Abstract
The present study aimed at the molecular characterization of pathogenic and non pathogenic F. oxysporum f. sp. lycopersici strains isolated from tomato. The causal agent isolated from symptomatic plants and soil samples was identified based on morphological and molecular analyses. Pathogenicity testing of 69 strains on five susceptible tomato varieties showed 45% of the strains were highly virulent and 30% were moderately virulent. Molecular analysis based on the fingerprints obtained through ISSR indicated the presence of wide genetic diversity among the strains. Phylogenetic analysis based on ITS sequences showed the presence of at least four evolutionary lineages of the pathogen. The clustering of F. oxysporum with non pathogenic isolates and with the members of other formae speciales indicated polyphyletic origin of F. oxysporum f. sp. lycopersici. Further analysis revealed intraspecies variability and nucleotide insertions or deletions in the ITS region among the strains in the study and the observed variations were found to be clade specific. The high genetic diversity in the pathogen population demands for development of effective resistance breeding programs in tomato. Among the pathogenic strains tested, toxigenic strains harbored the Fum1 gene clearly indicating that the strains infecting tomato crops have the potential to produce Fumonisin.
Highlights
In India, crops are grown under varied agro-climatic conditions and Fusarium spp., occur regularly causing considerable crop losses and produce several mycotoxins[1,2]
Fusarium wilt of tomato has been reported in India since the late 1960’s but so far there is no comprehensive study on the genetic diversity of the pathogen which occurs virtually in all production areas of the country
The pathogenic strains resulted in the development of the vascular wilt disease in the test tomato cultivars to various levels depending on their virulence
Summary
In India, crops are grown under varied agro-climatic conditions and Fusarium spp., occur regularly causing considerable crop losses and produce several mycotoxins[1,2]. Fusarium oxysporum is a species complex comprising ubiquitous soil borne plant pathogens with more than 150 host-specific forms or formae speciales[3,4]. Lycopersici (Fol) is an asexual fungus, genetic exchange occurs via somatic fusion and hetreokaryon formation between vegetative compatible strains[15]. Determining the level of genetic variability within pathogen populations is important since a high genetic variation indicates rapid evolution in response to the changing environmental conditions and the development of new races overcoming host resistance[20,21,22]. Elias et al.[23] studied the population structure of Fol based on RFLP analysis of the genomic DNA which provided genetic evidence that Vegetative Compatibility Grouping (VCG) was an indicator of evolutionary origin. Phoutthasone et al.[31] used virulence and AFLP markers for the genetic differentiation between Fol populations of Thailand
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