Mapping a novel heat-stable resistance to Meloidogyne in Lycopersicon peruvianum

The root-knot nematode heat-stable resistance locus from L. peruvianum LA21 57 was mapped on chromosome 6. All wild tomato LA2157 entries and the LA215 7 S-1 progeny tested were resistant to Mi-avirulent Meloidogyne spp. isolat es at 32 degrees C, indicating that the self-compatible accession is homozy gous for heat-stable nematode resistance. The novel resistance locus was ma pped on a RFLP linkage map; this map was based on a segregating F-2 populat ion obtained from the interspecific F-1 between L, esculentum cv 'Solentos' and L. pervianum LA2157. The inheritance of the heat-stable resistance was evaluated in 100 F-3 lines derived from one F-1 interspecific hybrid. The genotype of the resistance locus of the individual F-2 plants was based on the phenotypic classification of their F-3 lines, and the data were used to map the resistance locus on the arm of chromosome 6 with the closest linka ge to TG178. The position of the novel heat-stable resistance of LA2157 was localized in the resistance genes' cluster close to the location of gene M i-1. Cuttings of the F-3 lines expressed resistance to Mi-1-avirulent M. in cognita and M. javanica biotypes at 25 degrees C and at 32 degrees C (a tem perature at which Mi-1 resistance is not expressed). There was no differenc e in the segregating population for expression of heat-unstable resistance and heat-stable resistance to Mi-1-avirulent Meloidogyne spp. However, LA21 57 and cuttings of above F-3 lines were susceptible to a Mi-1-virulent M. i ncognita isolate at 30 degrees C and to a M. incognita isolate at 25 degree s C.