Caracterización de aislados de Fusarium oxysporum f. sp. niveum y búsqueda de nuevas fuentes de resistencia natural a la fusariosis vascular en sandía.

Fusarium wilt, one of the most important fungal diseases of watermelon worldwide, is caused by Fusarium oxysporum f. sp. niveum (E.F. Sm.) W.C. Snyder & H.N. Hansen (Fon). Fon is part of the collective species F. oxysporum, a global soil pathogen for which have been described numerous races, pathotypes or formae specialis according to the parasitized host or its specificity for plant genotype. The use of traditional control methods of such diseases (rotation, fungicides, etc. ...) does not allow reduce the effect of the pathogen mainly due to its ability to survive, thanks to the production of chlamydospore-type resistance structures that persist for a long time on the ground. At present, the most reliable and economic control method of Fusarium wilt is to find sources of natural resistance in watermelon varieties. In the present study, a protocol of artificial inoculation of the pathogen on watermelon seedlings in container has been optimized for subsequent characterization of a set of isolated Fon from the collection of fungal strains of the CITA and performing of a bioassay to screen for natural resistances against Fon race 2 among 38 entries of watermelon coming from different parts of Spain. Regarding the characterization of isolates of Fon, the results from tests pathogenicity against tester cultivars, the macromorphological characterization of colonies in culture, showed that they all belonged to race 2, although simultaneous methods of molecular characterization employed (sequencing ribosomal ITS region and molecular typing by analyzing microsatellites) were not able to differentiate with respect to representatives of the other races described for the group. Of the 38 entries tested, two of them showed some degree of resistance and / or tolerance to race 2 with a survival rate of 66, 66 per cent to 100 per cent of the total initial seedlings 30 days after inoculation. These entries could represent potential sources of natural resistance that can be exploited in subsequent improvement programs in watermelon