Choosing probe genotypes for the analysis of genotype-environment interaction in winter wheat trials

Genotype-environment interaction was analyzed in French multi-environment w heat (Tritictim aestivum L.) trials using probe genotypes and bi-additive f actorial regression. Probe genotypes are specific genotypes in which the co mparisons of yield components to reference values describe the most-importa nt environmental factors that limited grain yield. The time-period until fl owering was described by the deviation of kernel number from a threshold nu mber while the grain-filling period was described by the reduction of thous and-kernel weight from a potential value. The aim of this paper was to dete rmine the convenient number and the characteristics of probe genotypes to i nclude in wheat breeding trials. Two sets of genotypes were used to model genotype-environment interaction: set 1 with 12 varieties tested in 18 environments and set 2 with ten lines tested in 14 environments. Set 2 was used for validation. Seven probe genot ypes described the environments by providing environmental covariates, name ly differences in yield components, for further analysis of interaction in set 1 and set 2. Interaction was modelled with bi-additive factorial regres sions including differences in yield components. Several rounds of models w ere fitted to determine the optimal number of probe genotypes (i.e. environ mental covariates) to introduce. From the seven probe genotypes, all the po ssible combinations including one to seven genotypes were studied. Signific ance of the combinations was tested with critical values obtained from simu lations through 1,000 random permutations. Taking into account the informat ion available on the probe genotypes, one would think that two, three or fo ur probe genotypes would be sufficient, otherwise the number should reach f our or five genotypes. In all cases, these numbers will provide models more -parsimonious than the classical AMMI model. The important information to b e known on the probe genotypes prior their first multilocation experiment i s: interaction pattern, earliness, and differences in yield component. Test ed for the first time, a quadruplet is better than a triplet because the pr obability of choosing complementary genotypes increases with their number.