Abstract:

Sorghum (Sorghum bicolor L. Moench) is one of the most important food crops in the world, and it is also one of the earliest crops, which the heterosis has been commercially used due to the discovery and utilization of cytoplasmic sterility (CMS). There are seven types of CMS in sorghum, including A₁, A₂, A₃, A₄, A₅, A₆, and 9E. In this study, A₆ cytplasmic male sterile line A₆ Tx398 and its isogonic maintainer line B₆ Tx398 were used to observe and analyze the chromosomal behaviors of A₆ CMS during the microsporic meiosis. Compared with maintainer line B₆ Tx398, the abnormal chromosomal behaviors were not observed under biologic photomicroscope until the diplotene in prophase I. From then on to the tetrad formation, various abnormal chromosomal behaviors were found within the pollen mother cells (PMCs): compared with its B₆ line in most of the PMCs in prophase I, the number of homologous chromosomes was twice (2n=40) that of its isogenic line (2n=20), i.e. 20 pairs of homologs in a cell. In anaphase I, some homologs became lagged or even not divided and stayed near the equatorial plane. Cytoplasm of most PMCs did not divide to form a dyad in telophase II, so that in prophase II 40 sister chromosomes presented in a cell, which were arranged ring-like,  dispersed or X-like. In telophase II, two, three or four chromosomal groups were found in a cell. Some PMCs divided into triad other than tetrad with unequal number of chromosomes in each monad. The disorders of chromosomal behaviors during the pollen mother cell meiosis of A₆ CMS made the incompletion of the normal meiotic process, leading to the abortion of microsporogenesis and development.

Key words: Sorghum, CMS, Meiosis, Chromosomal behaviors