Showing papers in "Fitopatologia Brasileira in 2005"

Silicon and rice disease management

Abstract: The element silicon (Si) is not considered an essential nutrient for plant function. Nevertheless, Si is absorbed from soil in large amounts that are several fold higher than those of other essential macronutrients in certain plant species. Its beneficial effects have been reported in various situations, especially under biotic and abiotic stress conditions. The most significant effect of Si on plants, besides improving their fitness in nature and increasing agricultural productivity, is the restriction of parasitism. There has been a considerable amount of research showing the positive effect of Si in controlling diseases in important crops. Rice (Oryza sativa), in particular, is affected by the presence of Si, with diseases such as blast, brown spot and sheath blight becoming more severe on rice plants grown in Si-depleted soils. The hypothesis underlying the control of some diseases in both mono- and di-cots by Si has been confined to that of a mechanical barrier resulting from its polymerization in planta. However, some studies show that Si-mediated resistance against pathogens is associated with the accumulation of phenolics and phytoalexins as well as with the activation of some PR-genes. These findings strongly suggest that Si plays an active role in the resistance of some plants to diseases rather than forming a physical barrier that impedes penetration by fungal pathogens.

Sugarcane yellow leaf virus infection leads to alterations in photosynthetic efficiency and carbohydrate accumulation in sugarcane leaves

Abstract: Infection by Sugarcane yellow leaf virus (ScYLV) causes severe leaf symptoms in sugarcane (Saccharum spp.) hybrids, which indicate alterations in its photosynthetic apparatus. To gain an overview of the physiological status of infected plants, we evaluated chlorophyll a fluorescence and gas exchange assays, correlating the results with leaf metabolic surveys, i.e., photosynthetic pigments and carbohydrate contents. When compared to healthy plants, infected plants showed a reduction in potential quantum efficiency for photochemistry of photosystem (PSII) and alterations in the filling up of the plastoquinone (PQ) pool. They also showed reduction in the CO2 net exchange rates, probably as a consequence of impaired quantum yield. In addition, reductions were found in the contents of photosynthetic leaf pigments and in the ratio chlorophyll a/chlorophyll b (chla/chlb). Carbohydrate content in the leaves was increased as a secondary effect of the ScYLV infection. This article discusses the relation of virus replication and host defense responses with general alterations in the photosynthetic apparatus and in the metabolism of infected plants.

A risk infection simulation model for fusarium head blight of wheat

Abstract: Fusarium Head Blight (FHB) is a disease of great concern in wheat (Triticum aestivum). Due to its relatively narrow susceptible phase and environmental dependence, the pathosystem is suitable for modeling. In the present work, a mechanistic model for estimating an infection index of FHB was developed. The model is process-based driven by rates, rules and coefficients for estimating the dynamics of flowering, airborne inoculum density and infection frequency. The latter is a function of temperature during an infection event (IE), which is defined based on a combination of daily records of precipitation and mean relative humidity. The daily infection index is the product of the daily proportion of susceptible tissue available, infection frequency and spore cloud density. The model was evaluated with an independent dataset of epidemics recorded in experimental plots (five years and three planting dates) at Passo Fundo, Brazil. Four models that use different factors were tested, and results showed all were able to explain variation for disease incidence and severity. A model that uses a correction factor for extending host susceptibility and daily spore cloud density to account for post-flowering infections was the most accurate explaining 93% of the variation in disease severity and 69% of disease incidence according to regression analysis.

Identification of the major fungitoxic component of cinnamon bark oil

Abstract: The study was done to identify the most active fungitoxic component of cinnamon bark (Cinnamomum zeylanicum) oil that can be used as a marker for standardization of cinnamon extract or oil based natural preservative of stored seeds. Aspergillus flavus and A. ruber were used as test fungi. The hexane extracted crude oil and the hydro-distilled essential oil from cinnamon bark had complete growth inhibition concentration (CGIC) of 300 and 100 µl/l, respectively. Both oils produced three fractions on preparative thin layer silica-gel chromatography plates. The fraction-2 of either oil was the largest and most active, with CGIC of 200 µl/l, but the fungitoxicity was also retained in the other two fractions. The fraction-1 and 3 of the crude oil reduced growth of both the fungal species by 65%, and those of distilled oil by 45% at 200 µl/l. The CGIC of these fractions from both the sources was above 500 µl/l. The gas chromatography and mass spectrometry (GC-MS) of the fraction-2 of the hexane extract revealed that it contained 61% cinnamaldehyde, 29% cinnamic acid, and two minor unidentified compounds in the proportion of 4% and 6%. The GC-MS of the fraction-2 of the distilled oil revealed that it contained 99.1% cinnamaldehyde and 0.9% of an unidentified compound. The CGIC of synthetic cinnamaldehyde was 300 µl/l and that of cinnamic acid above 500 µl/l. The 1:1 mixture of cinnamaldehyde and cinnamic acid had CGIC of 500 µl/l. The data revealed that cinnamaldehyde was the major fungitoxic component of hexane extract and the distilled essential oil of cinnamon bark, while other components have additive or synergistic effects on total fungitoxicity. It is suggested that the natural seed preservative based on cinnamon oil can be standardized against cinnamaldehyde.

First report of Fusarium oxysporum f. sp. lycopersici race 3 on tomato in Brazil

Abstract: Fusarium wilt, caused by three races of Fusarium oxysporum f. sp. lycopersici, is one of the most important diseases of tomato (Lycopersicon esculentum). Races 1 and 2 are distributed worldwide whereas race 3 has a more limited geographic distribution with no report thus far in Brazil. Seven F. oxysporum isolates were obtained from wilted tomato plants of race 1 and 2-resistant hybrids 'Carmen' and 'Alambra' in Venda Nova do Imigrante (State of Espirito Santo), Brazil. Virulence assays were performed using a set of the race differential cultivars: 'Ponderosa' (susceptible to all races), 'IPA-5' (resistant to race 1), 'Floradade' (resistant to races 1 and 2) and 'BHRS-2,3' (resistant to race 3). All isolates were highly virulent to 'Ponderosa', 'IPA-5' and 'Floradade' and were able to infect only a few plants of 'BHRS-2,3'. An additional virulence test was conducted including the same set of cultivars plus Lycopersicon pennellii 'LA 716'. Identical results were obtained with L. pennellii displaying an extreme (immune-like) resistant response. These results indicated that all seven isolates could be classified as F. oxysporum f. sp. lycopersici race 3. This new Fusarium wilt might became an economically important disease since race 3-resistant cultivars adapted to Brazil are not yet available.

Escalas diagramáticas para avaliação da severidade do cancro cítrico

Abstract: Diagrammatic scales are important tools for disease severity assessment. Four diagrammatic scales for isolated small (SL), medium (ML), and large (LL) lesions and for symptoms associated with the leaf miner injuries (LM), were developed to standardize the severity assessments of citrus canker caused by Xanthomonas axonopodis pv. citri on leaves of citrus (Citrus sinensis). Each scale has eight levels of disease severity (percentage of diseased leaf area): 0.2 to 16% for SL; 0.6 to 25% for ML; 1.8 to 30% for LL and 0.5 to 30% for LM. Initially, six persons evaluated the severity of 447 digitalized images of symptomatic leaves using the four scales. Training was carried out and later on, disease severity was assessed in 115 new images. Linear regressions between actual and estimated disease severity were calculated by each person. All the scales were validated together considering the accuracy, precision and reproducibility of the evaluations. The scales were adequate to quantify the severity of citrus canker on leaves.

Potential of non-pathogenic Fusarium oxysporum isolates for control of Fusarium wilt of tomato

Abstract: This study was done to evaluate the efficiency of non-pathogeni c Fusarium oxysporum isolates (141/3, 233, 233/1, 245, 245/1, 251, 251/2, 251/5, and 257) in controlling vascular wilt caused by F. oxysporum f. sp. lycopersici, race 2 (isolates C-21A, TO11, and TO245) in tomato (Lycopersicon esculentum) cv. Viradoro seedlings. In order to determine the effect of non-pathogeni c F. oxysporum isolates in tomato plants, the root system of 30-day-old seedlings was immersed in conidial suspensions (10 6 ml -1 ) of each isolate and the seedlings were transplanted to a cultivation substrate. Thirty-five days after transplanting it was observed that the non-pathogenic F. oxysporum isolates were not pathogenic to the cv. Viradoro nor did they affect seedling development. The efficiency of the non-pathogenic F. oxysporum isolates in controlling Fusarium wilt was determined by immersing the tomato seedling roots in the conidial suspension (10 6 ml -1 ) of each isolate and then transplanting them into substrates previously infested with isolates of F. oxysporum f.sp. lycopersici, race 2 (10 5 conidia ml 1 of substrate). Evaluations were performed 35 days after transplanting, for severity in scale with 1=healthy plant to 6=dead plant or plant showing vessel browning and wilted leaves up to the leader shoot and seedling height. The non-pathogenic F. oxysporum isolates were efficient in reducing the severity of the disease and maintaining normal plant development. These results provide evidence of the antagonistic activity of non-pathogeni c F. oxysporum isolates in controlling vascular wilt caused by F. oxysporum f. sp. lycopersici race 2 in tomato. Additional keywords: biological control, Fusarium oxysporum f.sp. lycopersici race 2, nonpathogenic F. oxysporum.

Seleção de plantas resistentes e de fungicidas para o controle da podridão do colo do maracujazeiro causada por Nectria haematococca

Abstract: The collar rot of passion fruit (Passiflora edulis f flavicarpa), caused by Nectria haematococca and Phytophthora spp, is one of the main problems of the passion fruit producing areas in Brazil, and is responsible for yield decrease and constant migrations of the culture The control of the disease is basically preventive, and directed to avoiding the introduction of the pathogen in the area The objectives of this research were: 1) to evaluate methods of inoculation of N haematococca and the suscetibility of yellow passion fruit at different ages; 2) to evaluate "damping-off"; 3) to evaluate the behavior of different species of genera Passsiflora and different genotyps of P edulis f flavicarpa to the pathogen; and 4) to carry out tests of chemical control Inoculations in the collar zone of plants provided higher levels of disease compared to inoculations in the radicular system These results suggest that N haematococca penetrates through wounds Mortality was higher in younger plants and when N haematococca and Phytophthora nicotianae were together Among the 17 species of genus Passiflora tested for N haematococca, P nitida, P laurifolia, and P alata showed the lowest average number of lesions The most resistant genotypes of P edulis f flavicarpa to N haematococca were those from Morretes (PR), Sapucai (SP), and the Maguari variety Prochloraz, thiabendazole, thiram+thiabendazole, carbendazim, triflumizole, and captan controlled N haematococca The fungicides tested for curative treatment inhibited the development of the disease most effectvely when applied two days after inoculation when compared to seven days Prochloraz and carbendazim were outstanding for preventing the death of plants inoculated with N haematococca

Seleção assistida por marcadores moleculares visando ao desenvolvimento de plantas resistentes a doenças, com ênfase em feijoeiro e soja

Abstract: Marker assisted selection in the development of disease resistant plants, with emphasis on common bean and soybean Transfer of disease resistance alleles in plants can be expedited by the use of DNA molecular markers. If themarkers are tightlylinked to the resistance alleles they can be used for marker assisted selection (M.A.S.). One effective useof M.A.S. isfound in the process of pyramiding resistance alleles. By using M.A.S., in three backcross generations, the BeanBreeding Program of BIOAGRO, Federal University of Vicosa (Minas Gerais, Brazil), has obtained bean ( Phaseolus vulgaris )lines phenotypically similar to cultivar Ruda (recurrent) and resistant to anthracnose, rust and angular leaf spot. Seeds of BC 3 F 4 lines currently are being multiplied to undergo inoculation with specific pathogens and agronomic performance tests. The SoybeanQuality Breeding program of BIOAGRO used molecular markers to identify quantitative trait loci (QTLs) associated withresistance to soybean cyst nematode (SCN). Two microsattelite markers (Satt038 and Satt163) flanking the allele

Detection and partial characterization of a carlavirus causing stem necrosis of soybean in Brazil

Abstract: Stunting and stem necrosis were noticed in soybeans (Glycine max) grown in 2000/2001 in West Central Brazil the same condition was also observed in the following year in plantations as far as 2,000 km from the initial area. Based on transmission (mechanical, graft, insect vector), purification and serology, electron microscopy and molecular studies the causal agent was determined to be a whitefly-borne carlavirus which is possibly related to Cowpea mild mottle virus (CpMMV).

Intensidade da cercosporiose em mudas de cafeeiro em função de fontes e doses de silício

Abstract: O objetivo deste estudo foi avaliar o efeito dos silicatos de calcio e de sodio sobre a intensidade da cercosporiose (Cercospora coffeicola) em mudas de cafeeiro (Coffea arabica), cultivar Catuai IAC 99, nas doses 0; 0,32; 0,64; 1,26 g de SiO2.kg-1 de substrato. Foram realizadas cinco avaliacoes quinzenais nas quais se quantificou o numero de plantas doentes, o numero de folhas lesionadas por planta, o numero de lesoes por folha e o numero total de lesoes por planta. Essas avaliacoes foram utilizadas para construir a area abaixo da curva de progresso da doenca. Ao termino das avaliacoes, foram determinados os teores de macro, micronutrientes, silicio e lignina na parte aerea das mudas de cafeeiro. A menor area abaixo da curva de progresso do total de lesoes foi obtida com a dose de 0,84 g.kg-1 de silicato de sodio. Observou-se decrescimo linear para area abaixo da curva de progresso do numero de plantas doentes e aumento na concentracao de lignina nas folhas ate a dose de 0,52 g.kg-1 de silicato de sodio, enquanto no caule houve acumulo de SiO2 ate 0,53 g.kg.-1.

Transgenic passionfruit expressing RNA derived from Cowpea aphid-borne mosaic virus is resistant to passionfruit woodiness disease

Abstract: Sixteen transgenic yellow passionfruit (Passiflora spp.) plants (R0) were obtained which express a non-translatable transgenic RNA corresponding to the 3' region of the NIb gene and the 5' region of the CP gene, derived from the genome of a Brazilian isolate of Cowpea aphid-borne mosaic virus (CABMV). The transgenic plants were propagated by stem cuttings and challenged by sap inoculation with isolates CABMV-MG1 and CABMV-PE1. One transgenic plant (TE5-10) was resistant to the isolate CABMV-MG1, but susceptible to CABMV-PE1. The remaining transgenic plants developed systemic symptoms, equal to non-transformed plants, when inoculated with either isolate. The absence of virus in TE5-10 plants was confirmed by indirect ELISA. Transcription analysis of the transgene demonstrated that the TE5-10 plant did not accumulate transgenic mRNA, even before inoculation. After inoculation, viral RNA was only detected in plants inoculated with CABMV-PE1. These results confirm that the transgenic plant TE5-10 is resistant to isolate CABMV-MG1, and suggest that the resistance mechanism is post-transcriptional gene silencing, which is already activated in the transgenic plants before virus inoculation.

Variability of the wheat powdery mildew pathogen Blumeria graminis f. sp. tritici in the 2003 crop season

Abstract: Wheat (Triticum aestivum) powdery mildew, caused by the biotrophic fungus Blumeria graminis f. sp. tritici, is one of the most severe foliar diseases attacking this crop, reducing grain yields by 10% to 62% in Brazil. The disease can be controlled by genetic resistance of the host, but the pathogen has physiological specialization, which enables it to infect wheat cultivars that have remained resistant for years. The objective of this work was to evaluate the variability of pathogenic strains of B. graminis f. sp. tritici collected in Brazil and the effectiveness of wheat resistance genes to powdery mildew in the 2003 crop season. Plants of a differential series were inoculated with each monopustular isolate. Thirty-one combinations of effective and ineffective resistance genes were identified. Only the gene Pm4a+... remained totally effective to all isolates, and gene Pm6 was highly effective (below 10% of susceptibility), whereas genes Pm3a and Pm8 were totally ineffective (susceptible to all isolates). Genes Pm3c, D1, and D2 showed low effectiveness (above 50% of susceptibility), and genes Pm1, 2, 4a, 1+?, and 2+Mld had mean effective results to most strains (susceptibility between 10% and 49%). The virulence formula Pm1, 3c, 4a, 6, 1+?, 2+Mld, 4a+..., D2 (effective genes) / 2, 3a, 8, D1 (ineffective genes) was most frequently found, accounting for 15% of the occurrences. The most frequent number of ineffective genes was seven, ranging from three to ten.

Reação do trigo à Magnaporthe grisea nos diferentes estádios de desenvolvimento

Abstract: The blast of wheat (Triticum aestivum) was first reported in the State of Parana in 1986 and has now spread to all the major wheat growing areas of Brazil. The relation between leaf and neck blast resistance was studied utilizing three isolates and 15 wheat varieties. The relationship between incidence of blast in wheat spikes and infection of harvested seeds was examined using inoculation tests with three fungal isolates on five wheat cultivars. The varieties showing susceptible reaction at seedling stage were also susceptible to spike infection. The BH1146 was the sole variety resistant at seedling stage, which subsequently produced a significantly lower the incidence and severity of blast. A high positive correlation was observed between incidence and severity of diseased heads. The percentage of infected seeds was less in varieties exhibiting a resistant reaction to spike infection than in susceptible varieties.

Pathogenicity, molecular characterization, and cercosporin content of Brazilian isolates of Cercospora kikuchii

Abstract: Cercospora kikuchii, involved with the defoliation of soybean (Glycine max) plants, is normally associated with Septoria glycines in late season. Seventy-two isolates from different regions in Brazil, obtained mainly from purple stained seeds, showed phenotypic variation. Cercosporin content and rate of colony growth was higly variable among isolates. A strong correlation between cercosporin content and virulence was identified. Genetic variation among and within populations was evaluated based on 86 RAPD loci. The RAPD analysis clustered all isolates into seven groups. No relationship was observed between RAPD groups and geographic origin or cercosporin content. The sequence of the internal spacer regions (ITS1-5.8S-ITS2) from 13 isolates chosen according to the previous RAPD and clustering analysis showed high similarity (97%-100%) to the GenBank sequences of C. kikuchii (AY266160, AY266161, AY152577 and AF291708). It is clear from this work that Brazilian isolates of C. kikuchii from different geographic regions, are variable in relation to virulence, RAPD profiles and cercosporin content. Cercosporin content could be a good parameter for choosing an adequate isolate for screening resistant or tolerant cultivars. Considering that this pathogen is easily seed-borne, findings are expected to show the same haplotypes in different regions. Migration could be favoured by infected seeds as demonstrated by RAPD analysis.

Fungos antagonistas a Sclerotinia sclerotiorum em pepineiro cultivado em estufa

Abstract: White mold caused by Sclerotinia sclerotiorum may severely damage vegetables grown in greenhouses. To develop a biological control program for this pathogen proper antagonists are needed. This work aimed to select efficient fungi antagonists for controlling S. sclerotiorum on cucumber (Cucumis sativus) grown in greenhouses, and to evaluate the effect of the antagonist on the growth of the vegetable. An isolate of S. sclerotiorum obtained from cucumber and 112 fungi isolates belonging to four genera were used: Trichoderma, Fusarium, Penicillium, and Aspergillus. For the in vitro experiment, the cellophane method was used and eight Trichoderma virens isolates were selected that had inhibited the pathogen growth by 94 to 100%. Greenhouse experiments used sterilized and non-sterilized substrate in plastic cups and non-sterilized substrate in plastic bags. The substrate was inoculated with S. sclerotiorum and the eight isolates of T. virens were used as antagonists. All eight isolates controlled damping-off of plants caused by S. sclerotiorum, but the effect on cucumber growth varied according to the isolate and the substrate treatment.

Efeito de Saccharomyces cerevisiae na Produtividade de Sorgo e na Severidade de Doenças Foliares no Campo

Abstract: Saccharomyces cerevisiae e uma levedura com potencial para o controle de doencas de plantas, pois apresenta a capacidade de sintetizar compostos antibioticos, habilidade de competicao por espaco e nutrientes no filoplano de muitas especies vegetais, alem de possuir elicitores na parede celular. O presente trabalho teve como objetivos avaliar a produtividade de duas cultivares de sorgo (Sorghum bicolor) tratadas com a levedura, e verificar o controle da antracnose, causada por Colletotrichum sublineolum e da mancha foliar, provocada por Exserohilum turcicum. Os experimentos foram conduzidos em campo, em um delineamento de blocos ao acaso, com sete tratamentos e quatro repeticoes. Aplicacoes semanais de S. cerevisiae (Fermento Biologico Fleischmann - 25 mg/ml) reduziram significativamente a antracnose em sorgo cv. Tx-398B e melhoraram a produtividade da mesma. Na cv. 910753, uma unica aplicacao com a levedura foi suficiente para reduzir o progresso da mancha foliar, porem a produtividade nao foi elevada por qualquer um dos tratamentos. Conclui-se que S. cerevisiae apresenta um bom desempenho no campo para o controle de doencas foliares em sorgo, melhorando ou nao comprometendo a produtividade da cultura, na dependencia da cultivar utilizada.

Factors affecting density of airborne Gibberella zeae inoculum

Abstract: Fusarium head blight (FHB) is a disease of increasing concern in the production of wheat (Triticum aestivum). This work studied some of the factors affecting the density of airborne Gibberella zeae inoculum. Spore samplers were placed at the edge of a field in order to observe spore deposition over a period of 45 days and nights in September and October, the period that coincides with wheat flowering. Gibberella zeae colonies were counted for each period and values transformed to relative density. A stepwise regression procedure was used to identify weather variables helpful in predicting spore cloud density. In general, a predominant night-time spore deposition was observed. Precipitation and daily mean relative humidity over 90% were the factors most hightly associated with peak events of spores in the air. Models for predicting spore cloud density simulated reasonably well with the fluctuation of airborne propagules during both night and day, with potential to be integrated into an FHB risk model framework.

A Semi-Selective agar medium to detect the presence of Xanthomonas axonopodis pv. malvacearum in naturally infected cotton seed

Abstract: A semi-selective agar medium was developed for detection of Xanthomonas axonopodis pv. malvacearum (Xam) in cotton (Gossypium hirsutum) seed. The basic medium was peptone-sucrose-agar (PSA). Criteria for the semi-selective medium were the typical colony characters of Xam and its pathogenicity on cotton. Several systemic fungicides and antibiotics in different concentrations were tested alone or in combination with others. The final composition of the semi-selective agar medium was established after several attempts in order to inhibit most of the fungal and bacterial saprophytes and favour the development of Xam. It contained PSA + cyclohexamide, cephalexin, pencycuron, triadimenol and tolylfluanid. The bacteria were recovered from naturally infected seeds by the direct plating of 2,000 surface disinfected seeds on the semi-selective medium. The recovery of the pathogen from naturally infected leaf tissues and in dilution plating, on semi-selective medium and on nutrient agar, were comparable. Among the three detection methods tested, the semi-selective medium was found to be the most reliable and quantifiable. Degree of severity of angular leaf spot in the field was not always correlated with the level of infection in the seed. This is the first report of a semi-selective agar medium to detect the presence of Xam in naturally infected cotton seed.

Development of virus resistant transgenic papayas expressing the coat protein gene from a Brazilian isolate of Papaya ringspot virus

Abstract: Translatable and nontranslatable versions of the coat protein (cp) gene of a Papaya ringspot virus (PRSV) isolate collected in the state of Bahia, Brazil, were engineered for expression in Sunrise and Sunset Solo varieties of papaya (Carica papaya). The biolistic system was used to transform secondary somatic embryo cultures derived from immature zygotic embryos. Fifty-four transgenic lines, 26 translatable and 28 nontranslatable gene versions, were regenerated, with a transformation efficiency of 2.7%. Inoculation of cloned R0 plants with PRSV BR, PRSV HA or PRSV TH, Brazilian, Hawaiian and Thai isolates, respectively, revealed lines with mono-, double-, and triple-resistance. After molecular analysis and a preliminary agronomic evaluation, 13 R1 and R2 populations were incorporated into the papaya-breeding program at Embrapa Cassava and Tropical Fruits, in Cruz das Almas, Bahia, Brazil.

Effect of extracts from citric biomass, rusted coffee leaves and coffee berry husks on Phoma costarricencis of coffee plants

Abstract: Phoma leaf spot, caused by Phoma costarricensis poses a serious threat to coffee (Coffea arabica) production, especially in the highlands of the state of Minas Gerais, Brazil. Extracts of citric biomass, coffee berry husks and coffee leaves severely affected by rust caused by Hemileia vastatrix, were evaluated against P. costarricensis. In an in vitro assay, aqueous extracts of rusted leaves and berry husks plus the commercial extracts based on citric biomass named Ecolife® and Agromil® were tested at various dilutions on the mycelial growth inhibition of P. costarricensis. In vivo, coffee seedlings maintained in glasshouse, were sprayed with these extracts seven days before inoculation of P. costarricensis. Only extracts from citric biomass had inhibitory effects on the fungus. In vivo, Ecolife® (5 ml/l), Agromil® (5 g/l) and the aqueous extract of rusted coffee leaves (dilution 1:6) reduced Phoma leaf spot. Both, Ecolife® and the extract of rusted coffee leaves were significantly more effective in reducing the area under the lesion progress curve when applied at lower doses, indicating a possible effect on the induction of resistance.

Transformation of Xanthomonas axonopodis pv. citri by electroporation

Abstract: This studydescribe s the use of electroporation for transforming Xanthomonas axonopodis pv. citri ( Xac ), the causalagent of citrus( Citrus spp.) canker. It also evaluates the methodologyused for this species under different electrical parameters.The bacterium used in the study ( Xac 306) was the same strain used for recent complete sequencing of the organism. The use ofa plasmid (pUFR047, gentamycin r ) is reported here to beable to replicate in cells of Xac . Following the preparation andresuspension of competent cells of Xac at a density of ~4 x 10 10 cfu/ml, in 10% glycerol, and the addition of the replicativeplasmid, an electrical pulse was applied to each treatment. Selection of transformants showed a high efficiency of transformation(1.1 x 10 6 transformants/µg DNA), which indicates an effective, and inverse, combination between electrical resistance (50Ω) and capacitance (50 µF) for this species, with an electrical field strength of 12.5 kV.cm -1 and 2.7-ms pulse duration. Besides thedescription of a method for electroporation of

Biological and molecular characterization of an isolate of Tobacco streak virus obtained from soybeans in Brazil

Abstract: A virus was isolated from soybean ( Glycine max ) plants with symptoms of dwarfing and bud blight in WenceslauBraz County, Parana, Brazil. The host range and properties resembled those of Tobacco streak virus (TSV). The purifiedvirus showed three peaks in a frozen sucrose gradient. Antiserum was produced and the virus was serologically related toTSV. Electron microscopy detected 28 nm spherical particles. Coat protein (CP) had a Mr of 29.880 Da. A fragment of 1028nt was amplified, cloned and sequenced. One open reading frame with 717 nt was identified and associated to the CP. TheCP gene shared 83% identity with the sequence of TSV CP from white clover ( Trifolium repens ) (GenBank CAA25133).This is the first report of the biological and molecular characterization of TSV isolated from soybeans. It is proposed thatthis isolate be considered a strain of TSV named TSV-BR. Additional keywords : nucleotide sequence, Elisa, host range. RESUMOCaracterizacao biologica e molecular de um isolado de

Reprodução de Meloidogyne exigua em cultivares de cafeeiros resistentes e suscetíveis

Abstract: The resistance of the Iapar-59 coffee (Coffea arabica) cultivar to Meloidogyne exigua was compared with cv. IAC-Apoata, used as a resistance standard, and with susceptible cultivars Mundo Novo (IAC 379-19), Catuai (IAC 62) and Tupi (IAC 1669-33). One-year old plants were inoculated with 10,000 of M. exigua eggs and 93 days after inoculation, the reproduction of M. exigua was evaluated by determining the number of galls (NG), the number of eggs (NO), the reproduction factor (RF), reduction in the reproduction factor (RFR) and behaviour of the coffee plant. A lower degree of M. exigua reproduction was equally observed in 'Iapar-59' and 'Apoata', in which NG, NO and the FR were lower then those observed in 'Mundo Novo', 'Catuai' and 'Tupi'. Greater reduction in the reproduction factor (RFR) of M. exigua observed in 'Apoata' and 'Iapar-59' indicaties a resistance reaction of 'Iapar-59'.

Molecular characterization of Brazilian strains of Xanthomonas campestris pv. viticola by rep-PCR fingerprinting

Abstract: Bacterial canker of grapevine (Vitis vinifera), caused by Xanthomonas campestris pv. viticola was first detected in Brazil in 1998, affecting grapevines in the Sao Francisco river basin, state of Pernambuco. The disease was also reported in Juazeiro, Bahia and later in Piaui and Ceara. Due to its limited geographical distribution and relatively recent detection in Brazil, very little is known about the pathogen's biology and diversity. Repetitive DNA based-PCR (rep-PCR) profiles were generated from purified bacterial DNA of 40 field strains of X. campestris pv. viticola, collected between 1998 and 2001 in the states of Pernambuco, Bahia and Piaui. Combined analysis of the PCR patterns obtained with primers REP, ERIC and BOX, showed a high degree of similarity among Brazilian strains and the Indian type strain NCPPB 2475. Similar genomic patterns with several diagnostic bands, present in all strains, could be detected. Fingerprints were distinct from those of strains representing other pathovars and from a yellow non-pathogenic isolate from grape leaves. The polymorphism observed among the Brazilian strains allowed their separation into five subgroups, although with no correlation with cultivar of origin, geographic location or year collected.

First report of black rot of Colocasia esculenta caused by Ceratocystis fimbriata in Brazil

Abstract: Ceratocystis fimbriata was found sporulating in gray to black discolored areas on edible corms of Colocasia esculenta found in supermarkets in the states of Sao Paulo, Rio de Janeiro, Bahia, Rondonia and the Distrito Federal. In most cases thecorms were grown in the state of Sao Paulo. The black rot appeared to occur post-harvest. Sequences of rDNA indicated thatthe Colocasia sp. isolates belong to the Latin American clade of the C. fimbriata complex, but the isolates were more aggressivethan isolates from Ficus carica and Mangifera indica , in pseudopetioles of C. esculenta. Additional keywords: Aracerae , inhame, taro. RESUMOPrimeiro relato de Ceratocystis fimbriata causando podridao negra em inhame no Brasil Ceratocystis fimbriata foi encontrado em tuberculos de inhame ( Colocasia esculenta ), apresentando lesoes escuras, poucoprofundas, contendo estruturas de reproducao do fungo, cuja coloracao variava do cinza ao negro. As amostras foram coletadas emsupermercados, quitandas e varejoes nos Estados de Sao Paulo, Rio de Janeiro, Bahia, Rondonia e Distrito Federal que, na maiori a doscasos, comercializavam inhame produzido no Estado de Sao Paulo. Os sintomas de podridao negra indicam se tratar de uma doenca d epos-colheita. Sequencias de rDNA indicam que os isolados de

Evidências de indução de resistência sistêmica à ferrugem do eucalipto mediada por rizobactérias promotoras do crescimento de plantas

Abstract: A inducao de resistencia sistemica mediada por rizobacterias promotoras do crescimento de plantas foi avaliada para a ferrugem do eucalipto (Eucalyptus spp.) causada por Puccinia psidii. Para isso, mudas com cerca de 80 dias de idade, previamente enraizadas em substrato tratado com diferentes isolados de rizobacterias foram inoculadas com uma suspensao de inoculo de P. psidii ajustada para 2 x 104 urediniosporos/ml. As plantas inoculadas foram mantidas em câmara de nevoeiro com nebulizacao intermitente a 25 oC, no escuro por 24 h, e posteriormente transferidas para câmara de crescimento a 22 oC, com fotoperiodo de 12 h e intensidade luminosa de 40 mmoles.s-1.m-2. Utilizou-se um delineamento inteiramente casualizado com quatro repeticoes, cada uma delas com quatro plantas. Apos 13 dias da inoculacao, avaliaram-se numero medio de pustulas/folha, numero de uredinias/amostra e numero medio de esporos produzidos/uredinia. Os isolados FL2 e MF4 foram eficientes na reducao da severidade da ferrugem. Alem disso, o tratamento das mudas com rizobacterias, apenas uma semana antes da inoculacao, com P. psidii foi menos eficiente em reduzir a severidade da doenca do que o tratamento em que foram utilizadas mudas produzidas em substrato previamente rizobacterizadas, ou seja, com 80 dias. Estes resultados indicam que estes isolados de rizobacterias podem induzir maior resistencia a doencas foliares diminuindo a necessidade de aplicacao de fungicidas e otimizando a producao de mudas clonais de eucalipto.

Intensidade do mofo-branco do feijoeiro em plantio convencional e direto sob diferentes lâminas d'água

Abstract: A gradient of water depths, obtained with the line source irrigation system, and two bean (Phaseolus vulgaris) cultivars, under the conventional and the no-tillage cropping systems, demonstrated increases in white mold intensity caused by Sclerotinia sclerotiorum and sclerotium production with larger water depths. With an initial inoculum concentration of 0.2 sclerotia/kg of soil, the percentage of infected plants varied from 0 to 100% (1998) and from 0 to 12% (1999). A higher and more severe incidence of white mold was verified in plots planted with the cultivar of more prostrate habit, in the conventional cropping system. In both years, disease intensity, production of sclerotia and development of apothecia were lower in the no-tillage cropping system. Finally, in both experiments, about four times more sclerotia was present in the residue of grain collected from conventional tillage plots, than in the no-tillage plots, showing that the production of inoculum for the next crop is much larger in the former than in the latter. This is especially relevant, considering the importance of initial inoculum for monocyclic diseases, such as in the case of white mold, with direct implications for the sustainability of winter bean production in the dry season in Brazil.

Escala Diagramática para Avaliação da Severidade da Mancha Foliar do Eucalipto Causada por Quambalaria eucalypti

Abstract: Diagrammatic scale for assessment of eucalyptus leaf spot severity caused by Quambalaria eucalypti The leaf spot, caused by Quambalaria eucalypti, is presently one of the most serious diseases in eucalyptus (Eucalyptus spp.) nurseries in Brazil. Since the disease was only reported recently in Brazil, little is known about its epidemiology and control. As standardized and precise methods are needed for the disease severity evaluations, a diagrammatic scale containing eight levels (0,4; 1; 2; 4; 8; 16; 32 and 49%) of severity was developed in this study for the disease quantification. For the scale validation four inexperienced and four expert appraisers scored leaves with different levels of severity, initially without the use of the scale and later on with its use. The estimates were compared for accuracy and precision. Using of the scale the appraisers were able to get better levels of precision and accuracy. After training, the levels of precision and accuracy were also increased, mainly for the inexperienced appraisers. The greatest errors in the disease evaluations were observed between levels 15 and 30% of severity. Additional keywords: patometry, diagrammatic scale, severity, eucalypt, Quambalaria eucalypti.

Avaliação da tolerância de cultivares de soja à ferrugem asiática no oeste da Bahia

Abstract: Tolerance assessment of soybean cultivars to Asian rust caused by Phakopsora pachyrhizi in western Bahia The use of tolerance as a form of control for soybean rust can be a viable alternative, since qualitative resistance has been shown to be unstable in function of fungal variability. This trial was carried out at in western Bahia in 2003/04, with the objective of assessing the tolerance of the main soybean (Glycine max) cultivars used in the area. Four early maturity cultivars [MG/BR 46 (Conquista), Emgopa 315, BRS Corisco and M-SOY 8411] and four cultivars of late maturity (BRS Barreiras, M-SOY 9350, FT 106 and BRS Sambaiba) were assessed. Tolerance was quantified by determining the difference of yield in subplots treated and untreated with fungicide. The cultivars MG/BR 46 (Conquista) and M-SOY 8411 did not present significant yield differences; however, this could not be attributed to tolerance in function of the low severity observed in this trial. This difference could be attributed to escape, since when the rust obtained higher values of severity, the two cultivars were already in the final stages of development. Although the maximum severity observed in this trial has been low (30.5% for BRS Barreiras), except MG/BR 46 (Conquista) and MSOY 8411, the others cultivars assessed presented significant differences among the subplots treated and untreated with fungicide. This shows an absence of tolerance in the main cultivars commercially planted in western Bahia. It was observed that early maturity cultivars had inferior yield reductions than late maturity cultivars. Additional keywords: resistance, control, Glycine max.