CHROMOSOME MORPHOLOGY IN CYNODON DACTYLON (L.) PERS.

Abstract

The pachytene bivalents of the tetraploid Cynodon dactylon var. dactylon could all be identified on the basis of characteristic morphological features including knobs, prominent chromomeres, chromosome length, long arm length, short arm length, arm ratio and relative length. The bivalents could be separated into two sets of chromosomes, D and D', with the D genome being homologous to that found in the diploids, C. dactylon vars. aridus and afghanicus. The two sets are homoeologous as shown by the occasional formation of quadrivalents and the closeness of chromosome measurements, although chromomere patterns and knobs differed. C. dactylon var. dactylon therefore appears to be a segmental allotetraploid. In prophase somatic spreads of var. dactylon two sets of chromosomes could also be separated by heterochromatic patterns. In both the diploids, vars. aridus and afghanicus, and the tetraploid the somatic chromosomes could be homologised with their corresponding pachytene bivalents. The chromosomes were of different relative lengths during the two phases. A polyhaploid obtained from a twin seedling of C. dactylon var. dactylon showed both univalents and bivalents in a diplotene spread, supporting a segmental allopolyploid origin of var. dactylon. This plant reverted back to a tetraploid state before further studies could be made. Giemsa C-banding, using barium hydroxide at room temperature for 50 minutes and 2xSSC at 60°C for 30 minutes to pretreat the slides before staining, produced telomeric bands in the position of the knobs seen in standard acetocarmine squash.