Abstract
The present report deals with theoretical considerations on a possible loss of vigor in an improved allogamous plant variety during a period of seve. ral generations of breeding for seed production. For instance, the seed growers of leaf- or root-vegetables in Japan usually select only a very small number of mother-plants for propagation, the selection being based on a few char.a.cteristics of commercial value, without paying any attention to the heterotic vigor. concerning either the productivity or some injury -resi, stance of the variety. Under such circumstances, it should be expected that a random drift of allelic genes or chromosomes will soon occur, resulting in a loss of heterotic vigor.
