AN APHID-RESISTANCE LOCUS IS TIGHTLY LINKED TO THE NEMATODE-RESISTANCE GENE, MI, IN TOMATO

Tomato lines from diverse breeding programs were evaluated in the fiel d for resistance to a natural infestation of the potato aphid, Macrosi phum euphorbiae, in Davis, CA. It was noted that all lines that carrie d the nematode-resistance gene, Mi, displayed aphid resistance. A gree nhouse assay for aphid resistance was developed to investigate this re lationship. Association of nematode and aphid resistances in near-isog enic lines suggested that these traits are tightly linked. Analysis of an F-2 population segregating for nematode resistance indicated that aphid resistance segregated as a single major locus genetically linked to Mi. The name Meu1 is proposed for this locus. It is likely that Me u1 was introduced into tomato along with Mi from the wild species Lyco persicon peruvianum. The presence of aphid resistance in the line Mote lle, which contains a very small region of introgressed DNA, and the l ack of recombinants suggest that Meu1 is tightly linked to Mi or possi bly is the same gene, The map-based strategy currently being used to c lone Mi should be applicable to cloning Meu1.