Dissertationen zum Thema „Diplodia disease“

Mestrado em Engenharia Florestal e dos Recursos Naturais - Instituto Superior de Agronomia
Until a few years ago, the stone pine (Pinus pinea) was a species affected by few pathogens, but recently shoot blight and death of the shoots have been frequently reported in our country, causing serious concerns for producers and pine nut industry. By hindering the development of cones, this problem affects the production of pine nuts, the main resource of this forest industry. Lately, fungi belonging to different genera have been identified associated with shoot blight of stone pine. Some of these fungi, such as Sydowia polyspora, were unknown in Portugal and others, although present in our country (eg Pestalotiopsis spp.), were usually considered weak or stress parasites, affecting only weakened trees. The main aim of the present work was to contribute for the identification of the fungi associated to shoot blight of stone pine and to clarify their role in the expression of the disease. A total of 46 isolates from seven different sites were analysed. Identification was made based on cultural and morphological characteristics and phylogenetic analysis (ITS, TEF and TUB regions). Isolates of the most relevant species were tested for their pathogenicity. This work allowed to identify several species of fungi associated with shoot blight in stone pine, namely: Diplodia sapinea, Epicoccum nigrum, Pestalotiopsis australis, Pestalotiopsis sp. and Sydowia polyspora. The inoculation of one year-old P. pinea plants under controlled conditions allowed to confirm the pathogenicity of isolates of species D. sapinea and Pestalotiopsis sp.. The role of S. polyspora in the expression of these symptoms was not clarified, however, in the plants inoculated simultaneously with D. sapinea and S. polyspora isolates, the incidence of the disease was much higher than in the plants inoculated with D. sapinea alone, raising the hypothesis that S. polyspora may be potentiating the pathogenicity of D. sapinea. In this work, the fungus S. polyspora was identified for the first time in Portugal and for the first time in stone pine. It should also be pointed out that the isolate belonging to Pestalotiopsis sp., whose pathogenicity was proved in the present work, presents morpho-cultural and genetic characteristics different from those described for other species within this genus, being more aggressive than other known species within this genus
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The objective of the present study was to evaluate the effect of potassium and seed treatment of corn rot stalk disease. In experiment 1 and 2 were used five potassium doses (0, 40, 80, 120 and 160kg ha-1) in soils with levels of 190 and 120ppm of potassium respectively. In experiment 3, six doses of potassium (0, 65, 97.5, 130, 162.5, 195kg ha-1), but with levels of 40ppm in soil were tested. In experiment 4 was tested the potassium effect with seed treatment. The experimental design was a randomized complete blocks with four replications and plots of 21.0m2. The following corn hybrids were testes: Pioneer 30R50, NK Sprint and Agroeste 1560 respectively for experiment 1, 2, 3 and 4. Experiments were conducted according to corn technical recommendations. Grain yield, incidence of stalk rot were assessed. It was also determined the content of phenolic compounds. Data were submitted to analysis of variance using the F test, followed by the use of linear and nonlinear regression analysis. The following conclusions were taken: 1) potassium has effect on the incidence of CSR, only under conditions of low levels in the soil; 2) Seed inoculum is one way of introduction of CSR causal agent in areas not previously cultivated with corn; 3) potassium does increase phenolic acid concentration, given higher tolerance to corn stalk rot.
O objetivo do presente estudo foi avaliar o efeito da adubação potássica e do tratamento de sementes na incidência das podridões do colmo em milho, avaliando alguns efeitos fisiológicos e metabólicos. Nos experimentos 1 e 2 foram testadas cincos doses de potássio (0, 40, 80, 120 e 160kg.ha-1), em solos com níveis de 190 e 120ppm de potássio, respectivamente. No experimento 3, foram testadas seis doses de potássio (0, 65, 97.5, 130, 162.5, 195kg.ha-1), porém com níveis de 40ppm no solo. No experimento 4, foi testada a presença e ausência de potássio, associado ou não com tratamento de sementes. O delineamento experimental, para todos os experimentos, foi o de blocos ao acaso, com quatro repetições, parcelas de 21,0m2 (6,0 x 3,50m). Foram utilizados os híbridos: Pionner 30R50, NK Sprint e Agroeste 1560, respectivamente, aos experimentos 1, 2, 3 e 4. Na condução do estudo, as práticas culturais foram realizadas de acordo com as recomendações técnicas para a cultura do milho. Foi avaliado o rendimento de grãos e a incidência das podridões de colmo (PBCs) em milho, usando metodologia definida por Reis et al. (1998). Determinaram-se também o teor de compostos fenólicos no tecido do colmo do milho usando metodologia desenvolvida por Deschamps et al. (2002). Com base nos resultados, chegou-se às seguintes conclusões: 1) A aplicação de potássio em solos com baixos teores desse nutriente aumenta a tolerância da podridão da base do colmo em milho; 2) O potássio aumenta a concentração de ácidos fenólicos, proporcionando maior tolerância da podridão da base do colmo em milho; 3) O tratamento de sementes diminui a incidência da podridão da base do colmo em milho.

Thesis (Ph. D.)--University of Kentucky, 2005.
Title from document title page (viewed on March 2, 2006). Document formatted into pages; contains ix, 177 p. : ill. (some col.). Includes abstract and vita. Includes bibliographical references (p. 159-172).

Sterile triploid Atlantic salmon represent a solution to the issues of pre-harvest sexual maturation and mature escapees from open aquaculture systems. Although the initial problems of reduced performance and increased deformities in triploids have been thoroughly researched, there is a continued lack of information on their susceptibility and response to disease and routine on-farm treatments compared to diploids. Thus, the main aim of this thesis was to enhance the current understanding of triploid health and immunity through experimental disease challenges and treatments, and aid in determining their robustness and, therefore, suitability for aquaculture. A commercial furunculosis vaccine equally protected diploids and triploids against challenge with Aeromonas salmonicida, and adhesion scores were similar between ploidy (Chapter 2). Interestingly, triploids had lower white blood cell counts but increased cellular activity, e.g. respiratory burst, compared to diploids. Following experimental cohabitation infection with Neoparamoeba perurans, causative agent of Amoebic Gill Disease (AGD), ploidy did not affect the manifestation or severity of AGD-associated gill pathology, or the serum innate immune response (Chapter 3). Hydrogen peroxide, used to treat against parasitic diseases, elicited similar primary and secondary stress responses in both ploidy, but led to differences in the expression of stress (cat, gpx1, gr, hsp70, sod1, sod2) and immune (saa5, crp/sap1a, crp/sap1b, il1β) genes (Chapter 4). Finally, vaccination with different vaccine treatments (4 commercial vaccines, 6 different vaccine combinations and a sham-vaccinated control) showed no ploidy differences in adhesion score or antibody response, although vertebral deformities remained higher in triploids (Chapter 5). Increasing severity of vaccine treatments negatively affected weight, length and thermal growth coefficient in both ploidy. Triploids were heavier than diploids at smolt (+ 14 %) and post smolt (+ 32 %). Overall, this research shows that triploid Atlantic salmon respond as well as diploids to disease and treatment challenges, and supports their application into full-scale commercial aquaculture.

Diplodia pinea causes Diplodia tip blight on more than 30 different pine species. During the past 10 years, Diplodia tip blight has emerged as a serious problem in landscape and Christmas tree farms in this region. Surveys of diseased and symptomless Austrian pines revealed that latent infections of symptomless shoots by D. pinea were common. Latent infections may account for the recently observed rapid decline of mildly diseased pines in our region. To investigate the colonization habits of D. pinea within its host, molecular cytology was attempted and traditional histology was performed on naturally infected, diseased and asymptomatic Austrian pine tissues. I devoted much effort to developing a transformation system for D. pinea. Ultimately I did not succeed in this goal, but I was able to develop a highly efficient protocol for Agrobacterium tumefaciens-mediated transformation of another pathogenic fungus, Colletotrichum graminicola, in the process. The work that I did should help in future efforts to transform D. pinea, something that will be essential if it is to become a tractable system for the study of fungal latency. Traditional histological methods were more successful, and provided important information about the nature of latent infections. Very sparse epiphytic and subcuticular fungal growth was observed in healthy shoots, however, no fungal tissues were present within the shoots. In diseased and latently infected shoots, crevices created between the needle bundles and the shoots were filled with fungal material, and hyphae were observed colonizing the needle sheaths. Hyphae were also observed breaching the shoot epidermal layer in these crevices and colonizing the underlying periderm. D. pinea colonization was extensive in all tissues of diseased shoots early in symptom development. In contrast, localized pockets of degradation were observed in the periderm and adjacent cortical cells located around areas of needle attachment in asymptomatic, latently infected shoots. The mechanism that operates to prevent expansion of these infected pockets in the latently infected shoots is still unclear. Obvious signs of pine defense mechanisms were only observed in 2 shoots. My observations were consistent with the idea that colonization progresses into the vascular tissues, and that this results in symptom development. Vascular colonization may occur more readily if the host is stressed. My research lays the groundwork for future efforts to understand the nature of the transformation from latent to pathogenic infection.

Three F1 plants (WOB13, WOB21, and WOB26) from the hybridization of the diploid parents Rosa wichuraiana ‘Basye’s Thornless’ and ‘Old Blush’ (Rosa chinensis) were backcrossed to ‘Old Blush’ to produce three interspecific backcross populations to observe the segregation of several morphological and disease resistance traits. The qualitative traits of bloom habit, flower color, flower form, and presence of stem prickles were characterized in two locations in College Station, Texas. The quantitative traits of flower size, petal size, and number of flowers per stem were measured in College Station, Texas, and number of leaflets per leaf, powdery mildew resistance, and black spot resistance were measured in College Station and Overton, Texas. Reported modes of inheritance for flower color (pink co-dominant to white), flower form (double dominant to single), and stem prickles (prickles dominant to no prickles) agree with the results in this study. The segregation of the bloom (non-recurrent dominant to recurrent) habit trait showed a deficiency of recurrent blooming types. Sources of variation generation and/or genotype(generation) explained most of the variation for flower size, petal sizes, flowers per stem, leaflet number, powdery mildew, and black spot resistance. Different environmental conditions within the environment made replication effects significant for flowers per stem. Low incidence level of powdery mildew and different temperatures in College Station and Overton made environment effects significant. Environment x generation and environment x genotype(generation) were significant for black spot resistance. The genetic variance is about two times greater than the environment x genetic interaction which would allow selection to be done at one environment, even though black spot resistance may change some between environments. Additive gene action (no dominance) was observed for flower size, petal size, black spot resistance, and powdery mildew resistance. Gene action of partial dominance was observed for leaflet number. Gene action for flowers per stem could not be determined due to lack of variation.

This dissertation examines the nature of education at the senior high school level in Kunming, China, through a participant observation study in four high schools. It discusses Ronald Dore's theory of a 'diploma disease' in the context of the four schools, and the variants which affect it at the level of participants. The dissertation illustrates that the 'backwash effects' which are generated by the National University Entrance Examination are entrenched in the education system and have significant adverse effects on students and teachers. The academic and vocational streams of education are compared and contrasted as providing different paths through the opportunity structure and different outcomes for social mobility. The dissertation analyzes the selective and social distributive functions of senior high school education in Kunming, and suggests that informal methods outside of entrance examinations, such as the use of guanxi and monetary payments, are gaining influence in these realms. As these methods become more widely utilized in the face of increasing competition to enter university, expressions of discontent from those educational participants who are adversely affected are also becoming more apparent.

On the reefs of Bermuda, the coral Diploria labyrinthiformis is rarely infected with black band disease (BBD) while BBD-infected colonies of D. strigosa are common. This study investigated several possible explanations for the documented difference in BBD prevalence including: 1) temperature and light conditions differentially affect the progression of the disease among these two species; 2) the bacterial communities associated with each species are different and 3) the bacterial composition of BBD in Bermuda is unique from that of other geographical regions where D. labyrinthiformis has been reported with BBD. Results suggest that light and temperature are important variables in determining BBD progression for both species; reef location, rather than coral species dictates the coral associated bacterial diversity; and the BBD bacterial mat in Bermuda is unique compared to other regions of the Caribbean. Many factors are likely responsible for the low occurrence of BBD among D. labyrinthiformis in Bermuda.

Disease and bleaching are two conditions which commonly lead to coral death. Among coral species, susceptibility to disease and bleaching is variable, and Pseudodiploria strigosa tends to be diseased more than Diploria labyrinthiformis, while D. labyrinthiformis bleaches more readily. The focus of this dissertation was to investigate and compare multiple components of these two coral species, and identify how they may relate to disease and bleaching resistance. Compenetnts examined included the surface mucopolysacharide layer (SML) thickness, gene expression, microbial associates, and a white plague aquarium study. The SML thickness decresased with increasing temperature regardless of coral species, indicating that SML thickness does not likely play a role in differences between susceptablities of these two coral species. However, Diploria labyrinthiformis had a lower mortality rate at 31°C, had fewer differentially expressed genes assossiated with stress, and upregulated genes associated with innate immunity in the summer, all of which may contribute to its relative disease resistance. The bacterial associates of each coral species were also monitored. Differences between the two coral species were primarily caused by Clostridia, Gammaproteobacteria, and rare species which may contribute to the relatively higher disease susceptibility of P. strigosa. Lastly, an aquarium study suggested that a potential pathogen of the Roseobacter clade infects both D. labyrinthiformis and P. strigosa, and might be transmitted by the Cryptochiridae gall crab, indicating that potential disease vectors associated with these two coral species may also play a role in disease resistance and resilience.

In the tuberculosis patients, Mycobacterium tuberculosis can stimulate production of hydrogen peroxide in the host as a result of immune response. The H2O2 accumulate in pulmonary cells, causing oxidative stress that could lead to the cancer. We select TB patients for this study which investigates the effects of quercetin as there is an increased incidence of latent TB among the migrant population in the past few years and TB can increase the risk of cancer. Sperm and lymphocytes were treated with DNA damage inducers and quercetin (10µM, 25µM and 100µM), the responses evaluated using the Comet and micronucleus techniques. The gene expressions of COX1, COX2, P53 and Bcl-2 and catalase protein expression were investigated using the qPCR and Western blot techniques. The results showed that a substantial reduction of DNA damage in lymphocytes from TB patients and sperm from healthy donors from * P ≤ 0.0283 to *** P≤0.001in the Comet assay. In the MNi assay, the effect of quercetin in lymphocytes was more significant in reduce DNA damage, whereas the DNA damage induced by a food mutagen was significant, from *p 0.0405 to ***p 0.001. The qPCR showed significance down-regulation of COX1 and Bcl-2 gene expression, rated between *p 0.045 and **p 0.0074. However, the catalase protein was up-regulated by the nano form of quercetin when using lymphocytes from TB patients and showed significant changes at *p 0.0236. In conclusion, the nano form was found to be more efficient at the reduction of DNA damage in the Comet and micronucleus assays. Also, it down-regulated COX1 and Bcl-2 and up-regulated the catalase proteins indicating a possible role for quercetin, in genoprotection to TB through its enzyme modulating effect.
Libyan Embassy

In recent years, numerous studies have been initiated in order to understand what are the microorganisms involved in forest plants diseases and the role played by phytotoxins produced in the pathogenesis processes. The aim of the present thesis was to study the fungi and the phytotoxins associated with canker disease of the Italian cypress (Cupressus sempervirens L.) and the branch dieback of juniper (Juniperus phoenicea L.) which are plant diseases with noteworthy social and economical implications. Two phytotoxic dihydrofuropyran-2-ones, named afritoxinones A and B, were isolated from liquid culture of Diplodia africana, a fungal pathogen responsible for branch dieback of Juniperus phoenicea L. in Italy. Additionally, six others known metabolites were isolated from the same fungus and identified as: oxysporone, sphaeropsidin A, episphaeropsidone, R-(-)-mellein, (3R,4R)-4-hydroxymellein and (3R,4S)-4-hydroxymellein. The structures of afritoxinones A and B were established by spectroscopic and optical methods and determined to be as (3aS*,6R*,7aS)-6-methoxy-3a,7a-dihydro-3H,6H-furo[2,3-b]pyran-2-one and (3aR*,6R*,7aS)-6-methoxy-3a,7a-dihydro-3H,6H-furo[2,3-b]pyran-2-one, respectively. The phytotoxic activity of afritoxinones A and B and oxysporone was evaluated on host and non-host plants by cutting and leaf puncture assay. Oxysporone proved to be the most phytotoxic compound. Sphaeropsidone is a phytotoxic dimedone methyl ether produced by Diplodia cupressi the causal agent of a canker disease of cypress in the Mediterranean area together with episphaeropsidone which was also isolated from D. africana. Eight derivatives obtained by chemical modifications and two natural analogues were assayed for phytotoxic and antifungal activities, and a structure-activity relationship was examined. Each compound was tested on non-host plants and on five fungal pathogenic species belonging to the genus Phytophthora. The results provide insights into structure-activity relationships within these compounds. It was found that the hydroxy group at C-5, the absolute C-5 configuration, the epoxy group, and the C-2 carbonyl group appear to be structural features important in conferring biological activity. The conversion of sphaeropsidone into the corresponding 1,4-dione derivative led to a compound showing greater antifungal activity than its precursor. Furthermore white block shaped single crystals of sphaeropsidone were obtained and an X-ray diffraction study was carried out. From Diplodia cupressi were also isolated some unrearranged pimarane diterpenes named sphaeropsidins A-C. These latter and 14 derivatives obtained by their chemical modifications were assayed for antibacterial activity against Xanthomonas oryzae pv. oryzae, Pseudomonas fuscovaginae, and Burkholderia glumae, the causal agents of severe bacterial rice diseases. The results showed a strong and specific activity of sphaeropsidin A against X. oryzae pv. oryzae, while no activity was observed against the other two pathogens. The results of structure-activity relationships study showed that structural features important to impart this antibacterial activity are the presence of the C-7 carbonyl group and the hemiketalic lactone functionality. The C-13 vinyl group, the double bond of ring C and/or the tertiary C-9 hydroxyl group, as well as the pimarame arrangement of the tricylic carbon skeleton were also important for the antibacterial activity. This findings may be useful in devising novel compounds for practical application in agriculture.

Fusarium circinatum is a fungal pathogen that has had a serious impact on pine production throughout the world. It attacks most Pinus species including Pinus elliottii, Pinus patula and Pinus radiata. Infections in South Africa (SA) are largely on seedlings, and result in fatal seedling wilt. Accurate and quick detection systems suitable for field use are needed to monitor the spread of the disease and optimize fungicide applications. Detection of F. circinatum is currently based on visual observations of typical symptoms. However, symptoms are not unique to the pathogen and can be caused by other biotic and abiotic stress factors. Nucleic acid-based identification techniques using PCR are available for different fungal species. These are sensitive and accurate, but they are expensive and require skilled biotechnologists to conduct the assays. In this study an enzyme-linked immunosorbent assay (ELISA) was developed to identify F. circinatum in infected seedlings. This optimized ELISA is able to discriminate between F. circinatum and two other fungi that frequently affect pine. This method has advantages over other assays because of its ease of operation and sample preparation, sensitivity and the ability to run multiple tests simultaneously. Mycelium-soluble antigens from Diplodia pinea (=Sphaeropsis sapinea), F. circinatum and F. oxysporum were prepared in nutrient broth. Analysis of these antigens on SDS-PAGE indicated the presence of common antigens between the different fungal pathogens. Some antigens were expressed more by some isolates than by others. Separate groups of chickens were immunised with mycelium-soluble antigens from D. pinea, F. circinatum and F. oxysporum and exo-antigen from F. circinatum prepared in nutrient broth. A 34 kDa protein purified from SDS-PAGE specific for D. pinea was also used for immunisation. Five sets of antibodies were obtained including anti-D. pinea, anti-F. circinatum, anti-F. oxysporum, anti-F. circinatumexo and anti-D. pinea 34 kDa antibodies, respectively. Reactivity of these antibodies was evaluated against antigens prepared in nutrient broth using western blotting and ELISA. Western blot analysis indicated that immuno-dominant antigens for F. circinatum were larger than 34 kDa and their reactivity was not the same between different isolates. Each of the antibodies prepared using mycelium-soluble antigens showed increased reactivity when detecting its own specific pathogen, but cross-reactivity was observed. Anti-D.pineaantibodies showed minimal cross-reactivity with antigens from F. circinatum and F. oxysporum. Anti-F. circinatum antibodies cross-reacted with antigens from F. oxysporum but showed little cross-reactivity with D. pinea antigens. Anti-F. oxysporum antibodies showed more cross-reactivity towards antigens from F. circinatum than those from D. pinea. No reactivity was observed when anti-F. circinatum-exo antigen and anti-D. pinea 34 kDa antibodies were used in immuno-blotting analysis. Evaluation of antibody reactivity using indirect ELISA showed patterns similar to those observed on western blotting, where anti-D. pinea, anti-F. circinatum and anti-F. oxysporum antibodies showed the same cross-reactivity relationships. Anti-F. circinatum and anti-F. oxysporumantibodies showed a significant difference when reacting with antigens isolated from other pathogens including D. pinea, F. circinatum, F. oxysporum, F. solani, F. graminearum and F. culmorum (P = 0.001). No significant difference was observed when the antigens were detected with anti-D. pinea antibodies. Reactivity of anti-F. circinatum-exo and anti-D. pinea34 kDa antibodies was mostly similar to that of non-immune antibodies and showed no significant difference between detection of different antigens. Pine seedlings were artificially infected with the three fungal pathogens using a spore concentration of 1 – 1 x 106conidiaml-1.Infection was monitored using scanning electron microscopy. Results showed increased levels of mycelium growth on the stem and roots of the F. circinatum and F. oxysporum infected seedlings and on the leaves and stem in the case of D. pinea infected seedlings. These plant parts were used in ELISA tests for the detection of antigens. Isolation of antigens from the plant materials involved crushing plant parts in buffer and centrifugation of the suspension. The supernatant obtained was directly used in the assay. ELISA tests prepared in this study were sensitive enough to detect infection caused by 1 conidium ml-1at two weeks post inoculation. A positive reaction for detection of F. circinatum and F. oxysporum was indicated by an ELISA reading above an optical density at 405 nm. The plant material used in ELISA tests were further analysed using PCR. Results indicated that there was no cross-infection between seedlings and served as a confirmation of the disease-causing pathogen. This indicated that cross-reactivity observed was due to other factors such as common epitopes on the major antigens. Use of an ELISA dip-stick or ELISA using these antibodies should provide an easy, fast field test to identify infections of pine, discriminating between F. circinatum, F. oxysporum and D. pinea.
M.Sc.Agric. University of KwaZulu-Natal, Pietermaritzburg 2013.

Reduced banana yield owing to black Sigatoka Mycosphaerella fijiensis Morelet is a threat to the livelihoods of Ugandan subsistence farmers who depend entirely on the banana crop for food security. The objectives of this investigation were to: (i) assess farmers’ knowledge of black Sigatoka disease in central Uganda; (ii) document the qualities farmers would desire in the banana genotypes to be developed for black Sigatoka resistance; (iii) appraise the methods for assessing black Sigatoka resistance in diploid banana populations; (iv) determine the phenotypic variation for black Sigatoka resistance and agronomic traits in diploid and tetraploid bananas; (v) determine the influence of tetraploid and diploid parents on the black Sigatoka resistance and agronomic traits in the triploid progenies; and (vi) evaluate 2x by 2x banana progenies for yield and black Sigatoka resistance. A survey that focused on low and medium banana production zones in Uganda established that there was limited awareness of black Sigatoka disease as a constraint on banana production in the areas surveyed. It was also established that farmers liked local bananas because of their superior taste, early maturity, and marketability. There were farmers who had been exposed to new black Sigatoka resistant materials but never liked these new banana materials because of poor taste and lack of market. Farmers desired new banana materials with good taste on cooking, heavy bunches, resistance to pests and diseases, drought tolerance, and early maturing capacity in that order. The results indicated that the banana farmers in Uganda attached more importance to food quality attributes than to production attributes especially when considering new banana materials. This suggested that farmers mainly grow bananas for consumption. Three black Sigatoka assessment methods, youngest leaf spotted, disease development time and area under disease progress curve (AUDPC) were appraised using a diploid population. All the three methods were able to classify the diploid accessions into resistant and susceptible clones. The cultivar rankings of AUDPC correlated strongly with the rankings of disease development time. The cultivar rankings of AUDPC correlated positively with the rankings of youngest leaf spotted method. The youngest leaf spotted at flowering and AUDPC predicted significantly total number of leaves at flowering (R2 = 0.53). Overall AUDPC had the highest coefficient of determination (R2=0.84) in assessment of banana diploids for black Sigatoka resistance indicating that it accounted for the highest variation in disease response observed among the diploid clones. From this investigation it was recommended that AUDPC should be used to assess resistance on black Sigatoka in Musa species. A phenotypic analysis on the diploid and synthetic tetraploids, and a molecular analysis using RAPD markers on the tetraploid population were conducted. Results indicated that the diploid population had significant (P<0.001) variation for plant height, plant girth, days from flowering to harvest, bunch weight, number of suckers, youngest leaf spotted, total leaves at flowering, area under disease progress curve, and number of functional leaves at harvest. Principal component analysis showed that plant height and girth explained most of the variation observed in the diploid population. In the tetraploid population, significant differences were observed for plant height, plant girth, and number of suckers (P<0.05). In the tetraploids principal component analysis, indicated that youngest leaf spotted and total leaves at flowering had higher loadings on principal component one. Genetic distances computed from RAPD markers indicated limited genetic variability in the tetraploid population. Another investigation was also carried out to determine the influence of tetraploid and diploid parents on black Sigatoka resistance and agronomic traits in the triploid progenies generated from tetraploid-diploid crosses. The results indicated that diploids transferred black Sigatoka resistance to triploid progenies as measured by disease development over time, the number of functional leaves at flowering and at harvest. On the other hand, the female synthetic tetraploids influenced plant height and bunch weight in the triploid progenies generated from tetraploid-diploid crosses as observed from triploid progeny correlations and parent-offspring regressions. Therefore, it is important to select tetraploids with heavy bunch weights to generate high yielding triploids in tetraploid-diploid crosses. Lastly, this thesis investigated the relationship between bunch weight and black Sigatoka resistance traits in 2x by 2x progenies generated using a random polycross design. Phenotypic correlations revealed strong positive relationships between bunch weight with total leaves at flowering, youngest leaf spotted, plant girth, and days from planting to flowering among the 2x by 2x progenies. Linear regression analysis indicated that girth, total fingers and finger length significantly predicted bunch weight (R2=0.67). However, days from planting to flowering, and total leaves at flowering had strong indirect effects on bunch weight via plant girth. The results imply that selection for parents with good combining ability for girth, finger length and total fingers can improve bunch weight in a diploid population.
Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2009.

This dissertation examines the nature of education at the senior high school level in Kunming, China, through a participant observation study in four high schools. It discusses Ronald Dore's theory of a 'diploma disease' in the context of the four schools, and the variants which affect it at the level of participants. The dissertation illustrates that the 'backwash effects' which are generated by the National University Entrance Examination are entrenched in the education system and have significant adverse effects on students and teachers. The academic and vocational streams of education are compared and contrasted as providing different paths through the opportunity structure and different outcomes for social mobility. The dissertation analyzes the selective and social distributive functions of senior high school education in Kunming, and suggests that informal methods outside of entrance examinations, such as the use of guanxi and monetary payments, are gaining influence in these realms. As these methods become more widely utilized in the face of increasing competition to enter university, expressions of discontent from those educational participants who are adversely affected are also becoming more apparent.