Using a polyploid meiosis stability (PMeS) line as a parent improves embryo development and the seed set rate of a tetraploid rice hybrid

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.

Heterofertilization exhibited by trifluralin-induced bicellular pollen on diploid and tetraploid maize crosses

The heterofertilization rates and fertility of trifluralin-induced bicellular pollen were investigated in maize (Zea mays L.). A diploid inbred line, Oh43 (r1/r1), and a tetraploid line, Q28-1 (r1/r1/r1/r1), were pollinated with a trifluralin treated diploid stock heterozygous for R1-scm2. The gene R1-scm2 conditions purple pigmentation in both the embryo and the aleurone layer. Heterofertilized kernels were detected as discordant kernels, i.e., yellow kernel with purple embryo or purple kernel with white embryo. The diploid–diploid crosses treated with 0.2–0.3% Trefanocide solution (0.09–0.13% trifluralin) resulted in incidences of discordant kernels (3.7–4.8%) that were significantly higher than the control (2.3%). Most of the seedlings (86%) of the discordant kernels in the 0.3% treatment were triploids or triploid-class aneuploids. In tetraploid–diploid crosses, trifluralin treatments increased the number of plump kernels on the tetraploid ears. In the 0.3% treatment, 5.2% of ovaries produced plump kernels on the ears and most of the seedlings (92%) were tetraploids or tetraploid-class aneuploids, whereas in the control, only 1.5% ovaries produced plump kernels and most of the seedlings (98%) were triploids or triploid-class aneuploids. A high rate of discordance was observed among the plump kernels both in the treated plots (36.1–48.0%) and in the control (33.3%). Consequently, almost all of the plump kernels from the tetraploid–diploid crosses were considered to be the results of heterofertilization.Key words: trifluralin-induced bicellular pollen, chromosome doubling, heterofertilization, tetraploid–diploid cross, Zea mays L.