Genetic resources of Curcuma: diversity, characterization and utilization

The genus Curcuma (family Zingiberaceae) comprising over 80 species of rhizomatous herbs, is endowed with widespread adaptation from sea level to altitude as high as 2000 m in the Western Ghats and Himalayas. Having originated in the Indo-Malayan region, the genus is widely distributed in the tropics of Asia to Africa and Australia. Curcuma species exhibit inter- and intra-specific variation for the biologically active principles coupled with morphological variation with respect to the above-ground vegetative and floral characters as well as the below-ground rhizome features besides for curcumin, oleoresin and essential oil. Curcuma is gaining importance world over as a potential source of new drug(s) to combat a variety of ailments as the species contain molecules credited with anti-inflammatory, hypocholestraemic, choleratic, antimicrobial, insect repellent, antirheumatic, antifibrotic, antivenomous, antiviral, antidiabetic, antihepatotoxic as well as anticancerous properties. Turmeric oil is also used in aromatherapy and in the perfume industry. Though the traditional Indian Ayurvedic system of medicine and Chinese medicine long ago recognized the medicinal property of turmeric in its crude form, the last few decades have witnessed extensive research interests in the biological activity and pharmacological actions of Curcuma, especially the cultivated species. Turmeric powder obtained from rhizomes of Curcuma longa or related species is extensively used as a spice, food preservative and colouring material, in religious applications as well as a household remedy for bilary and hepatic disorders, anorexia, diabetic wounds, rheumatism and sinusitis in India, China and South-East Asia and in folk medicine. Cucuminoids, the biologically active principles from Curcuma, promise a potential role in the control of rheumatism, carcinogenesis and oxidative stress-related pathogenesis. Curcuma longa L. syn. Curcuma domestica Val., common turmeric, is the most economically valuable member of the genus having over 150,000 hectares under its cultivation in India. In addition to Curcuma longa, the other economically important species of the genus are C. aromatica, used in medicine and toiletry articles, C. kwangsiensis, C. ochrorhiza, C. pierreana, C. zedoaria, C. caesia etc. used in folk medicines of the South-East Asian nations; C. alismatifolia, C. roscoeana etc. with floricultural importance; Curcuma amada used as medicine, and in a variety of culinary preparations, pickles and salads, and C. zedoaria, C. malabarica, C. pseudomontana, C. montana, C. decipiens, C. angustifolia, C. rubescens, C. haritha, C. caulina etc. all used in arrowroot manufacturing. Crop improvement work has been attempted mainly in C. longa and to a little extent in C. amada. At present there are about 20 improved varieties of C. longa in India and one in C. amada, evolved through germplasm/clonal selection, mutation breeding or open-pollinated progeny (true turmeric seedlings) selection. Though work on morphological characterization of Curcuma species has been attempted, its molecular characterization is in a nascent stage except for some genetic fidelity studies of micropropagated plants and isozyme-based characterization. The genus has also been examined from the biochemical profiling and anatomical characterization angle. This article is intended to provide an overview of biological diversity in the genus Curcuma from a utilitarian and bio-prospection viewpoint.