First detection of Fusarium oxysporum f. sp. radicis–lycopersici across major tomato–producing regions in Brazil

Abstract

Fusarium oxysporum f. sp. lycopersici (FOL) races 1 and 2 were, up to recent years, the only pathogenic Fusaria associated with tomatoes (Solanum lycopersicum L.) in Brazil. However, recent outbreaks of F. oxysporum isolates with the ability to breakdown the I–2-mediated resistance prompted us to conduct nationwide surveys of the pathogens associated with vascular wilt of tomatoes. During these surveys, eight atypical F. oxysporum isolates (collected across five tomato–producing Brazilian states) displayed a peculiar ability of infecting accessions carrying the I–3 and I–7 genes (controlling resistance to FOL race 3 isolates). These observations suggested the involvement of either a new FOL race or of F. oxysporum f. sp. radicis-lycopersici (FORL) isolates. Koch’s postulates were fulfilled for these eight atypical isolates via root dipping inoculation (106 conidia mL− 1) of seedlings from two tomato cultivars ‘Ponderosa’ and ‘Dominador’. All eight isolates induced crown-rot symptoms only in ‘Ponderosa’, but not in ‘Dominador’ (which is resistant to FORL). To confirm the FORL identity, PCR assays were done using a set of race-specific and forma specialis-specific primers. A single amplicon of ≈ 947 bp was observed with the primer pair Sprl only with DNA template obtained from standard FORL isolates and from the eight atypical isolates, confirming the first detection of this forma specialis in Brazil. The geographical distribution of FORL isolates across major tomato–producing areas may require the incorporation of resistant factors into adapted cultivars.