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Universidade Estadual Paulista (UNESP) 2018

Parâmetros fisiológicos do cultivo de milho doce sob influência da deficiência hídrica

Souza, Mara Lúcia Cruz de

Titre : Parâmetros fisiológicos do cultivo de milho doce sob influência da deficiência hídrica

Physiological parameters of sweet corn cultivation under influence of water deficit

Auteur : Souza, Mara Lúcia Cruz de

Université de soutenance : Universidade Estadual Paulista (UNESP)

Grade : Mestre Agronomia – Irrigação e Drenagem 2018

Résumé
Water deficiency (WD) is a form of physical stress that affects the development of several agricultural crops, causing social and economic impacts in regions with low water availability. Several researches have been focusing on the study of water deficiency in maize crop in phenological stages critical to water scarcity. The aim of the present study was to evaluate the physiological and biochemical responses of sweet corn plants growing under water deficiency during the vegetative stage. The main hypothesis is that corn plants will produce interactive physiological responses, in order to reduce the impact of applied treatments. The experiment was conducted in protected environment in 30 L pots, irrigated via drip irrigation, under a randomized block design in a factorial scheme (3 x 3), three irrigation levels and three evaluation periods in subdivided plots. The treatments were delimited with the objective of simulating three levels of water deficiency : T1- Control (10 KPa) - conducted within the optimum humidity range for the maize crop until the end of the experiment ; T2- Moderate water deficiency (50 KPa) and T3- Severe water deficiency (70 KPa). The evaluations were divided in three seasons during the imposition of stress treatments, aiming to monitor the physiological and biochemical changes of the plants at 45, 52 and 59 DAE (days after seed emergence). Each treatment was composed of 4 replicates and the soil moisture was monitored by tensiometry, maintaining the vessels in field capacity until the beginning of the treatments. When the plants entered the V7 stage, the proposed treatments with water deficiency were started. At this stage, the first collection (E1) was performed to analyze different parameters, which consisted of the initial point of evaluations. Under moderate and severe WD there were alterations of the main physiological and biochemical parameters. The growth and biomass parameters of leaves, stem and roots were influenced by the interaction of the factors of irrigation depth and time of evaluation, except for plant height. The stem diameter was not influenced by the studied factors. The plants presented a decrease of relative water content (RWC) in the three evaluated seasons according to the severity of the stress. The pigments content was influenced by irrigation times and water depths, which showed a decrease for chlorophyll a and b and also carotenoids. The plants presented a gradual increase of electrolyte loss in the evaluation periods, demonstrating the negative effect of WD on the cell membranes structures. The gas exchange parameters were affected by the level of WD imposed on the plants. There was a decrease in photosynthetic rates (A), stomatal conductance (gs), transpiration (E) and internal CO2 concentration (Ci), which were proportional among the variables analyzed. The specific activities of the antioxidative enzymes (catalases, peroxidases and superoxide dismutases) increased in response to the severity of water stress. Protein contents reduced according to the evaluation and stress levels and Nitrate Reductase (NR) activity in leaves reduced in plants under moderate and severe WD

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