Estimativa de severidade do mofo-branco em lavouras de feijão utilizando-se sensores hiper e multiespectral

Neste estudo objetivou-se identificar comprimentos de onda e faixas espectrais provenientes de reflectâncias hiper e multiespectrais utilizando regressão PLS e promover avaliação comparativa desses métodos e de dez índices de vegetação, para determinar aqueles que melhor estimam níveis de severidade de mofo-branco em feijão. Foram implantados experimentos nos municípios de Viçosa e de Oratórios, estado de Minas Gerais. Reflectâncias hiperespectrais foram obtidas com espectroradiômetro cuja faixa útil de leitura adotada foi entre 440 e 900 nm. Reflectâncias multiespectrais foram obtidas de imagens de câmara constituídas de cinco bandas (vermelho, verde, azul, Red-edge e infravermelho). Os índices de severidade da doença foram baixos; em Viçosa a média foi de 5,8% e em Oratórios, 7,4%. Modelos matemáticos utilizando reflectâncias hiperespectrais tiveram melhor desempenho para estimar mofo-branco; a banda do red-edge apresentou os comprimentos de onda que melhor estimam a severidade do mofo-branco. Índices de vegetação resistentes a efeitos da reflectância de solo estimaram melhor o mofo-branco do que os demais índices

Independently founded populations of <i>Sclerotinia sclerotiorum</i> from a tropical and a temperate region have similar genetic structure

<div><p><i>Sclerotinia sclerotiorum</i> populations from tropical agricultural zones have been suggested to be more variable compared to those from temperate zones. However, no data were available comparing populations from both zones using the same set of markers. In this study, we compared <i>S</i>. <i>sclerotiorum</i> populations from the United States of America (USA, temperate) and southeast Brazil (tropical) using the frequency of mycelial compatibility groups (MCGs) and 13 microsatellite (SSR) markers. Populations were sourced from diseased plants within leguminous crops in New York, USA (NY; <i>n</i> = 78 isolates), and Minas Gerais State, Brazil (MG; <i>n</i> = 109). Twenty MCGs were identified in NY and 14 were previously reported in MG. The effective number of genotypes based on Hill’s number of order 0, which corresponded to the number of multilocus genotypes (MLGs) were 22 (95% CI = 15.6–28.4) and 24 (95% CI = 18.9–29.1) in NY and MG, respectively. Clonal fractions of MLGs were 71.8% (NY) and 78.0% (MG). The effective number of genotypes based on Hill’s number of orders 1 and 2 in NY were 8.9 (95% CI = 5.2–12.6) and 4.4 (95% CI = 2.6–6.1), respectively. For MG these indices were 11.4 (95% CI = 8.7–14.1) and 7.1 (95% CI = 5.1–9.0), respectively. There were no significant differences of allelic richness, private allelic richness, gene diversity, effective number of alleles and genotype evenness between the NY and MG populations. The populations were differentiated, with 29% of total variance attributed to differences between them and G''_ST and Jost’s D indices higher than 0.50. Cluster analysis revealed dissimilarity higher than 80% among most MLGs from both populations. Different alleles segregated in the populations but both had similar levels of genotypic variability.</p></div

Hierarchical cluster analysis according to complete linkage method from a dissimilarity matrix reflecting the percentage of allelic differences among the Multilocus Genotypes (MLGs).

<p>Clusters (G) were assigned for MLGs with at least 50% of similarity.</p

Frequency of the mycelial compatibility groupings (A and B) and multilocus genotypes (MLGs) (C and D) obtained from 13 microsatellite loci in the <i>Sclerotinia sclerotiorum</i> populations from New York, USA, and Minas Gerais, Brazil.

<p>The asterisk indicates the sum of the frequencies of two closely related MLGs, with a difference at the 8–3 locus (dinucleotide repeats). The MLG 1 has a 250 base pair (bp) allele while the MLG 2 has a 252 bp allele.</p

Diversity accumulation curves for different sample sizes with 95% confidence intervals (shaded areas) of the Hill’s numbers or effective number of genotypes of orders 0 (N0), 1 (N1) and 2 (N2) estimated for the <i>Sclerotinia sclerotiorum</i> populations from New York, USA and Minas Gerais, Brazil.

<p>The N0, N1 and N2 numbers correspond to genotype richness, the exponential of Shannon’s entropy, and the inverse of the Simpson’s concentration indices, respectively. Solid lines correspond to rarefaction (interpolation) and dashed lines to extrapolation curves up to the base sample size of 156 individuals which corresponds to double the smaller reference sample size (NY = 78). The 95% confidence intervals were obtained by a bootstrap method based on 200 replications.</p

Genotype accumulation curves for the <i>Sclerotinia sclerotiorum</i> populations from New York, United States (USA) and Minas Gerais, Brazil.

<p>The number of loci was randomly sampled (1,000 times) without replacement up to n − 1 loci. The 90% of the number of multilocus genotypes identified in each population are indicated by dashed lines.</p