Genotype × Environment Interactions and Stability Analysis for Forage Yield of Orchardgrass Clones 1

Abstract

The response of genotypes to procedures used in the breeding program and to a broad range of environmental conditions is important in the development of improved cultivars. Twenty orchardgrass (Dactylis glomerata L.) clones were evaluated for forage yield at three locations for 3 years (Exp. A) and 10 clones were evaluated three plant spacings for 3 years (Exp. B), resulting in nine environments for each experiment. Reproductive, vegetative, and total yields were obtained. The analysis of variance revealed significant differences among genotypes and among environments for all three yields within each experiment. Also, the first order interactions (genotypes ✕ locations, genotypes ✕ years, locations ✕ years, genotypes ✕ spacings, and spacings ✕ years) and the second order interactions (genotypes ✕ locations ✕ years and genotypes ✕ spacings ✕ years) were generally significant for all yields. Linear regression of clone average yield on the average yields of all clones in each environment resulted in regression coefficients (b values) which ranged from 0.581 to 1.746, 0.286 to 1.271, and 0.094 to 2.100 in Exp. A and from 0.332 to 1.337, 0.381 to 1.482, and 0.336 to 1.390 in Exp. B for reproductive, vegetative and total yields, respectively. Some of theb values differed significantly from the expected value of one. Average percentages of total variation due to linear regression were 80, 62, and 44 in Exp. A and 86, 92, and 89 in Exp. B for reproductive, vegetative, and total yields, respectively. The deviations from regression mean squares (S2d) for individual clones were not homogeneous and some were significantly different from zero. In the combined analysis of variance the variability due to regression and the pooled deviation from regression were significant. Both the coefficient of determination (r2) and the ecovalence stability index (w) varied with clones within each experiment, indicating marked stability differences among clones over the environments. Given the prevalence of the genotype ✕ environment interactions, utilization of the response index and the stability indices provided additional information permitting more effective comparisons of the orchardgrass clones for yield and adaptation.