Declínio dos citros: algo a ver com o sistema de produção de mudas cítricas?

Na atualidade, a citricultura paulista enfrenta sérios problemas com o surgimento de novas enfermidades limitantes ao processo produtivo. Uma das alternativas para prevenir essas enfermidades é, seguramente, a produção de mudas certificadas, com borbulhas e sementes de assegurada qualidade genética e sanitária, produzidas em containers ou sacos plásticos, sob fiscalização dos órgãos competentes, garantindo-se, assim, a sanidade das mesmas. No entanto, tem-se verificado que grande parte do processo operacional de produção de mudas cítricas foi parcialmente adaptado da produção de essências florestais (eucalipto), onde se insere, principalmente, o emprego de tubetes com comprimento de 12 cm. Tal prática desencadeia uma grave deformidade morfológica no sistema radical das mudas cítricas, reduzindo o seu potencial de crescimento, quando são plantadas a campo, em local definitivo. Como a principal causa desencadeadora do declínio dos citros parece ser o estresse hídrico, plantas oriundas desse sistema de produção de mudas, mostram-se muito mais vulneráveis ao estresse e, conseqüentemente, a esta anomalia. Como atualmente todas as mudas produzidas no Estado de São Paulo provêm desse sistema de produção, seguramente o declínio dos citros tenderá a ser, futuramente, muito mais freqüente e severo nos casos de combinações vulneráveis à sua ocorrência.Nowadays, São Paulo citrus culture faces serious problems with the outbreak of new diseases that limit the production process. One of the alternatives to prevent these diseases certainly is the production of certified seedlings, with shoot meristems and seeds of guaranteed genetic and sanitary quality, produced in containers or plastic bags, under the inspection of competent bureaus, thus assuring their health. However, it has been observed that a large part of the operational process of citrus seedling production has been partially adapted from the eucalypt production system, where, the use of plastic conic 12 cm-long cells were originally used. Such practice entails a severe morphological deformation of the root system on citrus seedlings, reducing their growth potential after field transplanting. Because the major triggering cause for citrus decline is the water stress, plants originating from this production system are much more vulnerable to the stress and, consequently, to this anomaly. Since all seedlings produced in São Paulo State come from this system, certainly citrus decline tends to be, in the near future, much more frequent and severe in the cases of vulnerable combinations for its occurrence

Pathogenicity, colony morphology and diversity of isolates of Guignardia citricarpa and G-mangiferae isolated from Citrus spp.

In the present study, the pathogenicity of 36 isolates of Guignardia species isolated from asymptomatic 'Tahiti' acid lime fruit peels and leaves, 'Pera-Rio' sweet orange leaves and fruit peel lesions, and a banana leaf were characterized. For pathogenicity testing, discs of citrus leaves colonized by Phyllosticta citricarpa under controlled laboratory conditions were kept in contact with the peels of fruit that were in susceptible states. In addition, pathogenicity was related to morphological characteristics of colonies on oatmeal (OA) and potato dextrose agar (PDA). This allowed the morphological differentiation between G. citricarpa and G. mangiferae. Polymerase chain reactions (PCRs) were also used to identify non-pathogenic isolates based on primers specific to G. citricarpa. A total of 14 pathogenic isolates were detected during pathogenicity tests. Five of these were obtained from leaf and fruit tissues of the 'Tahiti', which until this time had been considered resistant to the pathogen. Given that the G. citricarpa obtained from this host was pathogenic, it would be more appropriate to use the term insensitive rather than resistant to categorize G. citricarpa. A non-pathogenic isolate was obtained from lesions characteristic of citrus black spot (CBS), indicating that isolation of Guignardia spp. under these conditions does not necessarily imply isolation of pathogenic strains. This also applied to Guignardia spp. isolates from asymptomatic citrus tissues. Using fluorescent amplified fragment length polymorphism (fAFLP) markers, typically pathogenic isolates were shown to be more closely related to one another than to the non-pathogenic forms, indicating that the non-pathogenic isolates display higher levels of genetic diversity.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Susceptibility of fruits of the 'Valência' and 'Natal' sweet orange varieties to Guignardia citricarpa and the influence of the coexistence of healthy and symptomatic fruits

Em pomar de laranjeiras 'Valência' e 'Natal' avaliou-se a importância da presença de frutos sintomáticos da mancha preta citros (MPC) na severidade da doença nos frutos cítricos da safra subseqüente. Adicionalmente, avaliou-se o estádio de suscetibilidade dos frutos dessas variedades. Frutos foram protegidos com sacos de papel cristal a partir do estádio de 75% de pétalas caídas em outubro de 2000, até abril de 2001. Frutos foram expostos, em intervalos semanais, da 1ª à 24ª semana. Esse processo se deu tanto em plantas onde os frutos da safra remanescente foram previamente colhidos, como naquelas cujos frutos sintomáticos da safra remanescente permaneceram até a sua queda natural. Avaliou-se a severidade da doença usando uma escala de notas que variou de 0 (ausência de sintomas) a 6 (sintomas severos). Observou-se que para as duas variedades os conídios de Phyllosticta citricarpa, formados nas lesões dos frutos da safra remanescente, não provocaram incremento significativo na severidade da doença dos frutos da safra subseqüente. A proteção dos frutos até 10ª semana após a queda de pétalas não influenciou na quantidade final de lesões, indicando que as descargas de ascósporos que ocorreram a partir desse momento foram, provavelmente, responsáveis pela severidade da doença. Frutos que ficaram expostos entre a 20ª a 24ª semanas após a queda de 75% de pétalas mostraram-se sintomáticos, indicando que nesse estádio frutos encontravam-se suscetíveis ao patógeno.The importance of the presence of symptomatic fruits with citrus black symptoms (CBS) on the disease severity level in subsequent crop production was assessed in an orchard planted with Valência and Natal sweet orange varieties. Additionally, the period of susceptibility of the fruits of these varieties was evaluated. Fruits were covered with paper bags at the stage of 75% fallen petals and were then exposed to natural infection at weekly intervals, from October 2000 to April 2001. This process was carried out in plants where the fruits from the previous harvest had been picked as well as in plants where fruits remained until natural drop. The evaluation of disease severity used a scale that varied from 0 (absence of symptoms) to 6 (severe symptoms). It was observed that, for the Valência and Natal varieties, conidia of Phyllosticta citricarpa that had formed on the lesions of fruits from the previous harvest did not significantly increase the severity of disease on the fruits of the subsequent harvest period. In this study, the protection of the fruits until 10 weeks after petal drop did not affect the number of lesions, indicating that ascospore discharges after that date were, probably, responsible for disease severity. Fruits exposed between the 20th and 24th week after 75% of the petals had fallen were symptomatic, indicating that, at this stage, the fruits were still susceptible to the pathogen

Synthesis of selenium-linked neoglycoconjugates and pseudodisaccharides

The introduction of organoselenium moieties within the structure of carbohydrates has received attention recently. Herein, we report on the synthesis of selenium-containing neoglycoconjugates and pseudodisaccharides by the reaction of nucleophilic selenium species, generated from sugar diselenides, with chiral N-Boc aziridines and sugar tosylates. The reaction proceeds with moderate to good yields for various substrates. The introduction of organoselenium moieties within the framework of various sugars, with increased levels of complexity, thus allowing the synthesis of disaccharide and glycoconjugate mimetics. (C) 2012 Elsevier Ltd. All rights reserved.CNPqCNPqFAPERGSFAPERGSCAPESCAPESFAPESPFAPES

Influência da temperatura e da luminosidade no desenvolvimento de Guignardia citricarpa, agente causal da mancha preta dos frutos cítricos

O presente trabalho teve como objetivo avaliar sob condições de laboratório, o efeito de temperatura (15, 18, 20, 21, 24, 25, 27, 30, 33 e 35 ± 1 ºC) nas condições escuro, luz contínua e fotoperíodo 12/12 h, na produção de pseudotécios de isolados de Guignardia citricarpa, provenientes de regiões cítricolas dos Estados de São Paulo e Rio de Janeiro. Discos de folhas de limoeiro 'Cravo' (Citrus limonia), de 12 mm de diâmetro, foram autoclavados e depositadas (parte abaxial) na superfície do meio de cultura constituído por ágar-água 2%. Foram colocados quatro discos de folhas por placa onde, de forma conjunta e intercalar aos mesmos, depositaram-se dois discos obtidos de colônias de Phyllosticta citricarpa, com 21 dias de incubação. Foi, também, estudado o efeito da temperatura e do tempo de incubação (2, 8 e 16 h) na germinação dos ascósporos. Após 21 dias de incubação, a ótima temperatura ajustada pela função beta generalizada, para produção de pseudotécios deu-se a 26 e 22,5 a 27,5 °C, sob condição de escuro e de luz, respectivamente. Observou-se também produção de pseudotécios a 27 ºC em fotoperíodo 12/12 h. em estudo complementar foi verificado que, aos 19 dias, a 27 ºC, cerca de 90% dos pseudotécios haviam alcançado a maturidade, com abundante produção de ascósporos. A maior porcentagem de ascósporos germinados foi constatada na temperatura de 24 ºC, após 16 h de incubação. Dentre as vantagens alcançadas, incluem-se a possibilidade (i) da produção massal de ascósporos em curto período de tempo, e (ii) da padronização do inóculo, tanto qualitativa, quanto quantitativa.Four experiments were carried out at the FCAV-UNESP-Campus of Jaboticabal to evaluate the effect of temperature (15, 18, 20, 21, 24, 25, 27, 30, 33 e 35 + 1 ºC), and three light regimes (dark, continuous light and a 12/12 hour photoperiod) on the production of Guignardia citricarpa pseudothecia in citrus (Citrus sp.) areas of the States of São Paulo and Rio de Janeiro. In addition, the effects of those temperatures and periods of incubation (2, 8 and 16 h) on ascospore germination were also studied. Disks of Rangpur lime (Citrus limonia) leaves measuring 12 mm in diameter were autoclaved and transferred to Petri dishes containing 2% water-agar with the abaxial surface facing the medium. Four disks were placed in each plate equally spaced from each other. Two disks from colonies of Phyllostica citricarpa with 21 days of incubation were deposited in the center of each plate and incubated at the different temperatures. The effect of temperature on the photoperiod of 12/12 in the germination of ascospore of G. citricarpa was also evaluated. The generalized beta function was at 26, 22.5 and 27.5 ºC for conditions of darkness and light respectively. Pseudothecium production was observed in the photoperiod of 12/12 h. Mature ascospores were observed after 14 days of incubation, at 27 ºC. The highest percentage of germinated ascospores was obtained at temperatures around 24 ºC, after 16 h of incubation

Evaluation of fungicide applications to sweet orange at different flowering stages for control of postbloom fruit drop caused by Colletotrichum acutatum

Postbloom fruit drop (PFD), caused by Colletotrichum acutatum, produces blossom blight, fruit abscission and persistent calyces. in groves of Pera-Rio and Natal sweet orange located in Santa Cruz do Rio Pardo and Rincao, São Paulo, Brazil, four experiments were carried out to evaluate the effectiveness of fungicides sprayed alone or as mixtures, at different flowering stages for the control of PFD of citrus. The number of symptomatic flowers, the percentage of fruit set (FS), and the relationship between persistent calyces and total fruit weight per plant were evaluated. The fungicides carbendazim and folpet were sprayed at 0.50 ml and 1.25 ga.i. l(-1) of water, respectively, were superior by all the criteria to the other treatments. Carbendazim and folpet fungicides performed best when they were applied at the green bud through hollow ball stages. Difenoconazole, independent of application timing, was less effective by all criteria used. Application of mancozeb at 1.60 ga.i. l(-1) at the green bud stage followed by application of mancozeb in a tank mix with carbendazim or folpet at 1.0 ml and 1.25 g a.i. l(-1), respectively, during green bud bloom and hollow ball stages were effective for disease control. Carbendazim combined with 0.25% KNO3, reduced the number of persistent calyces and increased fruit production significantly. Applications must be made between green bud and hollow ball stages for best control. Applications only at hollow ball or open flower stages did not provide effective disease control. (C)2007 Elsevier Ltd. All rights reserved

Indução da expressão precoce de sintomas de Guignardia citricarpa em frutos de laranjeira 'pêra-rio' Induction of the precoce expression of Guignardia citricarpa symptoms in fruits of pera-rio sweet orange

O presente trabalho teve por objetivo avaliar a influência de diferentes concentrações de ethephon na expressão precoce de sintomas de Guignardia citricarpa em frutos de laranjeira 'Pêra-Rio'. Para tal, frutos assintomáticos e isentos de aplicações com fungicidas, com 20 e 28 semanas após a queda de pétalas, foram coletados em área de comprovada existência da doença, no município de Conchal-SP e levados ao Laboratório de Fitopatologia da FCAV/UNESP, em Jaboticabal-SP, onde foram tratados com soluções nas seguintes doses de ethephon: i) 1,57 g L-1; ii) 2,10 g L-1; iii) 2,42 g L-1; iv) Testemunha (água). Todas acrescidas de imazalil a 0,25 g L-1, para prevenir podridões de pós-colheita. Após os tratamentos, os frutos foram mantidos em câmara incubadora para B.O.D., calibrada à temperatura de 25ºC &plusmn;1ºC, por 15 dias. Posteriormente, os frutos foram submetidos a quatro avaliações, em intervalos semanais, sendo atribuídas notas que variaram de zero (ausência de sintomas) a 6 (sintomas severos). Os dados da severidade da doença observados nos frutos colhidos prematuramente e submetidos aos diferentes tratamentos com ethephon foram comparados aos observados em frutos ensacados e não ensacados, mantidos no campo até a maturação natural. Constatou-se maior equivalência de sintomas nos frutos com idade entre 20 e 28 semanas, quando estes foram tratados com 2,10 g L-1 de ethephon e avaliados entre 28 e 35 dias. Concluiu-se que o emprego de ethephon, nestas condições, viabilizou a expressão precoce dos sintomas da mancha preta em frutos contendo infecções quiescentes de G. citricarpa, com antecedência de, pelo menos, 105 dias antes da colheita. Tal resultado constitui-se, portanto, em alternativa de grande aplicabilidade na detecção precoce de sintomas de mancha preta.<br>The aim of this study was to evaluate the influence of different ethephon rates in the precocity expression of symptoms of black spot caused by Guignardia citricarpa in fruits 'Pêra-Rio' sweet orange, in the orchard located in Conchal, SP. Asymptomatic fruits without fungicides applications and with 20 and 28 weeks after petal fall were collected and taken to the Laboratory of Plant Pathology of FCAV/UNESP, in Jaboticabal/SP, where they were treated with the following ethephon rates: i) 1.57 g L-1; ii) 2.10 g L-1; iii) 2.42 g L-1; iv) (water) (control). For all treatments, Imazalil at 0.25 g L-1 was added to prevent post harvest fungal disease. After the treatments, the fruit were kept in a chamber with a temperature of 25ºC &plusmn; 1ºC, during 15 days. Therefore, the fruits were evaluated four times with weekly interval using a scale from 0 (absence of symptoms) to 6 (severe symptoms). The data of disease severity observed in fruits colleted prematurely, under different ethephon rates were compared to those fruits bagged and unbagged remained in orchard until natural maturation. Major symptoms equivalence was verified in fruits with age 20 and 28 weeks, when they were treated with 2.10 g L-1 of ethephon, and evaluated between 28 and 35 days. It is concluded that the use of ethephon in this conditions may cause a precocious expression of symptoms of black spot in fruits with quiescent infections of G. citricarpa with 105 days before of harvest. These results are an alternative of great applicability to precocious detection of citrus black spot