversity; but rapid diffusion of improved germplasm and subsequent incorporation into cassava landraces, seed banks or wild populations could obstruct the tracking and eradication of deleterious transgenes. Attempts to regulate traditional farming practices to reduce the risks could compromise cassava populations' adaptive potential and ultimately prove ineffectual.
Genetic diversity of Chinese summer soybean germplasm revealed by SSR markers
Hua Xie,Rongxia Guan,Ruzhen Chang,Lijuan Qiu
Chinese Science Bulletin , 2005, DOI: 10.1007/BF02897476
Abstract: There are abundant soybean germplasm in China. In order to assess genetic diversity of Chinese summer soybean germplasm, 158 Chinese summer soybean accessions from the primary core collection ofG. max were used to analyze genetic variation at 67 SSR loci. A total of 460 alleles were detected, in which 414 and 419 alleles occurred in the 80 Huanghuai and the 78 Southern summer accessions, respectively. The average number of alleles per locus was 6.9 for all the summer accessions, and 6.2 for both Huanghuai and Southern summer accessions. Marker diversity (D) per locus ranged from 0.414 to 0.905 with an average of 0.735 for all the summer accessions, from 0.387 to 0.886 with an average of 0.708 for the Huanghuai summer accessions, and from 0.189 to 0.884 with an average of 0.687 for the Southern summer accessions. The Huanghuai and Southern summer germplasm were different in the specific alleles, allelic-frequencies and pairwise genetic similarities. UPGMA cluster analysis based on the similarity data clearly separated the Huanghuai from Southern summer soybean accessions, suggesting that they were different gene pools. The results indicate that Chinese Huanghuai and Southern summer soybean germplasm can be used to enlarge genetic basis for developing elite summer soybean cultivars by exchanging their germplasm.
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.