The gray leaf spot disease, caused by the fungi Stemphylium solani and S. lycopersici, has been considered as a minor tomato disease in Brazil due to the use of varieties with genetic resistance in combination with fungicide sprays. However, recent reports of severe epidemics of the gray leaf spot in the various tomato-producing areas of the country suggest that the employment of resistant cultivars should be re-implemented as a control strategy. In the present study, 109 cultivated and wild Solanum (section Lycopersicon) accessions were evaluated to isolates of both S. solani and S. lycopersici. In the first assay, spore suspension (adjusted to 10(4) conidia/mL) of the isolates 'EH-1740' (S. solani) and 'EH-1749' (S. lycopersici) were employed to inoculate seedlings transplanted 15 days after sowing and kept in a greenhouse. Plants were inoculated 18 days after transplanting and evaluated 15 days after inoculation. Fifty-eight promising accessions identified in the first assay were evaluated again with the same isolates in a second experiment. The reaction of the accessions to the pathogens was evaluated every two days using as assessment criteria the incubation period, the severity of gray leaf spot, and the disease index. Disease severity values over time were used to calculate the area under the disease progress curve. Promising sources of resistance to both pathogens were identified in accessions of S. lycopersicum, S. habrochaites, S. peruvianum and S. pimpinellifolium. The resistant sources identified in S. pimpinellifolium and S. lycopersicum accessions probably have the gene Sm. However, S. habrochaites and S. peruvianum might be potential new sources of gene/alleles that confer resistance to both fungi. This diversity of Stemphylium resistance genes might be useful for tomato breeding programs in the future as well as in integrated management systems of the disease.
Solanum lycopersicum; Sm gene; gray leaf spot; genetic resistance; tomato
