Resumo em Inglês:

Fusarium wilt caused by Fusarium oxysporum f. sp. lactucae (FOLAC) is one of the most important problems for lettuce growers because it causes major losses in production. To identify cultivars with potential for use in the management of the disease, 102 accessions were evaluated for resistance to isolates of race 1 of FOLAC. Initially, preliminary screening was done, using the isolate Fus-173. Then, 47 materials selected as highly resistant and a susceptible control (Regina) were reevaluated for resistance to other isolates of FOLAC race 1 from different locations: Fus-202 and Fus-205, in October 2011, Fus-219 and Fus-222, in November 2011; and Fus-207, Fus-209, and Fus-220 in December 2011. Inoculation was performed on 25 day old seedlings in the greenhouse by the method of cutting the roots and immersing them in the conidial suspension. The evaluation was performed using a scale ranging from 0 (healthy plant) to 4 (dead plant). Resulting data was transformed into a disease index and submitted to an analysis of variance and means comparison by the Tukey test (P=0.05). Thirty-two accessions were identified with wide resistance spectrum to different isolates of the pathogen in the four periods of inoculation.

Resumo em Inglês:

Citrus leprosis (CL) was first described in South America in the 1920's. It is considered similar to a disease first observed back to 1860 in Florida. It is a destructive disease characterized by localized lesions on the leaves, fruits and stems, which may lead to the death of the affected plant if left untreated. Around 1940, CL was demonstrated to be transmitted by Brevipalpus mites in Argentina. Because little information exists on the status of CL pathosystem in Argentina and Paraguay, a survey was made in several citrus growing areas of these countries from 2009 to 2011, to evaluate its presence and relevance as well as the identification of the virus and the mite vector. CL was found in most of the sweet orange and/or mandarin orchards in Paraguay (Departamentos de Boquerón, Concepción, San Pedro, Cordillera, Alto Paraná, Itapúa) and Argentina (Provincias de Misiones, Corrientes, Entre Ríos). Incidence was usually low. The causal virus was identified as Citrus leprosis virus C (CiLV-C) by RT-PCR, electron microscopy and immunofluorescence. In all the visited regions in Paraguay and the region of Montecarlo, Argentina, the mites collected in plants infected by CiLV-C were identified as B. phoenicis.

Resumo em Inglês:

Some endophytes can synthesize molecules that elicit the induction of plant resistance to infection by pathogens. The objective of this study was to demonstrate that protein fractions 42 and 75 from Bacillus amyloliquefaciens and Bacillus pumilus were capable of acting as elicitors of induced resistance in tomato plants against Xanthomonas vesicatoria, following partial resolution by gel-filtration chromatography. Tomato plants sprayed with protein fractions 42 and 75 reduced, respectively, 63.5 and 56.6% of bacterial spot, compared with control plants. Additionally, these fractions promoted the increase of peroxidase (POX) and polyphenol oxidase (PPO) enzyme activities in treated plants. In SDS-PAGE stained with silver nitrate, protein fractions 42 and 75 appeared as simple bands with estimated molecular mass of 28 and 43 kDa, respectively. We report the partial characterization of two macromolecules synthesized by endophytic bacteria that act as elicitors of systemic resistance in tomato against X. vesicatoria.

Resumo em Espanhol:

Se realizaron bioensayos con 105 genotipos de Solanum phureja (papa criolla) para evaluar la resistencia a la sarna polvosa causada por Spongospora subterranea f. sp. subterranea. Estos fueron propagados por esquejes de tallo lateral. La inoculación se realizó con una solución a una concentración de 1x10(6) quistosoros mL-1. Se determinó el grado de resistencia o susceptibilidad de cada genotipo al patógeno en tres momentos diferentes: 1) después de 15 días de la inoculación se evaluó en el microscopio la presencia de zoosporangios en raíces; 2) en estado de floración, se observó la presencia de agallas de raíces; y 3) en la cosecha se evaluaron los tubérculos, observando la presencia de pústulas. Las plantas asintomáticas, aquellas donde no se observaron estructuras del patógeno o síntomas de la enfermedad, fueron evaluadas mediante la técnica de PCR con primers específicos. Los resultados mostraron que a los 15 días no fue posible discriminar el grado de resistencia de los genotipos. Igualmente no hubo presencia de síntomas de la enfermedad en los tubérculos, sin embargo sí se observaron síntomas de agallas en raíces en la evaluación en estado de floración. El genotipo más susceptible fue Criolla Colombia y 30 genotipos presentaron una alta resistencia sin presentar síntomas de la enfermedad o signos del patógeno, dentro de los cuales se incluye la variedad Criolla Paisa.

Resumo em Inglês:

In order to evaluate the resistance to Spongospora subterranea f. sp. subterranea on 105 genotypes of Solanum phureja (local name in Colombia papa criolla), bioassays were conducted through propagation by lateral stem cuttings. Inoculation was performed with a 1 x 10(6) sporeballs mL-1 solution. The level of resistance or susceptibility of each genotype to the pathogen was determined at three different times: 1) At 15 days after inoculation (DAI), the presence of zoosporangia was evaluated in roots under optical microscopy; 2) At flowering, the presence of galls was observed in roots and 3) At harvest, the tubers were screened for the detection of pustules. Asymptomatic plants, (i.e. plants seemingly without pathogen´s structures or disease symptoms) were evaluated by PCR using specific primers. At 15 DAI it was not possible to determine the degree of resistance in the genotypes and later there were no disease symptoms on tubers. Nevertheless, disease was detectable through gall formation on roots at the flowering stage. The most susceptible genotype was Criolla Colombia. Thirty genotypes, including the commercial variety Criolla Paisa, were highly resistant and presented neither pathogen´s structures nor symptoms.

Resumo em Português:

Corynespora cassiicola, agente causal da mancha alvo, causa prejuízos econômicos em diversas culturas. Como a disponibilidade de protocolos padronizados para a produção de inóculo facilitam a condução de testes de patogenicidade, os objetivos deste trabalho foram analisar o crescimento micelial em diferentes temperaturas; avaliar o crescimento micelial e a esporulação de isolados obtidos de diferentes hospedeiros em diferentes regimes de luz; avaliar o efeito da duração de umidade contínua para a máxima germinação dos esporos in vitro e a patogenicidade de sete isolados de C. cassiicola em diversos hospedeiros. As temperaturas para o maior crescimento micelial variaram de 23,3 a 29,5ºC; o crescimento de oito isolados foi indiferente aos regimes de luz, enquanto os outros seis foram mais influenciados pelo escuro contínuo; a maioria dos isolados esporulou mais sob luz contínua; cinco a vinte horas de umidade contínua foi a variação de tempo para que 85% dos esporos germinassem; quanto à patogenicidade, foi observado que o algodoeiro, o meloeiro e o pepineiro foram os hospedeiros mais suscetíveis, e menos suscetíveis, o tomateiro, aceroleira e o cafeeiro. Para produção massal de inóculo de C. cassiicola recomenda-se utilizar a temperatura de 25ºC sob luz contínua.

Resumo em Inglês:

Corynespora cassiicola is the causal agent of target spot on several crops of economic importance. Since the availability of standardized protocols for inoculum production makes the conduction of patogenicity tests easier, the objectives of this work were to evaluate the mycelial growth under different temperatures, to evaluate the mycelial growth and spore production under different photoperiods for isolates obtained from different hosts, to evaluate the effect of continuous humidity on spore germination, and the pathogenicity of seven isolates of C. cassiicola on several hosts. Temperatures between 23,3 and 29,5ºC allowed the best growth of the isolates. The growth of eight isolates did not respond to the photoperiods used whereas six isolates were sensitive to the dark. The best sporulation for the majority of isolates was under continuous light. Five to twenty hours of continuous humidity were enough for 85% of the spores to germinate. As for pathogenicity, cotton, melon and cucumber were the most susceptible hosts, while tomato, coffee and Antilles cherry were the least susceptible. For massal production of C. cassiicola inoculum, a temperature of 25ºC under continual light is recommended.

Resumo em Inglês:

The objective of this study was to understand the infection process of Fusarium oxysporum f. sp. phaseoli (Fop) in bean cultivars classified as resistant (Manteigão Fosco 11), intermediate (VP8) and susceptible (Meia Noite). Plants of the three cultivars were inoculated at 10 days after emergence with a suspension of 1×10(6) conidia of Fop per mL. At 43 days after the inoculation, stem segments were observed with a scanner electronic microscope. The cultivars Manteigão Fosco 11 and VP8 presented an occluding material in the xylem vessels, which may have restricted tissue colonization by Fop. The resistance of bean cultivars to Fop seemed also to be explained by structural differences in the xylem tissue.

Resumo em Inglês:

There is a lack of information about the level of resistance of cotton genotypes to a wider range of Ramularia areola isolates occurring across the cotton growing areas of Brazil. For this purpose, firstly it is necessary to know the existence or not of genotypic and phenotypic variability among the R. areola isolates from different geographical origins. The objective of the present investigation was to verify the existence of phenotypic variability among 23 R. areola isolates collected from six cotton growing states of Brazil. Two resistant genotypes, FMT 02102996 and CNPA BA 2003-2059, and the susceptible genotype FMT 701 were individually inoculated with 23 R. areola isolates under glasshouse conditions and the severity of infection was evaluated 30 days after inoculation. Genotypes CNPA BA 2003-2059 and FMT 02102996 were susceptible to three isolates and resistant to the rest of the isolates. Genotype FMT 701 was susceptible to all the isolates except the isolates 22.3 and 42.7. Results indicate the existence of variability among R. areola isolates and that the three genotypes are useful in distinguishing phenotypic variability within isolates of this pathogen.

Resumo em Inglês:

Tomato chlorosis virus (ToCV, genus Crinivirus, family Closteroviridae) is a whitefly-transmitted crinivirus with a bipartite RNA genome. This virus is emerging as a serious threat to tomato crops worldwide. To date, only three complete genomic sequences of ToCV have been described from North America, Spain, and Greece isolates. In this study, we present the fourth complete nucleotide sequence of the RNA 1 (8594 nt) and RNA 2 (8242 nt) components of a Brazilian ToCV isolate (ToCV-BR). The complete genome sequences of RNA 1 and RNA 2 have been deposited in the GenBank database under the accession numbers JQ952600 and JQ952601, respectively. The sequences of RNA 1 and RNA 2 shares the highest nucleotide identity of 99.6% and 99.5%, respectively, with the Greek isolate sequences. Phylogenetic analysis confirmed that both RNA 1 and RNA 2 of the Brazilian isolate are most closely related to the Greek isolate of that virus. These results suggest that ToCV may have been recently introduced to Brazil from Europe.

Resumo em Inglês:

Soil fumigation with the synthetic essential oil of mustard (93% allyl isothiocyanate) (EOM) was evaluated as a substitute of bio-fumigation with cruciferous plant species, using Sclerotium rolfsii and Sclerotinia sclerotiorum as test pathogens, together with its non-target effect on the general population of soil microorganisms. The mortality of the sclerotia of both fungi was dependent upon the concentration of EOM and the exposure period. Exposure to the EOM vapors delayed in vitro germination of the sclerotia.Total germination of the control sclerotia of S. rolfsii, after 120 h incubation, was 94%, of which 88% germinated within 48 h. In contrast, to the total germination of 77% or 47%, less than 3% germinated in 48 h when exposed for 4 or 7 days to 50 µl EOM/L. Exposure to 100 µl/l for 4 or 7 days resulted in the mortality of 50 and 100% sclerotia, respectively. The tendency for delayed germination and mortality was similar for the sclerotia of S. sclerotiorum. No viable sclerotia of either fungus were detected to the depth of 10 cm in the air dried, moist or wet soil fumigated for 7 days with the EOM at the rate of 150 µl/L. In the field plots, no viable sclerotia of S. rolfsii were detected after 7-day exposure to the EOM applied to the upper soil layer at the rate of 9, 12, or 18 ml/m² and covered with a plastic sheet, while 73, 50 and 15%, respectively, were recovered from uncovered plots. In field plots, the fluorescein diacetate hydrolysis decreased by EOM treatment. However, the colony forming units of actinomycetes and bacteria increased, but those of fungi decreased significantly. Soil fumigation with EOM can be used with several advantages, as a substitute of bio-fumigation with cruciferous plant species.

Resumo em Inglês:

Leifsonia xyli subsp xyli (Lxx) is the etiological agent of ratoon-stunting disease (RSD), one of the most important diseases that affects productivity of sugarcane crops. The lack of defined external symptoms in most plants is a challenge for the diagnosis of RSD facilitating its spread in production fields. In this study a Taqman® real-time polymerase chain reaction (qPCR) assay was developed for detection of the bacteria in different tissues of the plants and compared to conventional PCR and nested-PCR assays. The bacterial DNA was amplified by the nested-PCR and qPCR assays, indicating that conventional PCR lacks sufficient sensitivity to be used as a diagnostic tool for RSD. On the other hand, qPCR is more advantageous than nested-PCR for processing large amounts of samples since it does not need post processing steps for visualization of results and the level of bacterial infection can be quantified. Therefore by improving the diagnosis of RSD in field plants, it can be applied to monitor losses caused by the disease, as a tool to monitor the efficacy of sanitation procedures and in the development of new sanitizers for Lxx.

Resumo em Espanhol:

El hongo Trichoconiella padwickii es uno de los principales patógenos de la semilla de arroz en la provincia de Corrientes, Argentina. Con el objetivo de cuantificar la eficiencia de transmisión (ET) desde la semilla a coleóptilos de arroz se realizó un ensayo "in vivo", utilizando semillas de las variedades BRS Taim, Puitá Inta-CL e Irga 424. Las semillas se sembraron en bandejas plásticas conteniendo arena estéril como sustrato e incubadas en laboratorio en condiciones de 25 ± 2ºC y fotoperiodo de 12 h. La ET se evaluó a los siete días, sobre 400 coleóptilos sembrados en medio agar poroto 3%. El patógeno presentó los siguientes valores de ET: 7% para la variedad BRS Taim; 28,5% en Puitá Inta-CL y 8,1% en la variedad Irga 424. Se demostró la importancia de la semilla como fuente de inóculo de T. padwickii.

Resumo em Inglês:

With the objective of quantifying the transmission efficiency (TE) from rice seed to coleoptiles, a trial was conducted "in vivo" using seeds of the varieties BRS Taim, Puitá Inta-CL and Irga 424. Seeds were sown in plastic trays containing sterile sand as substrate and incubated in laboratory conditions at 25±2ºC and photoperiod of 12 h. The TE was evaluated after seven days using 400 coleoptiles put on agarbean medium 3%. The TE was 7%, 28.5% and 8.1% for varieties BRS Taim, Puitá Inta-CL and Irga 424, respectively, demonstrating the importance of seeds as an inoculum source of T. padwickii.

Resumo em Português:

Viroses causadas por vírus do gênero Badnavirus são responsáveis por grandes prejuízos à cultura do inhame no Nordeste brasileiro. O conhecimento da variabilidade destes patógenos pode fornecer informações importantes sobre seu potencial evolutivo, permitindo a elaboração de melhores estratégias de manejo da doença. A análise de 425 amostras foliares de inhame coletadas em três estados do Nordeste brasileiro, em 2010, revelou uma alta incidência (93,3%) de badnaviroses. Para avaliar a variabilidade genética dos badnavírus infectando inhame, um fragmento de 579 nucleotídeos correspondente à região codificante da transcriptase reversa (RT)/RNaseH dos isolados amostrados foi amplificada por PCR e sequenciada. A análise filogenética das sequências de nucleotídeos revelou que os isolados dividem-se em dois grupos. Um é altamente relacionado com Dioscorea bacilliform AL virus (DBALV), enquanto o outro forma um clado altamente divergente dentro do gênero Badnavirus. Os isolados de DBALV apresentam 70-98% de identidade nucleotídica entre si e foram detectados em todas as áreas avaliadas e em D. alata e D. cayennensis, as duas espécies de inhame mais cultivadas no Nordeste. Os isolados do outro grupo compartilham 47-58% de identidade com isolados de DBALV e 78-95% entre si e foram encontrados apenas em D. alata na Paraíba.

Resumo em Inglês:

Diseases caused by viruses of the genus Badnavirus are responsible for great losses in yam crops in northeastern Brazil. Knowledge of pathogen variability can provide important information about its evolutionary potential and may allow for development of better strategies for disease management. The analysis of 425 leaf samples of yam obtained in 2010 in three states of northeastern Brazil revealed a high incidence (93.3%) of badnaviruses. To evaluate the variability of yam-infecting badnaviruses, a 579-nucleotide fragment corresponding to the reverse transcriptase (RT)/RNaseH coding region was PCR-amplified and directly sequenced. Phylogenetic analysis of nucleotide sequences revealed that the isolates can be divided into two groups. The first group is highly related to Dioscorea bacilliform AL virus (DBALV), while the other set of sequences formed a highly divergent clade within the genus Badnavirus. The DBALV isolates have 70-98% nucleotide sequence identity with each other. DBALV was detected in all areas assessed and in the two most cultivated species of yam in the northeast (D. alata and D. cayanensis). The other group shares 47-58% nucleotide sequence identity with the DBALV isolates and 78-95% amongst themselves, and was found only in D. alata in the state of Paraíba.