Accessory Chromosomes and Their Meiotic Behaviour in Hybrids of Grain Sorghum and Johnson Grass
1976 Volume 41 Issue 2 Pages 193-200
Details
1976 Volume 41 Issue 2 Pages 193-200
Crosses between the grain sorghum species, S. subglabrescens (2n=20) and a diploid race of S. halepense (2n=20+4-6 B's) yielded F1s exhibiting constant and oscillating number of accessories only in the PMCs. Six hybrids showed only 4, two F1s had 4-6, in two others the accessories ranged from 6-8 and in one from 8-10. In the last hybrid, 6, 8 and 10 B chromosomes could be found in PMCs of an anther.
The size of the accessories was not appreciably large compared to the A-chromosomes and the former occurred only in pairs. They segregated independently of each other and exhibited normal separation, delayed disjunction, elimination and en-bloc movement at AI. Lagging of the B-chromosomes also occurred at AI and AII leading to their expulsion. Three B-pairs, B1, B2 and B3 could be recognised of which the former two presented configurations involving four or more chromosomes depending on their numerical strength. The presence of the B3 in all hybrids emphasises the importance of coexistence of accessories in gametes of the male parent for successful cross pollinations.
