Diversidade de Fusarium oxysporum f. sp. lycopersici e desenvolvimento e validação de marcadores moleculares ligados a genes de resistência em tomateiro

The tomato (Solanum lycopersicum L.) is one of the main vegetables crops in Brazil. The fungus Fusarium oxysporum f. sp. lycopersici (Fol) is the causal agent of one of the most important diseases of this crop, the Fusarium wilt. The chemical and cultural controls are expensive and not effective in most situations, therefore, the use of resistant cultivars is the best option to control this disease. The gene I (= Immunity) was one of the first disease resistance factors characterized in tomato. This gene confers high levels of resistance exclusively against Fol race 1 isolates. The resistance to Fol race 3 was identified in S. pennellii accessions ‘PI 414773’ and ‘LA716’ (the original source of the gene I-3) and characterized as dominant monogenic. The gene of S. pennellii ‘PI 414773’ was tentatively named as I-7. The genes I and I-7 have not yet been cloned and there are few molecular markers available to monitor the incorporation of these two factors. In this context, crosses were made among the genotypes ‘Ponderosa’ (susceptible to all three races), ‘Viradoro’ (resistant to race 1 isolates due to the presence of the gene I) and ‘LAM 205’ (resistant to race 3 isolates due to the presence of the gene I-7). Three populations were obtained segregating for loci I-7 and I individually or simultenously. These populations were characterized as resistance to Fol by root dip inoculation technique separately with races 1 and 3 isolates. For the identification of molecular markers linked to resistance to Fol it was used RAPD strategy combined with “bulked segregant analysis” (BSA). A collection of 520 RAPD primers was employed initially to search for polymorphisms between parental lines and wit an equimolar combination of genomic DNA extracted from resistant F2 individuals (= R bulk) and susceptible F2 individuals (= S bulk). Polymorphisms among the parental lines ‘Ponderosa’, ‘Viradoro’ and ‘LAM 205’were initially detected with 60 RAPD primers. From this initial set of potential markers, only 24 polymorphims were found to be stable. Samples of individuals from the F2 population were assessed to confirm the linkage between each polymorphism and the segregating resistance factor against either Fol race 1 or race 3 isolates. However, the RAPD screening was not able to detect stable polymorphic markers with close linkage with these two resistance factors. Thus, the polymorphisms found in this study may serve only as a database of genetic variability among genotypes for future linkage studies with other features/traits of interest for breeding programs.