Cytogenetic Studies of Plasmodial Sporocytes, Chromatin Disintegration, Desynapsis and Centromere Breakage in Pearl Millet.

Abstract

In pearl millet (Pennisetum americanum (L.) Leeke, n=7), in the selfed progenies of a line L. S. 326-3, a mutant with plasmodial sporocyte (syncyte) formation, chromatin disintegration, desynapsis and centromere breakage was identified and its cytogenetic features were studied. Two to 24-nucleate syncytes were formed due to suppression of cytokinesis during premeiotic mitoses. In syncytes, chromatin degeneration occurred from prepachytene to telophase I stages, thereafter only masses of empty cytoplasm were found. In uninucleate PMCs, chromatin extruded in prepachytene stages in some, degenerated upto diakinesis in several, and either bivalents or univalents (ranging from 1 to 14) were formed in the rest. Centric misdivision leading to telocentric chromosomes (ranging from 2 to 14 per cell) occurred in a proportion of PMCs at anaphase I. There was high sterility of male and female gametes.F2 and test cross progenies of mutant X normal segregated respectively to 9:3:3:1 and 1:1:1:1 ratios of (i) completely normal meiotic behaviour, (ii) syncyte formation and chromatin disintegration but without desynapsis and centromere breakage, (iii) desynapsis and centromere breakage but without syncyte formation and chromatin disintegration and (iv) meiotic behaviour like the original mutant. Crosses between the recombinants (ii) and (iii) above yielded progeny with completely normal cytological behaviour. The original mutant thus was a double mutant. The genes were designated as snd (syncyte formation and chromatin disintegration) and ds cb (desynapsis and centromere breakage).