Apomixis and sexuality in the Potentilla argentea complex I. Crosses with other species

Abstract

In crossing experiments plants from two different taxa in the Potentilla argentea group were used as pistillate parents. At first, a tetraploid aposporous biotype was used that was known to produce aberrants at a low frequency by fertilization of unreduced egg cells (BIII hybrids). In crosses with P. tabernaemontani and P. crantzii, one BIII hybrid resulted from each combination, the argentea X crantzii hybrid being, however, sublethal. The argentea X tabernaemontani hybrid seemed to reproduce only by fertilization of unreduced egg cells, leading to weak and sterile F2 offspring. The other argentea type used in the crosses was a sexual autotetraploid, derived by colchicine treatment from a facultatively apomictic biotype. It formed only BII hybrids, resulting from fertilization of reduced egg cells. Fairly vigorous F1 plants were obtained in the crosses with P. canescens, collina and intermedia. The F1 hybrids had a poor seed set, however, and in F2 sterility was the rule. The F1 hybrids were probably sexual except for P. argentea X canescens, where both apomictic (predominant) and sexual plants occurred. When crossed to P. tabernaemontani and P. crantzii, the sexual autotetraploid produced only sublethal hybrids, whereas no seed set was obtained in the cross with P. norvegica. The possible hybrid origin of some Potentilla groups is discussed as well as other problems concerning apomixis, polyploidy and hybridization. Particular consideration is given to changes in the mode of reproduction following hybridization or polyploidization. Previous work dealing with crosses in Potentilla is accounted for. 1970 Hereditas