Graphical Analysis of Rootstock × Site Interaction for Two NC-140 Multi-Location Apple Rootstock Trials Using GGEbiplot

Genotype × environment interaction can alter the performance of genotypes across environments and the rootstock × site interaction is usually significant for multi-location rootstock trials. Analysis of variance is used to test the hypothesis that there is no interaction, but when the interaction is significant, it provides no information about the nature of the interaction. Biplot methodology was developed for graphical analysis of genotype × environment data and displays the genotype main effect (G) and genotype × environment interaction (GE) of a genotype-by-environment data set, where the environment (E) main effects are removed and the G main effect and the GE are retained and combined. Biplot analysis was used to graphically evaluate rootstock × site interaction using data from the 1994 and 2003 NC-140 apple rootstock trials. Data for cumulative yield from the 1994 trial was used to demonstrate some different biplots and the types of information that can be obtained with GGEbiplot software. Differences in rootstock vigor were more apparent at high-vigor sites than at low-vigor sites. Therefore, for future rootstock trials attempts should be made to include sites with a range of vigor, rather than sites with geographical diversity. For trunk cross-sectional area, cumulative yield and cumulative yield efficiency, M.9 NAKBT337 was one of the most stable rootstocks and was less sensitive to site conditions than most other rootstocks. In general, M.26 and the Geneva rootstocks (G.16, G.41 and G.935) were less stable and responded to site conditions more than M.9 NAKBT337 and B.9.