Mining EST-Derived SSR Markers to Assess Genetic Diversity in Cassava (Manihot esculenta Crantz)
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Cassava (Manihot esculenta Crantz) is a very important staple and industrial crop in tropical and subtropical regions of the world. The paucity of markers is a serious limitation in marker-assisted breeding. A total of 35,992 expressed sequence tags (ESTs) from cassava, which were clustered in 13,173 unigenes, were used in this study. A total of 1,889 microsatellites were identified, with an average density of one simple sequence repeats (SSRs) every 4.40 kb. Of the 1,058 designed EST-SSRs from cultivars SC06, TMS60444, and W14, 431 were polymorphic. Then, 31 randomly selected EST-SSRs from the 431 polymorphic EST-SSRs were used to evaluate the genetic diversity of 76 cassava accessions. A total of 93 alleles were identified, and the number detected for each EST-SSR ranged from one to four. Based on the 93 alleles, the 76 cassava accessions could be classified into six groups, and the genetic similarity coefficient ranged from 0.55 to 0.94. This study demonstrated the potential of EST-derived SSRs in cassava. The resources developed in this study enriched the available molecular markers for cassava.
KeywordsDNA markers Microsatellite Cassava EST-SSR
This work was supported by the National Key Technology R & D Program (Pre 973) No. 2006CB708204. The authors wish to thank M. Ishitani, J. Tohme, M. Fregene, and other researchers from GeneTrop for their involvement in the development of the cassava EST database. We also thank Dr Bin Liu and F. Claude for their valuable comments on the manuscript.
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