Genotype x environment interaction is Fully analyzed when genotypes and environments are well characterized. Probe genotypes were studied in a simplified crop diagnosis to show how variates of yield components can strengthen characterization of environments by usual indicators of yield-limiting factors. The objective of this study was to determine the main limiting factors of yield and to analyze their effects in wheat (Triticum aestivum L,) trials. Fixed genotypes (Talent, Soissons, Camp-Remy, and Arminda) were studied as probe genotypes at five experimental stations of the Institut National de la Recherche Agronomique (I.N.R.A.) (Rennes, Mons, La Miniere, Dijon, and Ondes) during 1991 and 1992, Two important variates, the reduction of kernel number and the reduction of thousand kernel weight, were analyzed to characterize the environments during the formation of yield, The former described the time-period until flowering and the latter the grain-filling period. In addition, factors that limit yield were determined through indicators such as water deficits, the ratio between nitrogen absorbed and kernel number, radiation, temperature, development of diseases (powdery mildew, strike rust, leaf rust, leaf and glume blotch), and lodging. Our study resulted in providing critical values for grain yield, kernel number, and thousand kernel rr eight for the four probe genotypes. Then reductions of yield components could be determined and analyzed. They provide useful information for characterizing environments subjected to numerous yield-limiting factors. Our study also revealed that the biological variates (essentially susceptibility to powdery mildew and to lodging) affected yield more than the climatic variates.