Although the annual system generally intercepted more light than either phase of a biennial system, heavy self-shading appeared to be a problem in the annual system, leading to a reduction in actual yield compared to the potential yield indicated by flower numbers. It is suggested that the lower yield of annual systems is partially due to leaf loss on lower fruiting laterals caused by primocane shading. The results help to explain the high yields recorded in the fruiting years of biennial systems and suggest characteristics which should be considered in future breeding programmes.