Identification of QTLs controlling resistance to Pseudomonas syringae pv. tomato race 1 strains from the wild tomato, Solanum habrochaites LA1777.

KEY MESSAGE: Screening of wild tomato accessions revealed a source of resistance to Pseudomonas syringe pv. tomato race 1 from Solanum habrochaites and facilitated mapping of QTLs controlling disease resistance. Pseudomonas syringae pv. tomato (Pst) causes bacterial speck of tomato, which is one of the most persistent bacterial diseases in tomato worldwide. Existing Pst populations have overcome genetic resistance mediated by the tomato genes Pto and Prf. The objective of this study was to identify sources of resistance to race 1 strains and map quantitative trait loci (QTLs) controlling resistance in the wild tomato Solanum habrochaites LA1777. Pst strains A9 and 407 are closely related to current field strains and genome sequencing revealed the lack of the avrPto effector as well as select mutations in the avrPtoB effector, which are recognized by Pto and Prf. Strains A9 and 407 were used to screen 278 tomato accessions, identifying five exhibiting resistance: S. peruvianum LA3799, S. peruvianum var. dentatum PI128655, S. chilense LA2765, S. habrochaites LA2869, and S. habrochaites LA1777. An existing set of 93 introgression lines developed from S. habrochaites LA1777 was screened for resistance to strain A9 in a replicated greenhouse trial. Four QTLs were identified using composite interval mapping and mapped to different chromosomes. bsRr1-1 was located on chromosome 1, bsRr1-2 on chromosome 2, and bsRr1-12a and bsRr1-12b on chromosome 12. The QTLs detected explained 10.5-12.5% of the phenotypic variation. Promising lines were also subjected to bacterial growth curves to verify resistance and were analyzed for general horticultural attributes under greenhouse conditions. These findings will provide useful information for future high-resolution mapping of each QTL and integration into marker-assisted breeding programs.