Pseudomonas syringae pv. tomato (Pst) is identified as the causal agent of bacterial speck disease in tomatoes. The Pto/Prf gene cluster from Solanum pimpinellifolium was introgressed into several modern tomato cultivars by researchers, providing protection against Pst race 0 strains for many decades. However, virulent Pst race 1 strains, which evade Pto-mediated immunity, now predominate in tomato-growing regions worldwide. This shift has necessitated the search for new sources of resistance by scientists to maintain tomato crop health and productivity.
In this context, the identification of resistance to a Pst race 1 strain (Pst19) in the wild tomato accession S. pimpinellifolium LA1589 (hereafter referred to as LA1589) is reported, utilizing a rapid high-throughput seedling screen. Notably, LA1589 supports less bacterial growth than cultivars and does not exhibit a hypersensitive response to Pst19. This discovery indicates that LA1589 possesses a different mechanism of resistance, distinct from the Pto-mediated immunity found in previously bred cultivars.
To further explore this resistance, an existing set of 87 Inbred Backcross Lines (IBLs) derived from a cross between the susceptible Solanum esculentum E-6203 and S. pimpinellifolium LA1589 was tested for resistance to Pst19. Through single-marker analysis, three genomic regions associated with resistance were identified. Subsequent bacterial growth assays on these IBLs confirmed that these regions significantly contribute to resistance in planta, highlighting their potential for breeding resistant tomato varieties.
Expanding upon this finding, candidate genes associated with resistance in a cross between the Solanum lycopersicum var. lycopersicum cultivar Heinz BG-1706 and S. pimpinellifolium LA1589 were mapped. By comparing candidates from the two mapping approaches, 3 quantitative trait loci (QTL) and 5 candidate genes in LA1589 that play roles in resistance to Pst19 were identified. This work lays a foundation for molecular marker-assisted breeding, aiming to protect tomatoes from bacterial speck disease by leveraging genetic diversity found in wild tomato accessions.
Source: Frontiersin