Genetic mapping of a wide spectrum nematode resistance gene (Hero) against Globodera rostochiensis in tomato

The Hero gene confers resistance to a wide spectrum of pathotypes of the potato cyst nematode Globodera rostochiensis, This gene has been introgressed from the wild tomato species Lycopersicon pimpinellifolium into the cultivated tomato, We have used RFLP and RAPD analysis for the targeted search of the L. pimpinellifolium segment, The resistant line LA 1792 contains a single introgressed segment on chromosome 4, which is characterized by three RFLP markers from the high-density RFLP map of tomato. The map position of the Hero gene is not equivalent to any of the previously mapped G. rostochiensis resistance genes in potato. For the fine mapping of the Hero gene in large populations, four additional markers were identified in the introgressed region, After analyzing more than 800 gametes for recombination, we found that one marker is only 0.4 cM away from the Hero gene, YAC clones isolated from a region near the Hero gene indicate that in this area of the genome, the kb/cM ratio is relatively low (<450 kb/cM) and chromosome walking should be feasible in order to isolate this gene.