Development of novel specific molecular markers for the Sw-5b gene to assist with tomato spotted wilt virus-resistant tomato breeding

Tomato spotted wilt virus (TSWV) is a plant pathogen that causes devastating tomato yield losses worldwide. The Sw-5b gene is one of the most effective resistance genes for TSWV control in tomato plants, and has been widely used in resistance breeding. Molecular markers are specific DNA sequences with known locations on the chromosome; they are indispensable tools in marker-assisted selection, which detects the presence of target genes to expedite breeding. We developed gene-specific molecular markers for Sw-5b to facilitate the accurate distinction of resistance (Sw-5bR) and susceptibility (Sw-5bS) alleles of Sw-5b. Using these markers, we successfully detected Sw-5b and determined its genotype (homozygous Sw-5bR, heterozygous Sw-5bR/S, or homozygous Sw-5bS) in six tomato varieties. Then we successfully applied these markers to 46 commercial tomato cultivars to detect and determine the genotype of Sw-5b. The results revealed a striking absence of the Sw-5bR gene and high TSWV susceptibility among most of the analyzed commercial cultivars. With the assistance of the novel Sw-5b-specific molecular markers, we generated a TSWV-resistant and homozygous Sw-5bR Micro-Tom tomato line, demonstrating the practical application of these markers in plant breeding. In summary, we developed novel gene-specific molecular markers for Sw-5b, and applied them to distinguish Sw-5b alleles for TSWV resistance or susceptibility. This marker set provides a valuable tool for breeding TSWV-resistant tomato varieties.