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 ( 9 1 1 1 hybrids). In crosses with P. tabernaemontani and P. crantzii, one 9 1 1 1 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 9 1 1 hybrids, resulting from fertilization of reduced egg cells. Fairly vigorous F1 plants were obtained in the crosses with P. canescens, collina and intermedia. The F, hybrids had a poor seed set, however, and in Fz 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.

Reproductive differentiation into sexual and apomictic polyploid cytotypes in Potentilla puberula (Potentilleae, Rosaceae)

“…On the one hand, high degrees of apomixis were observed in numerous embryological studies (e.g. Rutishauser, 1943 a ; Smith, 1963 a ; Asker, 1970 b ), progeny surveys (Müntzing, 1928; Holm and Ghatnekar, 1996 a ) and an FCSS-based study (Dobeš et al , 2013). On the other hand, sexual reproduction but no or only marginal frequencies of apomixis were detected based on segregation patterns of isozyme markers and FCSS in individuals of P. argentea (Holm et al , 1997) and other Potentilla species (Dobeš et al , 2013), respectively.…”

“…apomeiosis and parthenogenetic origin of embryos) have been documented in at least 16 species (Gentscheff, 1938; Gustafsson, 1947; Löve, 1954; Asker, 1970 a ), while sexual reproduction was claimed for five species based on embryological evidence (Rutishauser, 1945; Håkansson, 1946; Czapik, 1961, 1962 a ). In order to initiate seed formation, in all Potentilla species including apomicts functional pollen is needed to fertilize the endosperm (Asker, 1970 b ), which usually receives a bi-nucleate female contribution (Dobeš et al. , 2013).…”

Prospects and limits of the flow cytometric seed screen – insights from Potentilla sensu lato (Potentilleae, Rosaceae)

“…Embryo sacs are usually eight-nucleate, as is commonly the case in angiosperms (Rutishauser, 1967), but a five-nucleate embryo sac has also been recorded (Eriksen & Fredrikson, 2000). In contrast to female gametogenesis, pollen is almost exclusively reduced because of regular meiosis (Müntzing, 1928; Rutishauser, 1943; Asker, 1970b, 1985). In all documented cases functional pollen is needed to initiate seed formation in both sexual species and apomicts, suggesting the general occurrence of pseudogamy in Potentilla (Asker, 1970b).…”

“…In contrast to female gametogenesis, pollen is almost exclusively reduced because of regular meiosis (Müntzing, 1928; Rutishauser, 1943; Asker, 1970b, 1985). In all documented cases functional pollen is needed to initiate seed formation in both sexual species and apomicts, suggesting the general occurrence of pseudogamy in Potentilla (Asker, 1970b). However, evidence for the role of pollen in seed production comes mainly from controlled crosses (e.g.…”

“…However, evidence for the role of pollen in seed production comes mainly from controlled crosses (e.g. Müntzing, 1928; Asker, 1970a,b). …”