Studies on the Cytology and Phylogeny of South Indian Grasses

Abstract

The cytology of 57 species belonging to 21 genera of the tribe Paniceae (sub-family Panicoideae) is reported in this paper. This includes 20 species which are studied for the first time. The somatic chromosomes of 29 species have been ex-amined from root tip cells and the meiotic divisions of pollen mother cells of 42 species have been studied. The chromosomes of most of the species are small-sized and about 1μ-1.5μ in length. The basic number 9 is found in 45 species and the other basic numbers recorded are 7, 8 and 10. Chromosome numbers in multiples of 8 is encountered in two species viz. Panicum maximum (2n=32) and Urochloa panicoides (n=16). About 77 per cent of the species now studied are polyploids. Intraspecific polyploidy is found in three species viz. Brachiaria ramosa (2n=36 and 72), Setaria verticillata (2n=18 and 54) and Paspalum commersonii (2n=40 and 60). The meiotic chromosome behaviour was regular in most species, but two species of Paspalum, viz. P. conjugatum and P. commersonii showed asynapsis of chromosomes. The three tribes Paniceae, Andropogoneae and Maydeae belonging to the subfamily Panicoideae have been recognised as a natural group in the recent systems of classification of the grasses. Data on chromosome numbers observed from this study and previous reports reveal that these three tribes represent one evolutionary line. It is evident that evolution of species in these tribes is accompanied by alterations in basic chromosome numbers and polyploidy.