No abstract

Gametophytic apomixis implies formation of unreduced embryo‐sacs and capacity of their egg cells for parthenogenetic development. Each of these processes, as well as their union to give matromorphous offspring, are known from several species with sexual reproduction. A comparative survey is given of meiotic modifications, occurrence of apospory, female and male parthenogenesis and aberrant endosperm formation in sexual and apomictic species. Knowledge and models concerning the genetic basis of apomictic reproduction are summarized, as well as effects upon apomixis of changes of chromosome number and of hybridization. In the author's opinion, the constituents or elements of apomixis are — with the possible exception of apospory—to a large extent quantitative traits under polygenic control.

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.

Material from localities in N. Scania, Sweden, was used in the present investigation. The chromosome number was 2n=56 in P. intermedia (as previously counted in Polish material) and 2n=70 in P. norvegica (as in many previous counts). Crossing experiments indicated pseudogamy in both species. Apomictic reproduction has been reported previously in P. intermedia, while P. norvegica has been supposed to be sexual. Embryologic studies gave evidence of obligate apospory in P. intermedia, while in P. norvegica some of the primary EMC:s undergo meiosis. In the latter species, partial sexuality is not quite excluded, although it reproduces mainly by apomixis. Meiosis on the male side is fairly irregular in P. intermedia while on the other hand P. norvegica has a quite regular bivalent formation, in spite of its high degree of polyploidy. P. intermedia is supposed to be of hybrid origin, being the result of crosses between P. argentea and P. norvegica. This remains to be proved experimentally, however, since crossing experiments between P. argentea and P. norvegica have so far failed to give any offspring.

By means of thin-layer chromatography, 1424 local varieties of barley were investigated. Two collections of Hordeum spontaneum and one of H. agriocrithon were also analysed. In H . vulgare three distinctly different flavonoid patterns were found, designated A, B and C. The B pattern could be divided into two types: B1 and Bz. The flavonoid pattern of H. spontaneum deviates sharply from those of H. vulgare. Hordeum agriocrithon has the same flavonoid pattern as the A pattern in H. vulgare. The flavonoid patterns A and B occur throughout the cultivated area of H . vulgare. However, differences in frequency between the A and B patterns were revealed when different areas were compared. Flavonoid pattern C is, with a few exceptions, found only in varieties of barley from Ethiopia. Controlled crossing experiments between the different flavonoid types of H. vulgare were performed on a limited scale. The phylogeny of H . vulgare in relation to H. spontaneum and H. agriocrithon is discussed. The flavone glycosides that constitute these differences are briefly reviewed. Sune Frcst, Institute of Genetics, S-223 62 Lund, Sweden