On the occurrence of unilateral incompatibility in Primula section Aleuritia Duby and the origin of Primula scotica Hook

The occurrence of unilateral incompatibility was tested for a distylous heteromorphic system, using crosses between a self-sterile and three self-fertile species in Primula L. section Aleuritia Duby. The crosses showed non-reciprocity but not in the same direction as would be predicted in the case of unilateral incompatibility. Pollen from the self-compatible (s-c) species was not always inhibited on the style of the self-incompatible (s-i) species, and cross-fertility between s-i and s-c crosses more resembled that between different s-c species, which was also non-reciprocal. Cytoplasmic-nuclear DNA interactions and the possibility of embryo-endosperm imbalance could both explain these results. In crosses between Primula farinosa L. (s-i diploid) and P. scotica Hook. (s-c hexaploid), heterostylous pin tetraploid offspring were produced. This result is discussed in relation to the genome of P. scotica and the possibility that pin morph plants may occur in wild P scotica populations.