Fig. 3. Relationship between the cultivar stability determined as the slope of the joint regression and the cultivar mean for (a) yield and (b) grain carbon isotope discrimination (¹³C) for the 24 durum wheat cultivars. Means for grain yield and ¹³C are symbolized with vertical lines. Numbers correspond to cultivars according to Table 2 1 to 8 = old, 9 to 16 = intermediate, and 17 to 24 = modern. Underlined numbers in Fig. 3a correspond to cultivars not carrying dwarfing genes.