Andhra University, Department of Botany Visakhapatnam 530 003, INDIA
Pachytene pairing was studied in two induced autotetraploids (L. esculentum cv. punjab chhoara and L. cheesmanii (LA 1136)) to have an understanding on the relationship between length of the chromosome, extent of heterochromatin and frequency and localization of partner exchanges.
Although partner exchanges were predominant in the proximal regions of the chromosome in both the species, sizeable number of them were found in heterochromatin in L. esculentum cv. Punjab Chhoara and in euchromatin in L. cheesmanii. Centric exchanges were formed both by long and short chromosomes. In short chromosomes, almost all the exchanges were centric. Long chromosomes, 1, 3 and 4 and median long chromosome 5 formed partner exchanges more frequently than the short chromosomes 10, 11, and 12. However, median long chromosome 6, which is weakly heterochromatic showed lower number of partner exchanges than chromosomes 7 and 8, which indicates that in addition to the length, heterochromatin content of the chromosome played an important role in the formation of partner exchanges.
The phenomenon of secondary pairing (close orientation of homologous bivalents even when they are not involved in quadrivalent formation) was studied with reference to chromosomes 1, 2, and 6 in L. esculentum cv. Punjab Chhoara; and 2 and 6 in L. cheesmanii. While complete heterochromatic stickiness was found in majority of pmcs for chromosome 2 in the former, it was only partial or even absent in the latter.
The present results differ to some extent from those of earlier investigators in other autotetraploids of Lycopersicon species.