Ecophysiological study of Centella asiatica (Linn.) Urban of Nepal

Abstract

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Centella asiatica (L.) Urban, commonly known as Indian Pennywort, is an important ethnomedicinal plant of tropical to subtropical region. It is a clonal perennial herb with a wide range of enthomedicinal uses such as blood purifier, memory enhancer, anticancer, antidepressive etc. Distribution pattern, abundance, life history traits, leaf nitrogen content, genetic diversity of population, and quantification of eight secondary metabolites of 21 populations of Centella asiatica from different habitats and regions of Nepal were studied. Effects of different environmental factors (moisture, soil texture, light and shading) and integrated manuring on growth traits and yield of C. asiatica were determined in pot-grown plants treated under randomized block design. Centella asiatica grows in a wide range of habitats from shady grassland, open grassland, to open agricultural land in tropical to temperate area in Nepal. In terms of density and plant biomass, partially shaded grassland was the most suitable natural habitat for C. asiatica. Density and biomass yields varied significantly with habitat types, with mean value of 72.53 pl/m 2 and 37.95 g/m 2 , respectively. The flowering peak was recorded in April-June and it little varies in different habitats. The freshly collected seeds had the highest viability which declined progressively as the duration of storage increased. Pretreatment like soaking seeds with GA 3 prior to sowing reduced the time required for initiation of germination. Seed germination of C. asiatica was affected adversely by salinity. Aqueous extract of some invasive plants viz. Chromolaena odorata, Parthenium hysterophorus, Ageratum conyzoides and Xanthium strumarium had inhibitory effects on germination, which threaten the population density of C. asiatica in nature. The pot experiment with different moisture levels (125% FWC (surplus water), 100% FWC, 70% FWC and 30% FWC) showed that the dry matter production and yield in Centella asiatica was highest in 100% FWC, followed by 70% due to higher growth characteristics such as number of primary branches, leaves, and leaf chlorophyll contents. Growth under four levels of shade (0, 30, 50 and 70%) showed that dry matter production and yield was significantly higher in 30% shade, followed by 50 %. Asiatic acid was significantly higher in 70% shading. There was no significant effect of shading on other measured secondary metabolites. Growth traits and yield of C. viii

asiatica was significantly higher in sandy loam soil than clay-loam and pure sand. All measured secondary metabolites were significantly higher in sand than in clay-loam and sandy loam. The pot experiment with different integrated manuring conditions (Urea: FYM, 100:0; 75:25; 50:50; 25:75; 0:100; and control - no manure) showed higher yield and better growth traits of Centella asiatica in integrated manuring .

Concentration of all secondary metabolites measured in present study was significantly higher in open agricultural land than in shady and open grasslands. Mean concentration of asiaticoside, the most important bioactive component of C. asiatica, was 1.8% (dw). Concentration of secondary metabolites was higher in samples from central Nepal than western and eastern Nepal. Asiaticoside content was inversely related with the altitude of samples collected. Asiaticoside content was higher in samples collected from 150600 m asl. Thus, a negative correlation was observed between altitude and asiaticoside

content while the opposite was for quercetin-3-O- glucuronide content. Concentration

of secondary metabolites was higher in wild than in transplanted samples. Essential oil

yield of Centella asiatica from different habitats ranged from 0.10 (open grassland) to

0.12% (shady grassland). Total yield of essential oil was higher in samples from

partially shaded habitat, but concentration of major components was higher in open

agricultural land.

Genetic diversity study of 21 different populations of Centella asiatica was carried out by morphological and molecular marker (RAPD). Morphological characters were significantly different among 21 populations. Two distinct morpho-types of Centella asiatica were clearly distinguished in dendrogram based on morphology; one with small leaves, dentate to serrate margin, and creeping form, and the other with large leaves, crenate to entire margin, and erect form. Molecular marker data showed similarity coefficient from 0.52-0.91 among the population indicating a moderate diversity of C. asiatica in Nepal. In conclusion, morphology, genetic character and active phytochemicals in Centella asiatica at different habitats and ecological regions of Nepal varied. Transplanted samples had lower amount of secondary metabolites than in wild samples.

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