Genome size and ploidy variations in pearl millet (<i>Pennisetum glaucum</i>) and napier grass (<i>Pennisetum purpureum</i>) genotypes

Abstract

Pennisetum glaucum (Pearl millet) and P. purpureum (Napier grass) are economically important members of the genus Pennisetum. The knowledge of variability in chromosome number, size and genomic content of the species could provide clues on the mechanisms responsible for decrease or increase in genomic content in the evolutionary pathway. In the present study, twenty nine genotypes consisting of 24 pearl millet and 5 Napier grass were assessed for inter- and intra-variations in chromosome number, ploidy status and genome content. Conventional cytogenetic was used for chromosome counting and flow cytometry technique for assessing genomic contents of the genotypes. Pearl millet genotypes were diploid (2n = 14) while Napier grass were mainly polyploid (2n = 28). Despite differences in the ploidy levels, the basic chromosome number was 7. The average 2C values was 4.86 pg and 4.58 pg for pearl millet and Napier grass genotypes respectively. The DNA content per haploid cell was higher among pearl millet genotypes and the genomic size were negatively related to chromosome number and ploidy levels, meanwhile, the GC richness was directly proportional to genomic size of the genotype. The mean channel values showed that the genotypes were nuclear haploid. The present study suggests that evolution and development of polyploidy was accompanied with loss in genomic content in Napier grass. It was also discovered that pearl millet with less number of chromosome, had higher genome size than Napier grass.