Location of a chromosome region linked to Alternaria Brown Spot resistance from the evaluation of tr

Alternaria Brown Spot resistance in citrus has been described in diploid progenies as controlled by a singlerecessive allele (r). The objectives of this study were (1) to map chromosome regions that could be associatedto Alternaria alternata resistance and (2) to analyse the inheritance of the resistance in triploid familiesresulting from 2n gametes and interploid crosses. Bulk segregant analysis coupled with genome scan (650Single Nucleotide Polymorphism –SNP– markers genotyped with GoldenGate array) was used to identifygenomic regions linked to the A. alternata resistance gene using a triploid progeny from a SrXrr cross. Theresults confirmed the monolocus inheritance of A. alternata resistance and revealed 44 SNPs differentiating theresistant and susceptible bulks within a 17 cM region near the centromere on chromosome III. De novo mappingfrom individual genotyping with 9 markers revealed that the A. alternata resistance gene could be located at9.7 cM from the centromere. Two flanking markers were selected to perform marker assisted selection. Threepopulations from 2xX2x crosses sharing the female genitor (SrXrr, SrXSr and SrXSS) and one population from a2xX4x cross (rrXSSrr) were evaluated for A. alternata resistance. Segregations indicate that 2xX2x crosses arebetter to obtain more resistant genotypes for a centromeric gene controlled by a recessive allele than 2xX4xcrosses, since less heterozygosity is transmitted by 2n gametes than by gametes of doubled-diploids.