Cytological Studies in Some Species of Panicum

Abstract

Cytology of four species of Panicum, viz., P. antidotale, P. cymbiforme, P. decompositum and P. repens, is described here. A variety of cytological techniques was tried and a suitable technique of fixation and cytological analysis for this material is described.
The first two species with 2n=18 chromosomes behave as true diploids showing very regular cytological behaviour.
The tetraploid taxon P. decompositum (2n=36) has proved to be very interesting cytologically. The chromosomes mostly associate as bivalents. About 10 per cent of the PMC's show the persistence of nucleolus till late metaphase I. Another interesting feature of this species is the presence of pronounced, clear and consistent secondary association of bivalents both at diakinesis and metaphase I. The bivalents tend to form 9 groups indicating x=9 as being the basic number for this species. The predominantly bivalent pairing (96 per cent of the cells), conspicuous absence of quadrivalent formation and the presence of heteromorphic bivalents both at diakinesis and metaphase I indicate the allotetraploid nature of this species.
The present material of P. repens shows the presence of 36 chromosomes which tend to associate largely as bivalents. The frequency of quadrivalent formation is too low to consider this taxon as autotetraploid. The occurrence of chromosome mosaicism, univalents at diakinesis and metaphase I, and the presence of chromatin bridges at the anaphase and the telophase stages indicate structural hybridity. It appears, therefore, that the species may be a segmental allotetraploid.
The role of hybridization and polyploidy in the evolution of the species under investigation is discussed.