Variation in rice landraces adapted to the lowlands and hills in Nepal R. C. Sharma*, N. K. Chaudhary, B. Ojha, L. Yadav, M. P. Pandey and S. M. Shrestha Institute of Agriculture and Animal Science, Rampur, Chitwan, Nepal Received 17 September 2005; Accepted 9 October 2006 Abstract The landraces of rice (Oryza sativa L.) possess wide diversity, which needs to be properly characterized for their use in genetic improvement. Replicated field studies were conducted in 1998, 1999 and 2000 at two sites in Nepal to determine diversity in 183 landraces of rice adapted to the lowlands and the hills in Nepal. Fourteen improved genotypes were also used for comparison. Thirteen agronomic traits were investigated. Shannon– Weaver diversity index (H) and Simpson’s index of diversity (D) were estimated to determine the level of gen- etic richness among the landraces. The landraces differed significantly for all traits. Except for plant height and maturity, at least one of the landraces compared well with the performance of improved cultivars. A principal component analysis separated the lowland- and hill-adapted landraces into two broad groups. Keywords: genetic diversity; landraces; Nepal; Oryza sativa; rice Introduction Rice (Oryza sativa L.) is cultivated across diverse agrocli- matic environments in five out of the six continents (Lu and Chang, 1980). Rice genotypes are classified pri- marily into the subspecies indica and japonica (Oka, 1958). The indica type comprises primarily tropical low- land genotypes, while the vast majority of cultivars grown in temperate regions are of the japonica type. The japonica type is also cultivated in high elevation and dryland areas of the tropics (Glaszmann and Arraudeau, 1986). The agroecosystem in Nepal is diverse because altitude ranges from 60 m above sea level (asl) in the southern plains to above 8800 m asl in the Himalaya, within a north – south stretch of , 230 km. The country is broadly divided into lowlands, foothills including valleys, mid- hills, high hills and mountains. Rice is grown in flatland, hills and high mountains from 60 to 3000 m asl (White- man, 1985; Nagamine, 1992; Gauchan et al., 2003; Bajra- charya et al., 2006). Diverse and agronomically useful wild rice genotypes have been found (Suh et al., 1997; Lu, 1999), and the diversity of Nepalese rice is reflected by a large collection of landraces and several wild rice species (Gauchan et al., 2003; IRRI, 2005). However, passport data for these landraces are limited, and as a result, they have contributed little to national and inter- national rice improvement. However, many landraces are still grown commercially for their traditional uses and desirable characters (Chaudhary et al., 2004). Pre- mium prices can be paid for special traits such as fineness of grain, cooking quality, taste and aroma (Gauchan et al., 2005). A few landraces show tolerance to water-submerg- ence and chilling (Sthapit et al., 1995; Sthapit and Wit- combe, 1998), as well as disease resistance (Karki, 1989; Sthapit et al., 1995). In some areas a combination of landraces and modern rice cultivars is grown, whereas in certain remote dis- tricts, exclusively landraces are cultivated (Gauchan et al., 2005). The success in breeding improved rice cul- tivars since the 1960 s has helped increase rice pro- duction, but has led to the replacement of a large number of landraces by a small number of improved cul- tivars. Thus a gradual but continuous loss of genetic diversity is affecting the viability of rice landraces in * Corresponding author: E-mail: rsharma@ecomail.com.np q NIAB 2007 ISSN 1479-2621 Plant Genetic Resources: Characterization and Utilization 5(3); 120–127 DOI: 10.1017/S1479262107837828