The tomato 1-3 gene originating from Lycopersicon pennellii confers resistance against the fungal pathogen Fusarium oxysporum f.sp. lycopersici (Fol) race 3. The gene has been mapped to chromosome 7 of tomato (Lycopersicon esculentum). As a first step toward
isolation of the 1-3 gene, RAF, the randomly amplified DNA fingerprinting technique was used on near-isogenic lines (NILs) and segmental introgression lines to identify RAF markers in the vicinity of 1-3. Using this technique, approximately 7,000 RAF markers were amplified and mapped relative to 1-3 on chromosome 7. One of these RAF markers called e06 was found to cosegregate with the resistance gene analogue (RGA) 332 in a 0.28 cM window also including 1-3. This RAF marker could now be used to initiate a chromosome walk to the 1-3 locus on chromosome 7.
RAF analysis was also employed to identify a potential novel gene
for resistance to Fol race 3. The analysis revealed that an additional novel resistance gene for race 3 resides in chromosome 5 of tomato. RAF analysis proved to be a rapid and efficient technique for detecting large numbers of DNA markers linked to two genes for resistance to Fol race 3. This research should hasten plant gene isolation of the 1-3 gene on chromosome 7 by map-based cloning. The discovery of the additional gene on chromosome 5 offers the possibility of pyramiding the two genes for a more durable resistance against Fol race 3.