Genetic variation in cultivated mungbean germplasm and its implication in breeding for high yield Tarika Yimram, Prakit Somta, Peerasak Srinives * Department of Agronomy, Faculty of Agriculture at Kamphaeng Saen, Kasetsart University, 1 Moo 6 Malaiman-Uthong, Kamphaeng Saen, Nakhon Pathom 73140, Thailand 1. Introduction Mungbean (Vigna radiata (L.) Wilczek) is an economically important legume crop in Asia. It is utilized in various ways where seeds and young pods are consumed as sources of protein, vitamins and minerals, while plant parts are used as fodder. Besides its rapid growth and early maturity, mungbean possesses an ability to associate with Bradyrhizobium bacteria which can fix atmospheric nitrogen (N 2 ). The crop also adapts well to various cropping systems in the tropics and subtropics. The world annual production area of mungbean is about 5.5 million ha (Weinberger, 2003), with a rate of increase of 2.5% per annum (Tomooka et al., 2005). Mungbean originated in India where its domestication is believed to have taken place (Smartt, 1990). However, mung- beans from West Asia also show high diversity (Sangsiri et al., 2007). At AVRDC-The World Vegetable Center (AVRDC), Taiwan, where the largest mungbean collection is maintained (5736 accessions in 2008), the majority of the germplasms originated from India (2705), Iran (579) and Afghanistan (281) (AVRDC, 2008). Materials from India and West Asia are important sources of genetic variation for mungbean breeding, sharing about 62% of the total germplasm collected. In general, genetic improvement of mungbean is limited to evaluation and selection from segregating progenies involving a few repeatedly used parental lines. This has resulted in relatively low genetic variability in this crop. As shown by Fernandez and Shanmugasundaram (1988), only 39 parental mungbeans were frequently used as parents in the AVRDC breeding program, and all elite breeding lines were derived from these parents. The pedigree information of 41 AVRDC breeding lines officially released by national programs in 20 countries from 1978 to 1994, as reported by Yang (1996), reveals that only 16 mungbean parents were involved (Somta and Srinives, unpublished data). To widen its genetic base, Field Crops Research 112 (2009) 260–266 ARTICLE INFO Article history: Received 5 January 2009 Received in revised form 26 March 2009 Accepted 28 March 2009 Keywords: Genetic diversity Germplasm evaluation Principal component analysis Cluster analysis Vigna radiata ABSTRACT We evaluated 9 qualitative and 21 quantitative traits in 340 diverse cultivated mungbean accessions collected at AVRDC-the World Vegetable Center, Taiwan to assess the extent and pattern of their diversity with respect to the traits measured. We also estimated broad-sense heritability (H) and expected genetic advance (GA) from selection of major quantitative traits. The germplasm displayed a wide range of diversity for most of the traits evaluated. High genetic variability, moderate to high H and GA were found in yield components, i.e. 100-seed weight, seed weight per plant, and number of pods per plant. Phenology traits such as plant height, days to flowering, and days to maturity also showed high genetic variability and H, while GA was high for plant height but relatively low for days to flowering and days to maturity. Cluster analysis grouped the germplasm into 5 major and 1 minor clusters. In general, germplasm from India and West Asia were present in all major clusters, while those from Southeast Asia and other origins were mainly grouped into one cluster. Principal component analysis revealed that the first three PCs explained 74.9% of the total variation. The variance explained by PC1 was due to the variation in almost all traits. PC2 originated principally from number of pods per plant, number of branches per plant, pod width and seed length. Two-dimensional plots of PCs revealed that mungbeans from India and West Asia were widely distributed with some overlapping, although they could be partially distinguished. Mungbeans from Southeast Asia were differentiated from those from India and West Asia. Since the mungbeans from India have been most frequently and widely employed in breeding programs, we recommend that the germplasm from West Asia be exploited more in cultivar development to enrich the breeding gene pool. The results from this experiment can help mungbean breeders choose the right combinations of parental genotypes carrying the desirable characters. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +66 34 281267; fax: +66 34 281267. E-mail address: agrpss@yahoo.com (P. Srinives). Contents lists available at ScienceDirect Field Crops Research journal homepage: www.elsevier.com/locate/fcr 0378-4290/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2009.03.013