Cotton (Gossypium hirsutum L.) growth and development, lint yield, and fiber quality are influenced by many management decisions. Three field experiments examining the interaction of plant population and planting date, and cultivar or herbicide and plant growth regulator application on these parameters were conducted in Virginia during 2005 and 2006 and in North Carolina, South Carolina, and Louisiana during specific years. Experiment I: Plant Population and Planting Date Lint yields were highest with populations of 8.9 and 12.8 plants m¯² compared to 5.3 plants m¯² in Virginia and North Carolina, while in Louisiana the highest yields resulted from populations of 5.8 and 9.5 plants m¯² compared to 17.1 plants m¯². Earlier planted (1 May) cotton produced higher yields relative to later planted (21 May) cotton in Louisiana, while yield was not influenced by planting date in Virginia and North Carolina. The impact of plant population and planting date on cotton appeared to be influenced significantly by heat unit accumulation. Experiment II: Cultivar and Mepiquat Pentaborate Application Mepiquat pentaborate (MPB) application consistently decreased plant height, HNR, and enhanced maturity for all cultivars, compared to untreated cotton. A trend of decreasing yield with increasing MPB application in Virginia was observed. These data suggests that cotton response to MPB application is influenced by cultivar maturity or fruiting interval. Experiment III: Trifloxysulfuron-sodium and Mepiquat Chloride Application Trifloxysulfuron-sodium (TFS) did not influence vegetative growth, maturity, or yield in comparison to untreated cotton. Mepiquat chloride (MC) application reduced vegetative growth and enhanced maturity in most years. The results of this experiment demonstrate that TFS application does not have the same effects on plant growth as MC application. / Master of Science

La déficience en potassium dans les parcelles de cotonnier est un phénomène répandu et en recrudescence. Le problème est d’autant plus marqué en Afrique sub-saharienne que les sols sont pauvres et les systèmes de culture peu intensifs. Les principaux effets de la carence en potassium référencés dans la littérature sont une réduction de la surface foliaire, une réduction de l’assimilation et une modification des règles de répartition des assimilats entre les compartiments de la plante (tiges, racines, fruits et feuilles). Les connaissances à l’échelle cellulaire sur le rôle du potassium sont nombreuses mais paradoxalement peu de modèles permettent l’intégration de ces résultats à l’échelle du plant et du peuplement. La raison provient de la multiplicité des mécanismes affectés et de la complexité à les intégrer à l’échelle du plant ou du peuplement. L’objectif de notre travail est de caractériser les effets de la carence en K sur la croissance et le développement du cotonnier avec suffisamment de variables intermédiaires explicatives pour pouvoir proposer un schéma conceptuel compatible avec les concepts utilisés dans les modèles de croissance de cette plante. Cet objectif implique ainsi de porter nos investigations à plusieurs échelles (peuplement, plante, organes, organites) et sur des variables-clés du fonctionnement physiologiques des plantes utilisées dans la modélisation courante telles que la photosynthèse ou le statut hydrique. Nos recherches nous ont aussi amené à mesurer d’autres variables non inclues dans les modèles courant, afin d’affiner notre compréhension du fonctionnement des plantes carencées (teneurs en sucres, vitesses de carboxylation, ouvertures stomatiques …). Pour satisfaire à ces objectifs, deux types complémentaires d’expérimentations ont été menés : 1) des essais en pleins champs, en condition pluviale strictes ont été conduits au Bénin, deux années de suite, sur deux sites différents : à Aplahoué en 2004 et à Savalou en 2005. Il s’agit d’essais comparant différents niveaux de fertilisation en potassium. L’objectif de ces essais était d’étudier les effets de la carence à l’échelle du peuplement. 2) Par la suite, une expérimentation en serre et en hydroponie a été conduite (Bordeaux, 2006) dans l’objectif d’analyser finement les processus affectés à l’échelle du plant et de l’organe. Les essais en peuplement comme l’essai en serre ont permis d’obtenir des gammes de teneur en potassium variées, grâce à des niveaux d’alimentation variés (3 niveaux au champ, 4 en serre). Les teneurs planchers des plantes les plus carencées se situaient aux alentours de 8 à 10 mg Kg-1, ce qui contraste avec les teneurs maximum mesurées qui avoisinaient les 30 mg g-1. L’indice foliaire des traitements carencés des essais en peuplement est inférieur aux témoins en raison d’un moins grand nombre de feuilles et d’une taille individuelle réduite. Dans les essais en serre, une importante réduction de la surface foliaire est aussi observée mais la part de la réduction de la surface individuelle dans la réduction de la surface totale est plus prononcée. L’analyse des dynamiques de croissance des surfaces foliaires montre que l’accroissement relatif des feuilles est identique quel que soit les niveaux de carence mais que la taille des organes à l’émergence est plus petite pour les plants carencés. En revanche, les entrenœuds des plants carencés ont à la fois une taille réduite à l’émergence et une croissance relative plus faible. A l’échelle du peuplement aucune différence d’efficience de conversion de la lumière n’est observée en conséquence, les réductions de biomasse sèche observée sont entièrement dues à une diminution de l’efficience d’interception du rayonnement. En revanche, l’efficience de conversion du rayonnement interceptée de l’essai en serre est affectée par la carence en K mais uniquement pour le traitement le plus carencé. / Potassium deficiency is a common phenomenon in cotton parcels. This problem is quite important in sub-Saharan Africa, where soils are poor and cropping systems are very low intensive. The main effects of potassium deficiency referenced in scientific literature are: (a) a reduction in leaf area, (b) a decrease in nutrient assimilation, and (c) a modification of nutrient repartition amongst compartments (i.e. stems roots, fruits, and leaves). Even though knowledge at the cellular level on the role of potassium is wide, ironically, only but a few models integrate results at the plant or stand levels. The reason comes from the multiplicity of mechanisms used and the complexity of integrating them throughout the plant or stand. The objective of our work is to characterize the effects of K-deficiency on the growth and development of cotton plants by including sufficient intermediate explanatory variables to provide a comparable scheme with the concepts used in growth models for this plant. This objective implies that our research focuses on different scales (i.e. stand, plant, organ, cell) and on physiological variables used in current models such as photosynthesis or water status. Our research had also led us to measure other variables not included in current models, to refine our understanding of the mechanisms of how deficient plants grows (i.e. sugar rates, carboxylation speed, stomata opening…). To meet these objectives, two complementary types of experiments were conducted: (i) field trials were performed in Benin on two different sites, Aplahoué in 2004 and Savalou in 2005, with strict rainfall conditions to compare different levels of potassium-fertilization and describe the effects of K-deficiency at the stand level. (ii) and a greenhouse hydroponic experiment was done in Bordeaux, France in 2006 to analyze the processes used throughout the plant and the organ. The field and the greenhouse tests had different levels of potassium fertilisation (2 to 3 levels in the field, 4 in the greenhouse) and gave us wide ranges of potassium contents in leaves. The minimum value of the leaf K content for the deficient plants were around 8 to 10 mg kg-1, which contrasts with the maximum values measured that were around 30 mg g-1. Potassium levels for the most deficient plants were around 8 to 10 mg Kg-1, while the highest levels measured were 30 g Kg-1. The leaf area index of deficient treatments is inferior to that of controls due to a lower number of leaves and smaller leaf sizes. In the greenhouse test, an important decrease of leaf area is observed but the proportion of the reduction due to a reduction in individual leaf size is more pronounced than in the filed experiments. The temporal analysis of the leaf area growth shows that the relative increase in size of the individual leaves is the same whatever the level of K-deficiency but that the size of the organs at emergence from apical buds is smaller for K-deficient plants. In counterpart, internodes of K-deficient plants have smaller lenght at emergence and a decreased relative growth rate. At stand level, no difference of light conversion efficiency is observed. As a result, observed reductions of dry biomass are essentially due to a decrease in light interception. However, radiation use efficiency in greenhouse tests are affected by K-deficiency but only for the most K-deficient treatment. Measures on gas exchanges made in greenhouse experiment also shows that photosynthesis is affected only for the most K-deficient treatments. This reduction is due to two concomitant effects: poor stomatal opening and a reduction in the maximum velocity of carboxylation. The relative distribution in biomass for all the tests is modified by the potassium-deficiency, benefiting leaves at the expense of the heterotrophic organs. This effect is observed at the plant level through an increase in the specific leaf weight and a relative decrease in stem and root biomass.

O herbicida 2,4-D é utilizado principalmente para o controle de plantas daninhas em condições de pós-emergência em culturas em que o herbicida é seletivo, bem como no manejo da vegetação em pré-plantio; no entanto, devido a suas características físico-químicas, pode ocasionar danos às culturas vizinhas sensíveis, através dos fenômenos de deriva da molécula durante as pulverizações. Sendo assim, é de fundamental importância o conhecimento técnico dos impactos causados pela deriva do herbicida 2,4-D em culturas sensíveis. No entanto, as informações existentes na literatura para dar suporte às possíveis liberações futuras de culturas resistentes a este herbicida são escassas. Os experimentos foram conduzidos em casa-de-vegetação e laboratório da Escola Superior de Agricultura \"Luiz de Queiroz\" - Universidade de São Paulo - ESALQ/USP. Os objetivos da presente pesquisa foram: (i) avaliar a influência do herbicida 2,4-D no desenvolvimento das culturas do algodão e soja em, diferentes estádios fenológicos, (ii) avaliar os possíveis danos causados pela deriva do herbicida 2,4-D no crescimento e desenvolvimento das culturas de algodão e soja, em diferentes estádios fenológicos, e (iii) observar através da microscopia eletrônica de varredura possíveis alterações nas estruturas foliares das plantas de algodão e soja após o contato com o herbicida. Curvas de doseresposta foram obtidas a partir de experimentos conduzidos em casa-de-vegetação. Para isso, foram conduzidos dois ensaios, sendo os tratamentos com o herbicida aplicado quando as plantas atingiram os estágios fenológicos: V2 (segundo nó vegetativo); R1 (início da floração para a cultura de soja), F1 (início da floração da cultura de algodão); e R6 (vagens da soja com enchimento pleno e folhas verdes) e C1 (algodão no final do florescimento efetivo e frutificação plena). No primeiro experimento os tratamentos utilizados foram: 0D (testemunha), 0,25D, 0,5D, 1D, 2D e 4D, sendo D a dose recomendada do 2,4-D, e no segundo experimento as doses utilizadas foram: 0D, 1D, 0,1D, 0,01D, 0,001D, 0,0001D. Utilizando as mesmas plantas da primeira etapa da pesquisa foram feitas amostragens das folhas para a caracterização foliar através de microscopia eletrônica de varredura. O 2,4-D comprometeu significativamente o crescimento e desenvolvimento das plantas de soja em todos os estádios fenológicos, com fitotoxicidade superiores a 65%. Resultados semelhantes foram obtidos na cultura do algodão, onde o menor nível de dano foi de 42,5% relativa à aplicação do herbicida no estádio fenológico R6 na dose de 0,25D. Observando os tratamentos nas subdoses do herbicida, na soja, verificou se que a maior porcentagem de fitotoxicidade foi obtida na dose de 0,1D, em todos os estádios fenológicos, os níveis de dano foram superiores a 50% na última avaliação. Em relação à cultura do algodão resultados semelhantes foram obtidos, com exceção do estádio fenológico R6, quando todos os estádios apresentaram porcentagem de fitotoxicidade superior a 40%. Em relação às características foliares do algodão e soja após aplicações de 2,4-D através da análise das características foliares em microscópio eletrônico de varredura, após a aplicação do herbicida, observou-se que o produto promoveu alterações nas estruturas foliares de algodão e soja em todas as doses estudadas. / The herbicide 2,4-D is used to control weeds in post-emergence conditions in crops which it is selective, as well in pre-planting vegetation management, however, due to its physical-chemical characteristics it may cause damage to susceptible neighbor crops, by the drift of the molecule during the spray. Therefore, it is of fundamental importance the technical knowledge of the impacts caused by the drift of the molecule during the application. The experiments were conducted in greenhouse and in the laboratory of the College of Agriculture \"Luiz de Queiroz\". So the objectives of this study were (i) to evaluate the possible damage caused by 2,4-D in the initial development of cotton and soybean crops (ii) to evaluate the possible damage caused by 2,4-D drift in the initial development of cotton and soybean crops and (iii) to observe by electron microscopy scanning possible changes in leaf structure of plants cotton and soybeans after contact with the herbicide. Dose-response curves were obtained from experiments conducted in the greenhouse. For that, it was conducted two trials, being the treatments with the herbicide sprayed when the plants reached the following phenological stages: V2 (second vegetative node); R1 (beginning of flowering for soybeans) and F1 (beginning of flowering in cotton); and R6 (soybean pods with full filling and green leaves) and C1 (cotton at the end of effective flowering and fruiting full). In the first experiment the doses were related to the effect of doses (0D, 0.25D, 0.5D, 1D, 2D, 4D), where D is the recommended dose of the herbicide 2,4-D, and in the second experiment evaluated the effect of underdoses (0D, 1D, 0.1D, 0.01D, 0.001D and 0.0001D). Using the same plants of the first and second step of the research it was sampled leaves for the foliar characterization by scanning electron microscopy. The 2,4-D affected significantly the growth and development of the soybean plants in all phenological stages, with phytotoxicity superior to 65%. Similar results were obtained in cotton, where the lower level of damage was 42.5% on the application of the herbicide on growth stage R6 with the 0.25D dose. Regarding to the application of doses of the herbicide 2,4-D on soybeans, it was observed that the highest percentage of phytotoxicity to the crop was at the dose of 0.1D; in all growth stages the damage levels were above 50% in the last evaluation. Regarding to the cotton crop, similar results were obtained, except for the R6 growth stage, every stage showed higher percentage of phytotoxicity than 40%. Regarding to the characteristics of the cotton and soybean leaves following 2,4-D application, it was found that the product caused alterations in leaf structure of the plants in all doses.

O herbicida 2,4-D é utilizado principalmente para o controle de plantas daninhas em condições de pós-emergência em culturas em que o herbicida é seletivo, bem como no manejo da vegetação em pré-plantio; no entanto, devido a suas características físico-químicas, pode ocasionar danos às culturas vizinhas sensíveis, através dos fenômenos de deriva da molécula durante as pulverizações. Sendo assim, é de fundamental importância o conhecimento técnico dos impactos causados pela deriva do herbicida 2,4-D em culturas sensíveis. No entanto, as informações existentes na literatura para dar suporte às possíveis liberações futuras de culturas resistentes a este herbicida são escassas. Os experimentos foram conduzidos em casa-de-vegetação e laboratório da Escola Superior de Agricultura \"Luiz de Queiroz\" - Universidade de São Paulo - ESALQ/USP. Os objetivos da presente pesquisa foram: (i) avaliar a influência do herbicida 2,4-D no desenvolvimento das culturas do algodão e soja em, diferentes estádios fenológicos, (ii) avaliar os possíveis danos causados pela deriva do herbicida 2,4-D no crescimento e desenvolvimento das culturas de algodão e soja, em diferentes estádios fenológicos, e (iii) observar através da microscopia eletrônica de varredura possíveis alterações nas estruturas foliares das plantas de algodão e soja após o contato com o herbicida. Curvas de doseresposta foram obtidas a partir de experimentos conduzidos em casa-de-vegetação. Para isso, foram conduzidos dois ensaios, sendo os tratamentos com o herbicida aplicado quando as plantas atingiram os estágios fenológicos: V2 (segundo nó vegetativo); R1 (início da floração para a cultura de soja), F1 (início da floração da cultura de algodão); e R6 (vagens da soja com enchimento pleno e folhas verdes) e C1 (algodão no final do florescimento efetivo e frutificação plena). No primeiro experimento os tratamentos utilizados foram: 0D (testemunha), 0,25D, 0,5D, 1D, 2D e 4D, sendo D a dose recomendada do 2,4-D, e no segundo experimento as doses utilizadas foram: 0D, 1D, 0,1D, 0,01D, 0,001D, 0,0001D. Utilizando as mesmas plantas da primeira etapa da pesquisa foram feitas amostragens das folhas para a caracterização foliar através de microscopia eletrônica de varredura. O 2,4-D comprometeu significativamente o crescimento e desenvolvimento das plantas de soja em todos os estádios fenológicos, com fitotoxicidade superiores a 65%. Resultados semelhantes foram obtidos na cultura do algodão, onde o menor nível de dano foi de 42,5% relativa à aplicação do herbicida no estádio fenológico R6 na dose de 0,25D. Observando os tratamentos nas subdoses do herbicida, na soja, verificou se que a maior porcentagem de fitotoxicidade foi obtida na dose de 0,1D, em todos os estádios fenológicos, os níveis de dano foram superiores a 50% na última avaliação. Em relação à cultura do algodão resultados semelhantes foram obtidos, com exceção do estádio fenológico R6, quando todos os estádios apresentaram porcentagem de fitotoxicidade superior a 40%. Em relação às características foliares do algodão e soja após aplicações de 2,4-D através da análise das características foliares em microscópio eletrônico de varredura, após a aplicação do herbicida, observou-se que o produto promoveu alterações nas estruturas foliares de algodão e soja em todas as doses estudadas. / The herbicide 2,4-D is used to control weeds in post-emergence conditions in crops which it is selective, as well in pre-planting vegetation management, however, due to its physical-chemical characteristics it may cause damage to susceptible neighbor crops, by the drift of the molecule during the spray. Therefore, it is of fundamental importance the technical knowledge of the impacts caused by the drift of the molecule during the application. The experiments were conducted in greenhouse and in the laboratory of the College of Agriculture \"Luiz de Queiroz\". So the objectives of this study were (i) to evaluate the possible damage caused by 2,4-D in the initial development of cotton and soybean crops (ii) to evaluate the possible damage caused by 2,4-D drift in the initial development of cotton and soybean crops and (iii) to observe by electron microscopy scanning possible changes in leaf structure of plants cotton and soybeans after contact with the herbicide. Dose-response curves were obtained from experiments conducted in the greenhouse. For that, it was conducted two trials, being the treatments with the herbicide sprayed when the plants reached the following phenological stages: V2 (second vegetative node); R1 (beginning of flowering for soybeans) and F1 (beginning of flowering in cotton); and R6 (soybean pods with full filling and green leaves) and C1 (cotton at the end of effective flowering and fruiting full). In the first experiment the doses were related to the effect of doses (0D, 0.25D, 0.5D, 1D, 2D, 4D), where D is the recommended dose of the herbicide 2,4-D, and in the second experiment evaluated the effect of underdoses (0D, 1D, 0.1D, 0.01D, 0.001D and 0.0001D). Using the same plants of the first and second step of the research it was sampled leaves for the foliar characterization by scanning electron microscopy. The 2,4-D affected significantly the growth and development of the soybean plants in all phenological stages, with phytotoxicity superior to 65%. Similar results were obtained in cotton, where the lower level of damage was 42.5% on the application of the herbicide on growth stage R6 with the 0.25D dose. Regarding to the application of doses of the herbicide 2,4-D on soybeans, it was observed that the highest percentage of phytotoxicity to the crop was at the dose of 0.1D; in all growth stages the damage levels were above 50% in the last evaluation. Regarding to the cotton crop, similar results were obtained, except for the R6 growth stage, every stage showed higher percentage of phytotoxicity than 40%. Regarding to the characteristics of the cotton and soybean leaves following 2,4-D application, it was found that the product caused alterations in leaf structure of the plants in all doses.