Race identification of Fusarium oxysporum f. sp. lycopersici isolates obtained from tomato plants in Nova Friburgo, Brazil

Fusarium wilt caused by Fusarium oxysporum f. sp. lycopersici (FOL) is one of the main diseases affecting tomato plants. Three races (races 1, 2 and 3) of the pathogen have been described around the world, including in Brazil. Nova Friburgo, Rio de Janeiro State, is one of the leading tomato producing regions. During summer, farmers have reported severe losses caused by wilt disease. The present work aimed to identify and characterize the disease and predominant FOL races found in this region. The study was conducted in 41 family farms on 246 harvested tomato plants. Fusarium wilt was identified based on visual diagnosis, isolation and microscopy tests. Race identification was performed using: (a) differential cultivars; (b) conventional PCR and (c) gene sequencing. From all the isolates obtained, 38 were characterized as Fusarium spp. and 24 (63.2%) were identified as race 3 of FOL by differential cultivars. From the 24 FOL isolates, eighteen were randomly selected for race identification by gene sequencing. SIX primers (SIX3, SIX4 and SIX-G12A-F2) were not efficient to characterize races 1, 2 and 3 of FOL. Primers uni, sp12, sp. 23, sprl, as well as, primer SIX3 only allowed to identify race 3. The SCAR OP-Z4 marker was not able to identify race 2. Our study shows the predominance of FOL race 3 in the Nova Friburgo region. Moreover, primers developed to identify FOL races in other parts of the world are not well adapted to differentiate Brazilian FOL isolates.