Interrelationships among and Repeatability of Several Stability Statistics Estimated from International Maize Trials

Importance and implications of genotype-by-environment interaction are well known to breeders and geneticists. Several methods of measuring stability of performance of genotypes across environments have been developed. Some of these methods have been compared empirically and statistically. The purpose of this investigation was to study rank correlations among Eberhart and Russells regression coefficient (bᵢ-ER) and deviation from regression (sd²₁); Shuklas σ²₁, s²₁ , and bᵢ-Sh; CVᵢ; and S²ᵢ statistics. The data used for calculating these statistics were obtained from five international maize (Zea mays L.) trials. Trial 1 involved 14 genotypes tested at 39 locations in 21 countries, trial 2 involved 23 genotypes tested at 46 locations in 27 countries, trial 3 involved 16 genotypes tested at 23 locations in 13 countries, trial 4 involved 18 genotypes tested at 25 locations in 15 countries, and trial 5 involved 12 genotypes tested at 17 locations in 10 countries. The statistic sd²ᵢ was highly rank correlated with σ²ᵢ and s²ᵢ, but not with other statistics. The bᵢ-Sh and bᵢ — ER statistics were highly correlated (rank) with each other as well as with S²ᵢ. None of the statistics was consistently well correlated with mean yield. Stability statistics were also calculated by grouping locations for a trial into high-yield (top 50%) and low-yield (bottom 50%) environments. Repeatability of all statistics between the two groups was generally negligible. Repeatability was also negligible between statistics estimated from each of two randomly chosen subsets of environments and from four randomly chosen subsets of environments. The high-yield environments were characterized by relatively low CVᵢ and the low-yield environments by relatively high CVᵢ. Cooperative investigation of CIMMYT, Mexico and Louisiana Agric. Exp. Stn. Approved for publication by the Director of the Louisiana Agric. Exp. Stn. as manuscript no. 87-09-1502.