Mapping of Gene Conferring Resistance to Root-Knot Nematodes at High Soil Temperature in Tomato

Root-knot nematodes (Meloidogyne spp.) can cause severe yield losses in tomatoes. The Mi-1.2 gene in tomato confers resistance to three Meloidogyne species such as M. incognita, M. arenaria and M. javanica, which are prevalent in tomato growing areas. However, resistance provided by Mi-1.2 gene breaks down at high soil temperatures (>28 C). Therefore, it is imperative that new resistance sources are identified and incorporated into commercial breeding programmes. We identified a tomato line, which was confirmed to provide resistance to Meloidogyne incognita at 32 C soil temperature. An F2 mapping population was generated by crossing the resistant line with a susceptible line and the segregation ratio showed that the resistance is conditioned by a single dominant gene designated RRKN1 (Resistance to Root-Knot Nematode 1). The RRKN1 gene was mapped using 111 Kompetitive Allele Specific PCR (KASP) markers and characterized. Linkage analysis showed that RRKN1 is located on chromosome 6 and flanking markers put the locus within a 270 kb interval. These newly developed markers can help pyramiding R-genes and generating new tomato varieties resistant to RKNs at high temperatures.