RFLP LINKAGE ANALYSIS OF THE CF-4 AND CF-9 GENES FOR RESISTANCE TO CLADOSPORIUM-FULVUM IN TOMATO

Four different populations segregating for one of the two closely linked (possibly allelic) tomato disease resistance genes to the fungus Cladosporium fulvum, Cf-4 and Cf-9, were generated and analysed for recombination frequencies between the Cf-genes and restriction fragment length polymorphism (RFLP) loci. The population consisting of F-2 progeny from the interspecific cross Lycopersicon esculentum carrying Cf-9 x L. pennellii was identified as the most useful for RFLP mapping of the Cf-4/9 locus and an RFLP map around this locus was constructed mainly using this population. The two closest markers identified were CP46, 2.6 cM distal, and a group of 11 markers including TG236, 3.7 cM proximal to Cf-4/9. A polymerase chain reaction (PCR)-based procedure for the rapid identification of recombination events between these two markers was developed. The regions of foreign DNA introgression surrounding Cf-4 and Cf-9 in near-isogenic lines were delimited.