Competition and yield compensation in relation to breeding sugar beet

Summary

Samples were prepared to simulate the populations which would be obtained from the random interpollination of known numbers of inbred lines. This was done by mixing together seed of a vigorous and a less vigorous genotype in calculated proportions. The less vigorous represented the inbred component which would result from selling and sibbing within the constituent lines, while the more vigorous represented the hybrid fraction. The difference in yield between the two genotypes was comparable with the level of enhancement which could be expected in the hybrids as a result of heterosis. Root yields of these populations in the field suggest that depression due to the presence of inbred individuals in a synthetic variety may be predicted by a mathematical model. Yields calculated from the model to allow for various levels of compensation enabled the order of magnitude of the compensation to be estimated. However, the presence of quite small numbers of less vigorous individuals was detectable. Given the limitations imposed by the assumptions necessary to simulate these varieties, the optimal number of lines for an open-pollinated variety may be predicted.