The soybean programme in Zimbabwe is over seventy years old. However, there is lack of information on breeding gains, genetic diversity, heritability, genetic advance, combining ability, gene action and relationships between grain yield and secondary traits available for breeding. Therefore, the aim of the present study was to characterise the genetic diversity of the available germplasm, determine gene action conditioning grain yield and estimate the breeding gains that have been realised since the inception of the breeding programme. Evaluation of 42 soybean genotypes for genetic diversity conducted during 2010/11 and 2011/12 cropping seasons, using phenotypic and molecular characterisation approaches, revealed evidence of wide diversity among the genotypes. The phenotypic traits and SSR markers assigned the soybean genotypes to 8 and 15 clusters respectively. The SSR marker technique was more polymorphic, informative and highly discriminatory. The clustering pattern and relatedness from SSR data was in agreement with the pedigree data while the phenotypic clustering was divorced from pedigree data. Genotypes, G41 and G7; G41 and G1; G41 and G42 were the most divergent; therefore, they could be utilized as source germplasm in cultivar development and commercial cultivars. Investigations on breeding gains involving 42 cultivars (representing a collection of all the varieties that were released in Zimbabwe from 1940 to 2013) showed that improvement in grain yield was slowing down. However, annual genetic gain was estimated to be 47 kg ha-1 year-1 representing an annual gain of 1.67%. Furthermore, grain yield ranged from 2785 to 5020 kg ha-1. Genotypes, G16, G15, G17, G1 and G42 exhibited superior performance in grain yield and other agronomic traits and are therefore, recommended for utilisation in the hybridisation programme. Seed protein concentration decreased by 0.02 year-1 while oil increased by 0.02, 100 seed weight increased by 0.21 g year-1 over time. In addition, number of days to 95% pod maturity and pod shattering increased by 0.35 and 0.38 days year-1 respectively while lodging declined by 0.31%. Results indicated that emphasis should be refocused on grain yield to restore the original linear increase. Assessment of the magnitude of GEI and stability of 42 released cultivars was done over 13 environments and two seasons using additive main effects and multiplicative interaction, cultivar superiority and rank analyses. Results showed that environment and GEI captured larger portion of the total sum of squares, which reveals the influence of the two factors on grain yield, hence, the need for evaluating soybean genotypes in multi-environment trials and over years. Further, the data revealed that GEI was of a crossover type because of differential yield ranking of genotypes. The three stability parameters selected two genotypes, G1 and G15, as the most productive, consistent and stable, thus they could be produced in diverse environments while G2, G4, G5, G7, G16, G40, G17, G18 and G31 were identified as unstable and suitable for specific adaptation. Correlation and path analyses showed that grain yield was positively and significantly correlated with number of branches per plant, number of nodes per plant, shelling percentage, and number of days from 95% pod maturity to first pod shattering, implying that breeding and selection for these traits probably improved grain yield. Number of nodes per plant, plant height and 100 seed weight exhibited highest direct effects on grain yield while, number of nodes per plant and plant height presented the highest indirect effects on grain yield. These results demonstrated that number of nodes per plant and plant height could be recommended as reliable selection traits for developing high yielding genotypes of soybean. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

O trabalho consiste no sistema de produção de trigo e na evolução de danos causados pela giberela. O estudo considera a inexistência de cultivares resistentes à doença, a baixa eficiência do controle químico e a presença de micotoxinas em grãos. O trabalho teve como objetivos confirmar a eficiência dos fungicidas protioconazol e metconazol; comprovar a eficiência da deposição de barra com bicos com jatos direcionados as laterais da espiga resultando na completa cobertura das anteras presas; comprovar a viabilidade de uso de um sistema de aviso (aplicação após o início da floração antes da ocorrência de chuvas previstas para as futuras 24-48 horas e tentar melhorar a eficiência no controle da giberela. O experimento foi instalado no campo experimental da Universidade Tecnológica Federal do Paraná no município de Pato Branco, Paraná, conduzido em duas épocas, sendo a primeira estabelecida no dia 6 de maio de 2014 e a segunda em 21 de maio de 2014. Foi utilizada a cultivar Ametista de domínio da OR Melhoramento de sementes, Passo Fundo, Rio Grande do Sul. Os tratamentos constaram de uma testemunha sem aplicação de fungicida e de uma e duas aplicações de protioconazol 17,5% + trifloxistrobina (Fox) 500 mL/ha; metconazol 8,0% + piraclostrobina 13% (Opera Ultra) 750 mL/há, a aplicação dos fungicidas foi feita antes da ocorrência de chuva prevista, com ocorrência de sete dias de chuva e um volume total de 85,2mm na primeira época, e de 16 dias de chuva e um acúmulo de 400 mm na segunda época, Na avaliação, segunda época, o metconazol + piraclostrobina com duas aplicação, estatisticamente foi o tratamento que apresentou menor incidência em espigas reduzindo de 100 para 63,3%; o metconazol + piraclostrobina teve melhor desempenho também na redução da incidência em espiguetas, de 80,3% para 34,7%; o controle em espigas teve melhor resultado na segunda época com duas aplicações de metconazol + piraclostrobina; em espiguetas, na primeira época, o metconazol + piraclostrobina com duas aplicação resultou no melhor controle com 67%; O metconazol + piraclostrobina com duas aplicações teve um aumento no rendimento de grãos de 547 kg/há. O peso hectolitro não apresentou diferença significativa com mesmo numero de aplicações, somente quanto ao numero de aplicações em ambas as épocas sendo que metconazol + piraclostrobina com duas aplicações em ambas as época variou de 81 e 79. Conclui-se que a eficiência do ensaio pode ser confirmada quando a direção da calda direcionada com jatos com ângulo de 30º para frente e 70º para trás, lançados pelas pontas acopladas em corpos de bico duplo leque perpendicular ao alvo na posição vertical atinge as laterais da espiga. E O metconazol + piraclostrobina se mostrou o fungicida mais eficiente em relação ao protioconazol + trifloxistrobina no controle da giberela e o rendimento de grãos na safra de 2014. / The work consists in wheat production system and the evolution of damage caused by wheat scab. The study considers the lack of resistant cultivars to the disease, the low efficiency of chemical control and the presence of mycotoxins in grains. The study aimed to confirm the effectiveness of fungicides prothioconazole and metconazole; prove the bar deposition efficiency with nozzles directed jets the side of the ear resulting in full coverage of trapped anthers; prove the viability of using a warning system (application after the start of flowering before the onset of rains provided for future 24-48 hours and try to improve the efficiency in controlling scab. The experiment was conducted in the experimental field of Technological University Federal do Paraná in the city of Pato Branco, Paraná, conducted in two seasons, the first established on May 6, 2014 and the second on 21 May 2014. It was used to cultivate Amethyst field of OR Improvement seeds, . Passo Fundo, Rio Grande do Sul Treatments consisted of a control without fungicide application and one and two applications of prothioconazole + 17.5% trifloxystrobin (Fox) 500 ml / ha; metconazole 8.0% + pyraclostrobin 13% ( Opera Ultra) 750 mL / ha In the evaluation, second season, metconazole + pyraclostrobin with two application statistically was the treatment that showed a lower incidence in spikes reducing from 100 to 63.3%;. metconazole + pyraclostrobin performed better also in reducing the incidence of spikelets, 80.3% to 34.7%; the control ears had better results in the second season with two applications of metconazole + pyraclostrobin; in spikelets, in his first season, metconazole + pyraclostrobin with two application resulted in better control with 67%; with two applications of metconazole + pyraclostrobin gave the highest yield even under climatic conditions favorable to disease; metconazole + pyraclostrobin in both seasons showed superior efficiency in controlling FHB giving greater weight gain; with two application of both fungicides, the hectoliter weight was 81 and 79, respectively, each fungicide; the application of fungicides was made in advance of expected rain, occurring seven days of rain and a total volume of 85,2mm the first time, and 16 days of rain and an accumulation of 400 mm in the second period; the test efficiency can be confirmed when the direction of the spray jets launched wings coupled in double nozzle bodies perpendicular to the target upright reaches the sides of the spike. The metconazole + pyraclostrobin proved the most effective fungicide against the prothioconazole + trifloxystrobin in wheat scab control in the 2014 harvest.

O trabalho consiste no sistema de produção de trigo e na evolução de danos causados pela giberela. O estudo considera a inexistência de cultivares resistentes à doença, a baixa eficiência do controle químico e a presença de micotoxinas em grãos. O trabalho teve como objetivos confirmar a eficiência dos fungicidas protioconazol e metconazol; comprovar a eficiência da deposição de barra com bicos com jatos direcionados as laterais da espiga resultando na completa cobertura das anteras presas; comprovar a viabilidade de uso de um sistema de aviso (aplicação após o início da floração antes da ocorrência de chuvas previstas para as futuras 24-48 horas e tentar melhorar a eficiência no controle da giberela. O experimento foi instalado no campo experimental da Universidade Tecnológica Federal do Paraná no município de Pato Branco, Paraná, conduzido em duas épocas, sendo a primeira estabelecida no dia 6 de maio de 2014 e a segunda em 21 de maio de 2014. Foi utilizada a cultivar Ametista de domínio da OR Melhoramento de sementes, Passo Fundo, Rio Grande do Sul. Os tratamentos constaram de uma testemunha sem aplicação de fungicida e de uma e duas aplicações de protioconazol 17,5% + trifloxistrobina (Fox) 500 mL/ha; metconazol 8,0% + piraclostrobina 13% (Opera Ultra) 750 mL/há, a aplicação dos fungicidas foi feita antes da ocorrência de chuva prevista, com ocorrência de sete dias de chuva e um volume total de 85,2mm na primeira época, e de 16 dias de chuva e um acúmulo de 400 mm na segunda época, Na avaliação, segunda época, o metconazol + piraclostrobina com duas aplicação, estatisticamente foi o tratamento que apresentou menor incidência em espigas reduzindo de 100 para 63,3%; o metconazol + piraclostrobina teve melhor desempenho também na redução da incidência em espiguetas, de 80,3% para 34,7%; o controle em espigas teve melhor resultado na segunda época com duas aplicações de metconazol + piraclostrobina; em espiguetas, na primeira época, o metconazol + piraclostrobina com duas aplicação resultou no melhor controle com 67%; O metconazol + piraclostrobina com duas aplicações teve um aumento no rendimento de grãos de 547 kg/há. O peso hectolitro não apresentou diferença significativa com mesmo numero de aplicações, somente quanto ao numero de aplicações em ambas as épocas sendo que metconazol + piraclostrobina com duas aplicações em ambas as época variou de 81 e 79. Conclui-se que a eficiência do ensaio pode ser confirmada quando a direção da calda direcionada com jatos com ângulo de 30º para frente e 70º para trás, lançados pelas pontas acopladas em corpos de bico duplo leque perpendicular ao alvo na posição vertical atinge as laterais da espiga. E O metconazol + piraclostrobina se mostrou o fungicida mais eficiente em relação ao protioconazol + trifloxistrobina no controle da giberela e o rendimento de grãos na safra de 2014. / The work consists in wheat production system and the evolution of damage caused by wheat scab. The study considers the lack of resistant cultivars to the disease, the low efficiency of chemical control and the presence of mycotoxins in grains. The study aimed to confirm the effectiveness of fungicides prothioconazole and metconazole; prove the bar deposition efficiency with nozzles directed jets the side of the ear resulting in full coverage of trapped anthers; prove the viability of using a warning system (application after the start of flowering before the onset of rains provided for future 24-48 hours and try to improve the efficiency in controlling scab. The experiment was conducted in the experimental field of Technological University Federal do Paraná in the city of Pato Branco, Paraná, conducted in two seasons, the first established on May 6, 2014 and the second on 21 May 2014. It was used to cultivate Amethyst field of OR Improvement seeds, . Passo Fundo, Rio Grande do Sul Treatments consisted of a control without fungicide application and one and two applications of prothioconazole + 17.5% trifloxystrobin (Fox) 500 ml / ha; metconazole 8.0% + pyraclostrobin 13% ( Opera Ultra) 750 mL / ha In the evaluation, second season, metconazole + pyraclostrobin with two application statistically was the treatment that showed a lower incidence in spikes reducing from 100 to 63.3%;. metconazole + pyraclostrobin performed better also in reducing the incidence of spikelets, 80.3% to 34.7%; the control ears had better results in the second season with two applications of metconazole + pyraclostrobin; in spikelets, in his first season, metconazole + pyraclostrobin with two application resulted in better control with 67%; with two applications of metconazole + pyraclostrobin gave the highest yield even under climatic conditions favorable to disease; metconazole + pyraclostrobin in both seasons showed superior efficiency in controlling FHB giving greater weight gain; with two application of both fungicides, the hectoliter weight was 81 and 79, respectively, each fungicide; the application of fungicides was made in advance of expected rain, occurring seven days of rain and a total volume of 85,2mm the first time, and 16 days of rain and an accumulation of 400 mm in the second period; the test efficiency can be confirmed when the direction of the spray jets launched wings coupled in double nozzle bodies perpendicular to the target upright reaches the sides of the spike. The metconazole + pyraclostrobin proved the most effective fungicide against the prothioconazole + trifloxystrobin in wheat scab control in the 2014 harvest.

Les plantes possèdent de multiples systèmes de défense contre les insectes phytophages. Dans un contexte agronomique, manipuler ces défenses au moyen de la sélection pourrait contribuer à réduire les dommages causés par les insectes ravageurs en augmentant la résistance naturelle des plantes. Cette stratégie se heurte cependant à des contraintes très fortes lorsqu'il s'agit de l'appliquer aux insectes. Après avoir détaillé ces contraintes, nous proposons une démarche alternative aux méthodes classiques. Celle-ci vise à identifier des traits-clés de la plante qui modulent son interaction avec le ravageur. Si de tels traits sont identifiés et validés expérimentalement, ils permettront ensuite de conduire la sélection sans nécessiter d'insecte. Nous avons testé cette démarche dans un système composé du colza (Brassica napus) et du méligèthe Meligethes aeneus, un ravageur majeur de cette culture. Le méligèthe est un coléoptère pollinivore dont les adultes sont généralistes mais ne pondent que sur certaines brassicacées. Les dégâts agronomiques sont causés par ces adultes qui, avant que la floraison ne démarre, détruisent les boutons floraux pour atteindre le pollen qu'ils contiennent. Quatre étapes cruciales de l'interaction ont été étudiées : l'attraction à distance, l'alimentation des adultes, la production et la ponte des œufs, et le développement larvaire. Six génotypes de colza ont été comparés dans une série d'expérimentations au laboratoire. La mise en relation des résultats de préférence/performance de l'insecte avec des profilages métaboliques larges de tissus floraux a permis d'identifier des traits-clés candidats. Les conclusions principales de ce travail sont (i) que la composition biochimique du périanthe est déterminante dans la stimulation de l'alimentation des adultes, et que cette stimulation pourrait être largement sous l'influence d'un petit nombre de composés dont le saccharose ; (ii) que cette stimulation détermine de façon majeure, par un effet domino, la production d'œufs en contraignant l'ovogenèse ; (iii) que la qualité nutritionnelle du pollen impacte à la fois les larves et les adultes, et que cette qualité pourrait être déterminée en bonne partie par la concentration en amidon et en certains glucosinolates (des métabolites secondaires typiques de quelques familles végétales dont les brassicacées). La combinaison des différents résultats obtenus permet également de proposer des hypothèses plus générales, parmi lesquelles le fait que le contexte agronomique dans lequel l'interaction a lieu ait largement influencé, voire perturbé, l'interaction qui liait le méligèthe et les brassicacées sauvages avant que les cultures de colza ne se généralisent. Cette thèse a montré qu'une nouvelle voie était peut-être envisageable pour contribuer à protéger les cultures de façon durable contre les insectes ravageurs, en particulier pour les systèmes agronomiques où les dégâts sont causés à un stade temporairement sensible de la culture. / Plants display multiple defense systems against phytophagous insects. Manipulating these defenses by means of selection could contribute to decrease damages caused by insect pests, by increasing natural resistance of crops. This strategy faces great constraints when applied to insects. We first detail these constraints and then propose an alternative approach to classical methods. It consists in identifying key plant traits that determine the intensity of the interaction between the plant and the pest. If such traits are identified, selection could be conducted on the basis if these sole traits, without needing any insect. We tested this approach in a system composed of oilseed rape (Brassica napus) and the pollen beetle (Meligethes aeneus), a major pest of this culture. This coleopteran generalist pollen feeder lays eggs only on certain brassicaceous plants. Agronomical damage arise before plant flowering and are caused by adults, which destroy flower buds to get the pollen they contain. Four crucial steps of the interaction were studied: attraction, adult feeding, egg production and oviposition, and larval development. Six oilseed rape genotypes were compared in a series of experiments conducted in the laboratory. By linking insect preference/performance to large metabolic profiling of bud tissues, we identified candidate key traits. Main conclusions of this work are (i) that biochemical composition of the perianth, especially a few compounds among which sucrose, is determinant for feeding intensity; (ii) that feeding stimulation has an important impact on egg production by constraining oogenesis; (iii) that pollen nutritional quality, probably mostly determined by starch and some glucosinolates, interacts with both pollen beetle larvae and adults. Combination of several results also allows drawing more general hypotheses about the oilseed rape - pollen beetle interaction. One of these is that the agronomical context in which the interaction takes place may have largely influenced, or even disturbed, the interaction that linked this insect and wild brassicaceous plants before oilseed rape cultivation. This thesis showed that a new way might be possible to protect cultures against insect pests. It could be both efficient and sustainable, especially in systems where agronomical damage is caused at a temporary vulnerable plant stage.

MSCAGR (Plant Production) / Department of Plant Production / Tepary bean (Phaseolus acutifolius) is an important food legume originating from South America and the South-western parts of the United States. The crop is produced in many countries worldwide including South Africa. It is highly tolerant to drought and the seed contains a wide range of vitamins, minerals and protein of high nutritional quality. The genetic base of tepary bean is narrow but can be widened by chemical mutagenesis. However, there are no reports on the impact of chemical mutagenesis on the root nodulation and seed storage proteins in tepary bean. Therefore, this study was designed to examine root nodulation attributes and seed storage proteins of three tepary bean genotypes in the early mutagenic generations (M2 to M4) derived through treatment with varying doses (0.0, 0.5, 1.0, 1.5 and 2.0 v/v) of ethyl methanesulfonate (EMS). The experiment on root nodulation attributes was laid out as a 3 x 5 x 3 (genotypes x EMS doses x mutant generations) factorial design replicated three times. At harvest, shoot height (SHT), primary root length (PRL), dry weights (shoot, root and nodule), number of nodules per plant (NNP) and grain yield components such as the number of pods per plant (NPP) and number of seeds per pod (NSP) were measured. Highly significant (P≤0.01) dose effects were observed for SHT, PRL, shoot dry weight (SDW) and root dry weight (RDW). Highly significant (P≤0.01) interaction effects of mutant generation x genotype x dose were observed for NSP. A highly significant (P≤0.01) positive linear relationship was observed between the NNP and nodule dry weight (NDW). Increase in the PRL suggested that tepary bean mutants could be important in drought tolerance. EMS treatment led to an enhanced partitioning of dry matter (assimilates) to the shoots and roots. There was a three fold increase in most of the root nodulation traits at the 0.5% EMS dose.The Kjeldahl method was used for crude protein determination whereas the sodium dodecyl sulphate – polyacrylamide gel electrophoresis (SDS PAGE) was utilized in determining the protein banding patterns of the bean. There were highly significant (P≤0.01) differences among the genotypes in crude protein accumulation. Highly significant (P≤0.01) mutant generation x genotype x dose were observed for seed protein accumulation. ‘Genotype 3’ attained the highest protein content (24.23%) at 1.5% EMS dose in the M4 generation. EMS doses ≥0.5% positively stimulated protein accumulation in all genotypes but high EMS doses (2.0%) depressed protein content. There were significant variations in seed storage protein profiles among the genotypes and mutant generations. ‘Genotype 6’ showed a distinct 15.0kDa protein fragment which was absent in the majority of the remaining genotypes. The presence of distinct protein subunits in the three genotypes could be used in varietal / NRF

<p>Heterosis, or hybrid vigor, is a phenomenon observed in both plant and animal systems where hybrid offspring perform better when compared to their parents. For hybrid plants, this can result in increased biomass, crop yields, and vigor when compared to the inbred parents. Even though heterosis has been used in agriculture for over a century, the molecular mechanisms that result in hybrid vigor remain elusive even after years of investigation. A molecular understanding of heterosis is desirable because it will speed up the process of breeding compatible inbred lines for developing hybrid seeds, and it will provide us with the knowledge to potentially engineer inbred lines that can mimic the beneficial phenotypic effects of heterosis, eliminating the need for farmers to buy new hybrid seeds every year. The goal of this research project is to identify genes that are required for heterotic phenotypes in maize. Our working hypothesis is that a mutation in genes that are essential for heterosis will cause an altered heterotic phenotype in hybrid maize plants. To test this hypothesis, we applied combined approaches of EMS mutagenesis, trait phenotyping in field and controlled conditions, bulk segregant analysis, whole genome sequencing, and bioinformatics analysis. First, we applied a forward genetics approach to identify mutant hybrids with altered heterosis and detected potential causal genes <em>via</em> whole genome sequencing. We identified one mutation occurring in a protein coding gene (gene ID <em>Zm00001eb305590</em>) located in a region of interest on chromosome 7, whose genotypes across various samples assayed fit the observed segregation pattern of hybrid traits. This mutation leads to a moderate or high-level codon change, indicating that this gene may play a role in mediating heterosis in maize. By investigating this gene with further studies, the learned knowledge could speed up the process of hybrid maize breeding by selecting compatible inbred lines through sequencing or by engineering hybrids that have favorable alleles for this gene.</p>

<p>While fresh vegetables (FVs) consumption is essential for public health, some high-profile outbreaks that cause severe illnesses are related to their consumption. To illustrate, the Center for Disease Control (CDC) and Prevention has estimated 48 million cases of foodborne illnesses in the U.S. per year; of them, about 46% are associated with FVs. The economic impact of food safety issues, estimated at $51 billion annually, is due to medical costs, productivity losses, and loss of consumer trust (Hoffman et al., 2021). </p> <p>The proliferation of risk mitigation methods (GAP, HACCP), food safety policies (FSMA), and information (labels, media, government) out in the market today, suggests that the way consumers understand food safety might be different from what policymakers, researchers, and retailers try to communicate. In addition, consumers' heterogeneous perceptions and beliefs can make communication with policymakers, researchers, and industry stakeholders ineffective when assessing food safety risks. </p> <p>Given the high demand for FVs and the communication mismatch with consumers, it is crucial to understand how consumers value food safety when purchasing FVs. This study clustered FVs consumers based on their food safety concerns. First, a Principal Component Analysis (PCA) identified the most relevant food safety dimensions. Later, using the food safety dimensions, this study segmented FVs consumers based on their food safety concerns. Finally, through a Multinomial Probit model (MNP), this study provided the main factors driving cluster membership.</p> <p>Our results suggest the existence of four segments of FVs consumers: “Worriers” (45% of our sample), who highly valued all the food safety characteristics when buying FVs. “Labelers” (20.3% of our sample) mainly valued attributes related to nutritional and environmental characteristics. “Pretty Vegetables” (17.3% of our sample) searched for the best and safest produce possible. Lastly, “DIYers” (17.3% of our sample) valued the least variables related to convenience in FVs. Finally, some of the main drivers of cluster membership were related to demographics, consumption, information sources, and perceptions about food safety of FVs consumers. These results can help policymakers, researchers, and retailers communicate food safety information more efficiently among different segments of consumers.</p>

<p dir="ltr">Pedicels are the slender stalks that attach the fruit to the plant. They play a crucial role in fruit development. The characteristics of the pedicel comprise complex traits that are controlled by multiple genes. To study whether genetic control of fruit mass was via control of pedicel characteristics, we used two unique hybrid apple populations: ‘20 Ounce’ x ‘Prairie Fire’ and ‘Edward VII’ x ‘Prairie Fire’. Both ‘20 Ounce’ and ‘Edward VII’ x ‘Prairie Fire’ produce large fruit over 200 g, whereas ‘Prairie Fire’ is a small-fruited crabapple with fruit size less than 2 g. These populations offer the potential to investigate how pedicel attributes relate to apple fruit size. Previous work established a correlation between pedicel characteristics and apple fruit mass. Specifically, pedicel length showed an inverse relationship, while pedicel diameter was directly related to fruit mass. Shorter and broader pedicels were expected to offer the least resistance to water and nutrient flows. We hypothesize that among the genes that control fruit mass, some govern pedicel length and diameter. Quantitative Trait Loci (QTLs) analysis (Linkage mapping) was performed, and 5 QTLs were associated with characteristics such as fruit mass, pedicel length and pedicel diameter with LOD scores of 4 and above. That being said, no common region was associated with both the fruit mass and pedicel characteristics. This does not support our hypothesis and suggests that different regions may be controlling all these traits. Knowledge of QTLs and subsequently genes that affect fruit mass and pedicel characteristics in apple have potential applications in apple breeding and fruit production. The identification and manipulation of these genes holds the promise of developing new apple cultivars with improved pedicel traits and ultimately fruit mass and enhanced fruit quality.</p>

This thesis reports the cell culture establishment and a somatic cell selection system optimized for the isolation of chlorsulfuron-resistant variants in asparagus (Asparagus officinalis L.). The development of this cell selection system benefited the isolation of chlorsulfuron-resistant variants from an elite asparagus genotype. A cell culture system, suitable for somatic cell selection, was established for asparagus genotype CRD 168. Friable callus was initiated from etiolated shoots in darkness and used to produce a high density of single cells in suspension. Cell density was estimated based on a linear relationship with settled cell volume. A mean plating efficiency of 0.19 % was recorded between 1-4x10⁵ cells/Petri dish. In vitro cell selection techniques were developed to identify mutant asparagus cells with resistance to a sulfonylurea herbicide, chlorsulfuron. A few key aspects were important to achieve this: a cell culture system for cell selection was initially established; a toxic concentration for the complete growth inhibition of the wild type asparagus cells was defined; rare, resistant cell colonies were isolated and characterized; and chlorsulfuron-resistant plants were regenerated. From about 50 million cells, 165 cell colonies were isolated in the presence of 8 nM chlorsulfuron. Characterization of these selected cell colonies yielded 24 escapes, 98 unstable variants, and 43 stable-resistant variants. Callus cultures from 34 of these stable variants retained resistance following 11 months growth in the absence of the selection agent. Plants were regenerated from 36 of these stable herbicide-resistant variants. Six of these chlorsulfuron-resistant variants were screened for their degree of resistance to chlorsulfuron, cross resistance to other acetohydroxyacid synthase (AHAS) inhibiting herbicides and AHAS enzyme activity. Cross resistance to imazamox was evident in four of the resistant variants, while lack of cross resistance to metsulfuron methyl was observed in all six resistant variants. A varying degree of resistance to chlorsulfuron was observed among the resistant variants. Both in the original and secondary callus, an uninhibited AHAS enzyme activity in all six resistant variants was recorded in the presence of high chlorsulfuron concentration (70-140 nM), compared to the total inhibition in the wild type. One chlorsulfuron-resistant variant, R-45, was used to compare the biochemical and physiological basis of resistance with the wild type. The AHAS enzyme activity in the tissue culture and greenhouse foliage of R-45 was significantly higher in the presence of up to 280 nM chlorsulfuron compared with the wild type. Chlorsulfuron retention was considerably higher due to the reduction of epicuticular wax deposits on the foliage of R-45, in comparison with the wild type. Consequently, the resistant line absorbed at least 1.6 fold more chlorsulfuron than the wild type plants. Therefore, foliar application of 15 g a.i./ha Glean (commercial formulation of chlorsulfuron) produced typical symptoms of chlorosis in R-45, similar to the wild type, in the greenhouse plants. Somatic cell selection was carried out using two elite asparagus genotypes, CRD 74 and Clone X. Of the 33 rare cell colonies isolated from Clone X, 22 unstable variants and 6 escapes were discarded. All five remaining resistant variants produced plants. One of the stable-resistant variants (Clone X-24) was evaluated for resistance to chlorsulfuron. Both in vitro shoot cultures and greenhouse-grown plants of Clone X-24 showed increased resistance to chlorsulfuron compared with the wild type. The AHAS enzyme activity in the foliar extracts also showed the presence of higher enzyme activity in Clone X-24.

MRDV / Institute for Rural Development / See the attached abstract below