Jurema Schons

Danos de Rhopalosiphum padi (L.) (Hemiptera: Aphididae) no trigo em função da duração e da densidade de infestação

Aphids are considered relevant pests on wheat either by direct damage through sap sucking or by indirect damage vectoring BYDV (Barley yellow dwarf virus). Rhopalosiphum padi L. has been observed infesting wheat fields with an increasing frequency. The knowledge and the available technology, besides being more related to other aphids species already recognized as pests, they are insufficient to control the specific problem of R. padi. Thus, this work evaluated the effects of feeding duration and infestation densities of R. padi on seedlings of wheat cv. Embrapa 16. Grain yield, yield components and the extent of symptoms were recorded. The experiment was carried out in the field under a completely randomized split-plot experimental design with four replications. The main plot was feeding duration (two and seven days) and the sub-plots were infestation densities (zero, two and 10 aphids per plant). Independent on feeding duration, 10 aphids per plant resulted in significant yield losses, reduction of number of heads and tillers per plant. Canopy dry matter was also reduced. Infestations of two and 10 aphids per plant resulted in continuous yellowing of wheat plants from tillering to the end of flowering stage. When aphids fed for seven days on wheat, more yellowing symptoms were observed at the flower stage in comparison with two days feeding.

Identification and Characterization of Wheat Streak Mosaic Virus Isolates in Wheat-Growing Areas in Brazil

Wheat streak mosaic virus (WSMV—Potyviridae, Tritimovirus), transmitted by the eriophyid mite Aceria tosichella Keifer (Acari: Eriophyidae), was considered a quarantine pest in South America. Since the first report of virus in Argentina, the vector has been found in Argentina, Uruguay and Brazil. The objective of this work was to determine the occurrence of WSMV in Brazil and characterize isolates from wheat-growing areas. Between 2009 and 2011, a total of 40 samples collected in wheat (Triticum aestivum) growing areas, where the presence of the mite was previously related, were tested by RT-PCR for virus detection. Six isolates of WSMV were obtained and characterized by sequencing. Two of them had their host range determined. The Brazilian WSMV isolates clustered in clade D are closely related to the Argentine isolate Arg2 (FJ348359). As expected, isolates were unable to infect dicotyledons plants. They caused mosaic in Triticum aestivum, Hordeum vulgare, Secale cereale, ×Triticosecale, and Zea mays, and they were also able to infect Avena sativa. The presence of WSMV in wheat-growing areas of the Brazilian state Rio Grande do Sul was confirmed, possibly having been introduced from a common source and/or direct vector bearing virus migration from Argentina.

Análise da resistência/tolerância da cultivar de trigo BRS Timbaúva ao Barley yellow dwarf virus - PAV

Barley yellow dwarf virus-PAV e a especie predominante na regiao sul-brasileira entre as especies de virus que causam o nanismo amarelo em cereais de inverno. A resistencia genetica e a tolerância ao virus e ao afideo vetor sao importantes estrategias de controle dessa virose. BRS Timbauva apresenta reducoes menores de produtividade, comparativamente a outras cultivares de trigo, quando exposta ao complexo afideo-virus, e e resistente ao vetor Rhopalosiphum padi. Esse estudo visou determinar se esta cultivar tambem apresenta resistencia ou tolerância ao BYDV-PAV. Os ensaios foram realizados comparando-se BRS Timbauva a Embrapa 16 (suscetivel e intolerante). A resistencia ao virus foi avaliada por meio de estimativas do titulo viral por ELISA. A tolerância foi estimada avaliando-se componentes morfologicos e de rendimento, considerando a reducao em relacao a plantas nao infectadas. O efeito da pressao de inoculo sobre a produtividade tambem foi avaliado. BRS Timbauva foi tao suscetivel a infeccao viral quanto Embrapa 16 porem, comparativamente a esta cultivar, em todos os ensaios os danos e reducao de produtividade em BRS Timbauva foram menores, o que sugere tolerância ao BYDV-PAV. O comportamento a campo desta cultivar pode estar associado a resistencia ao vetor e tolerância ao virus.

Avaliação de danos causados pelo Barley yellow dwarf virus: PAV em cultivares de trigo no Brasil

Assessment of damage caused by the Barley yellow dwarf virus in Brazilian wheat cultivars The aim of this study was to assess the damage caused by the Barley yellow dwarf virus (BYDV-PAV) in five wheat cultivars (BRS 177, BRS 179, BRS 194, BRS Camboata and BRS Angico) grown in a greenhouse at Embrapa (Empresa Brasileira de Pesquisa Agropecuaria), Passo Fundo, state of Rio Grande do Sul, Brazil, in 2005. The damage caused by the BDV-PAV was determined by the analysis of agronomic traits (plant height and dry matter) and yield (number of tillers, ears, and grains per plant; thousand-grain weight). The data were submitted to the analysis of variance and the means were determined by Tukeys test at 5%. The virus significantly affected all of the tested variables. Among the agronomic traits, dry matter was the most affected one, with rates between 26.1% (BRS 177) and 51.4% (BRS 179). Reductions in plant height ranged between 12.5% (BRS 177) and 15.5% (BRS Camboata). Total grain yield was greatly affected by the viral infection, with significant damage in all cultivars, with a reduction between 34.2% (BRS Camboata) and 60.8% (BRS 179). There was a reduction in the mean number of tillers per plant only in BRS Angico and BRS 179 cultivars, which amounted to 20 % and 26.6% respectively. The reduction in the mean number of grains varied between 26.1% (BRS Camboata) and 54.3% (BRS 179). Finally, the reduction in thousand-grain weight corresponded to 16.9% and 38.4% in BRS Camboata and BRS 194 cultivars, respectively. Additional keywords: Luteovirus, aphids, Triticum aestivum.

Incidência e índice de doença do mosaico do trigo em cereais de inverno e em gramíneas de verão, associados ao Polymyxa graminis

The Soil-borne wheat mosaic virus (SBWMV) is transmitted by the fungus Polymyxa graminis. To evaluate the incidence and the disease index (DI%) and the presence of the vector in the root system, an experiment was carried out using: oat (Avena strigosa and A. sativa), barley (Hordeum vulgare), triticale (Triticum secale), wheat (Triticum aestivum), Lilium multiforum, mayze (Zea mays), sorghum (Sorghum bicolor), Pannisetum americanum, Digitaria sp. and Brachiaria sp. The experiment was conducted during two sowing periods. Incidence was calculated based on the percentage of the symptomatic plants and grades (0-5) were given to determine the DI (%). Root segments were collected, then stained with solution of cotton blue-lactofenol and visualized in optical microscope. The quantity of resting spores groups was rated. No symptoms were observed on oat species, however, the presence of resting spores in moderate quantities was observed on barley. The incidence and DI (%) for the triticale and wheat in the first sowing period were higher than in the second one. A direct relationship between DI (%) and the quantity of resting spores on root was observed. No symptoms of SBWMV or resting spores in the root system of summer grasses were observed.

Diagnóstico biológico e molecular e análise da seqüência de nucleotídeos do gene da proteína capsidial de um isolado do Apple stem pitting virus

ABSTRACTBiological and molecular diagnosis and nucleotide sequence analysis of the coat protein gene of an isolate of Apple stem pitting virus Apple stem pitting virus (ASPV) was detected in samples of European pear ( Pyrus communis ) cvs. Starkrimsonand Abate Fetel, and Asian pear ( P. pyrifolia var. culta) cvs. Kousui and Housui. The samples were collected in thebeginning of autumn 2003 at the Experimental Station of Embrapa Uva e Vinho, Vacaria, RS. Using several combinationsof primers, DNA fragments of 269 and 1554 bp were amplified, the latter containing the complete coat protein gene(1131 nt) of ASPV. Another amplified fragment of 291 bp comprised part of the viral polymerase gene. These fragmentsare excellent tools for the diagnosis of ASPV in pear. Comparison of the nucleotide sequences with sequences of theGenBank showed 89% identity with sequences from the German isolate of apple, and 85 to 88% with Polish isolates,both from pear. The herbaceous indicator Nicotiana occidentalis

Atividade isoenzimática em plantas de trigo infectadas com o vírus SBWMV

O objetivo deste trabalho foi elucidar a atividade e a expressao isoenzimatica das esterases, das peroxidases e das aspartato aminotransferases em funcao da infeccao de plantas de trigo pelo Soil-borne wheat mosaic virus (SBWMV). Foram analisadas, aos 45 dias apos a emergencia, quatro cultivares e uma linhagem de trigo, com diferentes niveis de resistencia ao SBWMV: BRS Guabiju, BRS 194, BRS 179, BR 23 e PF 980524. De modo geral, ocorreram diferencas qualitativas e quantitativas intra e interpopulacional, quando comparadas plantas assintomaticas e sintomaticas ao SBWMV. Para o sistema esterase, nove padroes de bandas foram determinados e para peroxidase e aspartato aminotransferase foram detectados tres padroes de bandas, para ambas as condicoes. Padroes eletroforeticos foram observados para plantas infectadas, quando comparadas com as nao infectadas, destacando-se a atividade da esterase, o que permitiu identificar com maior precisao o estado metabolico e diferenciado das celulas.

Efeito do Soil-borne wheat mosaic virus sobre o metabolismo de cinco genótipos de trigo com diferentes níveis de resistência à doença

Com o objetivo de conhecer as alteracoes metabolicas promovidas pelo Soil-borne wheat mosaic virus (SBWMV), um dos virus economicamente mais importantes da cultura do trigo (Triticum aestivum), foram analisados os niveis de proteinas soluveis e determinadas as atividades da peroxidase e da protease em quatro cultivares (BRS Guabiju, BRS 194, BRS 179, BR 23) e uma linhagem (PF 980524) de trigo com diferentes niveis de resistencia ao virus. Os dados obtidos foram submetidos a analise de variância, comparando-se as medias, pelo Teste de Duncan a 5%. Os niveis de proteinas soluveis foram mais elevados nas plantas sem sintomas, enquanto que as atividades da peroxidase e da protease foram maiores em plantas com sintoma de mosaico do que em plantas assintomaticas. Alem disso, pode-se constatar que quanto maior a suscetibilidade do genotipo, maior o nivel de atividade da protease. Estes resultados sao promissores para estudos de inibicao da protease para controle de viroses.

Alterações no metabolismo de cinco genótipos de trigo com diferentes níveis de resistência ao Soil-borne wheat mosaic virus

Soil-borne wheat mosaic virus - SBWMV causes substantial economic losses to the wheat crop and can also infect a wide range of grass crops. An experiment was conducted in the experimental area of Embrapa Trigo, using five genotypes of wheat (BRS Guabiju, BRS 194, BRS 179, BR 23, and PF 980524) with different resistance levels to SBWMV. Samples were collected 45 days after emergence, and levels of sugars, proline concentration, and nitrate reductase activity were biochemically analyzed to understand the metabolic alterations induced by SBWMV. Nitrate reductase activity was higher in asymptomatic plants, as compared to the level observed in plants with symptoms. Sugar and proline levels were higher in plants with disease symptoms than in asymptomatic plants. The results show that the metabolic changes were caused by the SBWMV in the five different genotypes used in the experiment.