Fig. 2. Slopes of joint regression and main grain yield for the cultivars. The slope estimates the cultivar response to the fertility of each environment. Indication of the variability of the estimates is given by the ellipses at the 0.05 probability level. Mean grain yield is symbolized with a vertical dashed line. The horizontal line separates genotypes specifically adapted to favorable environments (slope > 1) and genotypes specifically adapted to unfavorable environments (slope < 1). Codes of the cultivars are the same as in Table 2.