He, Y.-C., Ge, J., Wei, Q., Jiang, A.-M., Gan, L., Song, Z.-J. and Cai, D.-T. 2011 Using a polyploid meiosis stability (PMeS) line as a parent improves embryo development and the seed set rate of a tetraploid rice hybrid. Can. J. Plant Sci. 91: 325-335. Polyploidy is widely accepted to play an important role in the evolution and breeding of plant species. However, a low seed set rate significantly hindered the development of polyploid rice breeding. Our results show that the seed set rate in polyploid meiosis stability (PMeS) line HN2026-4X was above 80%, but less than 40% in the other two tetraploid lines (4X indicates a tetraploid line and 2X indicates a diploid line). Furthermore, the seed set rate of Balilla-4X×HN2026-4X was also higher (67.18%) compared with that of Balilla-4X×NJ11-4X (37.26%), suggesting that the PMeS trait was transmitted to the next generation. The significantly higher seed set rate was attributed to the high pollen fertility and viability, as well as the normal meiosis of the HN2026-4X line as a male parent and also to successful embryogenesis. Investigations into embryo microstructure suggested that the embryo development pattern in Balilla-4X×HN2026-4X appeared normal at all stages, but many changes were discovered in Balilla-4X×NJ11-4X. The embryos were mainly defective at the four following stages: 1 d after pollination (DAP), 2-3 DAP, 4-5 DAP, and 10-15 DAP. The pattern of embryo developmental failure was similar in the two hybrids, but the abortive frequency in Balilla-4X×HN2026-4X was significantly lower than that of Balilla-4X×NJ11-4X at the respective stages. Additionally, aberrant fertilization, poor endosperm development, and abnormal embryo polarization also contributed to the low seed set in the hybrid of Balilla-4X×NJ11-4X. This study suggests that the PMeS line is a valuable resource, which could be used to develop tetraploid rice hybrids with superior yield.