Parent–progeny crossing scheme used to test S allele dominance interactions in the B4 × Ox progeny lines. Individuals' S genotypes are placed below their respective ‘flower' (pistil and stamen) images, whereas individuals' pistil and pollen S phenotypes are placed above their respective pistil and stamen images. The S phenotypes of each progeny were determined by testing compatibility of backcrosses with B4 and their respective O (Ox) parents; the majority of S phenotypes were explained by the S genotypes and dominance relationships described in the figure. Some progenies from the B4 × O19 cross were also either weakly self-compatible or compatible for both parental backcrosses. (a) Progenies where the first parent, B4, had an S1S1 genotype (OS-Bill-4, Hiscock, 2000) and the other parent had an SdomSrec genotype (O2, O4, O22 or O19; Brennan et al., 2002), where the Sdom allele had previously been identified as S2, S3, S4 or S6 respectively. (b) A progeny where the first parent was B4 and the other parent had S4S5 genotype where S5 was dominant over S4 in pollen only (O27, Brennan et al., 2002).