Normal diploid and derived tetraploid strains of Brassica campestris were grown in alternate 6-row plots at two locations. Rows of tetraploid rape, spaced 18 inches from diploid rows, were distinctly reduced in yield of seed, oil content and seeds per pod, whereas the seed yield of the diploid was not affected by the proximity of the tetraploid. The yield of the tetraploid increased as the distance from the diploid plots increased.Pollen germination studies and controlled crosses were made within and between ploidy levels. Seven and one-half hours after pollination of 2n and 4n stigmas, n pollen had germinated and made good penetration into stylar tissue whereas pollen tubes were just emerging from 2n pollen grains. It was concluded that pollen from diploid plants had a competitive advantage over pollen from tetraploid plants.No evidence of mature triploid seeds was found on tetraploid plants exposed to n pollen or on diploid plants exposed to 2n pollen. It is suggested that if triploid embryos were formed they aborted at an early stage in development.Comparative yield of seed and oil at 13 locations showed that the derived tetraploid strains yielded less than diploid varieties. This was true despite six to eight generations of selection for seed and oil yield, following synthesis of the tetraploid, and although the strains were isolated in groups according to level of ploidy.
