Categorizing coefficients of variation in sunflower trials

This study was carried out to categorize coefficients of variation (CV’s) associated with important traits of routine use in the sunflower breeding programs. Separate categories were obtained for the August/September and February/March sowings. Data were used from the intermediate and final sunflower experiments carried out by Embrapa Soybean and other collaborator institutions of the Network of Official Sunflower Trials. Taking into account the mean and the standard deviation of the CV’s obtained from the analyses of variance of the experiments, they were fitted into the low, medium, high and very high categories. An additional classification was made using the median and pseudo-sigma, in place of the mean and standard deviation, respectively. In this study it was ascertained that the CV’s categorization depended on the trait studied. Sowing date effects were more pronounced for seed and oil yield and plant height. For all assessed traits in February/March, the methodologies adopted were similar (regardless of the CV’s distribution) and satisfactory to assess the experimental accuracy of the trials. In the August/September trials there was good agreement between the results of the methodologies adopted and that of Gomes (1985) for seed and oil yield. For the other traits, the former methodologies were shown to be more adequate. The proposed CV’s categorizations for the sunflower traits use as maximum acceptable limits the values of 23.5% (August/September sowing) and 31.5% (February/ March sowing) for seed and oil yield, 6.0% for oil content (August/September and February/March) and plant height (August/September), 9.5% for plant height (February/March) and 4.5% for flowering and physiological maturity (August/September and February/March).