Effect of the Number of Parents on the Mean and Variance of Synthetic Varieties1

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Abstract
The effect of the number of parents per synthetic on the mean and variance of synthetic varieties was studied for diploid and autotetraploid species. The mean of synthetics with a small number of parents each will usually be less than the mean of the source population from which the parents were chosen, and the mean of the synthetics approaches the mean of the source population as the number of parents per synthetic increases. The genetic variance among the means of the synthetics decreases as the number of parents per synthetic increases, and the decrease is more rapid for the nonadditive than the additive portion.The findings indicated the following: (1) Selection among experimental hybrids or synthetics utilizes genetic variance more efficiently when the number of parents per experimental variety is small. (2) Hybrids make slightly more efficient use of nonadditive genetic variance than synthetics with a comparable number of parents, and most of the advantage of hybrids would be lost with one generation of seed increase. (3) Most of the progress in development of medium to broad‐based synthetics results from selection of the parents and very little additional gain would be expected from selection among medium to broad based combinations of the selected parents.

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