PubMed | University of Minnesota, Agricultural Research Council Small Grain Institute, Purdue University, Kenya Agricultural and Livestock Research Organization KALRO and 2 more.
Type: Journal Article | Journal: PloS one | Year: 2016
We combined the recently developed genotyping by sequencing (GBS) method with joint mapping (also known as nested association mapping) to dissect and understand the genetic architecture controlling stem rust resistance in wheat (Triticum aestivum). Ten stem rust resistant wheat varieties were crossed to the susceptible line LMPG-6 to generate F6 recombinant inbred lines. The recombinant inbred line populations were phenotyped in Kenya, South Africa, and St. Paul, Minnesota, USA. By joint mapping of the 10 populations, we identified 59 minor and medium-effect QTL (explained phenotypic variance range of 1% - 20%) on 20 chromosomes that contributed towards adult plant resistance to North American Pgt races as well as the highly virulent Ug99 race group. Fifteen of the 59 QTL were detected in multiple environments. No epistatic relationship was detected among the QTL. While these numerous small- to medium-effect QTL are shared among the families, the founder parents were found to have different allelic effects for the QTL. Fourteen QTL identified by joint mapping were also detected in single-population mapping. As these QTL were mapped using SNP markers with known locations on the physical chromosomes, the genomic regions identified with QTL could be explored more in depth to discover candidate genes for stem rust resistance. The use of GBS-derived de novo SNPs in mapping resistance to stem rust shown in this study could be used as a model to conduct similar marker-trait association studies in other plant species.
Tsilo T.J.,Agricultural Research Council Small Grain Institute |
Kolmer J.A.,Cereal Disease Laboratory |
Anderson J.A.,University of Minnesota
Phytopathology | Year: 2014
Leaf rust, caused by Puccinia triticina, is the most common and widespread disease of wheat (Triticum aestivum) worldwide. Deployment of host-plant resistance is one of the strategies to reduce losses due to leaf rust disease. The objective of this study was to map genes for adult-plant resistance to leaf rust in a recombinant inbred line (RIL) population originating from MN98550-5/MN99394-1. The mapping population of 139 RILs and five checks were evaluated in 2005, 2009, and 2010 in five environments. Natural infection occurred in the 2005 trials and trials in 2009 and 2010 were inoculated with leaf rust. Four quantitative trait loci (QTL) on chromosomes 2BS, 2DS, 7AL, and 7DS were detected. The QTL on 2BS explained up to 33.6% of the phenotypic variation in leaf rust response, whereas the QTL on 2DS, 7AL, and 7DS explained up to 15.7, 8.1, and 34.2%, respectively. Seedling infection type tests conducted with P. triticina races BBBD and SBDG confirmed that the QTL on 2BS and 2DS were Lr16 and Lr2a, respectively, and these genes were expressed in the seedling and field plot tests. The Lr2a gene mapped at the same location as Sr6. The QTL on 7DS was Lr34. The QTL on 7AL is a new QTL for leaf rust resistance. The joint effects of all four QTL explained 74% of the total phenotypic variation in leaf rust severity. Analysis of different combinations of QTL showed that the RILs containing all four or three of the QTL had the lowest average leaf rust severity in all five environments. Deployment of these QTL in combination or with other effective genes will lead to successful control of leaf rust. © 2014 The American Phytopathological Society.
Terefe T.G.,Agricultural Research Council Small Grain Institute |
Visser B.,University of the Free State |
Herselman L.,University of the Free State |
Prins R.,University of the Free State |
And 3 more authors.
European Journal of Plant Pathology | Year: 2014
Samples of wheat and triticale infected with leaf rust were collected from 2008 to 2010 in South Africa to identify Puccinia triticina races. Races were identified based on their virulence profile on standard differential lines. Eight races were identified from 362 isolates. The dominant races were 3SA133 (syn. PDRS) in 2008 (78 %) and 2009 (34 %), and 3SA145 (47 %) in 2010. Race 3SA145 (CCPS) identified in 2009 was a new race in South Africa with virulence for the adult plant resistance gene Lr37. Another new race, 3SA146 (MCDS), was identified in 2010. Race 3SA146 is also virulent for Lr37 but unlike 3SA145, it is virulent for Lr1 and Lr23 and avirulent for Lr3ka and Lr30. Microsatellite analysis showed that 3SA145 and 3SA146 shared 70 % genetic similarity with each other, but only 30 % similarity with other races in South Africa, suggesting that both represent foreign introductions. In seedling tests of 98 South African winter and spring cultivars and advanced breeding lines, 27 % were susceptible to 3SA145 and 3SA146 but resistant to 3SA133. In greenhouse studies of 59 spring wheat adult plants, 19 % of breeding lines and 46 % of cultivars were susceptible to 3SA145, whereas 29 % of the lines and 53 % of cultivars were susceptible to 3SA146. The cssfr6 gene-specific DNA marker confirmed the presence of Lr34 gene for leaf rust resistance in a homozygous condition in 28 wheat entries. Five entries were heterogeneous for Lr34. Several entries which were susceptible as seedlings to the new races carried Lr34. These lines are expected to show lower levels of leaf rust as adult plants. Results of these studies indicate a continued vulnerability of South African wheat cultivars to new races and emphasise the importance of regular rust monitoring and the need to incorporate genes for durable resistance. © 2014 KNPV.
Tolmay V.L.,Agricultural Research Council Small Grain Institute |
Booyse M.,Agricultural Research Council Infruitec Nietvoorbij
South African Journal of Plant and Soil | Year: 2016
Resistance-breaking biotypes of Diuraphis noxia have been reported in both the USA and South Africa where commercial cultivars with genetic resistance to this pest have been deployed. The need to identify novel Russian wheat aphid (RWA) resistance for deployment against new biotypes of RWA has driven the recent re-evaluation and characterisation of resistance in landraces of bread wheat from germplasm collections worldwide. Twenty-three genotypes already in use in a South African pre-breeding programme were evaluated with the extended spectrum of South African RWA biotypes, while four genotypes not yet tested with South African RWA were screened with RWASA1, RWASA2, RWASA3 and RWASA4 for the first time. Five accessions, namely PI 94355, PI 243781, PI 361836, PI 626580 and the check CItr 2401, were resistant to all four South African RWA biotypes. The previously unused accessions PI 094355 and PI 243781 will be incorporated into the programme. The sixth accession resistant to RWASA4, namely PI 366518, is susceptible to RWASA2 and RWASA3 and may possibly be unique, meriting emphasis in pre-breeding activities. The use of multiple, distinct resistance genes, including those with a moderate resistance reaction, is seen as the most responsible strategy for the stewardship of genetic resistance to RWA in bread wheat. © 2016 Southern African Plant & Soil Sciences Committee
PubMed | Agricultural Research Council Small Grain Institute and Iwate Biotechnology Research Center
Type: | Journal: Molecular plant pathology | Year: 2016
Plant-pathogenic fungi cause diseases to all major crop plants world-wide and threaten global food security. Underpinning fungal diseases are virulence genes facilitating plant host colonization that often marks pathogenesis and crop failures, as well as an increase in staple food prices. Fungal molecular genetics is therefore the cornerstone to the sustainable prevention of disease outbreaks. Pathogenicity studies using mutant collections provide immense function-based information regarding virulence genes of economically relevant fungi. These collections are rich in potential targets for existing and new biological control agents. They contribute to host resistance breeding against fungal pathogens and are instrumental in searching for novel resistance genes through the identification of fungal effectors. Therefore, functional analyses of mutant collections propel gene discovery and characterization, and may be incorporated into disease management strategies. In the light of these attributes, mutant collections enhance the development of practical solutions to confront modern agricultural constraints. Here, a critical review of mutant collections constructed by various laboratories during the past decade is provided. We used Magnaporthe oryzae and Fusarium graminearum studies to show how mutant screens contribute to bridge existing knowledge gaps in pathogenicity and fungal-host interactions.
Mupambwa H.A.,University Of Fort Hare |
Dube E.,Agricultural Research Council Small Grain Institute |
Mnkeni P.N.S.,University Of Fort Hare
South African Journal of Science | Year: 2015
South Africa is increasingly reliant upon coal-fired power stations for electricity generation. Fly ash, a byproduct of coal combustion, contains a high total content of essential plant nutrients such as phosphorus, as well as heavy metals. If the plant nutrient bio-availability in fly ash could be improved, and the toxic element content reduced, fly ash could contribute significantly as a fertiliser source in South African agriculture. In this review, we summarise up-to-date information on the soil fertility and detoxification benefits of fly ash composting, and identify information gaps in this regard. We discuss scientific studies on the potential of fly ash based composts to supply plant nutrients and to contaminate the environment. We also explore the roles of earthworms and microorganisms in improving the decomposition process, and hence the fertiliser value of fly ash composts. Although much progress has been made, further research efforts are required to optimise microbial and earthworm activity in the decomposition process, which could further enhance nutrient supply benefits and reduce toxic elements at higher fly ash incorporation rates. © 2015. The Author(s).
De Villiers C.I.,Agricultural Research Council Small Grain Institute
South African Journal of Plant and Soil | Year: 2014
Fusarium head blight (FHB), mainly caused by Fusarium graminearum, is a serious disease of wheat, barley, oat and maize. Yield losses up to 40% have been reported and grain may contain mycotoxins that are harmful to humans and animals. In South Africa no wheat cultivars are resistant to FHB and no fungicides have been registered locally. Genetic resistance has the potential to provide cost-effective control, therefore Fusarium-resistant wheat germplasm from the Scab Resistant Screening Nursery (SRSN) obtained at the International Maize and Wheat Improvement Center (CIMMYT) was imported and screened for Type II FHB resistance in the glasshouse. SST 825 (susceptible control), Sumai 3 (resistant control) and 13 entries from the ninth SRSN were screened. An area under the disease progress curve was calculated for each entry. SST 825 and Sumai 3 showed the highest and lowest FHB severities, respectively. Two entries were similar to SST 825 in their response to FHB, whereas seven entries were moderately susceptible. Three entries were moderately resistant, one entry was resistant, and Sumai 3 was highly resistant. © 2014 © Southern African Plant and Soil Sciences Committee.
Terefe T.G.,Agricultural Research Council Small Grain Institute |
Visser B.,University of the Free State |
Pretorius Z.A.,University of the Free State
Crop Protection | Year: 2016
To determine phenotypic diversity of Puccinia graminis f. sp. tritici (Pgt), the cause of stem rust of wheat, samples of infected stems were collected during 2009-2013 from commercial wheat fields, experimental plots, and rust trap nurseries across major wheat growing regions of South Africa (SA). Pgt races were identified based on their avirulence/virulence profiles on seedlings of 20 standard and five supplemental differential lines. Nine Pgt races were identified from 521 isolates pathotyped. Predominant races were TTKSF (2SA88, South African race notation) with 39%-85% frequency and BPGSC + Sr27,Kiewiet,Satu (2SA105) with 10%-20% frequency. Race TTKSF is virulent on major resistance genes such as Sr5, Sr6, Sr9e, and Sr38 and is one of the variants of the highly virulent Ug99 race group originally detected in East Africa. Race TTKSP (2SA106), also a member of the Ug99 lineage, was detected in 2009 and 2010. A new race virulent on Sr31, PTKST (2SA107), was detected in 2009. Two new races, TTKSF + Sr9h (2SA88 + Sr9h) and BFBSC (2SA108), were identified in 2010. Race TTKSF + Sr9h is similar to TTKSF except for its virulence on Sr9h. Race BFBSC appears related to Pgt races characterized by avirulence for Sr5 and often attacking triticale. Simple sequence repeat (SSR) analysis indicated that race BFBSC forms part of the non-Ug99 group of South African Pgt races. Despite some similarity in avirulence/virulence phenotype with the non-Ug99 races, BFBSC represents a third distinct genetic lineage within this group. Genes Sr13, 14, 22, 25, 26, 29, 32, 33, 35, 36, 37, 39, 42, and 43 that are effective against the new and other Pgt races can be used in resistance breeding in SA. Races like PTKST and TTKSF + Sr9h were also reported in other Southern African countries suggesting that they probably spread to SA from neighbouring regions. The new races are additions to nearly 30 Pgt races identified since the early 1980s, and suggest continued variability of the Pgt population in SA. Therefore, surveys should be conducted regularly to timely detect and manage new races, and utilize the latter in screening and identification of effective sources of resistance. © 2016 Elsevier Ltd.
Mwadzingeni L.,University of KwaZulu - Natal |
Mwadzingeni L.,Agricultural Research Council Small Grain Institute |
Shimelis H.,University of KwaZulu - Natal |
Tesfay S.,University of KwaZulu - Natal |
And 2 more authors.
Frontiers in Plant Science | Year: 2016
Drought stress is one of the leading constraints to wheat (Triticum aestivum L.) production globally. Breeding for drought tolerance using novel genetic resources is an important mitigation strategy. This study aimed to determine the level of drought tolerance among diverse bread wheat genotypes using agronomic traits and proline analyses and to establish correlation of proline content and agronomic traits under drought-stress conditions in order to select promising wheat lines for breeding. Ninety-six diversegenotypes including 88 lines from the International Maize and Wheat Improvement Center (CIMMYT)’s heat and drought nurseries, and eight local checks were evaluated under greenhouse and field conditions during 2014/15 and 2015/16 making four testing environments. The following phenotypic traits were collected after stress imposed during the heading to anthesis period: the number of days to heading (DTH), days to maturity (DTM), productive tiller number (TN), plant height (PH), spike length (SL), spikelet per spike (SPS), kernels per spike (KPS), thousand kernel weight (TKW) and grain yield (GY) and proline content (PC). Analysis of variance, Pearson’s correlation coefficient, principal component and stress tolerance index were calculated. Genotypes with high yield performance under stressed and optimum conditions maintained high values for yield components. Proline content significantly increased under stress, but weakly correlated with agronomic traits under both optimal and water limited conditions. The positive correlation observed between grain yield and proline content under-drought stress conditions provides evidence that proline accumulation might ultimately be considered as a tool for effective selection of drought tolerant genotypes. The study selected 12 genotypes with high grain yields under drought stressed conditions and favorable adaptive traits useful for breeding. © 2016 Mwadzingeni, Shimelis, Tesfay and Tsilo.
Jankielsohn A.,Agricultural Research Council Small Grain Institute
Journal of Agricultural and Environmental Ethics | Year: 2015
Meat production in South Africa is on an increasing trend. In South Africa rising wealth, urbanisation and a growing middle class means South Africans are eating more processed and high-protein foods, especially meat and dairy products. These foods are more land- and water-intensive than fruit, vegetable and grain crops, and further stress existing resources. Traditional agricultural farms cannot keep up with the increasing demand for animal products and these farms are being replaced with concentrated animal feeding operations. There are a wide variety of problems caused by intensive livestock production. The concerns regarding factory farming in South Africa are social issues affecting food security, health concerns, environmental concerns and ethical concerns. In order to ensure food security in future we need to consider these concerns and support more sustainable systems to produce our food. Animal agriculture, like many other industries, works on the principles of supply and demand. By decreasing the demand for these products, we can decrease their production. Individuals can do this by becoming vegetarian or vegan, but also by simply cutting down one’s consumption of meat, eggs, and milk produced in intensive livestock farms. Less meat would be produced, and there would be less harm to local communities, lower risk of zoonotic disease outbreaks, fewer greenhouse gas emissions, less land degradation and decrease of biodiversity, less damage to our water supplies and fewer animals living lives of suffering in factory farms. © 2015, Springer Science+Business Media Dordrecht.