ANÁLISE ESPACIAL E QUANTIFICAÇÃO DE INÓCULO DE MOFO BRANCO (Sclerotinia sclerotiorum (Lib) de Bary) NA CULTURA DA SOJA (Glycine max (L) Merril)

Abstract

The knowledge of the spatial dynamics of plant diseases, allied with the quantification of inoculum and monitoring of the meteorological conditions, is important for the adoption of adequate management strategies and with less environmental impact. The aim of this work was to characterize the distribution, spatial variability and possible relations between white mold attributes and soybean plants attributes, as well as to evaluate techniques for identification and quantification of ascospores of Sclerotinia sclerotiorum during soybean flowering. Samplings were carried out through a georeferenced grid on a field of 12 hectares (ha) in the municipality of Mauá-da-Serra-PR in the 2013/14 and 2014/15 crop seasons and, on a field of four hectares in the municipality of Ponta Grossa-PR in the 2015/16 crop season. Quadrats with a useful area of 7.2 m² were used to evaluate the following variables: sclerotia in the soil, crop stand, incidence, severity, yield, sclerotia produced at harvest, as well as bioaerosol deposition, soybean leaf parts and flowers on semi-selective medium to Sclerotinia sclerotiorum (MSS) and quantitative polymerase chain reaction (qPCR), at 36 sampling points in the Ponta Grossa- PR field, at three dates during soybean flowering. Data were analyzed using descriptive statistics, semivariogram adjustment and Pearson correlation matrix. The meteorological conditions observed in the three experiments were adequate for the development of soybean crop and white mold disease. The variables related to soybean plants, showed low or moderate coefficients of variation and the variables related to white mold showed a high coefficient of variation. The semivariograms adjustments showed differences in the three experiments, with pure nugget effect, linear, spherical and exponential adjustments. The variable sclerotia of soil showed pure nugget effect on the two experiments in Mauá-da-Serra. Significant positive correlations were found between the incidence of white mold and the production of sclerotia at harvest, in addition to negative correlation to yield in the three experiments. The identification of white mold inoculum with incubation on MSS was shown to be the most sensitive technique, but takes up to 15 days for the confirmation of S. sclerotiorum pathogen for bioaerossol, flowers and parts of soybean leaves. It was possible to optimize the protocol of DNA extraction and reaction cycle for qPCR, besides generating a standard curve with DNA from ascospores of S. sclerotiorum, adjusted to the linear model (R² =0, 99) and efficiency of 92.2%. The use of qPCR showed promise results for leaf parts, being possible achieve concluding results in one working day.