Supernumerary chromosomes in Alopecurus pratensis L.

Quantitative agronomic characters were studied in 10 populations of Alopecurus pratensis , and parent‐offspring relationships analysed in a northern and a southern related population in 8times8 diallel crosses, two among clones with 2n=28 (“N‐diallels”), and two among clones with 2n>28 (“U‐diallels”). Northern related populations generally gave higher fodder yield and less outwintering than southern related populations. The expected response to 10% selection for yield, based on the estimated broad sense heritabilities, varied between 10.6% and 22.4% for the four highest‐yielding populations. In the diallel analyses, general (g.c.a.) and specific (s.c.a.) combining abilities were always highly significant for plant height and spike length. However, there is a relatively stronger dominance than additive genetic effect for both characters. S.c.a. was partly significantly larger in the U‐ than in the N‐diallels, whereas g.c.a. was as a rule larger in the N‐ than in the U‐diallels. Plant height and spike length were 8.6% and 11.7% larger in the N‐diallels. It is proposed to select for normal chromosome number before one starts selection for g.c.a. in A. pratensis. And, by using high s.c.a. receptors and high g.c.a. donors for plant height (or fodder yield) in top‐crossed material, it is also suggested to take into consideration s.c.a. and reciprocal effects in this species.