Division of Botany, Indian Agricultural Research Institute, New Delhi-12
In a culture of Sorghum purpureo-sericeum grown at Delhi one stunted plant which had few tillers and which set no seeds was observed. The plant was found to be highly pollen as well as seed-sterile. Cytological examination showed that it had 10 A+3 B-chromosomes and was desynaptic. At the pachytene stage, partial pairing was noticed but by diakinesis the desynapsis became much more pronounced, the average number of bivalents present at metaphase I being less than two in a large majority of cells.
In addition to desynapsis, fragmentation was also observed in nearly 50 per cent. of the cells at metaphase I. Most of the fragments were of the B11 type; it is suggested that such chromosome breakage occurred before pachytene.
Several other types of meiotic abnormalities, both at first and second meiotic divisions, were also recorded and possible explanations are suggested. As a result of these irregularities the plant was 95-98 per cent, pollen sterile as opposed to 20-25 per cent, pollen sterility found in the normal sib with 10 A+3 B-chromosomes which had a nearly normal meiosis.
The relationship between desynapsis and fragmentation is not clear though the fact that desynapsis occurs as early as pachytene suggests that fragmentation is not the immediate cause of desynapsis. The possible utility of this material in studying the factors involved in crossing-over and chiasma formation have been indicated.
