Genetic and chemo-divergence in eighteen core collection of Zingiber officinale from North-West Himalayas

Highlights

• High molecular diversity was observed among North Western Himalayan Ginger population.

• Both molecular & oil based classification produced geographically concordant groupings.

• Hierarchical classification identified two distinct germplasm based on oil & molecular assessment.

• Potential role of microclimate in ascertaining essential oil chemistry.

Abstract

Eighteen Zingiber officinale germplasm, collected from North-Western Himalayan region and showing significant differences in morphology and aroma, were characterized both chemically and genetically. Molecular analyses employing ISSR, SSR and IRAP techniques revealed moderate to high variations in clonally propagated ginger crop. ISSR analysis showed primers ISSR 4 and 8, having 9 polymorphic loci each, exhibiting 100% polymorphism while in SSR and IRAP primers RM153, RM278 and primer combinations of RT6 with RT3, RT4 and RT7, respectively showed 100% polymorphism. Essential oil evaluation revealed 31 major components based on GC analysis of hydro-distilled volatile oil extracted from rhizome of the collected population. Pair-wise Euclidean dissimilarity distance ranged from 3.37 to 16.93 revealing moderate variation in oil profile. The multivariate analyses of the oil based data could explain 99.9% of cumulative variation. Hierarchical analyses of molecular and oil profiles, grouped all the 18 genotypes into two major clusters, clearly distinguishing two germplasm (161 and 179) genetically and chemically both. The study also revealed two genetically similar germplasm from Theri (146 and 147) based on all the three techniques. This distinctness in oil and molecular profiling of the germplasm points towards distinct genotypes from different regions of North Western Himalayas. Further, ISSR profiling and essential oil array based classification produced geographically concordant groupings. The study revealed existence of moderate diversity in the unexplored North Western Himalayas.

Introduction

Zingiberaceae family harbors many commercially important plants including Zingiber officinale (Ginger). Rhizome of the plant is used as spice, flavorant and herbal medicine for anti-emetic, antipyretic and hypotensive effects, since ancient time (Govindarajan, 1982). Due to its universal appeal and adaptability, ginger is cultivated in most tropical and subtropical countries (Ravindran and Nirmal, 2005). According to WHO, India is among the largest cultivator and exporter of ginger and ginger derived product globally, occupying 50% of world market in terms of ginger oil and oleoresin (WHO, 1999). The crop is grown throughout India from temperate hilly regions to subtropical wet areas. Cultivation is mostly based on developed varieties and cultivars or landraces selected by farmers over time, which are well adapted to local needs and prevailing environmental conditions. Most of these germplasm are grown by farmers over small marginal areas generally for self or local consumptions (Govindarajan, 1982, Ravindran and Nirmal, 2005).

Beside uses in medicine, ginger rhizome is the source of essential oil which is valued for its pleasant aroma ranging from sweet, warm to camphoraceous or citrus-like depending on the relative essential oil constituents which decide the quality and industrial usage of the oil (Gupta et al., 2011). Literature survey revealed hydro-distilled volatile oil of ginger is a combination of monoterpenes, oxygenated monoterpenes and sesquiterpenes, whose relative proportion depends on genotype and influenced by geographical locations (Sharma et al., 2002, Raina et al., 2005). In India, the oil obtained from the southern part of country is rich in sesquiterpenes and oxygenated sesquiterpenes whereas that from Northern India has more of oxygenated monoterpenes (Figueiredo et al., 2008, Gupta et al., 2011). Since environmental factors, in addition to genetic variation influence phyto-chemical profile, the chemical and molecular characterization becomes necessary for proper characterization of a medicinal plant.

Polymerase Chain Reaction (PCR) based techniques provide a simple, useful and definite method of molecular characterization, in contrast to chemical and morphological markers which are unreliable and affected by the environmental factors. These markers are reproducible, robust, polymorphic, dominant/co-dominant and unaffected by age thereby lowering the cost, time and labor for analyses (Zietkiewicz et al., 1994, Kalender et al., 1999). Molecular characterization using various molecular markers (ISSR, SSR, IRAP) have been successfully used in estimating the extent of genetic diversity at inter/intra-specific and varietal levels of a number of species in a wide range of crop from angiosperm (Joshi et al., 2000, Charters and Wilkinson, 2000, Charles et al., 2008) to gymnosperms (Yong et al., 2003). They have been also utilized in assessing genetic variation either specifically in Zingiber or more general in Zingiberaceae family (Jatoi et al., 2008, Kizhakkayil and Sasikumar, 2010). However, most of the earlier work published included genotypes from East Asian countries with medium to low genetic diversity.

Despite immense commercial importance of the crop, studies pertaining to essential oil variation and molecular genotyping of this clonally propagated crop are sparse (Jiang et al., 2006, Kavyashree, 2008) and no study pertaining to chemical-genetic relationship have been documented on germplasm utilized/available in North-Western parts of India. In the present study, ginger rhizome was collected from seven locations of North Western Himalayan India, which were being cultivated by the farmers of the two states. They are best adapted to the local climate and grown for local needs of the area. These germplasm were selected on the basis of differences in rhizome color, size and aroma. Genetic study was performed using three molecular marker techniques ISSR, SSR and IRAP and investigation was further extended to rhizome essential oil analysis to determine the variation in essential oil components.