30 research outputs found

    Incompatibilidade som√°tica em Rhizoctonia solani AG-1 IA da soja

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    O fungo Rhizoctonia solani AG-1 IA √© um dos pat√≥genos mais importantes que afeta a cultura da soja no Brasil, causando a mela ou queima foliar. A doen√ßa est√° associada com a fase teleom√≥rfica de R. solani, o basidiomiceto Thanatephorus cucumeris. Neste estudo, baseando em conhecimento pr√©vio sobre a biologia de R. solani AG-1 IA, duas hip√≥teses foram testadas. Na primeira hip√≥tese postulou-se a ocorr√™ncia de incompatibilidade som√°tica em popula√ß√Ķes de R. solani AG-1 IA. A segunda hip√≥tese testada foi de que esta popula√ß√£o de R. solani AG-1 IA da soja apresenta indica√ß√Ķes de estrutura sexual clonal. Duas amostras de isolados de R. solani AG-1 IA da soja obtidas no Maranh√£o e no Mato Grosso foram utilizadas. Na primeira amostra, foram selecionados isolados apresentando diferentes perfis de RAPD (Random Amplified Polymorphic DNA), procurando maximizar a diversidade dos isolados, e evitando a introdu√ß√£o de poss√≠veis clones no teste. Os isolados foram pareados em todas as combina√ß√Ķes poss√≠veis em meio de BDA mais carv√£o ativado e examinados quanto √†s intera√ß√Ķes som√°ticas resultantes. Seis grupos de incompatibilidade som√°tica (GCS) foram detectados entre 24 isolados do AG-1 IA. Entretanto, an√°lises microsc√≥picas dos pareamentos entre isolados indicaram maior freq√ľ√™ncia de incompatibilidade som√°tica, impossibilitando o grupamento em GCS. No geral, a metodologia de avalia√ß√£o das intera√ß√Ķes som√°ticas macrosc√≥picas em meio BDA + carv√£o ativado, n√£o se mostrou totalmente apropriada para discrimina√ß√£o das categorias de rea√ß√Ķes de compatibilidade entre isolados de R. solani AG-1 IA. Com a segunda amostra procurou-se determinar a ocorr√™ncia de clones na popula√ß√£o do pat√≥geno, ou seja, isolados que compartilham o mesmo padr√£o fenot√≠pico de RAPD e somaticamente compat√≠veis. No caso de R. solani AG 1 IA da soja, a gama de intera√ß√Ķes som√°ticas entre pareamentos de isolados e, principalmente, os desvios na associa√ß√£o estrita entre os GCS detectados neste trabalho, conjuntamente com os perfis de RAPD observados anteriormente por Fenille (11) e Meyer (20), s√£o consistentes com recombina√ß√£o. Entretanto, o pat√≥geno ainda apresenta um componente clonal expressivo na popula√ß√£o. de um total de 43 isolados, os exemplos de prov√°veis clones na popula√ß√£o do pat√≥geno totalizaram 16 isolados.Rhizoctonia solani anastomosis group 1 IA (AG-1 IA) is considered one of the most important pathogens affecting soybean in Brazil, causing the aerial or foliar blight. This disease is associated with the teleomorphase of R. solani AG-1 IA, the basidiomycete fungus Thanatephorus cucumeris. In this study, based on previous knowledge of the biology of R. solani AG-1 IA, two hypotheses were tested. In the first we postulated the occurrence of somatic incompatibility in populations of R. solani AG-1 IA. The second was that the population of R. solani AG1 IA from soybean has a clonal structure. Two population samples of R. solani AG-1 IA from soybean, obtained in Maranh√£o and Mato Grosso were analyzed. In the first sample, isolates with distinct RAPD (Random Amplified Polymorphic DNA) profile were selected to maximize the genetic diversity of isolates and to avoid the introduction of clones in the assay. The isolates were paired in all possible combinations in PDA plus charcoal medium and examined according to the resulting somatic interactions. Six somatic compatibility groups (SCG) were detected among 24 isolates of AG-1 IA. However, microscopic analyzes of the pairings indicated higher frequency of somatic incompatibility, resulting in the impossibility of grouping any two isolates of R. solani AG-1 IA into SCG. In general, the methodology for evaluating the macroscopic somatic interactions in PDA plus charcoal medium seemed not totally appropriate for discriminating between categories of somatic compatibility amongst isolates of R. solani AG-1 IA. With the second sample of isolates we aimed to determine the occurrence of clones in the population of the pathogen, i.e., isolates that share the same phenotypic RAPD profile and are somatically compatible. Considering the range of somatic interactions between pairings of R. solani AG-1 IA isolates and the deviations of the strict association between the GCS detected and the RAPD profile formerly observed by Fenille (11) and Meyer (20) are consistent with recombination. However, there is evidence for an expressive clonal component in the population. From a total of 43 isolates of R. solani AG-1 IA, 16 were probable clones.Funda√ß√£o de Amparo √† Pesquisa do Estado de S√£o Paulo (FAPESP

    O papel de Rhizoctonia spp. binucleadas na indução de resistência a mela da soja = The role of binucleate Rhizoctonia spp. inducing resistance to the soybean foliar blight

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    O papel de Rhizoctonia spp. binucleadas (RBN), no biocontrole de doen√ßas causadas por R. solani K√ľhn em v√°rias culturas, tem sido relatado na literatura. No entanto, n√£o h√° informa√ß√£o, no Brasil, sobre o potencial de RBN como agentes de biocontrole contradoen√ßas causadas por Rhizoctonia na soja. A hip√≥tese testada foi de que isolados de RBN podem induzir resist√™ncia na soja contra a mela, causada por R. solani do grupo de anastomose (AG) 1 IA. Desta forma, o objetivo deste trabalho foi avaliar isolados de RBN, obtidos de amendoim, feij√£o e soja quanto √† capacidade de induzir resist√™ncia na soja contra a mela, em condi√ß√Ķes de casa de vegeta√ß√£o. Esta pesquisa evidencia a a√ß√£o de RBN na indu√ß√£o de resist√™ncia em plantas de soja contra a mela. Entretanto, a manifesta√ß√£o e a efetividade do fen√īmeno de indu√ß√£o de resist√™ncia s√£o dependentes da √©poca de cultivo da soja.<br><br>The role of non-pathogenic binucleate Rhizoctonia spp. (BNR) onthe biocontrol of diseases caused by R. solani on many crops has been reported in the literature. However, in Brazil, there is no information about the potential of BNR as biocontrol agents against Rhizoctonia diseases on soybean. On this research we tested thehypothesis that BNR can induce resistance on soybean against the foliar blight caused by R. solani anastomosis group (AG) 1 IA. Thus, the objective of this research was to evaluate BNR isolates isolated from peanuts, snapbeans and soybean according to their ability forinducing resistance on soybean against the foliar blight disease, under greenhouse conditions. This research evidenced the role of BNR inducing resistance on soybeans against the foliar blight. However, both the occurrence and effectiveness of the phenomenon of induced resistance are dependent on the soybean cultivation season

    Ausência de patogenicidade de Xylella fastidiosa da escaldadura da folha da ameixeira na cultivar de pessegueiro flordasun

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    Xylella fastidiosa associated to plum leaf scald is reported to belong to the same group of the strain that causes the phony disease of peach. Plants of plum cultivars Santa Rosa and Harry Pickstone and peach cultivar Flordasun, grafted on peach rootstock, were inoculated by using buds collected from plum plants severely infected with X. fastidiosa. Peach plants did not develop symptoms of phony disease, after four years in the greenhouse. In contrast, plum plants from both cultivars inoculated either in the rootstock or in the canopy developed leaf scald symptoms. DAS-ELISA tests with antibody against X. fastidiosa and isolation on BCYE medium indicated the presence of the bacterium in plum tissues. These tests were negative for Flordasun peach for both stem and root samples.Xylella fastidiosa que causa a escaldadura-da-folha-da-ameixeira (EFA) é relatada como pertencente ao mesmo grupo do agente causal da "phony" do pessegueiro. Plantas de ameixeira, cultivares Santa Rosa e Harry Pickstone, e de pessegueiro, cultivar Flordasun, enxertadas sobre pessegueiro foram enxertadas com borbulhas procedentes de plantas de ameixeira severamente infectadas com X. fastidiosa. Após quatro anos de observação, em casa de vegetação, as plantas de pessegueiro apresentaram desenvolvimento normal, sem manifestar sintomas de "phony", enquanto as plantas de ameixeira das duas cultivares, enxertadas tanto na copa quanto no porta-enxerto, apresentaram sintomas de EFA. Teste sorológico de DAS-ELISA utilizando anticorpo para X. fastidiosa e isolamento em meio de cultura BCYE indicaram a presença do patógeno nos tecidos da copa das plantas de ameixeira, mas não nos tecidos do porta-enxerto pessegueiro. No pessegueiro cultivar Flordasun, os testes foram negativos, tanto nas amostras da parte aérea como da raiz

    Distinctively variable sequence-based nuclear DNA markers for multilocus phylogeography of the soybean- and rice-infecting fungal pathogen Rhizoctonia solani AG-1 IA

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    A series of multilocus sequence-based nuclear DNA markers was developed to infer the phylogeographical history of the Basidiomycetous fungal pathogen Rhizoctonia solani AG-1 IA infecting rice and soybean worldwide. The strategy was based on sequencing of cloned genomic DNA fragments (previously used as RFLP probes) and subsequent screening of fungal isolates to detect single nucleotide polymorphisms (SNPs). Ten primer pairs were designed based on these sequences, which resulted in PCR amplification of 200-320 bp size products and polymorphic sequences in all markers analyzed. By direct sequencing we identified both homokaryon and heterokaryon (i.e. dikaryon) isolates at each marker. Cloning the PCR products effectively estimated the allelic phase from heterokaryotic isolates. Information content varied among markers from 0.5 to 5.9 mutations per 100 bp. Thus, the former RFLP codominant probes were successfully converted into six distinctively variable sequence-based nuclear DNA markers. Rather than discarding low polymorphism loci, the combination of these distinctively variable anonymous nuclear markers would constitute an asset for the unbiased estimate of the phylogeographical parameters such as population sizes and divergent times, providing a more reliable species history that shaped the current population structure of R. solani AG-1 IA.ISSN:1415-4757ISSN:1678-468

    Caracteriza√ß√£o citomorfol√≥gica, cultural, molecular e patog√™nica de Rhizoctonia solani K√ľhn associado ao arroz em Tocantins, Brasil

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    No Estado do Tocantins, no Norte do Brasil, a incid√™ncia de rizoctoniose no arroz √© importante, causando danos significativos em lavouras de arroz irrigado. O principal objetivo deste trabalho foi determinar o grupo de anastomose (AG) de isolados de R. solani associados ao arroz naquela regi√£o, testando a hip√≥tese de que esses isolados pertencem ao grupo padr√£o de anastomose AG-1 IA, que tamb√©m √© o agente causal da mela em soja em √°reas √ļmidas do Norte do Brasil. Todos os quatro isolados de arroz foram caracterizados, atrav√©s de fus√£o de hifas, como AG-1 IA. A caracteriza√ß√£o cultural, em fun√ß√£o das temperaturas basais (m√≠nimas, m√°ximas e √≥timas), evidenciou que os isolados de R. solani de arroz apresentaram perfis semelhantes aos padr√Ķes AG-1 IA, AG-1 IB e AG-1 IC. Os isolados de arroz foram caracterizados como autotr√≥ficos para tiamina assim como os isolados padr√Ķes AG-1 IA, IB, IC, AG-4 HGI e o isolado da mela da soja. O teste de patogenicidade em plantas de arroz cultivar IRGA-409 e de patogenicidade cruzada √† cultivar IAC-18 de soja (suscet√≠vel √† mela), indicou que al√©m de causar a queima da bainha em arroz, esses isolados causam mela em soja. da mesma forma, o isolado SJ-047 foi patog√™nico ao arroz. As seq√ľ√™ncias de bases de DNA da regi√£o ITS-5.8S do rDNA dos isolados do arroz foram similares √†s seq√ľ√™ncias do AG-1 IA, depositadas no GenBank¬ģ - NCBI. A filogenia do ITS-rDNA indicou um grupo filogen√©tico comum formado pelos isolados do arroz, o isolado da soja e o isolado teste do AG-1 IA. Assim, com base em caracter√≠sticas citomorfol√≥gicas, culturais, filogen√©ticas e patog√™nicas, foi confirmada a hip√≥tese de que os isolados de R. solani pat√≥genos de arroz do Estado do Tocantins pertencem ao grupo de anastomose AG-1 IA, al√©m da indica√ß√£o de que esses isolados podem tamb√©m causar a mela em soja.In Tocantins State, Northern Brazil, the incidence of Rhizoctonia sheath blight on rice is important, causing significant yield losses on rice crops under irrigation. The main objective of this research was to determine the anastomosis group (AG) of R. solani associated with rice in that area, testing the hypothesis that these isolates are from the AG-1 IA, which is also associated with the soybean leaf blight occurring in wet areas of Northern Brazil. All the four rice isolates were characterized, by hyphal fusion, as AG-1 IA. By cultural characterization, based on basal temperatures for mycelial growth (minimum, optimum and maximum), the rice isolates had growth profile similar to the tester isolates AG-1 IA, AG-1 IB and AG-1 IC. The rice isolates were characterized as autotrophic for thiamine, as well as the AG testers AG-1 IA, IB, IC, AG-4 HGI and the soybean leaf blight isolate SJ-047. The pathogenicity test on rice IRGA-409 and the cross pathogenicity on soybean IAC-18 (susceptible to the leaf blight disease) indicated that, besides causing sheath blight, these rice isolates also cause leaf blight on soybean. Similarly, the soybean isolates SJ-047 was pathogenic to rice. The sequences from the ITS-5.8S region of rDNA from the rice isolates were similar to sequences of AG-1 IA deposited at GenBank¬ģ - NCBI. The ITS-rDNA phylogeny indicated a common phylogenetic group formed by these rice isolates, the isolate SJ-047 and the tester AG-1 IA. Thus, based on cytomorphological, cultural, phylogenetics and pathogenic attributes, the hypothesis that the rice isolates of R. solani from Tocantins all belong to the AG-1 IA was confirmed, besides the indication that these isolates can also cause soybean foliar blight
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