Distribution characteristics and marker exploitation of ESTSSRs in Medicago truncatula

New ESTSSRs markers by EST database of Medicago truncatula were developed and the distribution characteristic of ESTSSRs was analyzed. 6 688 of 285 285 EST sequences of M. truncatula from the National Center for Biotechnology Information (NCBI) were detected by SSRIT software, which accounted for 2.28%. Among them, 2 301 dinucleotide repeat elements, accounting for 34.4%, had the highest frequency and followed by 1 982 trinucleotide repeats, which accounted for 29.6% of the total ESTSSRs. The ratio of four to six nucleotide repeat elements was comparatively lower. Selecting 100 primer pairs randomly, 85 primer pairs showed clear amplification belts, accounting for 85% of designed primers and 29 primer pairs showed polymorphisms, accounting for 34.1% of primers available. Besides, 85 new M. truncatula ESTSSR markers have been developed.