Physical mapping of black spot disease resistance/susceptibility-related genome regions in Japanese pear (Pyrus pyrifolia) by BAC-FISH

Black spot disease, caused by Alternaria alternata Japanese pear pathotype, is one of the most harmful diseases in Japanese pear cultivation. In the present study, the locations of black spot disease resistance/susceptibility-related genome regions were studied by fluorescence in situ hybridization using BAC clone (BAC-FISH) on Japanese pear (Pyrus pyrifolia (Burm. f.) Nakai) chromosomes. Root tips of self-pollinated seedlings of ‘Osa Gold’ were used as materials. Chromosome samples were prepared by the enzymatic maceration and air-drying method. The BAC clone adjacent to the black spot disease-related gene was labeled as a probe for FISH analysis. Black spot disease-related genome regions were detected in telomeric positions of two medium size chromosomes. These two sites and six telomeric 18S-5.8S-25S rDNA sites were located on different chromosomes as determined from the results of multi-color FISH. The effectiveness of the physical mapping of useful genes on pear chromosomes achieved by the BAC-FISH method was unequivocally demonstrated.