CYTOLOGICAL STUDIES OF 2N MALE GAMETE FORMATION IN THE DIPLOID NON-HEADING CHINESE CABBAGE (BRASSICA CAMPESTRIS SSP. CHINENSIS (L.) MAKINO)

One plant per line with higher frequency of 2n pollen was screened from five lines of diploid non-heading Chinese cabbage (2n=2x=20) which naturally produce 2n pollen. The diploid non-heading Chinese cabbage (2n=2x=20) can be hybridized with tetraploid male sterile line (2n=4x=40) to produce tetraploid plants, and therefore, it was used to study the cytological mechanism of unreduced gamete (n=2x=20) formation. In the meiotic study of microspore mother cells (MMCs), it was found that the first meiotic division was normal, but at the second meiotic division, parallel and tripolar spindle appeared and dyads and triads were found at the tretrad stage, which lead to the formation of 2n pollen. Therefore, the formation of 2n gamete in non-heading Chinese cabbage is due to the first division restitution. It plays important role in the sexual polyploidization breeding of non-heading Chinese cabbage.