Com a continuação do aquecimento global, prevê-se o aumento dos períodos de seca, um dos mais importantes fatores abióticos a afetar o crescimento dos eucaliptos no Brasil. Nessa direção, as práticas silviculturais poderiam adaptar-se para favorecer os mecanismos de adaptação das árvores à seca. Assim, na Estação Experimental de Itatinga, foram avaliados os efeitos da adubação potássica sobre os aspectos produtivos e fisiológicos de um povoamento de Eucalyptus grandis, em primeira rotação, submetido à exclusão parcial de chuva durante trinta meses após o plantio. O dispositivo experimental foi um split plot, com três blocos completos e quatro tratamentos: dois regimes hídricos (100% e 63% das chuvas, com exclusão parcial artificial) e duas doses de K (0 e 4,5 kmol ha-1). A meta foi avaliar a influência da nutrição potássica sobre as características e a atividade fotossintética das folhas. A transpiração foi medida por sensores de fluxo de seiva para estimar a eficiência de transpiração do povoamento. O potencial foliar e as trocas gasosas foliares foram monitorados, enquanto os valores de \'delta\'13C do floema foram medidos, para avaliar o estado hídrico e o funcionamento estomático das árvores, em função da disponibilidade de K e de água. Os resultados mostraram que a adição de K atuou sobre vários mecanismos responsáveis pelo aumento do crescimento e da produção de madeira: aumento da área foliar total e individual, da duração de vida foliar, do tamanho e da turgescência celular foliar, da espessura foliar e dos espaços intercelulares no mesófilo foliar, da capacidade fotossintética, da condutância dos estômatos e do mesófilo, da exportação dos fotoassimilados, produzidos nas folhas-fontes, do fluxo de seiva, da eficiência de transpiração na produção de madeira, pelo aumento da repartição de biomassa nesse compartimento. Folhas com sintomas de deficiência de K mostraram concentrações de nutrientes, espaços intercelulares e atividade fotossintética inferiores, e concentrações de açúcares solúveis superiores, na comparação com o tratamento com K, sugerindo uma ligação entre nutrição, anatomia e fisiologia foliar. Durante o déficit hídrico, o E. grandis mostrou um comportamento isohidrodinâmico, associado ao fechamento estomático, ao ajustamento foliar osmótico, à diminuição na elasticidade das paredes celulares, ao aumento na eficiência de uso da água nas folhas, à diminuição da área foliar total e à rápida absorção da água nas camadas profundas do solo. A partir de aproximadamente 22 meses após o plantio, o estado hídrico das árvores diminuiu: (1) nas parcelas com exclusão parcial de chuva, em relação às parcelas sem exclusão parcial de chuva, e (2) nas parcelas com adição de K, em relação às parcelas sem essa adição. Embora a adição de K melhore as relações hídricas nas folhas, o controle dos movimentos estomáticos e as trocas gasosas foliares, ela agravou o estado hídrico das árvores durante períodos de seca intensa, devido ao maior crescimento e à demanda hídrica. Assim, os efeitos benéficos da adição de K sobre a adaptação à seca das árvores poderiam não contrabalançar o aumento do déficit hídrico durante períodos mais intensos de seca. Em relação às previsões futuras de seca, as empresas florestais, provavelmente, terão de adaptar a fertilização para minimizar a demanda de água e os riscos de mortalidade / Global warming is predicted to exacerbate drought, one of the most important abiotic stress factors affecting eucalypts growth in Brazil. Silvilcultural practices might be adapted to enhance drought adaptation mechanisms of trees. This study examined the effects of K addition on productive and physiological aspects of Eucalyptus grandis stands in first rotation submitted to partial through fall exclusion over thirty months after planting. A large-scale through fall exclusion experiment using a split plot design was conducted with three blocks and four treatments: two water regimes (100% and 63% of through fall with partial artificial exclusion) and two K doses (0 and 4.5 kmol ha-1). The influence of K nutrition on characteristics and photosynthetic activity of leaves was assessed Tree transpiration was measured from sap flow probes to estimate water use efficiency. Foliar water potential and gas exchange were monitored, and phloem \'delta\'13C was measured in order to evaluate tree water status and stomatal regulation depending on K and water availabilities. The results showed that K supply influence various mechanisms responsible for tree growth enhancement: increase in total and individual leaf area, leaf lifespan, cell turgor and cell size due to an increase in turgor, leaf thickness and intercellular spaces, photosynthetic capacity, stomata and mesophyll conductances, photoassimilate export from source leaves and transpiration efficiency for wood production through increase of biomass partitioning to this compartment. Leave with K-deficiency symptoms exhibited lower nutrient concentrations and photosynthetic activity, reduced intercellular spaces, and higher soluble sugar contents compared to healthy leaves, which suggested a strong link between nutrition, leaf anatomy and physiology. The adaptive mechanisms of E. grandis trees to cope with water restriction were an isohydrodynamic behavior associated with stomatal closure, osmotic adjustment, a decrease in wall cell elasticity, an increase in foliar water use efficiency, a decrease in total leaf area and a fast water uptake in very deep soil layers. From approximately 22 months after planting onwards, tree water status was lower: (1) in droughted plots compared to the rain-fed plots and, (2) in K-fertilized plots, compared to the K-unfertilized trees. Although K addition enhanced tree water relations, stomatal control and leaf gas exchange, it exacerbated tree water deficit during severe drought as a result of high water demand throughout tree development. Therefore, the beneficial effects of K supply on tree acclimation to drought may not counterbalance the increase in water deficit during severe water restriction periods compared to the K-unfertilized trees. Regarding future drought previsions, forest managers might have to adapt their fertilization regimes to minimize water demand and risks of mortality

O objetivo do trabalho foi avaliar, por meio de variáveis fisiológicas vegetais como fotossíntese, condutância estomática, transpiração foliar, concentração interna de CO2 e temperatura foliar, o efeito de insetos pragas de diferentes hábitos alimentares em suas plantas hospedeiras. Foram estimados os níveis de dano de um sugador, Orthezia praelonga Douglas, 1891, em limão cravo (Citrus limonia L.), e de Leucoptera coffeella (Guérin-Mènevile, 1842), um mastigador, em mudas de café 'Obatã'. Os ensaios foram realizados em condições ótimas de temperatura, com luz e CO2 saturantes, e diferentes porcentagens de área foliar lesionada, obtidas pela variação do número de insetos por folha, no caso de O. praelonga em limão cravo (de 0 a 35 cochonilhas/folha (0-6%), de 40 a 70 cochonilhas/folha (7-13%), de 80 a 220 cochonilhas/folha (14-40%) e >220 cochonilhas/folha (>40%)) ou por tecido vegetal consumido (intervalos de 0-25%, 26-36% e >37%), no caso de L. coffeella em mudas de cafeeiro. As leituras das variáveis fisiológicas vegetais foram feitas com um medidor portátil de fotossíntese (IRGA). Os dados foram analisados por meio de uma regressão não linear, e, nos dois casos, existe uma correlação negativa entre fotossíntese e área foliar lesionada, ou seja, quanto maior a área foliar lesionada, menor a fotossíntese; e o ponto de inflexão negativo da curva, no qual um pequeno aumento na área foliar lesionada resultou em uma grande perda fotossintética, é tomado como referência de nível de dano, sendo que o nível de controle destas pragas, esta abaixo destes valores. A condutância estomática, a transpiração foliar, a concentração interna de CO2 e a temperatura foliar, em ambos os casos, não demonstram uma correlação definida com a intensidade de danos. A transpiração foliar em limão cravo atacado por O. praelonga é maior nos pontos onde também é maior a condutância estomática, e nas folhas de café com ataque de L. coffeella a transpiração foliar mantem-se constante durante toda a curva, semelhante à variável condutância estomática. As relações matemáticas de fotossíntese/concentração interna de CO2, e fotossíntese/condutância estomática são, em ambos os casos, decrescentes, o que demonstra respectivamente queda na eficiência instantânea de carboxilação da rubisco e redução da eficiência intrínseca do uso da água em função do aumento da área foliar lesionada. A análise conjunta dos dados demonstrou que O. praelonga afeta o fotossistema I (PS I) de folhas de limão cravo; enquanto L. coffeella afeta, em primeiro plano, o fotossistema II (PS II). No caso de O. praelonga em limão cravo, determina-se a faixa de 7 a 13% de área foliar lesionada (de 40 a 70 cochonilhas/folha) como sendo o valor de nível de dano, e para L. coffeella em cafeeiro este valor ficou na faixa de 25 a 36% de área foliar lesionada (tecido consumido pelo inseto). Os valores obtidos em laboratório, necessitam ajustes efetivos na determinação do nível de controle destas pragas no campo. A técnica de leitura de fotossíntese mostrou-se adequada a este propósito, e a análise dessa variável demonstrou ser a melhor opção para tal correlação. / The goal of this work was to evaluate the effect of insect pests of different feeding habits in their host plants through readings of plant physiological variables as photosynthesis, stomatal conductance, leaf transpiration, internal carbon dioxide concentration and leaf temperature. Thus, one estimated the injury level of a sucking insect, Orthezia praelonga Douglas, 1891, in 'Rangpur' lime (Citrus limonia L.), and Leucoptera coffeella (Guérin-Mènevile, 1842), a chewing insect, in 'Obatã' coffee seedlings. The trials were carried out under optimum temperature conditions, with saturating light and CO2 , with different injured leaf area percentages, obtained by the variation of the number of insects per leaf, in the case of O. praelonga in 'Rangpur' lime (0-35 mealybugs/leaf (0-6%), 40-70 mealybugs/leaf (7-13%), 80-220 mealybugs/leaf (14-40%), and >220 mealybugs/leaf (>40%)), or through plant tissue consumed (0-25%, 26-36% and > 37% intervals), in the case of L. coffeella in coffee seedlings. Plant physiological variables readings were performed through a portable photosynthesis meter(IRGA). The data were analyzed by means of nonlinear regression, and, in both cases, a negative correlation was observed between photosynthesis and the injured leaf area, that is, the larger the injured leaf area, the lesser the photosynthesis; the negative inflection point of the curve, upon which a slight increase in the injured leaf area resulted in great photosynt hesis loss is taken as a damage level reference, and the control level of these pests is below these values. The stomatal conductance, leaf transpiration, internal CO2 concentration and the leaf temperature, in both cases, showed no defined correlation with the damage intensity. The leaf transpiration in 'Rangpur' lime attacked by O. praelonga is higher in points where the stomatal conductance is higher as well, and in coffee leaves attacked by L. coffeella the leaf transpiration remains constant throughout the curve, similarly to the stomatal conductance variable. The mathematical relationships of photosynthesis/internal CO2 concentration, and photosynthesis/stomatal conductance are, in both cases, decreasing, which respectively shows drop in instant Rubisco carboxylation efficiency and reduction of the intrinsic efficiency of water use according to the increase of the injured leaf area. The joint data analysis showed that O. praelonga affects photosystem I (PS I) of 'Rangpur' lime, while L. coffeella affects, at first, photosystem II (PS II). In the case of O. praelonga in 'Rangpur' lime the 7-13% range of the injured leaf area (40-70 mealybugs/leaf) is determined as the damage level value, and for L. coffeella in coffee the value ranges 25-36% of the injured leaf area (tissue consumed by the insect). The values found in laboratory require field validation for effective adjustments to determine the level to control these insect pests. Overall, the photosynthesis reading technique was shown adequate to this purpose, and the analysis of this variable was the best choice for such correlation.

As relações hídricas e fisiológicas em plantas de lima ácida ‘Tahiti’ sob estresse hídrico foram estudadas tendo-se como principais objetivos: (a) verificar a sazonalidade da evapotranspiração e o coeficiente de cultivo com o uso de lisímetro de pesagem baseado em célula de carga eletrônica, (b) determinar o limite crítico da água disponível em função da evapotranspiração, trocas gasosas e potencial de água na folha durante um período de estresse hídrico e (c) avaliar o efeito da supressão da irrigação durante diferentes períodos fenológicos sobre o desenvolvimento vegetativo, na produtividade e qualidade do fruto. Este experimento foi conduzido na Fazenda Areão do Departamento de Engenharia Rural da ESALQ/USP, em Piracicaba, SP, em um pomar de 1 hectare no espaçamento de 7 X 4 m com lima ácida ‘Tahiti’ (Citrus latifolia Tanaka) enxertadas em citrumelo ‘Swingle’ [Poncirus trifoliata (L.) Raf. x C. paradisi Macf.] irrigadas por gotejamento. Para as medidas fisiológicas, foram utilizados equipamentos portáteis como a câmara de pressão e analisador de gases por infravermelho além de medidas do desenvolvimento vegetativo e produtivo. O monitoramento da água solo foi realizado por tensiômetros e sondas de TDR. A Evapotranspiração de Referência foi obtida com uma estação agrometeorológica automatizada presente na área. Verificou-se um efeito sazonal na evapotranspiração, com uma redução superior a 50% no período verãoinverno, possibilitando a economia da irrigação no período. A evapotranspiração, trocas gasosas e potencial da água na folha ao amanhecer foram diminuídos pelo esgotamento de 40% da água disponível do solo por ocasião do final do período de inverno. A supressão da irrigação no período de Setembro a Março diminuiu o potencial matricial do solo e promoveu um estresse leve nas plantas não-irrigadas, não se observando efeitos negativos no desenvolvimento vegetativo, produtivo e na qualidade dos frutos formados. Recomenda-se o potencial da água no folha ao amanhecer para manejo da irrigação, mantendo-o maior que -0,6 MPa, para evitar o estresse hídrico em plantas de limeira ácida ‘Tahiti’. / Water and physiologic relations in acid lime trees under water stress were studied with the following purposes: (a) to verify the seasonal effect of evapotranspiration and the crop coefficient in non-stressed trees by weighing lysimeter; (b) to determine the critical soil water depletion for evapotranspiration, gas exchange as well as the leaf water potential during a stage of growing of the trees and (c) to determine the effect of the irrigation suppression on growth, yield and fruit quality during different phenological periods. The experiment was carried out an experimental farm at College of Agriculture Luiz de Queiroz (ESALQ), in Piracicaba and performed from 2003 to 2005 in a 1 hectare orchard planted with ‘Tahiti’ (Citrus latifolia Tanaka) grafted on ‘Swingle’ [Poncirus trifoliata (L.) Raf. x C. paradisi Macf. ] rootstock. The trees were spaced 7 x 4 m apart and drip-irrigated. For physiologic measurements were used portable equipments such as a pressure chamber and an infrared gas analyzer as well measurements of vegetative and productive growth. The soil water status was monitored by tensiometers and TDR probes. The reference evapotranspiration was obtained by an automatic weather station presented on the area. There was a seasonal effect on evapotranspiration with a reduction higher than 50% forward to summer-winter, being able to water savings in the period. The evapotranspiration, gas exchange and leaf water potential at predawn were decreased when the soil water available was depleted by 40% in the end of winter. The irrigation suppression from September and March decreased the soil matric potential and promoted a light stress level in non-irrigated trees, but without negative effects on vegetative, productive and fruit quality. We recommend the leaf water potential at predawn for irrigation scheduling, keeping higher than -0.6 MPa for avoid water stress in acid lime trees.

No description available.

No description available.

Dans le contexte de changement climatique, la compréhension des mécanismes régissant les pertes en eau de la vigne peut permettre d'adapter le matériel végétal pour maintenir la productivité de la vigne et la qualité du vin. L'adaptation à la sécheresse est un caractère complexe faisant intervenir des mécanismes physiologiques liés aux génotypes du greffon et du porte-greffe. Mais les effets du porte-greffe sur la régulation stomatique du greffon sont mal connus. La production par les racines de signaux chimiques tels que l'ABA et/ou hydraulique pourraient y contribuer. La réponse physiologique et moléculaire à la contrainte hydrique a été analysée sur de jeunes boutures pour 7 porte-greffes plus ou moins adaptés à la sécheresse et 2 cépages connus pour leur caractère iso ou anisohydrique. Puis 23 combinaisons greffon/porte-greffe issues de ces génotypes ont été étudiées. Une analyse métabolique sur l'accumulation de l'ABA et ses dérivés a été menée sur feuilles, racines et dans la sève xylémienne. Ces informations ont été couplées à des analyses transcriptomiques sur des gènes du métabolisme et de la signalisation de ABA, et codant des aquaporines de type PIP. L‘analyse conjointe des données physiologiques, métabolomiques et transcriptomiques ont permis d'identifier des composants moléculaires discriminant les porte-greffes selon leur fond génétique et leur adaptation à la sécheresse. Les réponses globales à la contrainte hydrique sont mieux coordonnées au sein d‘un même tissu qu‘entre racines et feuilles. A l‘échelle de la plante greffée, une prépondérance du signal hydraulique est probable. Certains gènes répondent spécifiquement aux interactions greffon/porte-greffe. / In the context of climate change, understanding the mechanisms governing the water loss of the vine is necessary to adapt the plant material to maintain the productivity of the vine and wine quality. The adaptation to drought is a complex trait involving physiological mechanisms related to scion and rootstock genotypes. But the effects of the rootstock on stomatal regulation graft are still unknown. Production by roots of chemical signals such as ABA and / or hydraulic ones be involved. Molecular and physiological responses to water stress were analyzed on young cuttings for 7 rootstocks more or less adapted to drought and 2 varieties known for their iso or anisohydric behaviour. Then 23 combinations scion / rootstock from these genotypes were investigated. Metabolic analyses for ABA and its derivatives was conducted in leaves, roots and in the xylem sap. The information was integrated with transcriptomic analyzes for genes involved in ABA metabolism and signaling, and encoding PIP aquaporins. Joint analyses of physiological data, metabolomic and transcriptomic allow the identification of the molecular components discriminating rootstocks according to their genetic background and their adaptation to drought. Global responses to water stress are better coordinated within the same tissue between roots and leaves. At the scale of the grafted plant, a preponderance of the hydraulic signal is likely. Some genes specifically respond to the scion / rootstock interactions.

No description available.

Doctor of Philosophy (PhD) / The Australian cotton industry has developed high yielding and high quality fibre production systems and attributes a significant contribution of this achievement to highly innovative breeding programs, specifically focused on the production of premium quality lint for the export market. Breeding programs have recently shifted attention to the development of new germplasm with superior stress tolerance to minimise yield losses attributed to adverse environmental conditions and inputs such as irrigation, fertilisers and pesticides. Various contributors to yield, such as physiology, biochemistry and gene expression have been implemented as screening tools for tolerance to high temperatures under growth cabinet and laboratory conditions but there has been little extension of these mechanisms to field based systems. This study evaluates tools for the identification of specific genotypic thermotolerance under field conditions using a multi-level ‘top down’ approach from crop to gene level. Field experiments were conducted in seasons 1 (2006) and 3 (2007) at Narrabri (Australia) and season 2 (2006) in Texas (The United States of America) and were supplemented by growth cabinet experiments to quantify cultivar differences in yield, physiology, biochemical function and gene expression under high temperatures. Whole plants were subjected to high temperatures in the field through the construction of Solarweave® tents and in the growth cabinet at a temperature of 42 oC. The effectiveness of these methods was then evaluated to establish a rapid and reliable screening tool for genotype specific thermotolerance that could potentially improve the efficiency of breeding programs and aid the development to high yielding cultivars for hot growing regions. Cotton cultivars Sicot 53 and Sicala 45 were evaluated for thermotolerance using crop level measurements (yield and fibre quality) and whole plant measurements (fruit retention) to determine the efficacy of these measurements as screening tools for thermotolerance under field conditions. Sicot 53 was selected as a relatively thermotolerant cultivar whereas Sicala 45 was selected as a cultivar with a lower relative thermotolerance and this assumption was made on the basis of yield in hot and cool environments under the CSIRO Australian cotton breeding program. Yield and fruit retention were lower under tents compared with ambient conditions in all 3 seasons. Yield and fruit retention were highly correlated in season 1 and were higher for Sicot 53 compared to Sicala 45 suggesting that fruit retention is a primary limitation to yield in a hot season. Thus yield and fruit retention are good indicators of thermotolerance in a hot season. Temperature treatment and cultivar differences were determined for fibre quality in seasons 1 and 3; however, quality exceeded the industry minimum thereby indicating that fibre quality is not a good determinant of thermotolerance. Physiological determinants of plant functionality such as photosynthesis, electron transport rate, stomatal conductance and transpiration rate were determined for cultivars Sicot 53 and Sicala 45 under the tents and an index of these parameters was also analysed to determine overall plant physiological capacity in the field. Physiological capacity was also determined under high temperatures in the growth cabinet using a light response curve at various levels of photosynthetically active radiation (PAR). Photosynthesis and electron transport rate decreased, whilst stomatal conductance and transpiration rate increased under the tents as well as under high temperatures in the growth cabinet. Photosynthesis and electron transport rate were higher for Sicot 53 but stomatal conductance and transpiration rate were higher for Sicala 45 under the tents. No cultivar differentiation was evident for plants grown under high temperatures in the growth cabinet. Temperature treatment and cultivar differences in physiological function were greater in a hot year (season 1), thereby indicating the importance of cultivar selection for thermotolerance in the presence of stress. Electron transport rate was correlated with yield in season 1, thus suggesting the suitability of this method for broad genotypic screening for thermotolerance under field conditions. Biochemical processes such as membrane integrity and enzyme viability were used to determine cultivar specific thermotolerance under high temperature stress in the laboratory, field and growth cabinet. Electrolyte leakage is an indicator of decreased membrane integrity and may be estimated by the relative electrical conductivity or relative cellular injury assays. The heat sensitivity of dehydrogenase activity, a proxy for cytochrome functionality and capacity for mitochondrial electron transport, may be quantified spectrophotometrically. Cellular membrane integrity and enzyme viability decreased sigmoidally with exposure to increasing temperatures in a water bath. Membrane integrity was higher for Sicot 53 compared with Sicala 45 under the tents and under high temperatures in the growth cabinet. No temperature treatment or cultivar differences were found for enzyme viability under the tents; however, enzyme viability for Sicala 45 was higher in the growth cabinet compared with Sicot 53. Relative electrical conductivity was strongly correlated with yield under ambient field conditions and under the tents, suggesting impairment of electron flow through photosynthetic and/or respiratory pathways, thus contributing to lower potential for ATP production and energy generation for yield contribution. Thus, the membrane integrity assay was considered to be a rapid and reliable tool for thermotolerance screening in cotton cultivars. Gene expression was examined for cultivars Sicot 53 and Sicala 45 grown under high (42 oC) temperatures in the growth cabinet. Rubisco activase expression was quantified using quantitative real-time polymerase chain reaction analysis and was decreased under high temperatures and was lower for Sicala 45 than Sicot 53. Maximum cultivar differentiation was found after 1.0 h exposure to high temperatures and hence, leaf tissue sampled from this time point was further analysed for global gene profiling using cDNA microarrays. Genes involved in metabolism, heat shock protein generation, electron flow and ATP generation were down-regulated under high temperatures in the growth cabinet and a greater number of genes were differentially expressed for Sicala 45, thereby indicating a higher level of heat stress and a greater requirement for mobilisation of protective and compensatory mechanisms compared with Sicot 53. Cultivar specific thermotolerance determination using gene profiling may be a useful tool for understanding the underlying basis of physiological and biochemical responses to high temperature stress in the growth cabinet. There is future opportunity for profiling genes associated with heat stress and heat tolerance for identification of key genes associated with superior cultivar performance under high temperature stress and characterisation of these genes under field conditions. This research has identified cultivar differences in yield under field conditions and has identified multiple physiological and biochemical pathways that may contribute to these differences. Future characterisation of genes associated with heat stress and heat tolerance under growth cabinet conditions may be extended to field conditions, thus providing the underlying basis of the response of cotton to high temperature stress. Electron transport rate and relative electrical conductivity were found to be rapid and reliable determinants of cultivar specific thermotolerance and hence may be extended to broad-spectrum screening of a range of cotton cultivars and species and under a range of abiotic stress. This will enable the identification of superior cotton cultivars for incorporation into local breeding programs for Australian and American cotton production systems.

Doctor of Philosophy (PhD) / The Australian cotton industry has developed high yielding and high quality fibre production systems and attributes a significant contribution of this achievement to highly innovative breeding programs, specifically focused on the production of premium quality lint for the export market. Breeding programs have recently shifted attention to the development of new germplasm with superior stress tolerance to minimise yield losses attributed to adverse environmental conditions and inputs such as irrigation, fertilisers and pesticides. Various contributors to yield, such as physiology, biochemistry and gene expression have been implemented as screening tools for tolerance to high temperatures under growth cabinet and laboratory conditions but there has been little extension of these mechanisms to field based systems. This study evaluates tools for the identification of specific genotypic thermotolerance under field conditions using a multi-level ‘top down’ approach from crop to gene level. Field experiments were conducted in seasons 1 (2006) and 3 (2007) at Narrabri (Australia) and season 2 (2006) in Texas (The United States of America) and were supplemented by growth cabinet experiments to quantify cultivar differences in yield, physiology, biochemical function and gene expression under high temperatures. Whole plants were subjected to high temperatures in the field through the construction of Solarweave® tents and in the growth cabinet at a temperature of 42 oC. The effectiveness of these methods was then evaluated to establish a rapid and reliable screening tool for genotype specific thermotolerance that could potentially improve the efficiency of breeding programs and aid the development to high yielding cultivars for hot growing regions. Cotton cultivars Sicot 53 and Sicala 45 were evaluated for thermotolerance using crop level measurements (yield and fibre quality) and whole plant measurements (fruit retention) to determine the efficacy of these measurements as screening tools for thermotolerance under field conditions. Sicot 53 was selected as a relatively thermotolerant cultivar whereas Sicala 45 was selected as a cultivar with a lower relative thermotolerance and this assumption was made on the basis of yield in hot and cool environments under the CSIRO Australian cotton breeding program. Yield and fruit retention were lower under tents compared with ambient conditions in all 3 seasons. Yield and fruit retention were highly correlated in season 1 and were higher for Sicot 53 compared to Sicala 45 suggesting that fruit retention is a primary limitation to yield in a hot season. Thus yield and fruit retention are good indicators of thermotolerance in a hot season. Temperature treatment and cultivar differences were determined for fibre quality in seasons 1 and 3; however, quality exceeded the industry minimum thereby indicating that fibre quality is not a good determinant of thermotolerance. Physiological determinants of plant functionality such as photosynthesis, electron transport rate, stomatal conductance and transpiration rate were determined for cultivars Sicot 53 and Sicala 45 under the tents and an index of these parameters was also analysed to determine overall plant physiological capacity in the field. Physiological capacity was also determined under high temperatures in the growth cabinet using a light response curve at various levels of photosynthetically active radiation (PAR). Photosynthesis and electron transport rate decreased, whilst stomatal conductance and transpiration rate increased under the tents as well as under high temperatures in the growth cabinet. Photosynthesis and electron transport rate were higher for Sicot 53 but stomatal conductance and transpiration rate were higher for Sicala 45 under the tents. No cultivar differentiation was evident for plants grown under high temperatures in the growth cabinet. Temperature treatment and cultivar differences in physiological function were greater in a hot year (season 1), thereby indicating the importance of cultivar selection for thermotolerance in the presence of stress. Electron transport rate was correlated with yield in season 1, thus suggesting the suitability of this method for broad genotypic screening for thermotolerance under field conditions. Biochemical processes such as membrane integrity and enzyme viability were used to determine cultivar specific thermotolerance under high temperature stress in the laboratory, field and growth cabinet. Electrolyte leakage is an indicator of decreased membrane integrity and may be estimated by the relative electrical conductivity or relative cellular injury assays. The heat sensitivity of dehydrogenase activity, a proxy for cytochrome functionality and capacity for mitochondrial electron transport, may be quantified spectrophotometrically. Cellular membrane integrity and enzyme viability decreased sigmoidally with exposure to increasing temperatures in a water bath. Membrane integrity was higher for Sicot 53 compared with Sicala 45 under the tents and under high temperatures in the growth cabinet. No temperature treatment or cultivar differences were found for enzyme viability under the tents; however, enzyme viability for Sicala 45 was higher in the growth cabinet compared with Sicot 53. Relative electrical conductivity was strongly correlated with yield under ambient field conditions and under the tents, suggesting impairment of electron flow through photosynthetic and/or respiratory pathways, thus contributing to lower potential for ATP production and energy generation for yield contribution. Thus, the membrane integrity assay was considered to be a rapid and reliable tool for thermotolerance screening in cotton cultivars. Gene expression was examined for cultivars Sicot 53 and Sicala 45 grown under high (42 oC) temperatures in the growth cabinet. Rubisco activase expression was quantified using quantitative real-time polymerase chain reaction analysis and was decreased under high temperatures and was lower for Sicala 45 than Sicot 53. Maximum cultivar differentiation was found after 1.0 h exposure to high temperatures and hence, leaf tissue sampled from this time point was further analysed for global gene profiling using cDNA microarrays. Genes involved in metabolism, heat shock protein generation, electron flow and ATP generation were down-regulated under high temperatures in the growth cabinet and a greater number of genes were differentially expressed for Sicala 45, thereby indicating a higher level of heat stress and a greater requirement for mobilisation of protective and compensatory mechanisms compared with Sicot 53. Cultivar specific thermotolerance determination using gene profiling may be a useful tool for understanding the underlying basis of physiological and biochemical responses to high temperature stress in the growth cabinet. There is future opportunity for profiling genes associated with heat stress and heat tolerance for identification of key genes associated with superior cultivar performance under high temperature stress and characterisation of these genes under field conditions. This research has identified cultivar differences in yield under field conditions and has identified multiple physiological and biochemical pathways that may contribute to these differences. Future characterisation of genes associated with heat stress and heat tolerance under growth cabinet conditions may be extended to field conditions, thus providing the underlying basis of the response of cotton to high temperature stress. Electron transport rate and relative electrical conductivity were found to be rapid and reliable determinants of cultivar specific thermotolerance and hence may be extended to broad-spectrum screening of a range of cotton cultivars and species and under a range of abiotic stress. This will enable the identification of superior cotton cultivars for incorporation into local breeding programs for Australian and American cotton production systems.

Made available in DSpace on 2016-08-12T19:18:34Z (GMT). No. of bitstreams: 1 RomuloMOF_TESE.pdf: 1235930 bytes, checksum: d0668b69077e4b615b5b9b7e4cd858f6 (MD5) Previous issue date: 2015-07-07 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The cowpea crop has great importance for the Brazilian Northeast, especially for the poorest population. One of the major problems encountered for this crop is drought stress caused by erratic rainfall, coupled with the high temperatures common in this region. The no-tillage system has features, such as reduction of soil water evaporation, higher water retention and lower soil temperature fluctuations, and can be a way to minimize the water stress in a cowpea crop. Two experiments were carried out at the experimental garden in the Departamento de Ciências Vegetais of the Universidade Federal Rural do Semi-Árido (UFERSA), in Mossoró city, RN, with the aim of evaluating the use and use efficiency of water, and the ecophysiological traits of cowpea plants under water shortage in tillage and no-till cropping systems. The first experiment was conducted in a randomized complete blocks design with subsampling and four replications. The treatments were the two cropping systems (tillage and no-till), and the subsamples were the six periods of irrigation suspension (2; 6; 10; 14; 18 e 22 days), applied at the beginning of the flowering stage. The plants parts dry mass and the leaf area 64 days after sowing (DAS), and the grain production, water use and water use efficiency at that 70 DAS were evaluated. For the second experiment, it was used a randomized complete blocks design with subsampling and sub-subsampling, with four replications. The treatments were the cropping systems (tillage and no-till), and the subsamples were three water availability conditions (no shortage, moderate shortage and severe shortage), and the sub-subsampling were the evaluation periods. Plants dry mass, leaf areas, photosynthesis, stomatal conductance, transpiration, lowest leaf CO2 internal concentration and leaf water potential were evaluated. In the first experiment, it was observed that the no-till system is promising for the cowpea crop, with better grain production and better water use efficiency. In this system, the cowpea cultivation was possible even under a moderate water shortage. Prolonged water shortage periods did affect the dry mass accumulation, grain yield and water use efficiency. In the second experiment, the water shortage affected all the studied variables, with the exception of the leaves water potential. The cowpea fully recovered all physiological traits after moderate and severe water shortage. Stomatal closure was the main mechanism of resistance to water shortage, and the cowpea may be considered as a water-saving species. The cropping system did not affect the photosynthesis rates. The plants had more dry weight and leaf areas at the no-till system / A cultura do feijão-caupi possui grande importância para a região Nordeste, principalmente para a população mais carente. Um dos grandes problemas encontrados para essa cultura é o estresse hídrico, provocado pela irregularidade das chuvas, aliado a altas temperaturas, comuns a esta região. O sistema de plantio direto possui características como redução da evaporação da água do solo, maior retenção do solo e menores oscilações da temperatura, e pode ser uma forma de minimizar o efeito do estresse hídrico para a cultura do feijão-caupi. Dois experimentos foram conduzidos na horta didática do Departamento de Ciências Vegetais da Universidade Federal Rural do Semi-Árido (UFERSA), no município de Mossoró-RN, com o objetivo de avaliar o consumo, e eficiência de uso da água, bem como as respostas ecofisiológicas de feijão-caupi sob estresse hídrico nos sistemas de plantio direto e convencional. O primeiro experimento foi realizado no delineamento experimental em blocos casualizados completos, no esquema de parcelas subdivididas, com quatro repetições. Nas parcelas, foram avaliados dois sistemas de plantio (convencional e direto) e nas subparcelas, seis períodos de suspensão da irrigação (2; 6; 10; 14; 18 e 22 dias) aplicados no início do período reprodutivo. Foram avaliadas a biomassa das partes das plantas e a área foliar, aos 64 dias após a semeadura (DAS) e o rendimento de grãos, consumo de água e eficiência de uso da água, aos 70 DAS. No segundo experimento, utilizou-se o delineamento experimental em blocos casualizados completos, no esquema de parcelas subsubdivididas, com quatro repetições. Nas parcelas, foram avaliados dois sistemas de plantio (direto e convencional), nas subparcelas, três condições hídricas (sem estresse, estresse moderado e estresse severo) e nas subsubparcelas, períodos de avaliação. Foram determinados: área foliar, matéria seca total, fotossíntese, condutância estomática, transpiração, concentração interna de CO2 e potencial hídrico foliar. No primeiro experimento, constatou-se que o sistema de plantio direto foi promissor para cultura do feijão-caupi, apresentando maior rendimento de grãos e maior eficiência de uso da água. Nesse sistema de plantio, foi possível o cultivo de feijão-caupi, sem perdas, mesmo com períodos de veranico moderados. Veranicos prolongados afetaram negativamente o acúmulo de biomassa, rendimento de grãos e eficiência de uso da água. No segundo experimento, o estresse hídrico afetou todas as variáveis avaliadas, com exceção do potencial hídrico foliar. O feijão-caupi apresentou recuperação de todas as características fisiológicas após estresse hídrico moderado e severo. O fechamento estomático foi o principal mecanismo de resistência à seca, sendo o feijão-caupi uma espécie conservadora. Os sistemas de plantio não afetaram as taxas de fotossíntese. O sistema de plantio direto promoveu maior acúmulo de biomassa e de área foliar