Abstract:
Microsatellites, or simple sequence repeats (SSRs) are very useful molecular
markers for a number of plant species. They are commonly used in cultivar
identification, plant variety protection, as anchor markers in genetic mapping, and in
marker-assisted breeding. Their utility is due to their abundance, hyper variability,
and suitability for high-throughput analysis. Early development of SSRs was
hampered by the high cost of library screening and clone sequencing. Currently,
large public SSR datasets exist for many crop species, but the numbers of publicly
available, mapped SSRs for cassava are relatively low. A database mining approach
to identify SSR-containing expressed sequence tags (EST) in the IITA/Craig Venter
Institute database was utilized. The overall aim of this study was to optimize and
characterize in terms of polymorphism new EST-SSR primers that may be useful for
diversity assessments and genetic linkage mapping in cassava. Seventy primer pairs
were synthesized and used to amplify SSRs from diverse cassava DNA genotypes.
This study identified 33 (63%) useful SSRs markers which were polymorphic in a set
of 24 cassava genotypes from South America and Africa together with four parents
of a mapping population from drought tolerant and four parents of a cassava brown
streak disease (CBSD) mapping population. The polymorphic information content
(PIC) values ranges were from 0.0 to 0.7381 and average allele frequency of 2.5. The
high proportion of (63%) polymorphic EST-SSRs obtained in this work validates the
use of transcribed sequences as a source of markers. These markers will be useful for
genetic mapping, diversity assessments and genomic research.
