Friday, March 11, 2011

PhD Thesis: Intraspecific variations in Andrographis paniculata Nees

Abstract: For the biodiversity- rich developing countries in the tropics, chemical and genetic prospecting of their plant genetic resources is a priority area not only to fish out genotypes/molecules of potential economic importance but also to add value to them. The present study essentially directed towards this objective, involves analysis of intraspecific variations in Andrographis paniculata Nees [കിരിയാത്ത്] (Acanthaceae), an important medicinal plant of India, presumably having its centre of origin and diversity in southern India and Sri Lanka. Specifically, the study is directed to: (i) elucidate biology of A. paniculata by understanding distribution, habitat, phenology of flowering/fruiting, cytology, breeding system and seed dormancy/ germination of the species; (ii) quantify the amount of genetic variability within A. paniculata and its patterns of interpopulation differentiation; (iii) assess the significance of inbreeding and gene flow to the level and pattern of diversity presently observed in A. paniculata; (iv) test the hypothesis that genetic distance can be significantly correlated with geographical distance; (v) identify superior genotype(s) with increased biomass and product (andrographolide) synthesis; and (vi) suggest conservation and utilization/improvement strategy for the species based on the data generated. Studies on biology of the species revealed that the plant is naturally self-pollinating, but possibility for cross-pollination could not be entirely ruled out. Intraspecific variation of A. paniculata was analysed using quantitative traits, isozyme and random amplified polymorphic DNA (RAPD) markers. The three approaches differed in the amount of variation detected. Analysis of the ten morphological characters revealed considerable diversity at inter-population level. Variation in the active principle (andrographolide) content was moderate with maximum concentration on dry weight basis (1.47%) was recorded in a population from Tamil Nadu (AP36) with a mean value of 0.95%. Product concentration did not correlate with allelic variations in any of the populations but AP36, with the highest concentration (in the leaves) averaged through three generations may help development of a cultivar.

RAPD assay revealed the highest polymorphism among the three markers tested. Twentyfive random primers generated an average of 1.61 bands (alleles) per primer (locus) with a mean polymorphism of 0.71. Isozymes on the other hand were analysed at 15 loci representing 8 enzyme systems. On an average the mean observed number of alleles per locus was 1.37 and the proportion of polymorphic loci was 0.32. Genetic differentiation estimated by Nei's distances suggested a common gene pool for the populations collected from Kerala while those from Tamil Nadu and elsewhere from India revealed more divergence. More or less, exotic populations exhibited similarity to Tamil Nadu populations which may shed light on their origin. In general, the genetic clustering derived from isozyme and RAPD data was in agreement with the geographical locations/distances. Further analysis of the two natural populations (Sirumalai and Nallamalai) collected from geographically isolated areas using Nei's distance and fixation indices indicated substantial divergence at the sub population level. This pointed out varied drift and bottleneck effects and differential gene flow between them. Local isolation, either natural or artificial, also promotes divergence of the populations. Further more, the within- populations diversity was significantly different between populations, indicating that evolutionary potential is not evenly distributed amongst populations. Regarding conservation of representative populations of A. paniculata, caution must be exercised due to sizeable differentiation at the local and withinpopulation levels. For practical conservation purpose and maintenance of maximum genetic variation within existing populations, outright collection of all the plants before seed set in a given locality by the local plant collectors should be discouraged.

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