Development of a real-time quantitative assay applied to the study of Fusarium oxysporum f. sp. melonis colonization in grafted melon plants
Haegi, A.; Catalano, V.; Luongo, L.; Vitale, S.; Scotton, M.; Ficcadenti, N.; Belisario, A.
Journal of Plant Pathology
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Fusarium oxysporum f. sp. melonis (FOM) is the causal agent of a devastating disease of melon. The fungus evolves in new races with different infection strategies to overcome resistance and grafting represents a widely used tool to confer resistance against new virulent races of FOM. We developed a real-time quantitative PCR (qPCR) assay for the detection of Fusarium oxysporum. The method is reliable, species-specific and sensitive (1 pg of fungal DNA) and suitable for the detection and quantification of FOM in grafted melon plants. qPCR was used to study disease development in Charentais-T (susceptible) and Nad-1 (resistant) melon cultivars, both used either as rootstock and scion inoculated with FOM race 1 and race 1,2. Results highlighted the effects of grafting on fungal development in planta: the principal significant effect on fungal development was due to the melon genotype used as rootstock. Moreover, in both combinations the resistant genotype (Nad-1) had an evident influence on both fungal races by reducing their development. A general characteristic in FOM/melon interaction is the ability of F. oxysporum to colonize melon plants independently from inducing symptoms. The work underlines the different infection pattern of the two FOM races: race 1,2 has the highest ability to grow in melon stems in the presence of host resistance, whereas race 1 is generally faster in colonizing melon plants in absence of resistance. The different behavior observed between FOM race 1 and 1,2, in colonizing melon plants, suggests a different genetic background as a probable result of independent evolutionary processes.