The tomato Rme1 locus is required for Mi-1-mediated resistance to root-knot nematodes and the potato aphid

The tomato Mi-1 gene confers resistance against root-knot nematodes (Meloid ogyne spp.) and a biotype of the potato aphid (Macrosiphum euphorbiae). Fou r mutagenized Mi-1/Mi-1 tomato populations were generated and screened for altered root-knot nematode resistance. Four independent mutants belonging t o two phenotypic classes were isolated. One mutant was chosen for further a nalyzes; rme1 (for resistance to Meloidogyne) exhibited levels of infection comparable with those found on susceptible controls. Molecular and genetic data confirmed that rme1 has a single recessive mutation in a locus differ ent from Mi-1. Cross-sections through galls formed by feeding nematodes on rme1 roots were identical to sections from galls of susceptible tomato root s. In addition to nematode susceptibility, infestation of rme1 plants with the potato aphid showed that this mutation also abolished aphid resistance. To determine whether Rme1 functions in a general disease-resistance pathwa y, the response against Fusarium oxysporum f.sp. lycopersici race 2, mediat ed by the I-2 resistance gene, was studied. Both rme1 and the wild type pla nts were equally resistant to the fungal pathogen. These results indicate t hat Rme1 does not play a general role in disease resistance but may be spec ific for Mi-1-mediated resistance.