Estimation of genotype x environment interaction for yield in green beans (Phaseolus vulgaris)

English: 1. The objective of this study was to establish the significance of GxE interaction on yield in snap beans, secondly to determine and compare the appropriate analytical method to describe the GxE interaction. Thirdly, to determine the optimal number of locations, years and replications required for efficient testing. 2. Nine snap bean varieties were included in trials at four locations, with the trials being repeated over three years (1998-2000).The pod yield was measured. The data was analysed applying the ANOVA, Finlay and Wilkinson, and the AMMI models. Variance components were also calculated to determine the influence of the different effects on the theoretical variance of the mean thus allowing for the optimal allocation of locations, years and replications. 3. The GxL, GxY and GxYxL interactions were significant for pod yield. The estimated variance components for yield shows that 02g, 0291' 02gy and 029lY contribute 23.5, 18.8, 4.9 and 34.8 percent respectively to the total phenotypic variance. The contribution of the error variance in these trials was 18.0 percent. 4. According to Finlay and Wilkinson, genotypes G3, G5 and G9 were classified as having average stability and high yields therefore good adaptability. Genotype G8 has above average stability while G1, G2, G4, G6 and G7 were classified as genotypes having average stability with low yields therefore poor adaptability. 5. The AMMI ANOVA subdivides the GxE effect further using principal component analysis. Genotypes G5 and G9 are classified as having high yields but low stability whereas genotypes G3 and G8 possessed both high yields and high stability. Genotypes G1, G2, G4 and G7 have low yields but are highly stable. Genotype G6 has low yields and low stability. The AMMI model was also used to classify the different locations. Location A and D can differentiate more amongst the genotypes whereas Location Band C have low discrimination amongst the genotypes. 6. According to the ANOVA, genotype G3 was classified as being most stable whereas the Finlay and Wilkinson, and the AMMI models identified genotype G8 as being most stable. The ANOVA ranked genotype G8 fourth for stability. Both AMMI and Finlay and Wilkinson models ranked genotype G1 fifth for stability but according to the ANOVA it was most unstable. Finlay and Wilkinson identified genotype G7 as being the most unstable while the most unstable genotype in the AMMI analysis was G6. The correlations between the stability rankings of the genotypes for the different methods were relatively low. 7. According to the estimated variance of a variety mean, two years, six locations and two replications is the optimum number of years, locations and replications for efficient testing of snap beans for yield in South Africa.