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 het eromorphic system, using crosses between a self-sterile and three self-fert ile species in Primula L. section Aleuritia Duby. The crosses showed non-re ciprocity but not in the same direction as would be predicted in the case o f unilateral incompatibility. Pollen from the self-compatible (s-c) species was not always inhibited on the style of the self-incompatible (s-i) speci es, and cross-fertility between s-i and s-c crosses more resembled that bet ween different s-c species, which was also non-reciprocal. Cytoplasmic-nucl ear DNA interactions and the possibility; of embryo-endosperm imbalance cou ld both explain these results. In crosses between Primula farinosa L. (s-i diploid) and P. scotica a Hook. (s-e hexaploid), heterostylous pin tetraplo id offspring were produced. This result is discussed in relation to the gen ome of II scotica and the possibility that pin morph plants may occur in wi ld Il scotica populations. (C) 1998 The Linnean Society of London.