Apomixis and sexuality in the Potentilla argentea complex II. Crosses within the complex

Abstract

The Potentilla argentea complex is mainly built up by apomicts on various levels of ploidy. In a previous paper, the results of crosses with other species were dealt with. Here, an account is given of crosses between taxa within the argentea complex. Most crosses involved a diploid, a tetraploid and a hexaploid biotype. The first-mentioned is a facultative apomict, whereas its autotetraploid is wholly sexual. The tetraploid biotype forms aberrants at a low frequency, whereas the hexaploid seems to be entirely constant. Natural tetraploids may have originated from crosses between the more widely distributed diploid (“P. argentea”) and hexaploid (“P. neglecta”) biotypes. The F1 hybrids were in many cases vigorous but had always a reduced seed set as compared with the parents. Crosses between sexual autotetraploid and apomictic tetraploid resulted in sexual F1 plants, whereas F1 hybrids from crosses between sexual autotetraploid and hexaploid apomicts showed a varying mode of reproduction. From crosses between apomictic tetraploid and hexaploid biotypes, one pentaploid and some heptaploid hybrids were obtained. The heptaploids, resulting from fertilization of unreduced egg cells, were apomictic, although two plants with further increased chromosome numbers were found in in the offspring. The pentaploid hybrid reproduced only by fertilization of unreduced egg cells. This mode of reproduction prevailed even in the next generation, leading to the formation of weak high-polyploid plants.