Made available in DSpace on 2015-03-26T13:42:33Z (GMT). No. of bitstreams: 1 texto completo.pdf: 244644 bytes, checksum: 7bb131def78ba69016b2b6a8a2dd140f (MD5) Previous issue date: 2014-02-27 / Linkage disequilibrium (LD) is defined as the non-random association between alleles of different loci in a population and association mapping (MA) refers to a statistically significant association between molecular marker and phenotypic trait. The objectives of this study were: (1) estimate the linkage disequilibrium in populations of popcorn related by cycles of selection using SNP markers, (2) compare the populations in the degree of LD, (3) evaluate changes in allele frequencies and (4) identify significant associations between markers and quality related characteristics of popcorn. In total 465 samples were evaluated, with 354 samples belonging to the population 'Viçosa' and 111 samples belonging to the population eija- asm Improvement Program popcorn, Federal University of Viçosa. The populations were subjected to the following cycles of selection: Viçosa cycle 1 and cycle 1 Beija-Flor, obtained after one cycle of selection among and within half-sib families, Viçosa cycle 4, obtained after four cycles of selection among and within half-sib families, Viçosa cycle 2 full-sib families (FIC), obtained after two cycles of selection among and within full-sib families, Viçosa S4, obtained by selection of progeny S4. Ninety-six SNPs markers in properly selected QTL regions for quality, already identified above were used. The following characters were measured: capacity expansion (ml/g), grain density (g/ml), sphericity of grains and 100 grains weight (g). In comparison the Viçosa c0 used as the reference population for the highest mean values for LD linking group found in Viçosa c2 fic (D' = 0,8911; r 2 = 0,1905) as well as to related and unrelated SNPs (D' = 0,8911, r 2 = 0,1905) . Regarding the MA significant associations (p < 0.05) were found for all traits, with thirteen associations related to the feature expandability, twenty three with the sphericity of the grains, eight with the weight of 100 grains and seventeen density of the grains. / Desequilíbrio de ligação (LD) é definido como a associação não aleatória entre alelos de diferentes locos em uma população e mapeamento associativo (MA) refere-se à associação estatística significativa entre o marcador molecular e a característica fenotípica. Os objetivos deste trabalho foram: (1) estimar o desequilíbrio de ligação em populações de milho pipoca relacionadas por ciclos de seleção utilizando marcadores SNP, (2) comparar as populações quanto ao grau de LD, (3) avaliar alterações de frequências alélicas e (4) identificar associações significativas entre marcadores e características relacionadas à qualidade do milho pipoca. No total foram avaliadas 465 amostras, sendo 354 amostras pertencentes à - populações pertencentes ao germoplasma do Programa de Melhoramento de Milho-Pipoca da Universidade Federal de Viçosa. As populações foram submetidas aos seguintes ciclos de seleção: Viçosa ciclo 1 e Beija-Flor ciclo 1, obtidas após um ciclo de seleção entre e dentro de famílias de meios-irmãos, Viçosa ciclo 4, obtida após quatro ciclos de seleção entre e dentro de famílias de meios-irmãos, Viçosa ciclo 2 famílias de irmãos completos (FIC), obtidas após dois ciclos de seleção entre e dentro de famílias de irmãos completos, Viçosa S 4, obtida por seleção de progênies S4. Foram utilizados 96 marcadores SNP devidamente selecionados em regiões de QTL pré-identificadas para qualidade. Os seguintes caracteres foram mensurados: capacidade de expansão (ml/g), densidade dos grãos (g/ml), esfericidade dos grãos e peso de 100 grãos (g). Em comparação a Viçosa c0, utilizada como população de referência os maiores valores médios de LD por grupo de ligação foram encontrados em Viçosa c2 fic r2=0,1905). Na análise de MA foram encontradas associações significativas (p < 0,05) para todas as características avaliadas, sendo treze associações relacionadas com a característica capacidade de expansão, vinte e três com a esfericidade dos grãos, oito com o peso de 100 grãos e dezessete com a densidade dos grãos.

Quality protein maize (QPM) has enhanced levels of two essential amino acids, lysine and tryptophan compared to normal maize. This makes QPM an important cereal crop in communities where maize is a staple crop. The main abiotic factor to QPM production is drought stress. Little information is available on the effect of drought stress on QPM. Therefore, the objectives of this study were to: (i) conduct diversity analysis of QPM inbred lines using morpho-agronomic and simple sequence repeat markers, (ii) screen available QPM inbred lines and F1 progeny for tolerance to seedling drought stress, (iii) determine the combining ability and type of gene action of QPM inbred lines for tolerance to seedling drought stress, grain yield and endosperm modification. The study was conducted in South Africa, at the University of Fort Hare. Morphological characterisation of 21 inbred lines was done using quantitative and qualitative traits. A randomised complete block design with three replicates was used for characterizing the inbred lines in the field. Genstat statistical software, version 12 (Genstat ®, 2009) was used for analysis of variance (ANOVA) and descriptive statistics. Analysis of variance was performed on all quantitative data for morphological traits. Data for qualitative traits was tabulated in their nominal classes. Traits that contributed most to the variation were days to anthesis, days to silking, anthesis-silking interval, plant height, number of kernel rows, ear length and grain yield. Cluster analysis grouped the inbred lines into three main clusters. The first cluster was characterised by tall and average yielding lines, while the second cluster showed the least anthesis-silking interval, and had the highest yield. Cluster three consisted of lines that were early maturing, but were the least yielding. Genetic distances between maize inbred lines were quantified by using 27 simple sequence repeat markers. The genetic distances between genotypes was computed using Roger’s (1972) genetic distances. Cluster analysis was then carried out using the neighbour-joining tree method using Power Marker software version 3.25. A dendrogram generated from the genetic study of the inbred lines revealed three groups that concurred with expectations based upon pedigree data. These groups were not identical to the groups generated using morpho-agronomic characterisation. Twenty one QPM inbred lines were crossed using a North Carolina design II mating scheme. These were divided into seven sets, each with three inbred lines. The three inbred lines in one set were used as females and crossed with three inbred lines in another set consisting of males. Each inbred line was used as a female in one set, and as a male in a second set. Sixty three hybrids (7 sets x 9 hybrids) were formed and evaluated in October 2011, using a 6x8 alpha-lattice incomplete block design with three replicates under glasshouse and optimum field conditions. A randomised complete block design with three replicates was used for the 21 parental inbred lines. Traits recorded for the glasshouse study were, canopy temperature, chlorophyll content, leaf roll, stem diameter, plant height, leaf number, leaf area, fresh and dry root and shoot weights. Data for the various traits for each environment, 25 percent (stress treatment) and 75 percent (non-stress) of field capacity, were subjected to analysis of variance using the unbalanced treatment design in Genstat statistical package Edition 12. Where varietal differences were found, means were separated using Tukey’s test. Genetic analyses for grain yield and agronomic traits were performed using a fixed effects model in JMP 10 following Residual Maximum Likelihood procedure (REML). From the results, inbred lines that were not previously classified into heterotic groups and drought tolerance categories were classified based on their total dry weight performance and drought susceptibility index. Inbred lines L18, L9, L8, L6 and L3, in order of their drought tolerance index were the best performers under greenhouse conditions and could be recommended for breeding new varieties that are tolerant to seedling drought stress. Evaluation of maize seedlings tolerant to drought stress under glasshouse conditions revealed that cross combination L18 x L11 was drought tolerant, while cross L20 x L7 was susceptible. Total dry weight was used as the major criteria for classifying F1 maize seedlings as being resistant or susceptible. General combining ability effects accounted for 67.43 percent of the genetic variation for total dry weight, while specific combining ability effects contributed 37.57 percent. This indicated that additive gene effects were more important than non-additive gene action in controlling this trait. In the field study (non-drought), the experimental design was a 6x8 alpha lattice incomplete block design with three replicates. On an adjacent field a randomised complete block design with three replicates was used to evaluate the parental inbred lines. The following variables were recorded: plant height, ear height, ears per plant, endosperm modification, days to silking and days to anthesis, anthesis-silking interval, number of kernels per row, number of rows per ear and grain yield. General analyses for the incomplete lattice block design and randomised complete block design for hybrid and inbred data respectively were performed using JMP 10 statistical software. Means were separated using the Tukey's test. Genetic analyses of data for grain yield and agronomic traits were conducted using a fixed effects model using REML in JMP 10. The importance of both GCA (51 percent) and SCA (49 percent) was observed for grain yield. A preponderance of GCA existed for ear height, days to anthesis, anthesis-silking interval, ears per plant and number of kernels per row, indicating that predominantly, additive gene effects controlled hybrid performance under optimum field conditions. The highest heritability was observed for days to silking (48.27 percent) suggesting that yield could be improved through selection for this trait. Under field conditions, variation in time to maturity was observed. This implies that these inbred lines can be recommended for utilisation in different agro-ecologies. Early maturing lines such as L18 can be used to introduce earliness in local cultivars, while early maturing single crosses such as L18 x L2, L5 x L9, L3 x L4 and L2 x L21 could be recommended for maize growers in drought prone areas such as the former Ciskei. Single crosses L18xL11, L16xL18, L8xL21 and L9xL6 had good tolerance to seedling drought stress. On the other hand, single crosses L18xL11 and L11xL13 had high grain yield and good endosperm modification. All these single crosses could be recommended for commercial production after evaluation across locations in the Eastern Cape Province. Alternatively they can be crossed with other superior inbreds to generate three or four way hybrids, which could then be evaluated for potential use by farmers in the Eastern Cape.

Breeding maize (Zea mays L.) for tolerance to acidic soils could improve maize yields. The current study aims to identify maize genotypes with tolerance to acidic soils, as well as identifying secondary traits associated with the tolerance to soil acidity. Ten maize varieties were screened for tolerance to aluminium (Al) toxicity under glasshouse, laboratory and field conditions. In the glasshouse, two soil acidity levels (limed and unlimed soil) were used and the experiment was set up in a complete randomised design (CRD) with three replications. The experiment lasted for 10 days and measurements were taken on plant height (PH), leaf area, stem diameter and dry matter. In the laboratory, a haematoxylin staining (HS) experiment was conducted to determine the response of 10 maize varieties to Al toxicity. Two Al concentrations (0 and 222 μM) were used and the experiment was set up in a completely randomized design with three replications. After 7 days, shoot length, was recorded. Five stress tolerance indices were estimated to determine the resilience of each genotype. A root growth stress tolerance index was also computed for both experimental procedures. In the field, two trials were established at two sites, namely Mbinja and Mpumaze. Limed and unlimed plots were used, and the trial was set up in a randomized complete block design with three replications. Maize kernel yield and other standard field parameters were recorded. Selection of tolerant genotypes from the field screening was also done using three indices, namely harmonic mean (HM), stress tolerance index (STI) and stress susceptibility index (SSI). Both the glasshouse and laboratory assays identified similar genotypes of maize as being tolerant. These tolerant genotypes were Ngoyi, PANBG3492 BT, PAN 6Q408 and PHB 3442 based on the root growth stress tolerance index (RGSTI). It was therefore demonstrated that these two assays produced the same level of efficiency in identifying tolerant genotypes using this index. Based on ranking of seedling vigour index under soil acidity stress, the top three genotypes at Mpumaze were PHB32W71, PAN6616 and Sahara while at Mbinja, the top three were PAN6616, PAN6Q408 CB and PAN6P110. The genotypes PANBG3492 BT, PAN6Q408 and PHB3442 were also found to be tolerant to acidic soils at seedling stage. These genotypes are recommended for further evaluation in more sites to confirm their tolerance and yield potential under acidic soils. The study also revealed that plant height, leaf area and stem diameter could be used for indirect selection for tolerance to Al toxicity under glasshouse conditions. The seedling vigour index was also effective in identifying tolerant genotypes under glasshouse conditions. On the other hand, shoot length stress tolerance index and the haematoxylin score were useful for indirect selection for tolerance to Al toxicity in the laboratory. In the field, it was observed that ear length, leaf area and ear diameter can be useful in identifying genotypes that are tolerant to soil acidity. They can therefore be useful as indirect selection criteria under field conditions. Additionally, the best selection indices for identifying soil acidity tolerant genotypes under field conditions were the HM and the STI. It is recommended that varieties that were identified as tolerant be further evaluated in several soil acidity hot spots to confirm their tolerance and stability of performance under field conditions. / Agriculture and  Animal Health / M. Sc. (Agriculture)

Made available in DSpace on 2015-03-26T13:42:32Z (GMT). No. of bitstreams: 1 texto completo.pdf: 1285006 bytes, checksum: 66befb25fdda54069e90bd93e5d2c031 (MD5) Previous issue date: 2014-07-10 / The corn crops occupies a prominent position in the agricultural activity in worldwide, being an of the most studied crops in the plant breeding, not so much for the case of corn starch. The corn starch Avati Morotî food is of greater importance for the Paraguayan peasant family and general public as source of typical food in several country regions. In most cases, the producers of this type of maize using seeds its own production of cultivars generally from low productivity, susceptible to disease, pests, and long cycle.Considering the importance of this type of corn for food security the Instituto Paraguayo de Técnologia Agraria (IPTA) is working in the plant breeding for to get early crops, being more productive and with low cost of ownership for small producers cultivars. The objective of this study was to evaluate the existence of interactions between genotypes and environments, and estimate the parameters of adaptability and stability of hybrids of corn starch by the method of Lin and Binns (1988); estimate genetic and phenotypic parameters as the simple correlations, partial and track, the genetic divergence and relative contribution of genetic diversity to characters by the method of Singh (1981) for 49 genotypes of corn starch in three environments in eastern Paraguay. The experimental design was a randomized block design with three replications, with plot containing 25 plants. The analysis of variance showed significant difference for all traits in the locality of Choré with 1% level of significance by F test for the location of Capitan Miranda; however, grain yield (GY) and plant aspect (AP) were not significant. The locality Yjhovy the (PG) was significant at 5%. The analysis of variance showed a significant interaction for genotype by environment at the 5% significance level for the F test, for all traits except male flowering. Most features of the showed interaction of complex type. The adaptability and stability proved more adaptable and stable hybrids, being also the most productive. The 41and 24 materials were genotypes that contained the lowest values of Pi general. In all locations, there was a significant genetic variability for all traits, including productivity the exception of the number of caterpillar (NL) and empty cobs (EV), the grain yield (GY) correlates positively with plant height and percentage of grains to the location of Choré and Yjhovy, lower positive correlation with GY were found with a diameter of cob (DE) and ear length (EC).Features percentage of grains (Pg) and ear length (EC) are those with the highest direct effect on PG between the primary components and secondary components were between plant height (APL) and prolificacy (PROL), the most indicated for indirect selection for grain yield. In all locations, there was a significant genetic variability among genotypes, with genotypes 48 the most divergent between them. From the dendrogram nearest neighbor two groups were formed for the localities Capitan Miranda and Choré, although for Yjhovy three groups were formed and the method of UPGMA were, three and four groups for the localities Capitan Miranda, Chore and Yjhovy, characters male flowering (FM) and plant height (APL) were the main contributors to genetic divergence. / A cultura de milho ocupa posição de destaque na atividade agropecuária no mundo, sendo umas das culturas mais estudadas na área de melhoramento genético, nem tanto assim para o caso de milho amiláceo. O milho amiláceo Avati Morotî constitui uns dos alimentos de maior importância para a população do Paraguai em especial à família camponesa do Paraguai e população em geral por ser parte constituinte de vários pratos típicos do país. Na maioria dos casos os produtores deste tipo de milho utilizam sementes de sua própria produção, geralmente provenientes de cultivares de baixa produtividade, suscetível à doenças e pragas e ciclo muito longo. Considerando as importâncias deste tipo de milho para a segurança alimentar, o IPTA (Instituto Paraguaio de Tecnologia Agrária) trabalha na área de melhoramento para obter cultivares precoces, mais produtivas de baixo custo de aquisição para os pequenos produtores. O objetivo deste trabalho foi avaliar a existência de interação entre genótipos e ambientes e estimar os parâmetros de adaptabilidade e estabilidade de híbridos de milho amiláceo pelo método de Lin e Binns (1988); estimar os parâmetros genéticos e fenotípicos, assim também as correlações simples, parciais e de trilha e estudar a divergência genética, assim também a contribuição relativa dos caracteres para diversidade genética pelo método de Singh (1981), para 49 genótipos de milho amiláceo, em três ambientes, na região Oriental do Paraguai. O delineamento experimental utilizado foi o de blocos ao acaso, com três repetições, com a parcela contendo 25 plantas. A análise de variância demonstrou diferenças significativas para todos os caracteres avaliados na localidade de Choré com nível de 1% de significância pelo teste F. No entanto, para a localidade de Capitan Miranda, a produtividade de grãos PG e aspecto da planta AP não foram significativos. A localidade Yjhovy o (PG) foi significativa aos 5%. A análise de variância conjunta mostrou uma interação significativa para híbridos por ambientes ao nível de 5 % de significância pelo teste F, para todos os caracteres, com exceção de floração masculina. A maioria das características apresentou interação do tipo complexa. A adaptabilidade e estabilidade revelaram híbridos mais adaptados e estáveis, sendo também, os mais produtivos. Os híbridos 41e 24 foram que contiveram os menores valores de Pi geral. Em todos os locais, observou-se a existência de variabilidade genética para todas as características entre eles a produtividade a exceção do número de lagarta e espiga vazia . A PG correlacionou-se positivamente com a altura de planta e porcentagem de grãos para a localidade de Choré e Yjhovy, menor correlação positiva com PG foi obtida com diâmetro de espiga DE e comprimento de espiga CE. Os caracteres porcentagem de grãos Pg e comprimento de espiga CE são os que apresentaram maior efeito direto sobre a PG entre os componentes primários, e entre os componentes secundários foram altura de planta APL e prolificidade PROL, sendo os mais indicados para seleção indireta para PG. Em todos os locais, observou-se a existência de variabilidade genética entre os híbridos, sendo o genótipo 48 o mais divergentes entre eles. A partir do dendrograma de Vizinho mais próximo foram formados dois grupos para as localidades de Capitan Miranda e Choré, embora para Yjhovy foram formados três grupos e pelo método de UPGMA foram dois, três e quatro grupos para as localidades de Capitan Miranda, Chore e Yjhovy. Os caracteres floração masculina FM e altura de planta APl foram os que mais contribuíram para a divergência genética.

MSCAGR (Plant Production) / Department of Plant Production / Smallholder farmers in Sub-Saharan Africa still obtain low grain yields in maize largely due to low soil fertility. The soils are inherently low in nitrogen (N) that is required for the proper development of the maize plant. Currently there are no commercial cultivars for low N tolerance locally. The combining ability approach can be used as a tool for breeding desirable cultivars. In order to improve grain yield in maize, it is important to consider ear prolificacy which is a major yield component. Therefore this study was designed to estimate combining ability in maize. Exotic germplasm from the International Maize and Wheat Improvement Center and the Institute of Tropical Agriculture as well as the local germplasm from the Agricultural Research Council was used in the study to generate crosses. One hundred and two crosses were evaluated together with a standard commercial check under low N and optimum N conditions. The specific objectives of the study were to determine general and specific combining ability for prolificacy among local and exotic inbred lines and evaluate the response of prolific hybrids to low N conditions. The hybrids were planted in the 2014/2015 summer season under irrigation in Potchefstroom, Cedara and Taung in field plots consisting of 0.75m x 0.25m spacing in a 0.1 alpha lattice design replicated twice. Data for agronomic attributes were recorded and subjected to analysis of variance using SAS version 9.1.3. Genetic correlations were analyzed using the Principal Components Analysis and factor analysis based on the correlation analysis and major traits. The results showed variation in agronomic performance among the inbred lines and their F1 hybrids. Inbred lines including TZEI63, T1162W, L15 and L17 showed positive GCA estimates for ear prolificacy at the different locations. Specific combining ability for prolific hybrids was positive at all locations and environments. The GCA:SCA ratio was close to unity; indicating that the number of ears per plant showed highly significant (P<0.01) correlation with grain yield. The hybrids showed ear prolificacy under the low N conditions. This trait can be used effectively in stress tolerance maize breeding programmes. / NRF