Selective genotyping to identify late blight resistance genes in an accession of the tomato wild species Solanum pimpinellifolium

Late blight (LB), caused by the oomycete Phytophtohra infestans, is one of the most destructive diseases of tomato (Solanum lycopersicum) and other Solanaceae species. Current disease control and prevention strategies are not sufficient to control the disease in tomato. Recent germplasm screening experiments led to the identification of a new source of resistance (PI 270443) in the tomato wild species S. pimpinellifolium. This study was conducted to identify genomic regions associated with LB resistance in this accession. A large F ₂ population (n = 986) derived from a cross between PI 270443 and a LB-susceptible tomato breeding line (NCEBR-2) was screened for LB resistance using a highly aggressive isolate of P. infestans. Twenty-five of the most resistant and 29 of the most susceptible, but surviving F ₂ individuals were identified based on disease evaluations conducted in the F ₂ and F ₃ progeny populations. The selected individuals were genotyped with 153 DNA markers located across the 12 tomato chromosomes. A selective genotyping approach led to the identification of two genomic regions on tomato chromosomes 1 and 10 associated with LB resistance in PI 270443. Identification of two genomic regions associated with resistance was consistent with a previous estimate of the number of LB resistance genes in this accession. Research is currently underway to fine map the two resistance genes and incorporate them into new tomato breeding lines and hybrid cultivars.