Tomato spotted wilt virus (TSWV) is a serious disease in several crops such as peanut, tomato, pepper, tobacco. One source of resistance in tobacco is the breeding line Polalta, which contains a TSWV resistance gene introgressed from N. alata. However, the resistance is associated with abnormal plant morphology and traditional backcrossing has been ineffective in producing normal plants with TSWV resistance. Molecular marker- assisted backcrossing allows for rapid identification of the plants that are most genetically similar to the recurrent parent and can be used to reduce the size of an introgressed chromosome segment. We applied AFLP (amplified fragment length polymorphism) technology and bulk segregant analysis to identify markers linked to TSWV resistance. One TSWV resistant bulk and two susceptible bulks were constructed by combining DNA from 5 doubled haploid lines from the cross K326 x Polalta for each bulk. An F 2 population of 89 plants was screened with the markers identified by BSA, and a 48 cM map with 27 markers constructed. Two flanking markers less than 1 cM from the TSWV resistance gene were isolated and sequenced to develop PCR based markers. An F 2 BC 2 population was screened to select resistant plants that have fewer Polalta-derived markers and more K326-derived markers. This approach should increase the chance to develop a plant with TSWV resistance and a normal phenotype.
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