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Tropical Plant Pathology, Volume: 39, Número: 1, Publicado: 2014
  • Letter from the Editors

    Zerbini, Francisco Murilo; Barreto, Robert W.; Paula Jr., Trazilbo J. de; Del Ponte, Emerson M.
  • Interactions between foliar diseases: concepts and epidemiological approaches Review Article

    Jesus Junior, Waldir C.; Paula Júnior, Trazilbo J.; Lehner, Miller S.; Hau, Bernhard

    Resumo em Inglês:

    This review deals with the phenomenon of plant disease interactions. The epidemiological implications of foliar diseases occurring simultaneously on the same crop are important because the establishment of disease management strategies depends on the knowledge of disease interactions. We discuss some concepts and the terminology related to the interaction studies and present related examples with special emphasis on interacting wheat diseases.
  • Influence of Fusarium spp. isolate and inoculum density on resistance screening tests in onion Articles

    Caligiore Gei, Pablo Fernando; Valdez, Jorge Gustavo; Piccolo, Ricardo José; Galmarini, Claudio Rómulo

    Resumo em Inglês:

    Fusarium basal rot (FBR), which is caused predominantly by Fusarium oxysporum and F. proliferatum, is the main limiting factor of onion crops. Resistant cultivars obtained in other countries do not behave as such in Argentina crop fields. The cultivars Antártica-INTA, Grano de Oro-Seminis, Valcatorce-INTA and TW-2007 (reported as tolerant) were tested with five Fusarium spp. isolates, using four inoculum concentrations. Disease incidence was recorded along 28 days and the area under disease progress curve was calculated. Diverse epidemiological models were fitted to experimental data. There were significant differences in the resistance level among cultivars, with TW-2007 being the most tolerant. Local Fusarium isolates were the most virulent ones. The concentration of 10,000 microconidia/ gram was the most lethal for all isolates. The absence of resistance to Fusarium in the four cultivars tested was confirmed. Inoculum concentration and isolate are critical factors in screening for resistance to FBR. Breeding based on the selection of genotypes against low virulence strains of Fusarium spp. and the presence of more aggressive strains in local fields may be one of the causes why varieties reported as resistant or tolerant behave as susceptible in our environment.
  • Potential for using crude extract of Sarocladium oryzae for suppression of rice blast Articles

    Côrtes, Marcio V. C. B.; Silva-Lobo, Valacia L.; Filippi, Marta C. C.; Lima, Débora C. S.; Prabhu, Anne S.

    Resumo em Inglês:

    Crude extract of an isolate of the fungus Sarocladium oryzae (CNPAF So 20G), containing the antimicrobial cerulenin, was produced and its antagonistic potential on the rice blast pathogen Magnaporthe oryzae was asessed. Cerulenin was detected in crude extract of S. oryzae through thin layer chromatography showing a Rf value of 0.63. The quantity of cerulenin in the crude extract was 237 µg.mL-1. The in vitro inhibition of germination and appressorial formation of M. oryzae was assessed on an artificial hydrophobic surface, using eight different doses of cerulenin ranging from 0.05 to 30.0 µg.mL-1. The LD50 values calculated based on the Probit-log analysis for germination and appressorial formation were 1.298 ± 0.123 µg.mL-1 and 0.0705 ± 0.0062 µg.mL-1 of cerulenin, respectively. The 30.0 µg.mL-1 of cerulenin dose inhibited 98% and 99%, germination and appressorial formation, respectively. The mode of action of cerulenin was studied by staining conidia with Calcofluor White and fluorescent microscopy showing its effect on plasma membrane. Crude extract of S. oryzae suppressed 63% of rice blast disease in greenhouse conditions. The results indicate that a product based on cerulenin and/or S. oryzae has a great potential to be used in biological control of rice blast.
  • Photosynthetic gas exchange and antioxidative system in common bean plants infected by Colletotrichum lindemuthianum and supplied with silicon Articles

    Polanco, Leonora R.; Rodrigues, Fabrício A.; Nascimento, Kelly J. T.; Cruz, Maria F. A.; Curvelo, Carmen R. S.; DaMatta, Fábio M.; Vale, Francisco X. R.

    Resumo em Inglês:

    This study investigated the effects of silicon (Si) on the resistance of common bean plants to anthracnose caused by Colletotrichum lindemuthianum. The plants were grown in a nutrient solution containing 0 (control) or 2 mM Si (+Si) and both photosynthesis and antioxidative metabolism levels were evaluated. The Si concentrations in the leaf tissues of +Si plants increased by 33% in comparison to those of control plants. Anthracnose severity was reduced by 34% in +Si plants in comparison to control plants. The net carbon assimilation rate, stomatal conductance to water vapor and transpiration rate values were significantly higher in +Si plants than in control plants. The activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR) tended to be higher in +Si plants than in control plants. The hydrogen peroxide concentration was significantly lower in +Si plants than in control plants. In conclusion, the Si supply was associated with lower anthracnose severity and up-regulation of antioxidant enzymes, which in turn might be associated with better gas exchange in +Si plants. The impaired photosynthetic performance in +Si plants was associated with stomatal limitations, whereas in control plants those impairments likely reflected dysfunctions at the level of biochemical reactions involved in CO2 fixation.
  • Experimental host range of Citrus leprosis virus C (CiLV-C) Articles

    Garita, Laura Cristina; Tassi, Aline Daniele; Calegario, Renata Faier; Freitas-Astúa, Juliana; Salaroli, Renato B.; Romão, Gerson O.; Kitajima, Elliot W.

    Resumo em Inglês:

    Citrus leprosis (CL) is a serious threat to the citrus industry, especially for sweet oranges. For a long time, Citrus spp. were considered the only susceptible hosts. However, other plant species were also found either experimentally or naturally to be susceptible to Citrus leprosis virus C (CiLV-C). To assess the experimental host range of CiLV-C, a large number of plant species were inoculated with Brevipalpus phoenicis, viruliferous to CiLV-C, under experimental conditions. Out of the 140 tested species (43 families), 59 species (24 families) developed localized chlorotic and/or necrotic lesions upon inoculation of leaves with viruliferous mites, and 40 species (18 families) of them yielded positive results for CiLV-C detection in at least one of the following assays: ELISA, RT-PCR, transmission electron microscopy and immunfluorescence. For those that developed lesions and yielded negative results in CiLV-C detection assays, the results may be attributed to the small number of lesions and their necrotic state with very little viral material. The fact that a considerable number of plant species are susceptible to the virus after mite inoculation brings up implications for the epidemiology, quarantine and evolution of the citrus leprosis pathosystem.
  • Rice grain resistance to brown spot and yield are increased by silicon Articles

    Dallagnol, Leandro J.; Rodrigues, Fabricio A.; Mielli, Mateus V. B.; Ma, Jian F.

    Resumo em Inglês:

    Brown spot, caused by Bipolaris oryzae, is one of the most important diseases of rice and can cause a reduction in yield and grain quality. The effect of silicon (Si) on the resistance of rice grains to brown spot was investigated. Plants from cv. Oochikara and its mutant, defective in the Lsi1 transporter (lsi1 mutant), were grown in hydroponic culture either with Si (+Si; 2 mM) or without Si (-Si). Panicle inoculation with B. oryzae was carried out at the beginning of the milk-grain stage. Panicles were harvested at physiological grain maturity. The supply of Si significantly increased Si concentration in husks compared to -Si plants. Si concentration in husks from cv. Oochikara was up to three times greater than the lsi1 mutant. In the presence of Si, brown spot severity was reduced by 88% in grains from cv. Oochikara and by 53% in grains from lsi1 mutant. Brown spot severity was 77% lower for grains of cv. Oochikara than for the lsi1 mutant, both plant types were grown in the presence of Si. Panicle inoculation reduced significantly the following yield components: number of grains per panicle, the weight of 1000 grains and the percentage of filled grains. Si significantly increased these yield components, especially for inoculated panicles. Considering kernel quality, the panicle inoculation with B. oryzae significantly reduced the yield of husked kernel, yield of whole kernel and kernel diameter, especially for grains from -Si plants. For panicles from +Si plants, the kernel quality was improved under inoculation, compared to -Si plants. Results from this study show that Si improved rice yield and kernel quality in panicles inoculated with B. oryzae. Furthermore the functional Lsi1 gene contributed significantly for increasing the yield of whole kernel and kernel diameter, possibly due to the increasing Si concentration in husks.
  • EF-1α gene and IGS rDNA sequencing of Fusarium oxysporum f. sp. vasinfectum and F. oxysporum f. sp. phaseoli reveals polyphyletic origin of strains Articles

    Silva, Fabiana Pires da; Vechiato, Marta Helena; Harakava, Ricardo

    Resumo em Inglês:

    The fungi Fusarium oxysporum f. sp. vasinfectum (Fov) and F. oxysporum f. sp. phaseoli (Fop) are important pathogens that cause wilt on cotton and common bean, respectively. In the present study, phylogenetic trees constructed with partial sequences of the translation elongation factor gene and ribosomal intergenic spacer region of Brazilian Fov and Fop strains revealed polyphyletic origin of strains within both formae speciales. This creates an obstacle for the development of specific molecular diagnostic methods and explains the failure of supposedly specific methods described in the literature to correctly discriminate formae speciales of F. oxysporum.
  • Identification of sources of seedling resistance to Phytophthora capsici in Cucumis melo Articles

    Pontes, Nadson de C.; Aguiar, Frederick M.; Boiteux, Leonardo S.; Lima, Milton L.P.; Oliveira, Valter R.; Café Filho, Adalberto C.; Reis, Ailton

    Resumo em Inglês:

    The employment of genetic resistance to minimize yield losses induced by Phytophthora capsici remains unexplored in melon (Cucumis melo). A diverse collection of melon accessions was evaluated against P. capsici isolates at the seedling stage. In the first screening assay, 105 accessions were evaluated using isolate PCpe-04 obtained from cucumber (Cucumis sativus). In a second assay, 31 accessions displaying high levels of resistance in the first assay were challenged with a distinct isolate (PCpe-09 also from cucumber). In a third assay, a subset of 14 selected accessions was re-evaluated using isolates PCpe-09 and PCmo-07 (from strawberry). In the last screening, seven accessions with high levels of resistance across all assays were challenged with five isolates from representative host species [PC-Vagem (snap bean), PCp-129 (Capsicum chinense), PCp-155 (C. annuum), PCpe-09 and PCmo-07] to assess their reaction against a varied sample of P. capsici isolates. For two accessions (CNPH-093 and L040), all plants remained free of symptoms after inoculation with all five isolates. Accessions WMR-29, CNPH 084, CNPH 088 and CNPH 092 were also free of symptoms to all isolates, except PCmo-07. These large-spectrum resistance sources might be useful for breeding programs aiming to incorporate resistance against P. capsici in elite melon lines.
  • Bitter gourd little leaf disease associated to 'Candidatus Phytoplasma asteris' Articles

    Win, Nang Kyu Kyu; Kim, Young-Hwan; Jung, Hee-Young

    Resumo em Inglês:

    Little leaf disease symptoms including dwarfed, thickened and puckered leaves and shortened internodes of bitter gourd (Momordica charantia L.) plants were observed in Meiktila, Myanmar 2012. The causal agent was detected by polymerase chain reaction using universal phytoplasma primers, and classified by sequencing of 16S rRNA gene, ribosomal protein (rp) gene and protein translocase subunit (secY) gene and RFLP analysis. The expected target phytoplasma DNA fragment of 1.8 kbp was amplified from the bitter gourd little leaf (BitLL) diseased samples. The 16S rRNA gene sequence analysis of BitLL phytoplasma showed 99.7% to 99.9% identity with members of 'Candidatus Phytoplasma asteris' associated with sesame phyllody (SP), periwinkle phyllody (PeP) and periwinkle little leaf (PeLL) diseases in Myanmar. Moreover, rp and secY gene sequences of the BitLL isolate were 99.7% to 100%, and 99.9% to 100% identity among the SP, PeP and PeLL phytoplasma. However, putative restriction analysis revealed that the BitLL isolate missed one Mse I site on rp gene sequence while other isolates had the same restriction sites. Phylogenetic analysis of the three genes confirmed that the phytoplasma belongs to the 'Ca. P. asteris'. This is the first report of 'Ca. P. asteris' infecting a member of the family Cucurbitaceae in Myanmar.
  • Reappraisal of the black mildews (Meliolales) on Hevea brasiliensis Articles

    Pinho, Danilo B.; Honorato Junior, Jaime; Firmino, André L.; Hora Junior, Braz T.; Mizubuti, Eduardo S. G.; Pereira, Olinto L.

    Resumo em Inglês:

    The rubber tree (Hevea brasiliensis) is host to several fungal species, including Irenopsis heveae as described by Hansford in 1961, which causes black mildew on leaves. One specimen of Irenopsis heveae from the state of Espírito Santo and two from the state of Pará were analyzed and showed some morphological differences. Some structures are similar to morphological characteristics as described and illustrated by Vincens in 1915 for Meliola heveae. Morphological comparisons with the type specimen of I. heveae and the alignment of the nucleotide sequences of the 28S rDNA region, however, indicate that the three samples belong to the same species. According to these data M. heveae and I. heveae are heterotypic synonyms with M. heveae being the older name. As the name I. heveae is already occupied by Hansford, Irenopsis vincensii is proposed as new name for the black mildew on H. brasiliensis. This is the first contribution of molecular sequence data for this species.
  • Evaluation of a cotton germplasm collection against Fusarium wilt race 3 isolates from Egypt Articles

    Abd-Elsalam, Kamel A.; Omar, Moawad R.; Asran-Amal, Abdelmogny; Mansour, Mahmoud T.; Aly, Aly Abd El-Hady

    Resumo em Inglês:

    Pathogenic variation of 30 isolates of Fusarium oxysporum f. sp. vasinfectum (FOV) race 3 was evaluated on seedlings of the highly susceptible cotton cultivar 'Giza 74' in greenhouse assays. FOV isolates were clustered based upon their virulence patterns. The clusters of FOV isolates were not related to their geographic origins. Fifty-five experimental cotton genotypes were evaluated under greenhouse conditions for resistance to Fusarium wilt, in autoclaved clay loam soil infested with a mixture of equal parts (w/w) of 30 isolates of FOV race 3 at a rate of 10 g/kg of soil. Eleven genotypes were rated as highly susceptible (survival frequency from zero to 24.7%) and 21 genotypes were rated as highly resistance (survival frequency of 79.6 to 100%). The remaining genotypes displayed variable levels of partial resistance. Since no wilt nursery has been established in Egypt, greenhouse tests will continue to be the only reliable method for screening cotton breeding materials for FOV resistance. The current absence of Fusarium wilt in commercial cotton fields in Egypt demonstrates the reliability of the adopted screening procedures in discriminating cotton genotypes for resistance to Fusarium wilt.
  • Genetic diversity studies of Papaya meleira virus Short Communications

    Daltro, Cleidiane B.; Abreu, Emanuel Felipe Medeiros; Aragão, Francisco Jose Lima; Andrade, Eduardo C.

    Resumo em Inglês:

    Papaya (Carica papaya) is a fruit crop of great economic and social importance for Brazil and other papaya-producing countries. Brazil is the second largest producer in the world. The papaya sticky disease, caused by Papaya meleira virus (PMeV), has caused great losses in the major Brazilian papaya-producing states. In order to estimate the genetic diversity of PMeV, latex samples were collected from papaya plants in the states of Bahia, Espírito Santo, Pernambuco, Ceará and Rio Grande do Norte, and total RNA was extracted. Specific primer for the replicase region allowed the amplification, by RT-PCR, of a fragment of approximately 560 bp from 31 isolates. The sequence analysis indicated a level of conservation greater than 88% among isolates. Furthermore, comparative analyzes indicated that PMeV has similarity with mycoviruses of the family Totiviridae. This phylogenetic relationship was reinforced by the presence of conserved motifs within in the RdRp regions from mycoviruses.
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