Abstract:
Burr samples of nine strains of subterranean clover (Trifolium subterraneum L.) were collected from field sward trials at monthly intervals during the summer and autumn months and tested for hard seed content. Similar tests were carried out on burrs exposed to an artificial environment in a laboratory oven, which simulated the temperature conditions on a bare soil surface during the hot summer months in the agricultural districts of Western Australia. The maximum level of hard-seededness for all strains was achieved in the late spring or early summer soon after field maturity. There was significant variation in the maximum hard seed content of the different strains. Over the summer and autumn months the hard seed content of all strains declined in the samples from the field and the laboratory. There was considerable variability among strains in the rate and pattern of decline in hard seed content, and in the percentage of hard seed remaining in the autumn. The agronomic significance of the strain variability and the possibility of its inclusion in a breeding and selection programme are discussed.