Magnesium decreases leaf scald symptoms on rice leaves and preserves their photosynthetic performance

The aim of this study was to investigate the effect of magnesium (Mg) on the photosynthetic gas exchange parameters ([net CO2 assimilation rate (A), stomatal conductance (gs), and internal CO2 concentration (Ci)], chlorophyll (Chl) fluorescence a parameters {minimal fluorescence (F0), maximum fluorescence (Fm), maximum quantum yield of photosystem II (Fv/Fm), photochemical quenching coefficient (qp), yield of photochemistry [Y(II)], yield of regulated energy dissipation [Y(NPQ)] and yield of non-regulated dissipation losses [Y(NO)]} as well as on the concentrations of chloroplastidic pigments in rice plants grown in a nutrient solution containing 0.5 or 1.5 mM of Mg (-Mg or + Mg plants, respectively) and non-inoculated or inoculated with Monographella albescens. A higher Mg supply decreased the leaf scald symptoms in addition to partially preserving the photosynthetic performance of rice leaves challenged with M. albescens. Photosynthetic impairments were associated with photochemical and biochemical dysfunctions at the chloroplast level. The images of Chl a fluorescence evidenced increases in both the Y(II) and qp coupled with decreases in Y(NPQ) associated with a higher Mg supply regardless of inoculation, suggesting increased electron transport rates and lower energy dissipation as heat. Notably, as the leaf scald developed, the use of light energy through photochemical reactions was continuously lost, especially for the inoculated -Mg plants. Interestingly, the lower values for F0, Fm, and Fv/Fm for -Mg plants were associated with greater photochemical dysfunctions and a progressive loss of photosynthetic pigments during the infection process of M. albescens. The underlying mechanism through which Mg can affect rice resistance against M. albescens remains to be fully elucidated

Modelagem para a estimativa da orientação de linhas de plantio de cafeeiros Modelling for estimating the orientation of coffee planting rows

A quantidade de radiação solar interceptada por uma cultura é uma importante variável meteorológica que determina o crescimento e o desenvolvimento de uma cultura agrícola e, dentre os sistemas de produção, a orientação das linhas de plantio poderá ser um componente bastante relevante quanto à interceptação da radiação solar direta (Rd) em ambas as faces. Portanto, este trabalho propõe como objetivo um modelo para recomendar a orientação adequada das linhas de cafeeiro na implantação, baseando-se naquela a proporcionar uma uniformidade na quantidade de Rd interceptada e acumulada durante o ciclo agrícola da cultura, em ambas as faces da linha de plantio. Para o teste do modelo, foram coletados dados de produção em uma área experimental de café irrigado por pivô central, na Fazenda São Thomé, em Pirapora-MG, em plantas alinhadas nas seguintes orientações, em relação ao norte geográfico, positivo no sentido horário e negativo ao contrário: -90º, -45º, 0º e 45º. Os resultados indicaram que as melhores orientações para a produtividade foram, sucessivamente, as de -45º e 0º, enquanto o modelo proposto estimou a orientação de -24º 16' como sendo a melhor para o plantio das linhas de cafeeiro.<br>The quantity of solar radiation intercepted by a crop is an important meteorological variable that determines the growth and development of a crop and among the production systems, the orientation of planting rows could be a very important component regarding the interception of direct solar radiation (Rd) on both faces. Thus the objective of this study proposes a model to recommend the adequate orientation of the planting rows of coffee in the deployment, based on that providing uniformity in quantity of intercepted and accumulated Rd during the crop cycle on both faces of the planting row. In order to test the model, production data were collected in an experimental area of the coffee crop irrigated by a center pivot in San Thomé Farm on Pirapora, state of Minas Gerais, Brazil, being this planting rows oriented in relation to geographic north, clockwise positive and negative rather, by 45º, -90º, -45º, and 0º. The results indicated that the best orientations for productivity were, successively, the -45 º and 0 º, while the proposed model estimates the orientation of -24º 16' as the best for planting rows of coffee crop