RESUMOOs viroides são os menores fitopatógenos conhecidos. Constituídos por uma molécula de RNA de fita simples, circular, que não é encapsidada e não codifica proteínas, são capazes de se replicar de maneira autônoma nas células do hospedeiro. Os viroides de citros pertencem à família Pospiviroidae (cujos membros apresentam uma região central conservada, replicam-se no núcleo das células hospedeiras e não apresentam atividade ribozimática) com cinco espécies: Citrus exocortis viroid, CEVd (Pospiviroid), Hop stunt viroid, HSVd (Hostuviroid), Citrus bark cracking viroid, CBCVd (Cocadviroid) e Citrus bent leaf viroid, CBLVd e Citrus dwarfing viroid, CDVd (Apscaviroid). Além disso, Citrus viroid original source (CVd-OS) e mais recentemente, Citrus viroid V (CVd-V) foram propostas como espécies tentativas do gênero Apscaviroid. Os viroides de citros são transmitidos via enxertia e disseminados principalmente pela propagação de material contaminado. Sabe-se que os viroides de citros infectam praticamente todas as espécies do gênero Citrus e afins. Porém, há somente duas doenças importantes descritas em citros, induzidas por viroides: (i) a exocorte; (ii) e a xiloporose (ou cachexia). Apesar dos viroides induzirem sintomas severos, ou simplesmente afetarem o tamanho das árvores, muitas espécies de citros são assintomáticas, sendo o controle baseado em medidas preventivas, como utilização de gemas livres de viroides aliadas a métodos confiáveis de indexação. A proposta desta revisão é apresentar ao leitor os recentes avanços nas pesquisas com viroides de citros, principalmente na taxonomia, distribuição geográfica, métodos de detecção, limpeza e indexação, epidemiologia e controle, além do histórico e importância desses patógenos para a citricultura mundial. Palavras-chave: Citrus exocortis, Hop stunt, Pospiviroid, Apscaviroid, Cocadviroid, Hostuviroid, Exocorte, Xiloporose. ABSTRACT Viroids in CitrusViroids are the smallest known plant pathogens consisting of a non-encapsidated, circular, single-stranded RNA that replicate autonomously in their host plants. Viroids are classified into two families (Pospiviroidae and Avsunviroidae). All citrus viroids belong to the Pospiviroidae family (species that present a central conserved region, replicate in the nucleus of infected cells and lack of ribozyme activity) with five citrus viroid species: Citrus exocortis viroid, CEVd (Pospiviroid), Hop stunt viroid, HSVd (Hostuviroid), Citrus bark cracking viroid, CBCVd (Cocadviroid) and Citrus bent leaf viroid, CBLVd and Citrus dwarfing viroid, CDVd (Apscaviroid). In addition, Citrus viroid original source (CVd-OS) and, more recently, Citrus viroid V (CVd-V) have been proposed as tentative species of the genus Apscaviroid. Citrus viroids are graft-transmitted and their dissemination occurs mainly by propagation of contaminated material. It is known that they have a broad host range, infecting species of citrus and plants of citrus-related genera. Two important diseases in citrus are viroid-induced: (i) exocortis; (ii) and cachexia. ...

Complexes of gadolinium(III) with N-octanoyl-N-methylglucamine (L8) and N-decanoyl-N-methylglucamine (L10) with 1 : 2 stoichiometry were synthesized and characterized by elemental analysis, electrospray ionization-tandem mass spectrometry (ESI-MS), infrared (IR) spectroscopy, and molar conductivity measurements. The transverse (r 2) and longitudinal (r 1) relaxivity protons were measured at 20 MHz and compared with those of the commercial contrasts. These complexes were incorporated in liposomes, resulting in the increase of the vesicle zeta potential. Both the free and liposome-incorporated gadolinium complexes showed high relaxation effectiveness, compared to commercial contrast agent gadopentetate dimeglumine (Magnevist). The high relaxivity of these complexes was attributed to the molecular rotation that occurs more slowly, because of the elevated molecular weight and incorporation in liposomes. The results establish that these paramagnetic complexes are highly potent contrast agents, making them excellent candidates for various applications in molecular MR imaging.

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Brazil is the world's largest sweet orange producer, with Pera sweet orange [Citrus sinensis (L.) Osbeck] as the main cultivar and Pera IAC as the most planted clone, due to its good overall horticultural performance and because the plants are preimmunized with the attenuated and protective PIAC isolate of the citrus tristeza virus (CTV). Field-selected elite Pera sweet orange trees selected in Bebedouro, on Northern São Paulo state, were previously submitted to shoot tip grafting and preimmunized against CTV. Thirteen of these clones were evaluated in the present study comparatively with the Pera IAC and the Pera Olímpia clones in a trial set up in 1998 under rain-fed conditions in Bebedouro. All the scions were grafted onto Rangpur lime (C. limonia Osbeck) rootstock. The experiment was conducted following a completely randomized design, with 15 treatments (clones), six replications and one plant in the plot. Stem pitting severity, plant growth, fruit yield and quality were evaluated. As Pera IAC and Pera Olímpia, the thirteen pre-immunized clones did not develop stem pitting symptoms characteristics of Pera reaction to CTV. The Pera clones Milton Teixeira, Fazenda União-35 Anos and Alexandre Maróstica-1949 had similar fruit yield, production efficiency and total soluble solids content in the juice than the Pera IAC standard variety, yet they showed remarkably later fruit maturation. Index terms: Citrus sinensis, fruit yield and quality, CTV, cross protection. Desempenho de clones selecionados em campo de laranjaPera no norte do Estado São Paulo, Brasil RESUMO O Brasil é o principal produtor de laranjas do mundo. A laranja Pera [Citrus sinensis (L.) Osbeck] é a principal variedade de laranja cultivada no Brasil, sendo o clone IAC o mais importante, por ser pré-imunizado com a estirpe fraca e protetiva PIAC do vírus da tristeza dos citros, entre outras boas características. Plantas elite de laranja Pera selecionadas em campo na região de Stuchi et al.