Bibliography

Using bioformatics tools, we identified 646 Simple Sequence Repeats (SSRs) in silico from a unigene set of 8,577 Expressed Sequence Tags (ESTs) in cassava for the development of genic microsatellite markers. A total of 346 primer pairs were designed. Of these, 96 primer pairs were tested for polymorphism among diverse, cultivated genotypes of cassava (M. esculenta) from Africa and South America and three wild species. The cassava array comprised landraces as well as elite lines, five of which have previously been used as parents of mapping populations. Ninety percent of the primers amplified DNA fragments. Candidate EST-SSRs were analyzed on high resolution agarose gels and on ABI 3100 Genetic Analyzer. The number of alleles ranged from 1 to 8 which is lower compared to microsatellites derived from genomic sources. Approximately 80% of the microsatellites detected only one or two alleles per accession indicating a low degree of duplicated loci, a surprising finding for a highly heterozygous species such as cassava. Several markers showed cross-genus amplification across castor bean (Ricinus communis) and leafy spurge (Euphorbia esula), thus showing transferability from cassava to other taxa of the Euphorbiaceae. This study provides an in-depth view of the frequency of microsatellites in the cassava transcriptome, demonstrates the successful development of genic SSRs, and also indicates that available EST and genomic resources of leafy spurge and castor bean can be utilized for microsatellite marker development in cassava.