LONG-RANGE PHYSICAL MAPS OF 2 LOCI (APS-1 AND GP79) FLANKING THE ROOT-KNOT NEMATODE RESISTANCE GENE (MI) NEAR THE CENTROMERE OF TOMATO CHROMOSOME-6

The root knot nematode resistance gene Mi in tomato has been mapped in the pericentromeric region of chromosome 6. With the objective of iso lating Mi through a map-based cloning approach, we have previously ide ntified and ordered into a high-resolution genetic linkage map a varie ty of tightly linked molecular markers. Using pulsed-field gelelectrop horesis and various rarely cutting restriction enzymes in single, doub le and partial digestions, we now report long-range physical maps of t he two closest flanking markers, acid phosphatase-1 (Aps-1) and GP79, which span over 400 and 800 kb, respectively. It is concluded that the physical distance between both markers is larger than predicted on th e basis of genetic linkage analysis. Furthermore, two RFLP markers (H3 F8 and H4H10) which map genetically to the same locus as Aps-I do not show physical linkage, indicating severe suppression of recombination in this region of the chromosome. Finally, no evidence was obtained sh owing the presence of a CpG island near Aps-1.