BMC Genomics 2006, 7:245 http://www.biomedcentral.com/1471-2164/7/245 Total SSR numbers were normalized by calculating rela- tive abundance. This was calculated as the number of SSRs per Mb of sequence analyzed so that the three sequence sets of different sizes could be compared. The relative den- sity (bp/Mb) of each set of ESTs sequences was calculated by dividing the number of base pairs in the sequences (bp) contributed by each SSR by the total length of sequences examined (Mb); see Figures 1 and 2 Primer design and cross-transferability P3_in.pl and P3_out.pl perl scripts, which complement the MISA program, were adapted and used for automated selection and transfer of SSR-containing sequences from the database to the Primer3 program. Parameters used for the Primer3 program were as follows: optimal Tm of 57°C with a minimum and maximum of 50°C and 64°C respectively, and 50–75% GC content. The probability of dimer or hair-loop formation was low. The size of the PCR product is expected to be between 50 and 300 bp and no secondary structure. To search for cross-transferability between paired P. infestans-P. sojae, P. infestans- P. ramorum and P. ramorum- P. sojae, each designed primer pair from each species was compared against all the SSR-containing sequences from the other species. The EMBOSS 3.0 Primersearch utility was used for this purpose. Cross-transferability among the three species was assessed manually. In order to track all the data generated during this research, a MySQL relational database was designed and implemented. This database can be accessed at the URL listed in the references section [30] Statistical analysis A proportion test was performed to evaluate differences between variables [67]. All statistical tests were performed using Statistix 8.0. Abbreviations EST: Expressed Sequence Tag. SSR: Simple Sequence Repeat. EST-SSR: EST-derived SSR. 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