Abstract
Leaf mold, caused by the fungus Cladosporium fulvum, is a serious disease of tomato. In the current study, the main physiological races of C. fulvum collected from three northeastern provinces of China were identified using a set of identification hosts. The results showed that the prevalent pathogenic physiological races were 1.2.3, 1.3, 3, 1.2.3.4, and 1.2.4. F1, F2, and BC1 tomato plants were obtained by crossing C. fulvum-resistant cultivar 03748 carrying the Cf-6 gene and susceptible cultivar 03036. Three 10-mer oligonucleotide random amplified polymorphic DNA (RAPD) primers and two simple sequence repeat (SSR) primers were selected for the further molecular marking analysis after 210 RAPD primers and 50 SSR primers were screened using the bulked segregate analysis method. The polymorphic DNA bands were amplified among parents, 10 F1 plants, 184 F2 plants including 145 resistant plants and 39 sensitive plants using three RAPD primers and two SSR primers so that three RAPD molecular markers and two SSR molecular markers linked to the Cf-6 loci were identified. Three RAPD markers were linked to the Cf-6 resistant locus separated with 8.7 cM, 20.3 cM, and 33.4 cM. Also, one RAPD codominant marker S374619/559 was found. The locations of the two SSR markers were 12.6 cM and 9.7 cM away from the Cf-6 locus. After cloning and sequencing two specific DNA fragments closely connected to the Cf-6 resistant and susceptible alleles respectively, in the RAPD codominant marker S374619/559 and one codominant sequence characterized amplified region marker S674619/559 was converted from RAPD marker S374619/559. In the RAPD marker S374619/559, the length difference of two specific fragments, 619-bp fragment and 559-bp fragment, is the result of one insertion (60 bp) in the 619-bp fragment. These markers will facilitate the selection of resistant tomato germplasm containing the Cf-6 gene and cloning of Cf-6 to breed new C. fulvum resistant tomato cultivars.
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