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This study was intended to analyze the photosynthetic performance of rice leaf blades infected with Monographella albescens by combining chlorophyll (Chl) a fluorescence images with gas exchange and photosynthetic pigment pools. The net CO2 assimilation rate, stomatal conductance, transpiration rate, total Chl and carotenoid pools, and Chl a/b ratio all decreased but the internal CO2 concentration increased in the inoculated plants compared with their noninoculated counterparts. The first detectable changes in the images of Chl a fluorescence from the leaves of inoculated plants were already evident at 24 h after inoculation (hai) and increased dramatically as the leaf scald lesions expanded. However, these changes were negligible for the photosystem II photochemical efficiency (Fv/Fm) at 24 hai, in contrast to other Chl fluorescence traits such as the photochemical quenching coefficient, yield of photochemistry, and yield for dissipation by downregulation; which, therefore, were much more sensitive than the Fv/Fm ratio in assessing the early stages of fungal infection. It was also demonstrated that M. albescens was able to impair the photosynthetic process in both symptomatic and asymptomatic leaf areas. Overall, it was proven that Chl a fluorescence imaging is an excellent tool to describe the loss of functionality of the photosynthetic apparatus occurring in rice leaves upon infection by M. albescens.

This study investigated the effect of silicon (Si) on the resistance of rice plants of the cv. ‘Primavera’ cultivar that were grown in a nutrient solution with 0 (−Si) or 2 mm (+Si) Si to leaf scald, which is caused by Monographella albescens. The leaf Si concentration increased in the +Si plants (4.8 decag/kg) compared to the −Si plants (0.9 decag/kg), contributing to a reduced expansion of the leaf scald lesions. The extent of the cellular damage that was caused by the oxidative burst in response to the infection by M. albescens was reduced in the +Si plants, as evidenced by the reduced concentration of malondialdehyde. Higher concentrations of total soluble phenolics and lignin‐thioglycolic acid derivatives and greater activities of peroxidases (POX), polyphenoloxidases (PPO), phenylalanine ammonia‐lyases (PAL) and lipoxygenases (LOX) in the leaves of the +Si plants also contributed to the increased rice resistance to leaf scald. In contrast, the activities of chitinases and β‐1,3‐glucanases were higher in the leaves of the −Si plants probably due to the unlimited M. albescens growth in the leaf tissues, as indicated by the larger lesions. The results of this study highlight the potential of Si in decreasing the expansion of the leaf scald lesions concomitantly with the potentiation of phenolic and lignin production, and the greater activities of POX, PPO, PAL and LOX rather than simply acting only as a physical barrier to avoid M. albescens penetration.

Leaf scald, caused by Monographella albescens, is one of the major diseases in rice worldwide. This study investigated the effect of silicon (Si) on the photosynthetic gas exchange parameters [net CO 2 assimilation rate (A), stomatal conductance to water vapour (g s ), transpiration rate (E)] and internal CO 2 concentration (C i ), chlorophyll (Chl) fluorescence a parameters [minimal fluorescence (F 0 ), maximum fluorescence (F m ), maximum quantum yield of photosystem II (F v /F m )], photochemical quenching coefficient (q p ), effective quantum yield of PSII [Y(II)], quantum yield of regulated energy dissipation [Y(NPQ)] and quantum yield dissipation non-regulated [Y(NO)] and the concentrations of pigments in rice plants grown in nutrient solutions containing either 0 (−Si) or 2 mM Si (+Si) and non-inoculated or inoculated with M. albescens. Leaf scald severity decreased with higher foliar Si concentration. For the inoculated +Si plants, A, g s and E were significantly higher in comparison with the inoculated −Si plants, in which C i was significantly increased. Similarly, the concentrations of Chl a , Chl b , total Chl a+b and carotenoids were higher for the +Si plants in comparison with the −Si plants. Changes in the images of Chl a fluorescence were first observed precisely on the −Si plants leaves in comparison with the +Si plants. A decrease of q P and Y(II) in inoculated −Si plants, in comparison with the inoculated +Si plants, was accompanied by an increase in Y(NPQ) and Y(NO). Notably, the extent of the leaf areas was much more evident for Y(II) and q P in comparison with F 0 , F m and F v /F m , suggesting that Y(II) and q P were good predictors in detecting the early effects of leaf scald on the leaf photosynthesis. For the +Si non-inoculated plants, changes in Y(II) were associated with alterations in both Y(NPQ) and Y(NO) compared with non-inoculated −Si plants. In conclusion, the photosynthetic performance (as demonstrated by the gas exchange and Chl a fluorescence parameters) and the pigment pools of rice plants infected with M. albescens were preserved by Si supply and, therefore, provided an increase in rice resistance against leaf scald.

A escassez de informações referentes ao consumo hídrico de mudas de espécies florestais freqüentemente dificulta o planejamento da irrigação em viveiros comerciais, levando muitas vezes, a adoção de medidas ineficientes de manejo, provocando perda no padrão de qualidade das mudas. Dessa forma, procurou-se neste trabalho investigar a máxima capacidade de retenção de água (MCRA) no substrato em que as mudas de eucalipto podem ser submetidas e determinar o coeficiente de cultivo (Kc) para o clone híbrido de E. urophylla x E. grandis. O estudo foi realizado em casa de vegetação, localizada na área experimental do Programa de Pós-Graduação em Ciências Florestais vinculado ao Centro de Ciências Agrárias da Universidade Federal do Espírito Santo (CCA-UFES) no município de Alegre, ES, montado num delineamento inteiramente casualizado, com cinco tratamentos de disponibilidade hídrica no substrato (90, 80, 70, 60 e 50% da MCRA), com quatro repetições. De acordo com os resultados obtidos, verificou-se que a disponibilidade hídrica no substrato de 70% da MCRA pode ser utilizada para a produção de mudas clonais de eucalipto, sem afetar o crescimento e o padrão de qualidade. O Kc estimado para as mudas de eucalipto em condições de viveiro foi de 1,25. AbstractDetermination of maximum capacity of water retention in substrate for production plants in Eucalyptus nursery. The scarcity of information regarding water consumption of seedlings of forest species often complicates the planning of irrigation in commercial nurseries, often leading the adoption of inefficient management measures, causing loss in the quality of seedlings. Thus, this study sought to investigate the capacity of water retention in the substrate in which the eucalyptus seedlings can be submitted and determine the crop coefficient (Kc) for the hybrid clone of E. urophylla x E . grandis. The study was conducted in a greenhouse located in the experimental area of the Post-Graduation of Forest Sciences bound to the Center for Agrarian Sciences, Federal University of Espírito Santo in the city of Alegre, ES, built in a completely randomized design with five treatments of water availability in the substrate (90, 80, 70, 60 and 50% of MCRA) and four replications. According to the results, it was found that water availability in the substrate MCRA of the 70% can be used for the production of minicutting, without affecting standards of growth and quality. The Kc for eucalyptus seedlings in nursery conditions was 1.25.Keywords: Coefficient of cultivation; irrigation management; Eucalyptus urophylla x E. grandis.

ResumoEste estudo teve como objetivo avaliar as respostas das relações hídricas e das trocas gasosas em quatro clones de eucalipto (97, 11, 75, 84), estabelecidos em vasos plásticos, de modo a subsidiar a seleção precoce desses materiais genéticos para o estabelecimento em áreas com diferenciada disponibilidade de água no solo. As plantas cresceram em vasos, com teor de água próximo à capacidade de campo, durante um período de 150 dias, sendo, em seguida, iniciados os manejos hídricos diferenciados, mantidos até o final do experimento, que durou cerca de 250 dias. O déficit hídrico promoveu redução nos valores de fotossíntese, condutância estomática, transpiração, eficiência no uso da água e potencial hídrico foliar dos clones no final do experimento. O clone 11 apresentou o menor valor de fotossíntese, condutância estomática e transpiração quando submetido à deficiência hídrica. Os clones 97 e 75 apresentaram os maiores valores de fotossíntese e potencial hídrico foliar nas plantas submetidas ao déficit hídrico, evidenciando serem os mais indicados para plantio em áreas com elevada deficiência hídrica no solo. Palavras-chave: Potencial hídrico foliar; manejos hídricos; fotossíntese. Abstract Water relations and gaseous changes in the precocious selection of Eucalyptus clones for environments with varying soil water availability.This study had as objective to evaluate the answers of the water relations and of the gaseous changes in four eucalyptus clones (97, 11, 75, 84), established in plastic vases, in way to subsidize the precocious selection of this genetic materials for the establishment in areas with varying soil water availability. Plants grew in vases, with water content at field capacity, during a period of 150 days, after that until the end of the experiment that lasted about 250 day, soil water regime was diversed. Water deficit regimes promoted reduction in the photosynthesis values, stomatal conductance, transpiration, efficiency in the use of the water and leaf water potential of the clones in the end of the experiment. Clone 11 presented the smallest photosynthesis value, stomatal conductance and transpiration when submitted to the water deficiency. The clones 97 and 75 presented the largest photosynthesis values and leaf water potential, in plants submitted to the alternated water regime of irrigation and deficit, showing to be the most suitable for planting in areas with high soil water deficiency.

Objetivou-se com este estudo, investigar as limitações fotossintéticas em folhas de café arábica, ‘Catuaí Vermelho’ (IAC 144), submetido ao déficit hídrico, utilizando para isso, os parâmetros de trocas gasosas da fotossíntese [assimilação líquida de CO2 (A), condutância estomática (gs), taxa de transpiração (E) e concentração interna de CO2 (Ci)], os parâmetros de fluorescência da clorofila a {fluorescência mínima (F0), fluorescência máxima (Fm), eficiência quântica máxima do fotossistema II (Fv/Fm), rendimento da fotoquímica [Y(II)], rendimento da dissipação de energia regulada [Y(NPQ)] e o rendimento das perdas de dissipação não regulada [Y(NO)]}, bem como as concentrações de pigmentos cloroplastídicos e o extravasamento de eletrólitos (EE) em folhas de plantas cultivadas a 30, 60 e 100% de água disponível (AD) no substrato. De acordo com os resultados obtidos foi verificado que o déficit hídrico afetou negativamente a fotossíntese das plantas, seja através da menor eficiência de utilização de energia pelo aparato fotoquímico, quanto por decréscimos significativos obtidos em gs, os quais, estiveram associados à diminuição nos valores de A. Redução em Y(II) e aumentos em Y(NPQ) e Y(NO) foram associados ao déficit hídrico, sugerindo que houve diminuição na taxa de transporte de elétrons, levando a um menor aproveitamento da energia luminosa para a fotoquímica. Curiosamente, os valores de F0, Fm e Fv/Fm não estiveram associados com a perda de função fotoquímica, de clorofilas e ao dano celular provocado pela intensificação do déficit hídrico.

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