1,721,057 research outputs found
Solvent retention capacity and swelling index of glutenin as selection tools in South African bread wheat breeding
No full textTo release wheat varieties which comply with strict end-use quality criteria and to deal with the polygenic nature of quality breeding, a breeder needs to be informed of quality potential in early generation populations. This research aimed to determine the use of two small scale rapid tests, solvent retention capacity (SRC) and swelling index of glutenin (SIG) as selection tools for bread wheat quality breeding. Seventeen hard red winter wheat cultivars grown in the dryland summer rainfall region, 22 hard red spring wheat cultivars grown in the irrigated summer rainfall region and nine hard red spring wheat cultivars grown in the winter rainfall region were evaluated with the SRC test requiring a 0.3 g flour sample and the SIG test requiring a 0.04 g flour sample. The relationships of the SRC and SIG parameters with grain, milling, rheological and baking quality-related parameters were determined. Combined ANOVA showed highly significant differences (p≤0.001) among cultivars, environments and cultivar x environment interaction for the measured quality parameters, and the SRC and SIG parameters. Variation between genotypes was large and genotypes contributed significantly to the variance in lactic acid SRC, distilled water SRC, sodium carbonate SRC, sodium bicarbonate SRC, sucrose SRC and lactic acid SIG, indicating the potential of these parameters for selecting improved bread wheat quality. SRC values were significantly (p≤0.001) correlated with bread making quality parameters. The highest correlations were between lactic acid SRC and flour protein content (r=0.67, p≤0.001) in the winter rainfall region and lactic acid SIG and flour protein content (r=0.75, p≤0.001) in the irrigated summer rainfall region. Correlations between SRC, SIG and bread making quality parameters were inconsistent across regions, except for lactic acid SRC and lactic acid SIG with flour protein content and lactic acid SRC, sucrose SRC and lactic acid SIG with alveogram dough strength.
Regression coefficients for grain, milling, rheological and baking quality-related characteristics, as predicted by the SRC and SIG parameters, were low to moderately low (12% to 60%), indicating that the SRC and SIG parameters are poor predictors for most of the bread wheat quality parameters in South African wheat. Lactic acid SRC and distilled water SRC were the most common predictor variables, explaining the variation in the models for grain and milling characteristics. Lactic acid SRC, sucrose SRC and lactic acid SIG were responsible for contributing to the variation in most of the models for rheological and baking quality-related characteristics. The alkaline water retention capacity method (sodium bicarbonate SRC) was not effective in predicting bread wheat quality in this study and was initially developed for soft wheat applications. The lactic acid SRC solvent test was the most useful for assessing bread wheat quality in this study and is recommended for the evaluation of hard red winter and spring wheat bread making quality potential.Winter Cereal Trus
Genotype by environment interaction and resource optimization in sugarcane variety evaluation in Swaziland
No full textEnglish: The primary aim of this study was to assess the genotype by environment interaction (GEI) in the sugarcane Variety Evaluation Programme (VEP) of the Swaziland Sugar Association (SSA). This was achieved by pursuing the specific objectives: to evaluate the adaptability and phenotypic stability of imported sugarcane genotypes in Swaziland; to determine the optimum combination of locations, replications and crop-years necessary to provide an adequate level of discrimination among genotypes within the SSA VEP; and to undertake a combined data analysis of irrigated sugarcane variety trials in Swaziland and South Africa. Data from replicated trials established across locations, seasons and crop-years were used, and the GenStat® 17th Edition software was used for the analyses.
The study indicated that the main effects of variety, location and crop-years were significant, showing genetic diversity amongst the tested material and the complex environments under which they are tested. Consequently, these resulted in significant genotype by environment interactions (GEI). For sucrose yield, variety x location and variety x crop-year interactions were significant, while the higher order interaction (variety x location x crop-year) was not significant. Consistently, environments accounted for a larger portion of yield variation. The ratio of variety:GEI was largely dependent on the source of varieties. Varieties imported from Mauritius had a larger GEI effect than variety effect, while South African varieties had larger variety than GEI effects. This is attributed to the fact that conditions at which South African varieties are tested are similar to those in Swaziland. The grouping of test environments according to season clearly indicated that seasonal effects are stronger than location effects, as a result more emphasis should be put on testing across seasons than locations/soil types. Variety M1176/77 proved to be high yielding, stable and widely adapted to the sugarcane growing conditions of Swaziland, while M1400/86 was high yielding but specifically adapted to good draining soil conditions.
To model the optimum number of locations, replications and crop-years necessary to provide adequate discriminating ability among varieties, the broad sense heritability was used. The results indicated that four locations, four replications per trials, and four crop-years were sufficient for variety testing within the industry. While the data used for the combined analysis of irrigated sugarcane variety trials of Swaziland and South Africa were
largely unbalanced, the analysis indicated potential for SSA to utilise results from SASRI post-release trials to inform the industry’s variety recommendation. Both industries should consider pooling together testing resources and conduct variety evaluations at regional level. It is envisaged that making these adjustments will ensure that SSA derives maximum benefit from the resources used to test imported varieties.Afrikaans: Die hoofdoel van hierdie studie was om genotipe by omgewing interaksie (GEI) in die suikerriet Cultivar Evaluasie Program (VEP) van die Swaziland Suiker Assosiasie (SSA) te bepaal. Dit is bereik deur spesifieke doelwitte: om die aanpasbaarheid en fenotipiese stabiliteit van ingevoerde suikerriet genotipes in Swaziland te bepaal; om die optimum kombinasies van lokaliteite, herhalings en gewas-jare te bepaal wat nodig is om ‘n goeie vlak van diskriminasie tussen genotipes binne die SSA VEP te kry; en om gekombineerde data analise van besproeide suikerriet cultivar proewe in Swaziland en Suid Afrika te doen. Data van gerepliseerde proewe oor omgewings, seisoene en gewas-jare is gebruik, en GenStat® 17th uitgawe sagteware is gebruik vir analise.
Die studie het getoon dat hoofeffekte van cultivar, omgewing en gewasjare betekenisvol was, wat genetiese diversiteit in die getoetsde materiaal en die komplekse omgewings waar dit getoets is, getoon het. Dit het gevolglik gelei tot betekenisvolle genotipe by omgewings interaksies (GEI). Vir sukrose opbrengs, was cultivar x omgewing en cultivar x gewas-jaar interaksies betekenisvol, terwyl hoër vlak interaksie (cultivar x omgewing x gewas-jaar) nie betekenisvol was nie. Die omgewings het konstant vir ‘n groot deel van die variasie gesorg. Die verhouding van genotipe:GEI was grootliks afhanklik van die bron van die cultivars. Cultivars ingevoer vanaf Mauritius het ‘n groter GEI effek as cultivar effek getoon, terwyl Suid Afrikaanse cultivars groter cultivar as GEI effekte getoon het. Dit kan toegeskryf word aan die feit dat toestande waaronder Suid Afrikaanse cultivars getoets word, ooreenstem met toets-toestande in Swaziland. Die groepering van toetsomgewings volgens seisoen het duidelik getoon dat die seisoen effekte groter as omgewingseffekte was, daarom moet daar meer aandag gegee word aan toetsing oor seisoene as oor omgewings/grondtipes. Cultivar M1176/77 het hoë opbrengs gegee, was stabiel en wyd aangepas in die suikerriet groeitoestande van Swaziland, terwyl M1400/86 hoë opbrengs gegee het, maar spesifiek aangepas was vir grond met goeie dreinering.
Om die optimum aantal omgewings, herhalings en gewas-jare te modeleer wat goeie diskriminasie tussen cultivars sal gee, is breë sin oorerflikheid gebruik. Die resultate het aangedui dat vier lokaliteite, vier herhalings per proef en vier gewas-jare genoeg was vir cultivar toetsing binne die industrie. Terwyl die data wat gebruik is vir die gekombineerde analise van besproeide suikerriet cultivar proewe van Swaziland en Suid Afrika grootliks
ongebalanseerd was, het die analise die potensiaal vir SSA getoon om die resultate van SASRI se na-vrystellingsproewe te gebruik om industrie cultivar aanbevelings te maak. Die alternatief is dat beide industrië dit kan oorweeg om evaluasie hulpbronne bymekaar te gooi en om cultivar evaluasies op streek vlak te doen. Die verwagting is dat hierdie aanpassings sal sorg dat SSA maksimum voordeel trek uit die hulpbronne wat gebruik word om ingevoerde cutlivars te evalueer.Swaziland Sugar Association (SSA
The nature and causes of sugarcane genotype x environment interactions: integrated approaches to analysis and interpretation
No full textInformation on the nature and causes of G x E interactions in the rainfed parts of the South African sugar industry were lacking. The aim of this study was to systematically analyse, identify causes, and explore more comprehensive methods of analysing and understanding the G x E interactions of sugarcane, in order to optimize future MET networks. Data from plant breeding selection trials and post-release evaluation trials were systematically analysed using various statistical approaches combined with the use of soil and climatic data and crop models. Statistical methods based on multivariate methodologies such as GGE biplot, AMMI, and pattern analysis, were used to explore the effects of different environmental factors on sugarcane performance and agronomic traits. The age at harvest was the main factor causing different genotypic responses in the midlands region, which was unique in comparison with the coastal and hinterland regions that shared similar characteristics. In the midlands region, two testing sites were identified as being redundant and were recommended for removal from the trial network in favour of a testing site in a frost pocket. In the coastal/hinterland region, three sites were identified as being redundant. Along the coast, time of harvest influenced G x E interactions, with yields showing stronger correlations to stalk population in the early season and stalk weight in the late season. In all regions, site x ratoon interactions accounted for more variation in yield than genotype x ratoon interactions, suggesting that variation in ratoon performance is influenced more by site differences than genotype differences. The repeatable component of G x E interaction (genotype x site) was larger than the non-repeatable components (genotype x ratoon and genotype x site x ratoon) on the long cycle program on the coast, however, this was not the case on the short cycle. This suggests that more effort be placed on identifying more diverse test sites on the short cycle. In addition to providing direct recommendations for the industry selection programs, this study also illustrated novel methods of understanding sugarcane growth in different environments. The benefits of using a crop growth model to characterize sugarcane METs for water stress were illustrated throughout the study. The further use of the crop model to establish sugarcane growth phases also proved useful, and is likely to be more valuable when diverse datasets are analysed. Trials were characterized in terms of basic climatic and soil variables, which proved to be invaluable in understanding the causes of G x E interactions. The characterisation of the current sites ensures that future site selection will be more rigorous, as plant breeders will be more aware of the conditions to select for or against. The study showed that the integration of empirical and analytical statistical approaches was more valuable than using either approach in isolation, as is conventionally done in sugarcane. Additionally, these techniques were applied across many trial series and shown to produce repeatable results. The different strategies used to investigate sugarcane trait relations in this study have not been reported elsewhere, and future sugarcane studies dealing with similar traits (or other traits associated with lower level plant processes) may benefit from applying these methodologies. Furthermore, the integration of these multivariate methods with the largest ever simulation of sugarcane METs has opened new doors for the combined use of crop and statistical models in sugarcane research – an area not previously explored for this crop. The study illustrated novel methods of identifying factors responsible for sugarcane G x E interactions and introduced new ways of characterizing sugarcane METs through the use of crop growth models and supplementary environmental data.South African Sugarcane Research Institute (SASRI
Genetic variability of fruit characteristics in Kiyomi tangor progenies of citrus
No full textEnglish: In a citrus breeding programme, information on the breeding value of available parents and
the heritability of specific characters can be an important aid to the breeder when planning
controlled crosses for cultivar improvement. By quantifying the genetic variation in a
population the breeder can study the relationships between the hybrids and parents and
gain an understanding of how certain characteristics are inherited. Therefore a study was
undertaken to investigate the genetic variation in the progenies of six mandarin families,
where female parent Kiyomi tangor was crossed with male parents Dancy, Hansen, Rishon,
Roma, Shani and Sunburst mandarins. Data were collected over a two year period for the
fruit quality characteristics of rind colour, fruit size, fruit shape and fruit internal quality.
A significant level of variation was found between the families for all the fruit characteristics
studied. The within family variation was larger than the between family variation and
indicated a high level of genetic variation within the families, while the within tree variation
was found to be lower than the within family variation. Data collected over a two year period
showed significant year and year x family variation for many of the fruit characteristics. The
intraclass correlation coefficient, relevant to selection within the families, was found to be
fairly low for all the fruit characteristics studied and indicated that the variation found within
the families was only partly genetic and non-genetic factors contributed to the variation in the
phenotype. Therefore only two years of testing will not be reliable and a mean performance
over multiple years data is recommended for effective selection.
All the families showed an improvement in the population for rind colour, fruit shape and the
fruit internal quality while half of the families showed an improvement for fruit size. All the
families showed heterosis with some individuals being superior to both parents. Families
with male parents Hansen, Rishon, Shani and Sunburst had a rind colour superior to the
other families, while the Kiyomi x Rishon family had larger fruit with a more round fruit shape
and the Kiyomi x Roma family had a superior internal quality. This study revealed the male
parent to have a large influence on the progeny and male parents with a deeper orange rind
colour, larger fruit size, better fruit shape and superior internal quality resulted in families
with a greater improvement in the population. Therefore only male parents of the highest
quality should be used as parents in breeding programmes in order to increase the chance
of obtaining a superior new cultivar.Afrikaans: In In sitrus teelprogram is die teelwaarde van die beskikbare teelouers sowel as die erflikheid
van spesifieke eienskappe van onskatbare waarde tydens die beplanning van gerigte
kruisings vir spesifieke teeldoelwitte. Deur die genetiese variasie in In teelpopulasie te
kwantifiseer kan die teler die verwantskap tussen kruisingsnageslag en ouers bestudeer en
sodoende meer leer oor hoe sekere eienskappe oorgeërf word. Dit is dus met dié doel dat
die genetiese variasie in die nageslag van ses mandaryn families ondersoek is waar Kiyomi
tangor as vroulike ouer gekruis is met Dancy, Hansen, Rishon, Roma, Shani en Sunburst
mandaryne as manlike ouers. Data t.o.v. die vrugkwaliteitseienskappe van skilkleur,
vruggrootte, vrugvorm en interne kwaliteit is oor In tydperk van twee jaar versamel.
Daar is betekenisvolle variasie tussen die families t.o.v. alle vrugkwaliteitseienskappe
gevind. Die variasie t.o.v. vrugkwaliteitseienskappe binne families was groter as die variasie
tussen families en dui op In hoë genetiese variasie binne families, terwyl die variasie binne In
boom kleiner was as in In familie. Data ingesameloor In tydperk van twee jaar wys In
beduidende jaar x familie variasie t.o.v die meeste vrugeienskappe. Die intraklas
korrelasiekoeffisiënt wat gebruik word vir seleksie binne families was redelik laag vir al die
vrugeienskappe wat bestudeer is. Dit dui daarop dat die variasie van 'n fenotipe sowel
geneties as nie-geneties van aard is. Twee jaar van evaluering is nie voldende nie en
evaluering oor 'n aantal jare sal meer betroubaar wees vir doeltreffende seleksie.
AI die families het In verbetering in skilkleur, vrugvorm en interne kwaliteit getoon terwyl die
helfte van die families In verbetering in vruggroote gehad het. Heterose het in al die families
voorgekom en sommige individue van die nageslag het beter vertoon as beide die ouers.
Families met Hansen, Rishon, Shani en Sunburst as manlike ouers se skilkleur was beter as
die ander families, terwyl die Kiyomi x Rishon familie groter en ronder vrugte gehad het en
die Kiyomi x Roma familie In beter interne vrugkwaliteit. Hierdie studie het getoon dat
manlike ouers In beduidende invloed op vrugeienskappe van die nageslag het en dat
manlike ouers met In dieper rooi skilkleur, groter vrugte, beter vrugvorm en beter interne
kwaliteit aanleiding gegee het tot families waarvan die nageslag In groter verbetering getoon
het. Dit is dus belangrik dat slegs manlike ouers van uitstaande kwaliteit as teelouers
gebruik moet word in In teelprogram ten einde die kanse te verhoog om In uitstaande nuwe
kultivar te verkry
Prospects for marker assisted improvement of African tropical maize germplasm for low nitrogen tolerance
No full textNitrogen (N) is one of the most yield limiting nutrients in maize. However, farmers in sub-Saharan Africa (SSA) use very little N due to low income. Nitrogen Use Efficient (NUE) varieties can provide a partial solution to the problem through efficient N uptake and utilisation. Designing an effective breeding strategy for improving any trait of interest requires knowledge of quantitative genetic parameters, genomic regions associated with the traits and the use of efficient selection methods. The objectives of this study were to 1) assess the efficiency of indirect selection for grain yield under low N stress conditions through grain yield under optimum N conditions and through secondary traits under low N conditions, 2) identify single nucleotide polymorphism (SNP) marker loci significantly associated with grain yield and secondary traits under low N and optimumconditions, 3) map and characterize the quantitative trait loci (QTL) for grain yield and some secondary traits under optimum and low N stressed conditions, and 4) evaluate the accuracy of genomic selection for improvement of grain yield and other secondary traits under optimum and low N stressed environments. Results showed that genetic variance for grain yield was highly affected by low N stress, more than secondary traits, and low correlation was observed between optimum and low N environments for grain yield. This lead to low relative efficiency of indirect selection for grain yield under low N using grain yield under optimum conditions. The efficiency of indirect selection for grain yield under low N through secondary traits under low N conditions was also low. The efficiency of selection could be enhanced through identification of genomic regions and associated markers linked with grain yield under low N. A total of 158 putative protein coding genes associated with significant SNPs, of which seven linked with four known genes, were identified through a genome-wide association study. Markers associated with the putative and known genes could be used for marker assisted selection (MAS) in NUE breeding. In addition, a total of 155 significant QTL were identified for grain yield and six secondary traits under optimum and low N stress conditions in five doubled haploid (DH) lines derived from bi-parental lines. Interestingly, for grain yield, plant height, ear height and leaf senescence, the highest number of QTL were found under low N stressed environments compared to optimumconditions, indicating the availability of QTL under low N. However, no common QTL between optimum and low N stressed conditions were identified for grain yield and anthesis silking interval. Lack of significant QTL for grain yield common across populations and between management conditions indicates that MAS cannot be an efficient method for selection of grain yield under both optimum and low N conditions. An alternative to MAS is genomic selection, which uses information from all markers. In this study, the magnitude of both genome-wide and phenotypic predictions was negatively affected by low N stress, and phenotypic prediction ability was always higher than genome-wide prediction ability for all traits under both N conditions. Low N stress had a larger effect on the prediction accuracy for grain yield than other secondary traits. In general, genomic selection that uses information from all markers is a promising method for the improvement of the selection efficiency for grain yield under low N.Borlaug LEA
Genetic variability of fruit characteristics in Kiyomi tangor progenies of citrus
No full textIn a citrus breeding programme, information on the breeding value of available parents and the heritability of specific characters can be an important aid to the breeder when planning controlled crosses for cultivar improvement. By quantifying the genetic variation in a population the breeder can study the relationships between the hybrids and parents and gain an understanding of how certain characteristics are inherited. Therefore a study was undertaken to investigate the genetic variation in the progenies of six mandarin families, where female parent Kiyomi tangor was crossed with male parents Dancy, Hansen, Rishon, Roma, Shani and Sunburst mandarins. Data were collected over a two year period for the fruit quality characteristics of rind colour, fruit size, fruit shape and fruit internal quality. A significant level of variation was found between the families for all the fruit characteristics studied. The within family variation was larger than the between family variation and indicated a high level of genetic variation within the families, while the within tree variation was found to be lower than the within family variation. Data collected over a two year period showed significant year and year x family variation for many of the fruit characteristics. The intraclass correlation coefficient, relevant to selection within the families, was found to be fairly low for all the fruit characteristics studied and indicated that the variation found within the families was only partly genetic and non-genetic factors contributed to the variation in the phenotype. Therefore only two years of testing will not be reliable and a mean performance over multiple years data is recommended for effective selection. All the families showed an improvement in the population for rind colour, fruit shape and the fruit internal quality while half of the families showed an improvement for fruit size. All the families showed heterosis with some individuals being superior to both parents. Families with male parents Hansen, Rishon, Shani and Sunburst had a rind colour superior to the other families, while the Kiyomi x Rishon family had larger fruit with a more round fruit shape and the Kiyomi x Roma family had a superior internal quality. This study revealed the male parent to have a large influence on the progeny and male parents with a deeper orange rind colour, larger fruit size, better fruit shape and superior internal quality resulted in families with a greater improvement in the population. Therefore only male parents of the highest quality should be used as parents in breeding programmes in order to increase the chance of obtaining a superior new cultivar
Assessment of genetic diversity of sorghum [sorghum bicolor (l.) Moench] germplasm in East and Central Africa
No full textThe study of genetic diversity in crops has a strong impact on plant breeding and maintenance of genetic resources. Comprehensive knowledge of the genetic biodiversity of cultivated and wild sorghum germplasm is an important prerequisite for sustainability of sorghum production. Recurrent droughts resulting from climate change scenarios’ in many East and Central Africa countries, where sorghum is a significant arable crop, can potentially lead to genetic erosion and loss of valuable genetic resources. This study aimed at assessing the extent and pattern of genetic diversity and population genetic structure among sorghum accessions from selected countries in East and Central Africa (Sudan, Kenya, Uganda, Ethiopia, Eritrea, Rwanda and Burundi) using39 microsatellites markers. The studied loci were polymorphic and revealed a total of 941 alleles in 1108 sorghum genotypes. High levels of diversity were revealed with Sudan (68.5) having the highest level of genetic diversity followed by Ethiopia (65.3), whereas Burundi (0.45) and Rwanda (0.33) had the lowest level of genetic diversity. Analysis of molecular variance indicated, all variance components to be highly significant (p<0.001). The bulk of the variation was partitioned within countries (68.1%) compared to among countries (31.9%). Genetic differentiation between countries based on FST values was high and highly significant (FST=0.32). Neighbour-joining (NJ) analysis formed two distinct clusters according to geographic regions, namely the central region (Kenya, Burundi, Uganda and Rwanda) and the eastern region (Sudan, Ethiopia, and Eritrea). Population structure analysis revealed six distinct populations corresponding to NJ analysis and geographical origin of accessions. Countries clustered independently with small integration, which indicated the role of farmers’ practices in the maintenance of landrace identity and genetic diversity. The observed high level of genetic diversity indicated that germplasm from East Africa should be preserved from genetic erosion, especially in countries with the highest diversity
Crop-to-wild geneflow: environmental risk assessment for the release of genetically modified sorghum in Kenya
No full textEnglish: The important socio-economic position enjoyed by sorghum has made it a target for genetic modification to enhance productivity and/or nutritional quality. However, there are growing environmental concerns that through geneflow, transgenes might escape from genetically modified (GM) sorghum to its sexually compatible wild and/or weedy relatives, with possible negative effects. Characterising the levels and dynamics of geneflow in the wild-weedy-domesticate complex of sorghum in traditional groecosystems of Africa, including Kenya, is of interest to biosafety regulators. This study used approaches based on population genetics theory to (i) characterise the genetic structure of the wild-weedy-domesticate complex of S. bicolor at a country scale in Kenya and (ii) to estimate the extent and direction of geneflow between cultivated and wild-weedy populations at a local scale in the country. The structure and dynamics of diversity was first estimated and compared at country scale by genotyping 329 cultivated and 110 wild sorghum individuals using 24 microsatellite markers. Subsequently, the magnitude and direction of geneflow between the two congeners was estimated at a local scale by analysing 483 individuals comprising of 15 wild-weedy and 12 cultivated sorghum populations using 10 microsatellite markers. Overall, cultivated sorghum harboured lower diversity than its wild counterpart. Levels of genetic diversity in cultivated and wild sorghum differed significantly among regions, with most of the diversity being partitioned more within than among the crop’s growing regions. There were generally low levels of differentiation within and between cultivated and wild sorghum at country scale, but the extent of crop-to-wild genetic proximity varied among sorghum growing regions. These findings may reflect important historical geneflow between cultivated sorghum and its progenitor, with the level of crop-to-wild genetic exchange varying among regions. At local scale, the extent of geneflow was approximately nine times higher from cultivated sorghum to its wild-weedy relatives than vice versa. Additionally, the extent of crop-to-wild geneflow varied significantly among farms. Overall, this study suggests that deployment of GM sorghum in Kenya’s agroecosystems will most likely lead to movement of transgenes into sympatric populations of its wild-weedy relatives.Afrikaans: Die belangrike sosio-ekonomiese posisie van sorghum het dit die ideale gewas vir genetiese modifikasie vir produktiwiteit en/of voedingskwaliteitsverbetering gemaak. Daar is egter groeiende kommer oor die omgewing, aangesien geenvloei transgene ontsnapping vanaf geneties gemodifiseerde (GM) sorghum na wilde en/of onkruid kruisingsversoenbare verwante kan veroorsaak, met moontlike negatiewe effekte. Die karakterising van die vlakke en dinamika van geenvloei in die wilde-onkruidagtigeverboude kompleks van sorghum in tradisionele agro-ekosisteme van Afrika, Kenia ingesluit, is van belang vir bioveilgheidsreguleerders. Hierdie studie het die benadering van populasiegenetikateorie gebruik om (i) die genetiese struktuur van die wildeonkruidagtige- verboude kompleks van S. bicolor binne die hele Kenia te karakteriseer en (ii) om die hoeveelheid en rigting van geenvloei tussen verboude en wilde-onkruidagtige populasies op ‘n plaaslike vlak binne die land te bepaal. Die struktuur en dinamika van diversiteit is eers bepaal en toe nasionaal vergelyk deur 329 verboude en 110 wilde sorghum individue met 24 mikrosatelliet merkers. Daarna is die hoeveelheid en rigting van geenvloei tussen die twee groepe op plaaslike skaal bepaal deur toetsing van 483 individue bestaande uit 15 wilde-onkruidagtige en 12 verboude sorghum populasies met 10 mikrosatelliet merkers te evalueer. In die geheel het verboude sorghum minder diversiteit as die wilde groep getoon. Vlakke van genetiese diversiteit in verboude en wilde sorghum het betekenisvol tussen streke verskil, met meer diversiteit binne as tussen streke. Daar was oor die algmeen lae vlakke van differensiasie binne en tussen verboude en wilde sorghum op nasionale vlak, maar die gewas-na-wilde genetiese afstand het tussen sorghum produksie areas gewissel. Hierdie bevindinge kan die belangrike historiese geenvloei binne verboude sorghum en die bron van afkoms reflekteer, met die vlak van gewas-na-wilde uitruiling wat verskil tussen streke. Op ‘n plaaslike vlak was die hoeveelheid geenvloei ongeveer nege keer hoër van verboude sorghum na die wildeonkruidagtige verwantes as andersom. Verder het die vlak van gewas-na-wilde geenvloei betekenisvol tussen plase verskil. In die geheel dui hierdie studie aan dat die vrystelling van GM sorghum in Kenia se agro-ekosisteem waarskynlik na die beweging van transgene na simpatriese populasies van die wilde-onkruidagtige verwantes sal lei
Mutation breeding for in planta modification of amylose starch in cassava (Manihot esculenta, Crantz)
No full textCassava provides more dietary energy per unit area than any staple crop but native cassava starch has limited food and industrial applications. Different transgenic biotechnology approaches and ex situ physical and chemical starch modifications have been used to obtain desirable traits suitable for various food applications. But consumers are skeptical about the safety of the genetically modified foods and chemical residues. To meet the demand, gamma irradiation (this is energetic electromagnetic wave) which does not leave any residue, was used as a tool to induce in planta variation in amylose production. The four highest amylose producing plants N441P54 (32.7%), N223P12 (31.1%), N373P2 (27.2%), N329P11 (26.8%) and four lowest amylose producing plants N96P16 (14.0%), N353P6 (13.9%), N166P2 (13.2%), N476 P22 (11.7%) observed in the M1V2 generation were found to be significantly different from any one of the four controls HO008 (19.7%), HO001 (22.0%), UCC090 (22.6 %) and UCC026 (20.9%). Mutation is uncontrollable and could also lead to unexpected useful mutants. From this study four unexpected putative free-sugar mutants were identified, which could be used for bioethanol and glucose syrups production; two exceptional deep fissured and flaky mutants for the food industry; seven mutants with transition from A- to C-types of X-ray diffraction patterns with very high levels of crystallinity indexes suitable for replacing acid modified starches in pressing tablets in the pharmaceutical industries were discovered. Based on DSC classification, three gelatinization categories were observed. These were plants without gelatinization transition, plants with gelatinization transition and plants with merged gelatinization and melting transitions, occurring within gelatinization zone during calorimetric scanning from 25 – 110°C. The first and third categories included most of the putative mutants described in the research chapters and they were suitable for shortening the starch processing time required in most commercial starch applications in industry
Genetic linkage mapping of field resistance to cassava brown streak disease in cassava (Manihot esculenta Crantz) landraces from Tanzania
No full textCassava brown streak disease (CBSD) is an important biotic constraint to cassava production in cassava growing areas of east, central and southern Africa. A study was initiated to study the genetics of CBSD resistance and search for molecular markers associated with disease resistance. Two resistant and two susceptible cassava parents were selected based on their flowering ability, genetic distance and phenotypic reaction to CBSD. They were crossed in a half diallel to produce six families and F1 progeny plus parents were screened for their reaction to CBSD and evaluated for yield traits at two locations. Results indicated that general combining ability (GCA) was higher than specific combining ability (SCA) for CBSD root necrosis, CBSD severity in the shoot at three, six and nine months after planting (MAP), cassava mosaic disease (CMD) severity at three, six and nine MAP and harvest index indicating the importance of additive gene action in controlling CBSD resistance. Results indicated that CBSD resistance was quantitatively controlled by polygenic genes. Higher SCA than GCA was detected for number of roots per plant, fresh root weight per plant and fresh shoot weight per plant indicating the importance of non-additive gene effects in controlling yield traits. The Namikonga x Albert cross was used to generate a segregating mapping population comprising of 190 F1‟s which was planted and screened for CBSD reaction at two locations and genotyped using 605 SSR markers. A total of 220 polymorphic SSR markers, tested on 60 F1 and 51 S1, were finally used for linkage analysis and four genetic linkage maps were produced. The maps produced included integrated (male and female), Namikonga (female), Albert (male) and Namikonga-S1maps which spanned a distance of 995.46cM, 779.48 cM, 854.26 cM and 524.58 cM consisting of 174, 131,123 and 124 mapped SSR markers respectively. Mean map distance between markers ranged from 4.23 cM in Namikonga-S1 to 6.94 cM in Albert map while average map length per linkage group was 43.23 cM, 45.85 cM, 47.46 cM and 30.86 cM for integrated, Namikonga, Albert and Namikonga-S1 maps respectively. The linkage maps were used for QTL analysis and three putative QTL were detected on the integrated map on linkage groups C4, C16 and C18 linked to NS945, ESSRY105 and two flanking markers SSRY4 and ESSRY96 respectively. One QTL linked to NS667 was detected on Namikonga map on linkage group N4 while four putative QTL were detected on the Namikonga-S1 map on linkage groups S1 (at Chambezi and Naliendele in 2008), S8 and S12a at Chambezi 2008 and on S17 at Naliendele 2008. These QTL were respectively found to be linked to SSRY295, NS347 and SSRY4. These findings will have an implication in breeding for CBSD resistance. The observed relative importance of additive gene effects will mean that a mass recurrent selection will be the most efficient approach for CBSD resistance breeding in cassava. Markers associated with CBSD resistance will greatly improve selection efficiency for CBSD resistance in which selection for resistant genotypes can efficiently be done at seedling stage.Rockefeller FoundationAGR
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