Extraordinarily polymorphic ribosomal DNA in wild and cultivated rice
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Extraordinarily polymorphic ribosomal DNA in wild and cultivated rice Liu, K. D., G. P. Yang, S. H. Zhu, Q. Zhang, X. M. Wang and M. A. Saghai Maroof. 1996. Genome 39:1109-1116. ABSTRACT A sample of 481 rice accessions was surveyed for ribosomal DNA (rDNA) intergenic spacer length polymorphism to assess the extent of genetic diversity in Chinese rice germplasm. The materials included 83 accessions of the common wild rice mostly from China, 348 entries of cultivated rice representing almost all the rice growing areas in China, and 50 cultivars from South and East Asia for comparison. A total of 42 spacer length variants (slvs) were detected. To our knowledge, this is the largest number of rDNA slvs ever detected in a plant species. These slvs comprised a step-ladder series with the sizes of steps being extremely heterogeneous ranging from ca.21 to 311 bp. Eighty rDNA phenotypes were formed of the 42 slvs. Wild rice has much greater number of rDNA slvs than cultivated rice, while cultivated rice showed a larger number of rDNA phenotypes than wild rice. Indica and japonica groups contained about equal number of slvs. But the slv distribution was significantly differentiated: indica rice was preferentially associated with longer slvs, and japonica with shorter ones. The results may have significant implications regarding the origin and evolution of cultivated rice as well as the inheritance and molecular evolution of rDNA intergenic spacer in rice. Key words rDNA, Oryza rufipogon, O. sativa, germplasm diversity, evolution.