Submitted by Reginaldo Soares de Freitas (reginaldo.freitas@ufv.br) on 2016-09-06T17:45:49Z No. of bitstreams: 1 texto completo.pdf: 3005523 bytes, checksum: 55080e7cc13a34e94047adc722f4b917 (MD5) / Made available in DSpace on 2016-09-06T17:45:49Z (GMT). No. of bitstreams: 1 texto completo.pdf: 3005523 bytes, checksum: 55080e7cc13a34e94047adc722f4b917 (MD5) Previous issue date: 2012-04-02 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A espécie fúngica Alternaria euphorbiicola foi isolada a partir de tecidos severamente infectados de Euphorbia heterophylla, uma das plantas daninhas mais nocivas à agricultura brasileira. A rapidez e a severidade dos sintomas produzidos pela inoculação de A. euphorbiicola em E. heterophylla levaram à suspeita de produção de compostos fitotóxicos pelo fungo, despertando o interesse pela identificação de tais compostos em busca de novas moléculas que possam ser utilizadas como modelos para o desenvolvimento de novos herbicidas. Em investigação preliminar, a atividade fitotóxidade de filtrados de culturas em meio líquido do fungo foi evidenciada, bem como a influência de diferentes condições de cultivo sobre a fitotoxicidade de filtrados de cultura. As condições de cultivo que resultaram na produção de filtrados de cultura apresentando fitotoxicidade elevada foram utilizadas para fins de isolamento e identificação de metabólitos fitotóxicos. Filtrados de cultura formada em meio de Jenkis-Prior foram submetidos a isolamento guiado por bioensanio, levando à caracterização de fração cromatográfica composta por diferentes ácidos graxos com atividade fitotóxica comprovada e à identificação do composto fitotóxico tirosol. Através de ensaio com punctura de folhas, tirosol, foi capaz de causar despigmentação e necroses severas sobre folhas de E. heterophylla (ED50 36,9 mM). O composto foi aplicado sobre folhas de soja, milho e de diferentes espécies daninhas. Mesmo em concentração elevada (100 mM), o composto apresentou baixa toxicidade contra as diferentes espécies, demonstrando, assim, atividade seletiva para a planta hospedeira do fungo. O potencial de tirosol como herbicida natural para o controle de E. heterophylla foi avaliado através de ensaio por aspersão. A concentração mínima de tirosol capaz de provocar a morte de 100% das plantas de E. heterophylla foi de 40 mM. Posteriormente, o fracionamento guiado por bioensaio de filtrados de cultura em meio de Fries levou ao isolamento dos compostos anidromevalonolactona, (R)-(–)-mevalonolactona e cicloglicilprolina. Estes compostos foram capazes de produzir, em curtos intervalos de tempo, sintomas similares aos produzidos pela inoculação do fungo na planta hospedeira, o que sugere a participação destes compostos nos estágios iniciais da interação planta-patógeno. Os resultados obtidos no trabalho indicam que os metabólitos fitotóxicos isolados de culturas do fungo Alternaria euphorbiicola podem constituir-se em modelos promissores para a síntese de análogos com atividade herbicida para o manejo de Euphorbia heterophylla. / The fungal specie Alternaria euphorbiicola was isolated from severely infected tissues of Euphorbia heterophylla, regarded as one of the most nocive weed in the Brazilian agriculture. The aggressiveness and rapid development of symptoms produced by inoculation of A. euphorbiicola on E. heterophylla sparked the interest in investigating the production of phytotoxins by this fungus in the search for new molecules that can be used as models for the development of new herbicides. In a preliminary investigation, the phytotoxicity of culture filtrates of the fungus and the influence of different growing conditions on the in vitro production of phytotoxic metabolites were proved. The growing conditions resulting in highly phytotoxic culture filtrates were selected to the isolation and identification of phytotoxic metabolites. Filtrates of cultures formed in Jenkins-Prior medium were subjected to bioassay-guided isolation procedures, leading to the characterization of a phytotoxic chromatographic fraction constituted mainly by middle chain fatty acids and to the isolation of the phytotoxin known as tyrosol. Through a puncture leaf assay, tyrosol was able to cause severe depigmentation and necrosis on leaves of E. heterophylla (ED50 36.9 mM). The compound was also applied on the leaves of soybean, corn and different weed species. Even at high concentration (100 mM), the compound showed low toxicity against these different species, thereby demonstrating selective activity for the fungal host plant. The potential of tyrosol as a natural herbicide for chemical control of E. heterophylla was assessed by a leaf spray assay. The minimum concentration of tyrosol capable of causing the death of 100% of the plants was 40 mM. Subsequently, a bioassay-guided fractionation of filtrates from cultures formed in Fries medium lead to the identification of the compounds anhydromevalonolactone, (R)-(–)-mevalonolactone and cycloglycilproline. All these compounds were able to produce symptoms similar to those produced by inoculation of the fungus on the host plant, in short time intervals, suggesting the possible involvement of these compounds in the early stages of plant-pathogen interaction. The results obtained in this work indicate that the phytotoxic metabolites produced by Alternaria euphorbiicola may constitute promising start points to the synthesis of analogues with herbicide activity for the management of Euphorbia heterophylla.

Made available in DSpace on 2016-06-02T20:34:35Z (GMT). No. of bitstreams: 1 4393.pdf: 23560579 bytes, checksum: 0869152d96e7734e1dd6786fa23cb550 (MD5) Previous issue date: 2012-05-03 / Universidade Federal de Sao Carlos / The study of phytopathogenic fungi Alternaria alternata has improved the chemical of this micro-organism. The fungus was grown up in large scale incubated in rice medium for 26 days. After grown period was interrupted an extract of the microorganism was made and fractionated using several chromatographic techniques, obtaining 11 different classes of metabolites which are: alternariol monomethyl éter, alternariol, altertoxin, altenuen, altenusin, uridine, uracila, 5 -inosil, ergosterol, peróxido de ergosterol e triglycerides. Also, a study was made via LC-MS in order to identify some toxins produced by A. alternata like a pathogen of citrus, and it was possible to identify four of these. Other research via LC-MS was the study of co-cultivation of the fungus A. alternata, the causal agent of alternaria brown spot, and Guignardia citricarpa, the causal agent of citrus black spot. In this study was possible to observe the variation in concentration of alternariol and thenuazonic acid, mycotoxins produced by A. alternata when this fungus is in contact with G. citricarpa. The study identification of the volatiles produced by A. Alternaria in different ways contributed significantly to improve the knowledge of their chemistry. Once, the A. alternata is a pathogenic fungus of 'Murcott' a study was performed via scanning electron microscopy (ESEM). Thus it was possible to observe the penetration of this fungus by stomatal cavity of young leaves of citrus. In order to search for natural inhibitors to control the disease, were tested several classes of natural products against the A. alternata, and some alkaloids, a xxvi coumarin, a xanthyletin, and a flavonoid substances showed Higher inhibition of mycelial growth, spore germination and appressorium formation. With the aim to obtain information on natural inhibitors were tested metabolites produced by A. alternata opposite and G. citricarpa, the results indicated that alternariol monomethyl ether and alternariol were substances that had a potential fungistatic against the causal agent of citrus black spot. / O estudo do fungo fitopatógeno Alternaria alternata contribuiu com a química desse micro-organismo. O fungo foi cultivado em larga escala utilizando como meio de cultura arroz por um período de 26 dias. Após esse período o crescimento foi interrompido e foi feito um extrato do microorganismo o qual foi fracionado utilizando várias técnicas cromatográficas obtendo 11 metabólitos de distintas classes sendo eles: alternariol monometil éter, alternariol, altertoxina, altenueno, altenusina, uridina, uracila, 5 -inosil, ergosterol, peróxido de ergosterol e triglicerídeo. Além disso, foi feito um estudo via LC-MS buscando identificar algumas toxinas de citros produzidas por A. alternata, sendo que foi possível a identificação de quatro dessas. Outra pesquisa realizada via LC-MS foi o estudo de co-cultivo entre os fungos A. alternata, o agente causal da mancha marrom de alternaria, e Guignardia citricarpa, o agente causal da mancha preta de citros. Nesse estudo foi possível observar a variação de alternariol e ácido tenuazônico, micotoxinas produzidas por A. alternata, quando este fungo está em contato com outro fitopatógeno. O estudo de identificação dos voláteis produzidos por A. alternaria em diferentes meios contribuiu muito para um maior conhecimento de sua química. Sabendo que A. alternata é um fitopatógeno de tangor Murcott foi realizado um estudo via microscopia eletrônica de varredura (MEV) a qual foi possível observar a penetração desse fungo pela cavidade estomatal de folhas jovens desse citros. Visando a busca de inibidores naturais para o controle da doença, foram ensaiadas diversas classes de produtos naturais frente a A. alternata, sendo que alcalóides e uma cumarina, a xantiletina, foram as substâncias que apresentaram uma maior inibição no crescimento micelial, germinação de esporos e formação de apressórios. Pensando em inibidores naturais, foram ensaiados metabólitos produzidos pelo A. alternata frente ao G. citricarpa, e os resultados obtidos revelaram que alternariol monometil éter e alternariol foram as substâncias que apresentaram um potencial fungistático frente ao agente causal da mancha preta de citros.

Made available in DSpace on 2014-06-11T19:35:00Z (GMT). No. of bitstreams: 0 Previous issue date: 2000-06-01Bitstream added on 2014-06-13T19:05:00Z : No. of bitstreams: 1 verzignassi_jr_dr_botfca.pdf: 678064 bytes, checksum: 1a9c22b2b6f4814a330b0bfcccb5c204 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Com o objetivo da redução da aplicação de fungicidas na produção de alho, foram estudados os efeitos dos Microrganismos Eficazes (E.M.-4 e E.M.-5) sobre o controle da mancha púrpura, a produção da cultura e as propriedades físicas, químicas e biológicas do solo. Os experimentos foram conduzidos, em condições de campo, por dois e três anos, na Fazenda de Ensino, Pesquisa e Produção da Unesp em São Manuel, SP. O E.M. foi aplicado nos bulbilhos de alho antes do plantio, adicionado ao material orgânico incorporado ao solo e pulverizado nas plantas após incubação ou não com melaço. A utilização do E.M. + melaço (não incubado) não proporcionou controle da doença nos experimentos. No entanto, com a incubação do E.M. + melaço houve redução na severidade da mancha púrpura em um experimento e incremento na emergência e número de folhas verdes por planta em ambos os experimentos. A altura das plantas, superbrotamento, produção, bulbos de maior valor comercial (classes 5+6+7) e as propriedades físicas (densidade do solo, condutividade hidráulica, estabilidade dos agregados, resistência à penetração e infiltração de tinta), químicas e biológicas do solo (conteúdo de polissacarídeos, carbono da biomassa microbiana do solo e atividade da desidrogenase) não foram alteradas pela utilização do E.M. A adição de material orgânico ao solo promoveu maior agregação do solo (estabilidade dos agregados), independentemente dos tratamentos empregados. No entanto, a densidade do solo, a condutividade hidráulica e a resistência à penetração não sofreram alterações com a adição do material orgânico. / With the purpose to reduce fungicides application for garlic production, the effects of Effective Microorganisms (E.M.-4 and E.M.-5) were studied on the control of garlic purple blotch, garlic yield and physical, chemical and biological properties of the utilized planting soil. Experiments were carried out under field conditions, for two and three years, an experimental farm, belonging to São Paulo State University, located in São Manuel, São Paulo, Brazil. E.M. was applied on garlic cloves before planting, additioned to the incorporated organic matter and sprayed on garlic aerial part after incubation or not with molasse. When E.M. plus molasse (not incubated) was utilized the control of purple blotch was not observed in two experiments. However, with the incubation of E.M. with molasse, the results showed a reduction of purple blotch severity in one experiment as well as an increment of seedling emergency and number of green leaves per plant in two experiments. Plant height, bulbil sprouting, yield, bulbs with higher market grades (classes 5+6+7) and soil physical (bulk density, hidraulic conductivity, stable soil aggregates, resistance to soil penetration and tint infiltration) chemical and biological (polyssacharides, carbon of microbial biomass and dehydrogenase content) proprieties were not affected by E.M. utilization. Organic matter addition promoted soil agreggation in all treatments, however, soil bulk density, hidraulic conductivity and resistance to soil penetration was not changed by organic matter addition.

Submitted by Mario BC (mario@bc.ufrpe.br) on 2016-11-28T13:13:21Z No. of bitstreams: 1 Celma Cardoso Peixoto.pdf: 1809049 bytes, checksum: 2c1b8859bd46d99b602026bcba5684c1 (MD5) / Made available in DSpace on 2016-11-28T13:13:21Z (GMT). No. of bitstreams: 1 Celma Cardoso Peixoto.pdf: 1809049 bytes, checksum: 2c1b8859bd46d99b602026bcba5684c1 (MD5) Previous issue date: 2015-02-26 / Early blight caused by species from Alternaria genus affects several solanaceous of economic importance. Previous studies have shown that the species A. tomatophila and A. grandis prevail as causal agents of disease on tomato and potato, respectively. The control of this disease is based on the use of protective and systemic fungicides. However, there are reports of the existence of other species of Alternaria causing early blight in plants of the Solanácea family. This study aimed to perform molecular, morphological and biological characterization of Alternaria isolates from cultivated and wild solanaceous from different regions of Brazil. Molecular characterization of the isolates was done by sequencing and phylogenetic analysis of the genes Alt a1, GPD and Calmodulin. Morphological characterization was performed by measurement of dimensions of the conidia and quantification of the number of septa and rostrums. Biological characterization of Alternaria isolates was done by evaluation of host range and by the in vitro sensitivity to tebuconazole. Phylogenetic analysis of the genes Alt a1, GPD and Calmodulin allowed the identification of the species A. tomatophila, A. mimicula and A. dauci from tomato, and the species A. grandis and A. solani from potato and from lobeira, respectively. Morphologic caracteristics of most isolates corroborate the molecular characterization. The isolate EH1642-BA, identified as A. solani, was able to cause early blight on all solanaceous hosts evaluated except the sweet pepper. EH1823-CE of the specie A. tomatophila and EH1548-DF of A. grandis isolates from tomato and potato, respectively, had not specificity for their original host plants. However, the isolates EH1143-RS of the specie A.dauci and EH1377-CE of A. mimicula showed specificity for original host causing typical symptoms of early blight only on tomato. Alternaria isolates from tomato and eggplant caused disease on wild invasive solanaceous Datura stramonium and Physalis pubescens and isolates from D. stramonium and Nicandra physaloides caused symptoms of early blight on tomato, potato and jiló. In the sensitivity tests to the fungicide tebuconazole in general the isolates showed high sensitivity under in vitro conditions. The results obtained in this study confirmed the occurrence of A. tomatophila and A. grandis as causal agents of early blight on tomato and potato, respectively, and in this work were detected for the first time in Brazil the presence of A. dauci and A. mimicula associated with the disease on tomato. It has been found that some wild solanaceous can act as pathogen inoculum sources and the tebuconazole was efficient in the in vitro control for the isolates evaluated. / A pinta-preta, causada por fungos do gênero Alternaria, afeta diversas solanáceas importantes economicamente e as espécies A. tomatophila e A. grandis prevalecem como agentes causais da doença em batateira e tomateiro, respectivamente. O controle se baseia no uso de fungicidas protetores e sistêmicos. Todavia, existem relatos da existência de outras espécies de Alternaria causando pinta-preta em plantas da família Solanácea. O presente trabalho teve como objetivos realizar a caracterização molecular, morfológica e biológica de isolados de Alternaria oriundos de solanáceas cultiváveis e silvestres de diferentes regiões do Brasil. A caracterização molecular foi feita mediante sequenciamento e análises filogenéticas das regiões Alt a 1, GPD e Calmodulina. A caracterização morfológica foi conduzida por meio da mensuração das dimensões dos conídios e quantificação do número de septos e rostros. Na caracterização biológica realizou-se a avaliação da gama de hospedeiras solanáceas e testes in vitro de sensibilidade ao fungicida tebuconazole. As análises filogenéticas dos genes Alt a 1, GPD e Calmodulina possibilitaram a identificação das espécies A. tomatophila, A. mimicula e A. dauci oriundos de tomateiro, e também das espécies A. grandis e A. solani provenientes de batateira e lobeira. As características morfológicas da maioria dos isolados concordaram com a caracterização molecular. O isolado EH1642-BA identificado como A. solani foi capaz de causar pinta-preta em todos os hospedeiros exceto o pimentão. Já o EH1823-CE da espécie A. tomatophila e o EH1548-DF de A. grandis provenientes de tomateiro e batateira não apresentaram especificidade para as duas plantas hospedeiras originais. Contudo, os isolados EH1143-RS da espécie A.dauci e EH1377-CE de A. mimicula mostraram especificidade por hospedeira de origem ocasionando sintomas típicos da pinta-preta apenas em tomateiro. Isolados obtidos de tomateiro e berinjela causaram doença nas invasoras silvestres Datura stramonium e Physalis pubescens e isolados originários de D. stramonium e Nicandra physaloides provocaram sintomas em tomateiro, batateira e jiló. Em relação à sensibilidade ao tebuconazole verificou-se que em termos gerais os isolados apresentaram alta sensibilidade ao produto sob condições in vitro. Os resultados obtidos no presente estudo confirmaram a ocorrência de A. tomatophila e A. grandis como agentes causais da pinta-preta em tomateiro e batateira e foram detectadas pela primeira vez no Brasil a presença das espécies A. dauci e A. mimicula associadas à doença em tomateiro. Verificou-se ainda que solanáceas invasoras podem atuar como fontes de inóculo do patógeno e que o tebuconazole apresentou eficiência no controle in vitro para todos os isolados avaliados.

Allium sativum and Tulbaghia violacea are some of the most important medicinal plants used by South African traditional healers for the treatment of flu, fever, cold, tuberculosis, asthma and many more diseases. However, growth, yield and quality are constrained by excessive and under fertilization. This study was carried out to determine, firstly, the effect of N source (ammonium sulphate and calcium nitrate) on yield and quality of A. sativum and T. violacea plants. Secondly, to determine the best season for harvesting T. violacea and lastly, to determine the antifungal effects of A. sativum and T. violacea plant extracts against plant pathogens Altenaria solani and Sclerotium rolfsii. Both plants were treated with both N sources applied as topdressing treatments at a total of 0, 50, 100, 150 and 200 kg.ha-1, divided into three applications at three week (A. sativum) and three month (T. violacea) intervals. A. sativum plants were sampled at 54, 82, 112, 140 and 175 days after planting (DAP) while, T. violacea plants were sampled monthly for ten months. Parameters recorded were growth analysis, yield and bioactivity for both plant species. Both nitrogen sources improved plant growth and yield of A. sativum and T. violacea plants. Calcium nitrate at 150 kg•ha-1 and ammonium sulphate at 200 kg•ha-1 produced the highest at 24 t•ha-1 and 27 t•ha-1, respectively. Ammonium sulphate improved bioactivity of leaves with the highest bioactivity recorded at 82 and 112 DAP. Yield obtained from the autumn harvest was not affected by N source. Ammonium sulphate and calcium nitrate at 200 kg•ha-1 produced the highest yields of 23.6 t•ha-1 and 23.5 t•ha-1, respectively. In contrast, yield obtained from the winter harvest was affected by N source at 200 kg•ha-1, with significantly better yield of 30.8 t•ha-1 with calcium nitrate compared to 27.4 t•ha-1 with ammonium sulphate. Crude extracts of T. violacea bulbs that were treated with ammonium sulphate significantly inhibited the growth of plant pathogenic fungi, whereas extracts from plants treated with calcium nitrate showed low bioactivity. Extracts from plants grown with ammonium sulphate at 100 kg•ha-1 were more effective in controlling growth of plant pathogens when compared to other N levels. The minimum inhibitory concentration (MIC) effects of A. sativum against S. rolfsii and A. solani were at 0.01 mg•mL-1. The MIC of T. violacea extracts against A. solani was at 0.006 mg•mL<Sup>-1. The MIC of T. violacea extracts were better than previously reported in literature. Therefore, A. sativum and T. violacea plant extracts can be used as fungicides against S. rolfsii and A. solani diseases for crops such as tomato and potato. / Dissertation (MInstAgrar)--University of Pretoria, 2010. / Plant Production and Soil Science / unrestricted

Early blight (Alternaria solani Sorauer)is a major foliar disease of potatoes in most growing regions of the world and is underestimated in South Africa. This project studies the epidemiology and control of the disease in South Africa. A decision support system (DSS) for early blight in South Africa was developed and evaluated in field trials. This early blight DSS is the first such system to be developed in South Africa and once incorporated with the late blight model, will represent innovative technology for use in the South African potato industry. Trends in weather variables and concentrations of airborne conidia of A. solani were monitored. Distinct seasonal variation was noted. Peaks in spore concentration coincided with periods favourable for spore formation and dispersal; most notable was diurnal periodicity and interrupted wetting periods. The results obtained from these measurements will be useful in improving early blight DSSs for southern Africa. Isolates of A. solani from various potato-growing regions in South Africa were characterized using virulence, vegetative compatibility (VC) and random amplified microsatellite (RAMS) primers. Neither the virulence assays nor VC tests sufficiently characterised the population. Analysis of RAMS profiles revealed 27% genetic diversity among the isolates. This value is similar to diversity values obtained by previous authors studying A. solani, however, it is relatively high for an asexually reproducing fungus. There was no evidence for geographical clustering of isolates, indicating that isolates are widespread across South Africa. A survey on control practices and grower perceptions of early blight in South Africa was conducted using a questionnaire. These questionnaires were distributed to growers from 10 potato-growing regions in South Africa. Results highlighted the most popular control methods and cultivars in the South African potato industry. The majority of respondents indicated that they would use an accurate, cost-effective early blight DSS, and that more research is necessary on early blight in South Africa. A survey on control practices and grower perceptions of early blight in South Africa was conducted using a questionnaire. These questionnaires were distributed to growers from 10 potato-growing regions in South Africa. Results highlighted the most popular control methods and cultivars in the South African potato industry. The majority of respondents indicated that they would use an accurate, cost-effective early blight DSS, and that more research is necessary on early blight in South Africa. Estimated crop losses ranged from 1% - 60%, with an average of approximately 20%. This is the first comprehensive epidemiological study to be conducted on early blight in South Africa and has highlighted the need for further research. / Thesis (DPhil (Plant Pathology))--University of Pretoria, 2006. / Microbiology and Plant Pathology / unrestricted

The initial phase in the development of a biological control strategy is screening of biological control agents. Secondary to this phase is the establishment of accurate, effective application techniques. However, successful control requires a thorough understanding of all factors affecting the relationship between host plant, pathogen and other microbes. The purpose of this study was to screen and identify potential bacterial antagonists against Alternaria, a fungal citrus pathogen, attachment of the antagonists to bees, and bee dissemination of the antagonist to citrus flowers. A total of 568 bacterial epiphytes were screened on agar plates for antagonism against Alternaria. Only eight of these isolates, which were identified as Bacillus subtilis, B licheniformis, B. melcerons, B. polymyxa, B. thermoglycodasius, B. sphaericus, B. amiloliquefaciens, and B. coagulans, showed inhibitory effects on the growth of Alternaria. The most effective isolates were B. subtilis and B. licheniformis. Further screening was done with B. subtilis and B. subtilis commercial powder (Avogreen). These bacteria were sprayed on citrus flowers for colonisation studies. Mean populations of B. subtilis and the commercial powder recovered from the flowers were 104 and 103 cfu/stamen respectively. The organisms colonised the styler end and ovary of the flowers when observed under scanning electron microscope (SEM). Avogreen was placed in an inoculum dispenser, which was attached to the entrance of the hive. Honeybees emerging from the beehive acquired 104 cfu/bee. The powder attached to the thorax and thoracic appendages, as revealed by SEM. One active beehive was placed in an enclosure with fifteen flowering citrus nursery trees in pots for dissemination trials. Mean populations of commercial B. subtilis recovered from the flowers visited by bees were 104 cfu/stamen. Electron microscope studies revealed that the antagonist was colonising the styler end and ovary of the flowers. Field dissemination studies were unsuccessful due to low yields. / Dissertation (Magister Institutiones Agrariae)--University of Pretoria, 2003. / Plant Production and Soil Science / unrestricted

Citrus is the main fruit crop in the world and Spain is the 6th producer and the major exporter for the fresh fruit market. Seedlessness is one of the most important fruit quality traits for this market since consumers do not accept seedy fruits. Recovery of triploid hybrids has become an important breeding strategy to develop new seedless citrus varieties and several of them have been already released from citrus breeding programs worldwide. Despite the undisputable importance of polyploidy in plant species, their genetics are much less well known than those of their diploid counterparts. Citrus triploid hybrids can be routinely recovered from sexual polyploidization (2x ¿ 2x) or interploid crosses (2x ¿ 4x and 4x ¿ 2x). In 2x ¿ 2x sexual crosses, spontaneous triploid hybrids arise from the union of an unreduced (2n) megagametophyte with haploid pollen. In the case of interploid sexual crosses (2x ¿ 4x and 4x ¿ 2x), triploid hybrids result from the fecundation of a diploid gamete arising from the tetraploid parent and a haploid gamete arising from the diploid parent. The genetic and phenotypic structures of triploid populations greatly depend on the parental heterozygosity restitution (HR) in the diploid gamete at each locus, which is mainly affected by the triploid recovery strategy. In 2x ¿ 2x crosses, HR depends on the underlying mechanism leading to the unreduced gamete formation, which are genetically equivalent to First Division Restitution (FDR) or Second Division Restitution (SDR) mechanisms. Moreover, under each restitution mechanism, HR also depends on the locus-centromere genetic distance. In the case of interploid crosses, parental heterozygosity restitution from tetraploid parents depends on the double reduction frequency. In citrus, the unreduced gamete formation mechanism is still controversial; FDR has been the mechanism proposed for sweet orange, whereas SDR has been proposed for clementine. On the other hand, inferring the allelic configurations of genetic markers is a main challenge in polyploidy crops to infer genotypic and gametic structures with the objective to analyze meiosis and inheritance mechanisms. According to this scientific context, the objectives of the thesis where: (i) to develop a new approach for allele dosis assignation when using co-dominant markers, (ii) to implement and apply methods for the analysis of 2n gametes origin and locate centromeres, and (iii) to take advantage of this knowledge to locate a major gene of resistance to Alternaria Brown Spot (ABS) which is a major constraint for triploid mandarin breeding. For microsatellite (SSR) markers, we have demonstrated that triploid progeny genotyping can be successfully performed using the microsatellite allele-counting peak ratio (MAC-PR) method. However, SSR analysis remains relatively costly and time consuming compared with actual SNP genotyping methods. Moreover, with the increasing availability of EST databases and whole genome sequences, SNPs have become the most abundant and powerful polymorphic markers that can be selected along the entire genome. In this thesis, a new method based on competitive allele-specific PCR has been developed to assign SNP allele dosage in an accurate, simple, and cost effective way. Combining the MAC-PR and the new developed SNP genotyping methods offers the possibility to utilize a broad range of molecular markers in genotyping triploid genotypes. Both methods have been used in further works included in this thesis. SDR has been demonstrated as the mechanism underlying unreduced gamete production in `Fortune¿ mandarin by genotyping triploid progenies with SSR markers. In addition, a new method to locate the centromere, based on the best fit between observed heterozygosity restitution within a linkage group and theoretical functions under either partial or no chiasma interference hypotheses has been developed and successfully applied. To expand the knowledge of the mechanism underlying unreduced gamete formation to other citrus genotypes besides clementines and `Fortune¿ mandarin, a maximum likelihood method based on parental heterozygosity restitution of centromeric loci was developed and successfully applied in sixteen mandarin cultivars. The new method developed in the study allows inferring the restitution mechanism both at population level and even at individual level. Maternal origin of 2n gametes was confirmed for all triploid hybrids and SDR was proposed as the restitution mechanism for all analyzed progenies. The information acquired from the mode of heterozygosity restitution in citrus was useful to determine the genetic and phenotypic structures of new triploid populations arising from different breeding strategies. We studied these structures for the resistance to Alternaria brown spot (ABS), a serious fungal disease producing necrotic lesions on fruits and young leaves in susceptible citrus genotypes. In the present work, different approaches were combined taking advantage of the particular genetic structures of 2n gametes resulting from SDR to map a genome region linked to ABS resistance in triploid citrus progeny. The monolocus dominant inheritance of the susceptibility, proposed on the basis of diploid population studies, was corroborated in triploid progeny. A 3.3 Mb genomic region linked to ABS resistance was located near the centromere on chromosome III, which includes clusters of resistance genes. SSR and SNP markers were developed for an efficient early selection of ABS resistant hybrids and they are currently used in our breeding program to perform marker assisted selection. The knowledge obtained in this thesis on the mechanism of sexual polyploidization and inheritance of concrete traits in citrus will allow implementing much more efficient triploid breeding programs on the basis of current and future needs. Indeed, applied outcomes of this PhD are already routinely used in the IVIA triploid breeding program. / Cuenca Ibáñez, J. (2013). Mechanisms of sexual polyploidization and inheritance in triploid citrus populations [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/34671 / TESIS / Premios Extraordinarios de tesis doctorales

Thesis (M. Agricultural Management (Plant Production)) -- University of Limpopo, 2020 / Tomato is a major vegetable crop produced in Limpopo province by subsistence and commercial farmers. Biotic and abiotic factors such as diseases and drought affect its productivity and yield negatively. The most economically important tomato disease in Limpopo is early blight, caused by Alternaria solani. Early blight affects tomato growing under stressful conditions such as drought. The main aim of this study was to evaluate water management in tomato production and its effect on tomato yield, early blight occurrence and severity under smallholder farming systems in Giyani. A survey study and field experiments on early blight occurrence and severity were conducted in the Greater Giyani municipality in Limpopo province. Firstly, a survey of early blight was conducted in tomato fields selected from three service centres namely Guwela, Hlaneki and Mhlava Willem. Twenty five potential tomato grower’s farms were randomly selected for survey based on the location and production management strategies. A second study was carried out by establishing field experiments at two farms in the same area, namely: A hi tirheni Mqekwa and Duvadzi farms. The experiments were laid out in a randomized complete block design (RCBD) in a split plot arrangement, with irrigation as the main plot treatment and tomato variety as the subplot treatment. Each treatment was replicated four times. The irrigation treatments consisted of full irrigation up to field capacity and deficit irrigation. The tomato varieties planted were HTX14, Rodade, STAR9006 and Commander, and were irrigated with a drip irrigation system. The overall survey results showed that Guwela s/c had high disease incidence and the lowest disease severity as compared to the other two service centers. The lowest disease incidence was observed at Hlaneki s/c whilst Mhlava willem s/c had the highest disease severity. The two water treatments (full and deficit irrigation) in both farms have shown no significant pairwise differences among xx the volumetric water content means. There was no significant difference (P≥0.05) in early blight disease severity in both farms. Results shows that, all tomato varieties did not differ significantly (P≥0.05) in yield observed between treatments at Duvadzi and A hi tirheni Mqekwa Farm. Deficit irrigation can be used effectively to produce high yields in tomato production provided the cropping season window does not coincide with the hottest time of the year. Full and deficit irrigation did not have influence on the early blight disease incidence on tomato plants. Key words: Alternaria solani; disease incidence; disease severity and drip irrigation

Seed germination is pivotal in the life cycle of native plants in a restorative context because initiation of the metabolic processes critical to establishment is key to survival in such a competitive environment. Dormancy characteristics of some native plants including the subject species, Astragalus utahensis, have evolved mechanisms to control germination in order to maintain a seed bank and ensure germination at the right time under optimal conditions. In vitro germination studies confirm beneficial interactions between Alternaria and Aspergillus fungi and Astragalus utahensis seed. Inoculated seed trials (1.0 x 106 spores/mL) exhibited a highly significant difference in percent germination between the uninoculated control at 5.0 % germination and seeds inoculated with Alternaria and Aspergillus germinating at 95 % and 55 %, respectively. Germination trials conducted in the greenhouse revealed a beneficial relationship between fungal spore inoculation and seed germination. Control seeds germinated in soil at a rate of 16.0 %; three times as high as exhibited in vitro. Seed inoculated with either Alternaria or Aspergillus seeds germinated in soil at the same rate of 50.0 %. A seed germination trial conducted in the field demonstrated a beneficial response with Aspergillus inoculation. Fall plantings on two sites near Fountain Green and Nephi, Utah confirm this beneficial response to Aspergillus spore inoculation. These field trials indicated a highly significant response with the germination of scarified control seed at 14.7 % and the Aspergillus and Alternaria treated seed germinating at 29.3 and 19.3 %, respectively. Greenhouse germination trials with spore-inoculated seed indicated a 100% survival rate. Astragalus utahensis seeds germinated at an accelerated rate when inoculated with Aspergillus and Alternaria spores in-vitro. The beneficial germination response of fungal inoculated seeds indicates the efficacy of these treatments in dormancy contravention in hard-seeded species.