Quantitative genetics generally is based on the properties of the randomly fertilized (RF) population or inbred derivatives of it. Simple hybrids and hybrid swarms do not conform to this model; and only some properties of hybrid means appear to have been available. In this paper, several genetical properties are derived, including genotype and allele frequencies, genotypic variance, broad-sense heritability, and outbreeding coecient. The earlier mean is con®rmed, and hybrid vigour is examined critically. These results make it possible to evaluate quantitatively both natural selection and forward selection (in plant breeding) from hybrids. An important ®nding is that hybrids with maximum hybrid vigour do not maximize genetic advance from forward selection, i.e. evolution is unlikely to enhance hybrid vigour. Another ®nding is that the concepts of additive genetic variance and narrow-sense heritability are inappropriate for hybrids, owing to the genetic disequilibrium inherent from their origin, and to the ephemeral nature of their population structure.
Spring establishment and herbage production of sheep's burnet (~ang~isorba mino: ssp. muricata) were compared with blf?sfoot tre~011 (Lotus corniculatus) and lucerne (Medicago sativa) at Riverside in the lower North Island of New Zealand. The trial includedbinary mixturesof sheep's burnet and the legumes. Emergence of similar swards was also investigated at Flock House, a warmer site, in the lower North Island. Emergence of the three species was similar at each site but for sheep's burnet at Flock House (66.2%), it was greater than that at Riverside (26.5%). Both legumes emerged faster than sheep's burnet with lucerne being the quickest. The results suggested that sheep's burnet is best sown alone or with other slowly emerging species. Early foliar dry weight and leaf area of sheep's burnet and lucerne were similar and greater than that of birdsfoot trefoil. However, over three summer mowings (7-8 em high), total herbage mass for all pure and mixed swards was similar and averaged 6.3 t DM/ha. Sheep's burnet provided useful ground cover and forage mass.
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