Rafael Augusto Vieira

Resistência de genótipos de videira à ferrugem

O objetivo deste trabalho foi avaliar a resistencia a ferrugem causada pelo fungo Phakopsora euvitis, em genotipos de videira, e a efi ciencia da infeccao de acordo com a idade das folhas e concentracao de inoculo. A avaliacao foi feita em 15 genotipos, com base nos seguintes componentes de resistencia: numero de pustulas (uredios) por cm2; tamanho das pustulas; numero de esporos produzidos por pustula; e periodo latente. Os componentes de resistencia, com excecao do periodo latente, apresentaram grande variacao quantitativa. A analise multivariada desses componentes diferenciou cinco grupos de genotipos. Os genotipos mais resistentes foram as cultivares porta-enxertos IAC313, IAC572 e IAC766, em que a efi ciencia da infeccao foi baixa, com pustulas menores e menor producao de urediniosporos, alem de reacao de hipersensibilidade no tecido em torno das pustulas. O grau de infeccao aumenta com o aumento na concentracao do inoculo. A ferrugem coloniza, indiscriminadamente, folhas jovens e folhas maduras de videira.

Fungitoxidade in vitro de extratos vegetais sobre Exserohilum turcicum (Pass) Leonard & Suggs

Helminthosporiose is caused by the fungus Exserohilum turcicum and represents one of the main diseases in popcorn grown in Brazil. Due to its characteristics, such as plant size, planting area extension and economic profitability, the use of genetic resistance and chemical control has constituted the main procedure against such disease. The use of pesticides in agriculture has resulted in risks to the human health and frequent damages to the environment. Thus, the fungitoxic effect of plant extracts of Achillea millefolium (yarrow), Cymbopogon citratus (lemon grass), Artemisia camphorata (camphor) and Rosmarinus officinalis (rosemary) on the mycelial growth of E. turcicum was evaluated by using two culture media (PDA - potato dextrose agar, and LCH - lactose-casein hydrolysate) in order to set alternative methods for controlling helminthosporiose. Rosemary and camphor extracts led to higher mycelial growth inhibition in both culture media, whereas yarrow and lemon grass extracts stimulated mycelial growth in LCH medium.

Genetic analysis of tropical rust resistance in popcorn lines

The objectives of this study were to identify promising popcorn lines and hybrids for genetic resistance to tropical rust (Tr, Physopella zeae) in diallel crosses of nine lines derived from a large part of Brazilian popcorn germplasm and to estimate genetic parameters for Tr resistance. Crosses and checks were tested in a random block design, with artificial inoculations under greenhouse conditions. Plots consisted of a single 14-L pot, with four plants. Tr was measured by severity and area under the disease progress curve. Data was analyzed by Griffings diallel model, and genetic parameters were estimated. Heritability estimates to Tr resistance was medium. Specific combining ability-SCA had significant effects (P 0.10). This indicated the major importance of non additive gene effects. In general, breeding possibilities for resistance was restricted. The line 9 (L7.4) had the most outstanding GCA for resistance to Tr, and hybrids 1×7 and 3×6 had outstanding SCA and were recommended for breeding.

Diagrammatic scale for assessment of Septoria apiicola and Cercospora arracacina in Arracacha.

ABSTRACT Diagrammatic Scale for Assessment of Septoria apiicola and Cercospora arracacina in Arracacha Leaf spots, caused by the fungi Septoria apiicola and Cercospora arracacina, are among the most serious leaf diseases that affect arracacha. Since standardized methods for disease evaluation are necessary, this work proposes a diagrammatic scale for assessment of these diseases. Leaves presenting different severity levels were collected and the minimum and maximum severity limits were determined. The intermediary severity levels were determined according to “Weber-Fechner´s stimulus response law” and the scale had seven severity levels (0.7; 2; 4; 8; 17; 32 and 53%). Scale validation was carried out by four experienced raters and four inexperienced raters, who estimated severity with and without the use of the scale, using 50 leaves with different levels of disease. The actual severity and the estimated severity values were analyzed through linear regression, and the estimates were compared for accuracy and precision. By using the scale, the raters obtained higher precision and accuracy levels, and the variance of the absolute errors in the assessment of the disease presented values within acceptable limits. The proposed scale was thus considered appropriate for evaluation of leaf spots in arracacha.

Progress of Asian soybean rust and airborne urediniospores of Phakopsora pachyrhizi in southern Brazil

Asian soybean rust, caused by the fungus Phakopsora pachyrhizi, was reported at epidemic levels in 2003/2004 and is the main soybean disease in Brazil. The aim of this study was to investigate the spread of Asian soybean rust and to quantify airborne urediniospores in the region of Campo Mourao, Parana State, Brazil. Three experiments were conducted under field conditions during the 2007/08 and 2008/09 crop seasons. Using the disease gradient method, provided by the application of increasing levels of the fungicide tebuconazole, four Asian soybean rust epidemics at different intensities were obtained in each experiment. To quantify the urediniospores, weathercock-type spore collectors were installed during and between the two crop seasons. Disease progress curves were plotted for each epidemic, and maximum severity was estimated. The curves were fit to the logistic model, which provided higher coefficients of determination and more randomly distributed residuals plotted over time. Analyses of the area under the disease progress curve showed that the largest epidemics occurred in the 2007/2008 crop season and that the progress rates were higher for severity, even among plants protected with the fungicide. The number of urediniospores collected in the air was related to the presence of soybean plants in the cultivated crops. The quantity of urediniospores was also positively correlated to the disease severity and incidence, as well as to cumulative rainfall and favorable days for P. Pachyrhizi infection.

Detecção do Sugarcane mosaic virus no Paraná e limpeza somaclonal por cultura de tecidos

An isolate of Sugarcane mosaic virus (SCMV) associated with mosaic symptoms in the RB925268 sugarcane clone was identified in Parana state. Axilary buds of 4 to 8 mm used as explants were regenerated into plantlets using MS medium with and without ribavirin antiviral, at concentrations of 10 to 60 mg/L. Ribavirin was toxic to sugarcane at all concentrations, resulting in plant death at concentrations of 30 mg/L or higher. The complete elimination of SCMV was obtained in MS medium with 25 mg/L ribavirin concentration, confirmed by sap inoculation into Sorghum bicolor cv. Rio and by RT-PCR.

Levantamento da incidência de Leifsonia xyli subsp. xyli em plantios de cana-de-açúcar do noroeste do Paraná

Ratoon stunting disease caused by Leifsonia xyli subsp. xyli is one of the most important bacterial diseases of sugarcane (Saccharum spp.). A ratoon stunting desease survey was carried in 32 sugarcane producing areas from two mills in the northwest region of Parana State through a dot blot serological protocol and a polymerase chain reaction-based assay. A total of 1395 samples were collected in areas planted with 8 varieties and 2 sugarcane clones collected from plants at different harvest periods. The bacterium was detected in the fibrovascular fluid of the SP77-5181 variety from a producing area in a 23% rate of incidence. These data indicated that Leifsonia xyli subsp. xyli is present in the northwest region of Parana.