Karyological relationships in Indian species of Drimia based on fluorescent chromosome banding and nuclear DNA amount.

The genus Drimia (syn. Urginea), commonly called squill, represents a species complex, infrageneric delimitation being ill-defined due to morphological variability, population variation within species and polyploidy. In the present study, fluorescent chromosome banding and measurements of nuclear DNA content by flow cytometry were performed in five Indian species of Drimia: Drimia indica, Drimia polyantha, Drimia razii, Drimia wightii and Drimia coromandeliana to elucidate taxonomic relationship and obtain possible insights into the evolutionary processes within this group. All taxa analyzed exhibited similar karyomorphology with subtle differences accounted by nucleolar chromosomes. Nuclear DNA content ranged from 20.41 pg/2C in D. polyantha to 40.80 pg/2C in D. coromandeliana and was positively correlated with chromosome number (r = 0.67, P = 0.02) and total diploid chromatin length (r = 0.59, P = 0.06). Fluorescent chromosome banding revealed the presence of CMA(+ve)/DAPI(-ve) signals associated with nucleolar chromosomes presumably coincident with NOR in all species and unique CMA(+ve) signals in diploid populations of D. indica. Satellite polymorphism between homologous NOR-bearing chromosomes was observed which supports hybrid origin of the taxon. UPGMA dendrogram and scatter diagrams based on karyological parameters indicated a close relationship of D. indica, D. razii and D. polyantha while D. wightii and D. coromandeliana appeared distant. D. wightii appeared more close to D. indica than to all other species based on genome size and karyomorphology. As a whole, D. indica showed high intra-specific variability with populations exhibiting intergrading characters with other species. In conclusion, it is likely that hybridization followed by reproductive isolation of polymorphic forms arising by adaptation to different ecological niches resulted in species diversification of Drimia in India, probably from a common ancestor similar to D. indica.

An improved method of genome size estimation by flow cytometry in five mucilaginous species of Hyacinthaceae.

The family Hyacinthaceae constitutes about 900 species of bulbous geophytes usually characterized by high mucilage content. Taxonomic delimitation of Hyacinthaceae has been controversial since the time of Linnaeus due to the absence of reliable discriminating characters. Pattern of genome size variation can thus be considered as an added character to aid intergeneric and intrageneric relationship of the group. However, reports on genome size estimation by flow cytometric analysis of these plants are rare due to the presence of mucilage, which causes problem with nuclei sample preparation. To overcome this problem five reported nuclei isolation buffers were tested in Drimia indica of which Galbraith's buffer gave comparatively better results and was further modified by increasing pH, detergent concentration, and replacing sodium citrate by citric acid. The modified buffer enabled better sample preparation with increased yield, lesser debris, and improved DNA peak CV. The standardized buffer was used to estimate the 2C values of Drimia indica, Drimia nagarjunae, Drimia wightii, Drimia coromandeliana, and Ledebouria revoluta for the first time by flow cytometric analysis. This study also opens up the scope for further improvement in sample preparation for flow cytometric analysis of mucilaginous plants, which is otherwise problematic due to nuclei clumping and increased viscosity of sample.