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We used an in silico approach to survey and compare microsatellites in transcript sequences of four sequenced members of genus Fusarium. G + C content of transcripts was found to be positively correlated with the frequency of SSRs. Our analysis revealed that, in all the four transcript sequences studied, the occurrence, relative abundance and density of microsatellites varied and was not influenced by transcript sizes. No correlation between relative abundance and transcript sizes was observed. The relative abundance and density of microsatellites were highest in the transcripts of Fusarium solani when compared with F. graminearum, F. verticillioides and F. oxysporum. The maximum frequency of SSRs among all four sequence sets was of trinucleotide repeats (67.8%), whereas the dinucleotide repeat represents <1%. Among all classes of repeats, 36.5% motifs were found conserved within Fusarium species. In order to study polymorphism within Fusarium isolates, 11 polymorphic genic-SSR markers were developed. Of the 11 markers, 5 were from F. oxysporum and remaining 6 belongs to F. solani. SSR markers from F. oxysporum were found to be more polymorphic (38%) as compared to F. solani (26%). Eleven polymorphic markers obtained in this study clearly demonstrate the utility of newly developed SSR markers in establishing genetic relationships among different isolates of Fusarium. [ABSTRACT FROM AUTHOR]

Fusarium oxysporum is a ubiquitous species complex of soil-borne plant pathogens comprising of many different formae speciales, each characterized by a high degree of host specificity. In the present investigation, we surveyed microsatellites in the available express sequence tags and transcript sequences of three formae speciales of F. oxysporum viz. melonis ( Fom), cucumerium ( Foc), and lycopersici ( Fol). The relative abundance and density of microsatellites were higher in Fom when compared with Foc and Fol. Thirty microsatellite primers were designed, ten from each forma specialis, for genetic characterization of F. oxysporum isolates belonging to five formae speciales. Of the 30 primers, only 14 showed amplification. A total of 28 alleles were amplified by 14 primers with an average of two alleles per marker. Eight markers showed 100% polymorphism. The markers were found to be more polymorphic (47%) in Fol as compared to Fom and Foc; however, polymorphic information content was the maximum (0.899) in Foc SSR-3. Nine polymorphic markers obtained in this study clearly demonstrate the utility of newly developed markers in establishing genetic relationships among different isolates of F. oxysporum. [ABSTRACT FROM AUTHOR]