| Tomato yellow leaf curl disease became one of the most prevalent and damaging tomato diseasesin tomato production in the world. The best way to reduce this damage is by breeding resistant ortolerant tomato cultivars. So far, five resistance genes have been mapped, i.e. Ty-1, Ty-2, Ty-3, Ty-4andTy-5, derived from several wild tomato species. The breeding programs have been based on the transferof these resistance genes into the cultivated tomatoes by marker-assisted selection. But resistance toTYLCV was still associated with some undesirable traits due to the longer genetic distance of theknown linked molecular markers. So it is necessary to develop tightly linked molecular markers andfurther fine mapping TYLCV resistance genes, which is very significant to develop tomato cultivarswith high resistance to TYLCV and provide academic guidance to analysis disease resistancemechanisms. So far, most of developed cultivars only have a single resistance gene, which makeresistance reduced under the high disease pressure. So it is important and promising to pyramid allresistant genes in a single genotype to reach the maximum level of resistance.The Ty-2gene, which is a single dominant gene derived from S. habrochiates f. glabratumaccession 'B6013', was previously mapped to a19cM region on the long arm of chromosome11delimited by molecular markers TG36and TG393. Later, Ty-2gene was located to a6.7cM intervalbetween C2_At2g28250and T0302. The objective of this present research is to fine mapping of Ty-2gene based on the previous research. Resistance levels of different genes were also discussed throughpyramiding resistances from different wild tomato species in a tomato line in this study. The mainconclusions were as follows:1. Two hundred forty-two pairs of primers were designed according to the tomato genome sequencebetween markers C2_At2g28250and T0302on chromosome11by a tool of BatchPrimer. Theseprimers, in addition to the primers of18markers already in Tomato-EXPEN map, allowed amplificationamong homozygous resistance control E951-7, heterozygous resistance control TyQueen, andhomozygous susceptible control Horizon. Fifty-six polymorphic molecular markers were developed,including16SCAR markers and40CAPS markers. With21polymorphic markers, a high-resolutiongenetic map of Ty-2gene was constructed, in which, average genetic distance was0.05cM.2. From over11000plants derived from F1hybrid H9205from H24, nearly157plants were selected forcarrying a recombined introgression between flanking markers C2_At1g07960and T0302. The progenyof each recombinant was genotyped with additional molecular markers developed from the tomatopublic genomic sequence within the target region and evaluated by TYLCV. The results indicated thatTy-2was located between markers UP8and M1, a distance of0.4cM and an interval of300,000baseson a single scaffold of the tomato assembly. In this screening, a PCR-based co-dominant SCAR markertightly linked to the Ty-2locus, P1-16, can be used in the breeding program for efficient selection ofhigh-levels of begomovirus resistance. The PCR fragment sizes for resistant and susceptible controlwere300bp and600bp, respectively. 3. Thirty-five genes were predicted within around300kb of Ty-2gene target region based on thegenome sequence of S.lycopersicum H1706. Five genes, i.e. Solyc11g069620.1, Solyc11g069660.1,Solyc11g069920.1, Solyc11g069670.1and Solyc11g069930.1, which contained the conserved domainsof NB-ARC class and located in the recombinant area, were selected as Ty-2candidate genes.4. Fourteen materials harboring different resistance genes were selected from the population developedwith susceptible cultivar8083, near-isogenic line E846(Ty-2+), and Fla.726(Ty-3+Ty-4+), and evaluatedwith TYLCV disease. Results indicated that the material with single Ty-2gene showed high resistanceto TYLCV, and the material with single Ty-3was tolerance to TYLCV; while the material with singleTy-4gene exhibited sever susceptible symptoms. The plants containing both Ty-2and Ty-3or Ty-2andTy-4were all resistant to TYLCV, while the plants containing both Ty-3and Ty-4were all tolerance. Thedifferent genes showed the additive effect and the plant containing Ty-2, Ty-3and Ty-4genes exhibitedthe highest resistance to TYLCV.
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