Antonia dos Reis Figueira

Comparison of techniques for detection of barley yellow dwarf virus-PAV-IL

Detection of barley yellow dwarf virus (BYDV)-PAV-IL by an improved nucleic acid hybridization technique, using a nonradioactive probe with chromogenic and chemiluminescent substrates, was compared with detection by polymerase chain reaction (PCR), double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) with polyclonal antibodies, and triple antibody sandwich ELISA with polyclonal and monoclonal antibodies. Each method was used to detect purified virus and virus in sap extracts from infected oat leaves. The detection limits for both ELISA procedures were 1 ng of purified BYDV-PAV-IL and the equivalent of 78 ng of infected tissue. Nucleic acid hybridization with either chemiluminescent or chromogenic substrates also detected as little as 1 ng of purified BYDV-PAV-IL, but it was slightly more sensitive at detecting virus in tissue extracts (25 ng of infected tissue). The most sensitive detection technique was PCR amplification, which could detect as little as 0.1 pg of RNA extracted from purified virus and detected viral RNA in the equivalent of 0.5 pg of infected leaf tissue.

Characterization of Coffee ringspot virus-Lavras: a model for an emerging threat to coffee production and quality.

The emergence of viruses in Coffee (Coffea arabica and Coffea canephora), the most widely traded agricultural commodity in the world, is of critical concern. The RNA1 (6552nt) of Coffee ringspot virus is organized into five open reading frames (ORFs) capable of encoding the viral nucleocapsid (ORF1p), phosphoprotein (ORF2p), putative cell-to-cell movement protein (ORF3p), matrix protein (ORF4p) and glycoprotein (ORF5p). Each ORF is separated by a conserved intergenic junction. RNA2 (5945nt), which completes the bipartite genome, encodes a single protein (ORF6p) with homology to RNA-dependent RNA polymerases. Phylogenetic analysis of L protein sequences firmly establishes CoRSV as a member of the recently proposed Dichorhavirus genus. Predictive algorithms, in planta protein expression, and a yeast-based nuclear import assay were used to determine the nucleophillic character of five CoRSV proteins. Finally, the temperature-dependent ability of CoRSV to establish systemic infections in an initially local lesion host was quantified.

Herança da Resistência ao Watermelon mosaic virus em Melancia (Citrullus lanatus L.)

The genetic control of resistance of the non-commercial watermelon accession PI 595201 to the Watermelon mosaic virus (WMV) was studied. Parental lines Crimson Sweet (P1 - susceptible parent) and PI 595201 (P2 - resistant parent), generations F1, F2 and backcrosses to both parents were tested. Symptom severity after mechanical inoculation with WMV was rated on a scale from 1 (no symptoms) to 5 (intense mosaic and foliar distortion). Crimson Sweet had a mean value of 4.0, whereas PI 595201 had a mean value of 1.0, demonstrating the contrasting reaction of these lines for WMV resistance. The heritability estimates were > 0.8, indicating that genetic gains from selection are feasible. The additive-dominance model was suggested to explain resistance inheritance. The hypothesis of monogenic control of WMV resistance in watermelon was rejected with an indication that the resistance of PI 595201 is under oligo or polygenic control, possibly by complete dominance in the direction of higher levels of resistance. The estimated number of genes that control WMV resistance was 4.16.

Caracterização de genótipos de tomateiro resistentes a begomovírus por marcador molecular co-dominante ligado ao gene Ty-1

The objectives of this study were to evaluate tomato genotypes for begomovirus resistance and to assess SSR-47 fingerprinting patterns associated with alleles Ty-1, in hybrids of fresh-market tomato with commercial potential. Twenty-four experimental genotypes, heterozygous at Ty-1 locus, were infected with begomovirus via grafting, and showed intermediate symptoms compared to the ones identified by homozygous Ty-1/Ty-1 lines and by susceptible genotypes Ty-1+/Ty-1+, which indicates the incomplete dominance of the Ty-1 allele. These hybrids were considered to possess partial resistance to begomovirus. The experimental hybrids TEX-246, TEX-261, TEX-253, TEX-256, TEX-262, TEX-252, TEX-251 and TEX-268 combined high total yields with high mean fruit mass. The hybrids TEX-246, TEX-253, TEX-256, TEX-262 and TEX-252 showed also longer half-life for fruit firmness and were thus considered competitive with current commercial hybrids used as checks. The molecular marker SSR-47 was effective for fingerprinting of tomato genotypes bearing the resistance allele Ty-1. The graft-induced infection of begomovirus showed symptoms in the genotypes tested that are in agreement with the results of fingerprinting with the marker SSR-47.

Identificação de xanthomonas axonopodis pv. phaseoli e x. axonopodis pv. phaseoli var. fuscans através da técnica de pcr

Este trabalho teve por objetivo verificar a viabilidade de utilizacao da tecnica de PCR, usando primers considerados especificos, para identificacao de Xanthomonas axonopodis pv. phaseoli (Xap) e x. axonopodis pv. phaseoli var. fuscans (Xapf), visando criar bases para sua utilizacao em diagnose rotineira e em programas de certificacao de sementes. Foram incluidos no estudo 42 isolados da bacteria provenientes de locais distintos, alem de outros generos, especies e patovares, para ser verificada a especificidade dos primers. Os resultados obtidos permitem concluir que os primers utilizados sao adequados para identificacao de Xap e Xapf, embora dois isolados patogenicos nao tenham sido amplificados. Foi observada tambem a amplificacao de uma banda fraca para X. axonopodis pv. vitians, com o mesmo numero de pares de bases, o que sugere existir homologia entre estes patovares, na regiao amplificada.

Complete genome sequence of the first Andean strain of potato virus S from Brazil and evidence of recombination between PVS strains

An isolate of the Andean strain of potato virus S (PVS), named BB-AND, was detected for the first time in a Brazilian potato crop, fully sequenced and analyzed. A comparison of BB-AND with other PVS isolates (Andean and Ordinary) showed that BB-AND is quite distinct. The lowest amino acid sequence identity to the only other fully sequenced Andean isolate was found in ORF 1 (82%) and ORF 6 (87%). Recombination analysis showed that the isolate Vltava (AJ863510), from Germany, is a recombinant between PVSO and PVSA isolates, with the recombination event located between nucleotides 6125 and 8324.

Vírus da mancha anular do cafeeiro (Coffee ringspot virus - CoRSV): influência na qualidade da bebida e na produção de grãos de café

Coffee ringspot virus (CoRSV), transmitted by the tenuipalpid mite Brevipalpus phoenicis, has been found in high incidences in several regions of the state of Minas Gerais. It induces chlorotic spots on the leaves and fruits and may induce severe fall of the leaves with implication in the yield. An evaluation was made on the effects of CoRSV-infected coffee berries on the beverage quality as well as on the weight of the beans. Infected beans had less reducing sugars and presented an increase in the electrical conductivity. The quality of the beverage prepared from infected fruits was lower than that of healthy fruits. There was a reduction of about 5% in the weight of beans from infected fruits.

Análise temporal e controle da mancha-anular e do ácaro vetor do Coffee ringspot virus

The objective of this work was to evaluate the population fluctuation of the mite Brevipalpus phoenicis, vector of the Coffee ringspot virus (CoRSV) - the causal agent of the coffee ringspot disease -, as well as its distribution in coffee plants, and the effect of acaricides in its control in coffee crops. The experiment was carried out at the municipality of Coromandel, in the region of Alto do Paranaiba, MG, Brazil, during two years. In the second year, the progress of the disease was evaluated, and the relationship between the mite population and disease incidence was determined. Ringspot disease and mites were detected throughout the year, with larger populations and disease incidence in the months with lower rainfall and mild temperatures. Pearson analyses showed negative correlation between the climatic parameters and the mite population. In the analysis of the disease incidence in different periods, a positive correlation was found among the first and subsequent evaluations. Regarding spatial distribution, mite presence was observed in the whole plant; however, leaves are preferred by the adults, whereas the fruit are preferred for oviposition. The acaricides are effective in keeping the mite population at low levels, with consequent reduction of disease incidence.

Otimização da técnica de PCR para a detecção de Xanthomonas axonopodis pv. phaseoli em sementes de feijão

O crestamento bacteriano comum, causado por Xanthomonas axonopodis pv. phaseoli (Xap), e a principal bacteriose do feijoeiro no Brasil, sendo transmitida principalmente por sementes. O presente trabalho teve como objetivo aperfeicoar uma tecnica, por meio de diferentes metodos de preparacao do extrato, para a deteccao de Xap, bem como sua deteccao simultânea com Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff) nos extratos de sementes de feijao,via PCR. A partir de amostras de sementes de feijao inoculadas artificialmente com Xap e lotes comerciais, foram avaliados: extrato bruto obtido diretamente das sementes, extrato concentrado por filtracao em membrana de 0,22µM de diâmetro, extrato concentrado por centrifugacao e extrato plaqueado em meio semi-seletivo XCP1 com e sem antibioticos (BIO-PCR). Avaliou-se a presenca simultânea de Xap e Cff em 10 lotes comerciais de sementes de feijao atraves da reacao multiplex, utilizandos-se os primers X4c, X4e, CffFOR2 e CffREV4. A partir do extrato bruto, do extrato concentrado por centrifugacao e por filtragem em membrana Millipore® nao foi possivel a deteccao de Xap nas sementes de feijao artificialmente contaminadas nem nos 47 lotes comerciais de sementes/ graos de feijao. A tecnica de BIO-PCR permitiu a deteccao de Xap a partir de extratos de sementes de feijao artificialmente contaminadas e em 18 dos 47 lotes comerciais. A tecnica de deteccao simultânea de Xap e Cff no mesmo gel e viavel, por amplificar fragmentos de DNA tipicos de cada fitobacteria. O uso do meio de cultura XCP1 sem adicao de antibioticos permitiu detectar Xap com periodo de incubacao menor em um dia em comparacao a deteccao utilizando-se o meio de cultura com antibioticos

Combining ability of summer-squash lines with different degrees of parthenocarpy and PRSV-W resistance

The aim was to assess heterosis in a set of 16 summer-squash hybrids, and evaluate the combining capacity of the respective parental lines, which differed as to the degree of parthenocarpy and resistance to PRSV-W (Papaya Ringspot Virus-Watermelon strain). The hybrids were obtained using a partial diallel cross design (4 × 4). The lines of parental group I were 1 = ABX-037G-77-03-05-01-01-bulk, 2 = ABX-037G-77-03-05-03-10-bulk, 3 = ABX-037G-77-03-05-01-04-bulk and 4 = ABX-037G-77-03-05-05-01-bulk, and of group II, 1′ = ABX-037G-77-03-05-04-08-bulk, 2′ = ABX-037G-77-03-05-02-11-bulk, 3′ = Clarice and 4′ = Caserta. The 16 hybrids and eight parental lines were evaluated for PRSV-W resistance, parthenocarpic expression and yield in randomized complete-block designs, with three replications. Parthenocarpy and the resistance to PRSV-W were rated by means of a scale from 1 to 5, where 1 = non-parthenocarpic or high resistance to PRSV-W, and 5 = parthenocarpic or high susceptibility to PRSV-W. Both additive and non-additive gene effects were important in the expression of parthenocarpy and resistance to PRSV-W. Whereas estimates of heterosis in parthenocarpy usually tended towards a higher degree, resistance to PRSV-W was towards higher susceptibility. At least one F1 hybrid was identified with a satisfactory degree of parthenocarpy, resistance to PRSV-W and high fruit-yield.