STUDIES IN BRITISH PRIMULAS

Abstract

Crosses between three diploid species Primula veris, P. vulgaris and P. elatior show marked seed incompatibility. Crosses between the corresponding three autotetraploids give results which are closely comparable with those for the diploids. In both, reciprocal interspecific crosses always produce different and characteristic syndromes of seed development. Crosses between a diploid and its autotetraploid also show marked seed incompatibility of a similar kind. The data can be interpreted in terms of a hypothesis which assigns different genetic values to the genomes of the species and in which it is assumed that the genetic value of an autotetraploid is twice that of its diploid. The degree of seed failure can then be shown to be related to the difference in the genetic values of the paternal and maternal contributions to the tissues of the seed (embryo and endosperm). The hypothesis has been tested by making crosses between a diploid species and the autotetraploid of a different species ( P. veris 2n—P. elatior 4n), in which there are both qualitative and quantitative differences in the genetic contributions of the parents. The results agree fairly well with expectation, but not exactly. The results are discussed in the light of current theories of seed incompatibility, and suggestions for further work, both in Primula and other genera, are made.