Meiotic abnormalities in North-Eastern Himalayan (NEH) maize

Asynapsis: In two collections of Sikkim Primitive maize from Nagaland, viz., N-3 and N-4, meiotic abnormalities were observed. Chromosomes at pachytene stage in these two collections do not spread well and remain as a knot-like structure of thin chromatin surrounding nucleolus. At metaphase I, there is a complete lack of chiasma formation and all the 20 chromosomes are scattered as univalents. It was also observed that homologues always remained attached end-to-end, or a remnant of prior attachment was at least visible. In N-3 all plants studied showed this abnormality, whereas in N-4 not all plants but a few showed abnormal meiosis. Anaphase showed abnormal segregation of chromosomes. Besides laggards, micronuclei and hexads were consistently observed. Surprisingly, no seed sterility was observed in the ears of these two collections, indicating that there was normal megasporogenesis in the pistillate spikelets and that fertilization was effected only by normal pollen grains formed by 10:10 chromosome segregation during Anaphase I in PMCs. The pollen grains with abnormal chromosome number were nonfunctional, as none of the plants studied had any deviation from the normal chromosome number of 20.

Centromeric fusion: The phenomenon of centromeric fusion was consistently observed in almost all collections of maize from NEH. Fusion persisted up to diakinesis stage. In the same plant or even in the same anther different cells showed different chromosomes involved in centromeric fusion. In some cases it was also observed that a particular chromosome was more frequently involved than others. As a whole, fusion of centromeres of non-homologous chromosomes seemed to be a random event.

The fusion of centromeres of non-homologous chromosomes has no effect on the normal segregation of chromosomes belonging to the two bivalents involved, as subsequent meiotic events were completely normal.

Sudhansu Dash, J. K. S. Sachan and K. R. Sarkar
 
 

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