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Verbi Pereira F.M.,Embrapa Instrumentaao Agropecuaria | Bastos Pereira Milori D.M.,Embrapa Instrumentaao Agropecuaria | Pereira-Filho E.R.,Federal University of São Carlos | Venancio A.L.,Embrapa Instrumentaao Agropecuaria | And 4 more authors.
Analytical Methods | Year: 2011

The citrus greening (or huanglongbing) disease has caused serious problems in citrus crops around the world. An early diagnostic method to detect this malady is needed due to the rapid dissemination of Candidatus Liberibacter asiaticus (CLas) in the field. This analytical study investigated the fluorescence responses of leaves from healthy citrus plants and those inoculated with CLas by images from a stereomicroscope and also evaluated their potential for the early diagnosis of the infection caused by this bacterium. The plants were measured monthly, and the evolution of the bacteria on inoculated plants was monitored by real-time quantitative polymerase chain reaction (RT-qPCR) amplification of CLas sequences. A statistical method was used to analyse the data. The selection of variables from histograms of colours (colourgrams) of the images was optimized using a paired Student's t-test. The intensity of counts for green colours from images of fluorescence had clearly minor variations for healthy plants than diseased ones. The darker green colours were the indicators of healthy plants and the light colours for the diseased. The method of fluorescence images is novel for fingerprinting healthy and diseased plants and provides an alternative to the current method represented by PCR and visual inspection. A new, non-subjective pattern of analysis and a non-destructive method has been introduced that can minimize the time and costs of analyses. © 2011 The Royal Society of Chemistry.

Pereira F.M.V.,Embrapa Instrumentaao Agropecuaria | Milori D.M.B.P.,Embrapa Instrumentaao Agropecuaria | Venancio A.L.,University of Sao Paulo | Russo M.D.S.T.,Embrapa Instrumentaao Agropecuaria | And 3 more authors.
Talanta | Year: 2010

This study investigated the organic and inorganic constituents of healthy leaves and Candidatus Liberibacter asiaticus (CLas)-inoculated leaves of citrus plants. The bacteria CLas are one of the causal agents of citrus greening (or Huanglongbing) and its effect on citrus leaves was investigated using laser-induced breakdown spectroscopy (LIBS) combined with chemometrics. The information obtained from the LIBS spectra profiles with chemometrics analysis was promising for the construction of predictive models to identify healthy and infected plants. The major, macro- and microconstituents were relevant for differentiation of the sample conditions. The models were then applied to different inoculation times (from 1 to 8 months). The models were effective in the classification of 82-97% of the diseased samples with a 95% significance level. The novelty of this method was in the fingerprinting of healthy and diseased plants based on their organic and inorganic contents. © 2010 Elsevier B.V. All rights reserved.

Cerqueira S.D.C.A.,Federal University of Sergipe | Romao L.P.C.,Federal University of Sergipe | Lucas S.C.O.,Federal University of Sergipe | Fraga L.E.,São Paulo State University | And 6 more authors.
Fuel | Year: 2012

The reduction of Cr(VI) to Cr(III) in aqueous solution, and the subsequent removal of Cr(III) using in natura peat or its humin fraction, was characterized by electron paramagnetic resonance (EPR), ultraviolet-visible (UV-Vis) spectroscopy and X-ray photoelectron (XPS) spectroscopy. EPR spectroscopy g-factors ranging from 2.0029 to 2.0030 indicated the presence of organic free radicals (OFR) associated with carbon atoms. The spin densities of the samples increased with pH in the range pH 2.0-pH 6.0. An XPS spectroscopy peak at 579.0 eV was attributed to Cr(VI), and peaks at 576.8 eV and 677.3 eV to two different chemical forms of Cr(III). Removal of chromium increased with the reduction of Cr(VI) to Cr(III), and removal rates after 50 h were 13% (peat) and 15% (humin) at pH 6.0, and 70% (peat) and 80% (humin) at pH 2.0. The greater efficiency of the humin fraction in the reduction/removal process is discussed in terms of the chemical structures of these materials. © 2011 Elsevier Ltd. All rights reserved.

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