The Self-Incompatibility System in Ranunculus Repens (Ranunculaceae)

Abstract

The investigated material consists of 11 original plants collected in the neighbourhood of Lund; four I1 families, totalling 18 plants (range 3–8 plants); four F1 families, totalling 52 plants (range 10–18 plants); and four backcross families, totalling 311 plants (range 60–87 plants). Self-incompatibility prevailed both in original and in inbred and crossbred plants, as judged from seed-setting data in situ under greenhouse conditions. Of the intercrosses (no complete diallels) among I1 and F1 siblings, 13.8% and 0%, respectively, were judged to be incompatible. Parental plants pollinated by backcross families (P × BC, 308 combinations tried) had 4.2 % cases of cross-incompatibility. Calculations were applied to these data, aiming at minimum degrees of cross-incompatibility to be expected in different intercrosses at different numbers of S-loci, considering (1) pure disomic inheritance, (2) an autotetraploid with chromosome or (3) random chromatid assortment, (4) an amphidiploid with two S-gene systems brought together, acting independently of one another, or (5) interdependently, with functional incompatibility specificities being formed through interaction not only within but also between the two systems. It was concluded that the data indicate an S-gene system with disomic inheritance of one team of at least 4 loci with complementary cooperation. To explain the presence of such an S-gene system in a tetraploid, it is speculated that self-incompatibility genes on a polysomic level are accompanied by too high degrees of cross-incompatibility to be retained in the long run and have gradually to adopt disomic formation of incompatibility specificities.