Supernumerary chromosomes in Alopecurus pratensis L.: I. A cytological and cytogenetic study in populations and diallel crosses

摘要

Mitosis and meiosis have been studied in 10 populations of Alopecurus pratensis from Norway (Nos. 1–7), Finland (No. 8), Iceland (No. 9), and U.S.A. (No. 10), and the cytogenetic parent-offspring relationships were analysed in two diallel crosses among clones from a northern (No. 1) related population. The species A. pratensis is stated to be allotetraploid (2n=28), but some populations are supposed to be segmental auto-allotetraploid (2n28) because of a high frequency of supernumerary chromosomes. The frequency of supernumerary chromosomes and the seed production were significantly different between a northern (No. 1) and a southern (No. 7) population. Supernumerary chromosomes consisted of fragments, “B-chromosomes”, and autosomes, and a theory about their origin is suggested. In the N-I diallel among 8 clones with normal chromosome number, 13.3 % of the progenies had supernumerary chromosomes, whereas in the U-I diallel among 8 clones possessing supernumerary chromosomes, 11.6 % of the progenies had normal chromosome number. “Supernumerary chromosomes” was inherited as a quantitative character. General – (g.c.a.) and specific – (s.c.a.) combining ability, as expression for additive (D) and dominance (H) gene effects, respectively, were highly significant. Reciprocal effects were, however, significant too, and might also play a role in practical breeding programs with the species.