A GENOMIC SEARCH FOR THE GENE CONFERRING RESISTANCE TO FUSARIUM-WILT IN TOMATO

Fusarium wilt is an economically important disease of tomatoes, caused by the soil-born fungus Fusarium oxysporum f. sp. lycopersici. There are three host-specific races of this pathogen. The dominant tomato ge ne I-2 confers resistance to race 2. The I-2 fusarium resistance gene was mapped genetically to chromosome 11 of tomato; between the RFLP ma rkers TG105 and TG36, 0.4 centiMorgan (cM) from TG105. A mean value of 43 kb for each cM was assigned in the vicinity of I-2. We have genera ted new RFLP markers in the region by chromosome walking from TG105 to wards 1-2 on lambda clones, and by subcloning a 350 kb long YAC clone (YAC 8) that contains TG105. These RFLP markers were mapped physically on YAC 8 by PFGE. The location of I-2 relative to these markers was g enetically estimated using a recombinant inbred (RI) segregating popul ation. The order of the markers according to the RI population is inco nsistent with their order on the physical map. A cDNA clone, D14, that was isolated by YAC 8, turned out to be 53% similar to xanthine dehyd rogenase from mammals and flies. Antibodies raised against a part of t he protein encoded by D14 recognize cross reacting material of MW 80 k D, that is highly enriched in nodules of legumes, and seems to be indu ced by various environmental and pathogenic stress conditions.