Abstract
Soybean is worldwide a crop of great importance, however, with its expansion, diseases causing great yield loss such as the powdery mildew surge (Erisyphe diffusa U. Braun & S. Takam). Objective of the present study was to estimate the ideal number of evaluations of the resistance of soybean genotypes to powdery mildew by means of repeatability studies with the traits: ILA (infection of the leaf area), ILS (infection of the leaf blade surface) and ILU (infection of the leaf underside), using the treatments no control - NC, partial control - PC (fungicide 80% sulphur at ILA > 40%) and total control - TC (presence of symptoms). Only trait ILA presented estimates of repeatability (ANOVA and principal components), with 85- 90% of stability in 3 or 4 measurements (PC and NC methods). These results and the high values found for R 2 indicate that selection based on this parameter is possible.
Highlights
To determine the reaction of soybean genotypes to powdery mildew in different evaluation periods, seeds treated with the fungicide tetramethylthiuram disulfide (TETD) were sown directly in pots (3 liters) filled with a substrate composed of a homogenized mixture of soil and dung under daily irrigation until sowing
According to Gravina et al (2004), the significance stated in the analysis of variance indicates the existence of additional and non-additional genetic variability among the evaluated genotypes
Estimates of the number of evaluations needed for certain coefficients of determination The analysis of variance is an alternative way of obtaining the repeatability coefficient, in which the temporal environment effect is removed from the error, or the temporal effect of the environment is confounded with the error
Summary
Repeatability studies are of great importance in genetic improvement studies since once a certain genotype is selected for its performance or integrant structures of the same, it is expected that this performance lasts throughout the entire life cycle. The veracity of this expectation can be confirmed by the repeatability coefficient of the study trait, which can be estimated when a trait is measured on a same individual, repeatedly, in time or space. Our study had the objective of estimating the ideal number of evaluations of powdery mildew-resistance in soybean genotypes to by means of repeatability studies
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