The interrelation of burr burial, seed yield and dormancy in strains of subterranean clover

Prevention of burr burial drastically reduced the yield of viable seed in subterranean clover. This occurred through reductions in total burr number, number of mature burrs, number of seeds per burr, individual seed weight and seed viability. Strains differed markedly in their ability to produce seed in unburied burrs. A simple selection criterion based on changes in individual seed weight was proposed as a guide to screening for this character. When this criterion was applied to a wide range of strains, it appeared that later-maturing types were the most capable at producing seed in unburied burrs. The initial level of hardseededness was lower in seed from unburied burrs; also the rate of breakdown of hardseededness was faster in this seed, although the size of the effect varied between strains. Defoliation during the flowering period increased the initial level of hardseededness in seed from both buried and unburied burrs. Seed produced in buried burrs generally had a faster rate of breakdown of embryo dormancy than seed from unburied burrs, although the response varied between strains. The implications of these findings for future breeding and improvement in subterranean clover are discussed.