Relative yield as a measure of entry performance in variable environments

The traditional approach of presenting and analyzing actual (uncoded) yield data from variety trials conducted across sites has drawbacks. The purpose of this paper is to present the theoretical and practical advantages of using relative yield. Both hypothetical and field data were used for illustration. Relative yield was calculated as a ratio of entry yield at each site to the site mean. It was shown that relative yield has three major advantages: (i) conversion of the simple entry variance of yield across sites to a practical, agronomic stability measure, allowing easy comprehension of the genotype-by-environment (GxE) structure, (ii) equal weight given to each site when calculating entry means across sites, and (iii) ease in comparing large numbers of entries tested in different experiments at the same site and year. Plant breeders are encouraged to use routinely relative yield, and to adopt the variance of relative yield across sites as a powerful, yet simple, stability measure.