Identification of a Major QTL and Development of a CAPS Marker Associated with Stem Blight Resistance in BC1 Populations Derived from Interspecific Crosses Between Asparagus officinalis L. and Asparagus kiusianus Makino

Stem blight, caused by Phomopsis asparagi, is the most serious disease affecting the cultivation of asparagus (Asparagus officinalis L.) in the warm regions of East and Southeast Asia, including Japan. Although Asparagus kiusianus, a wild species endemic to Japan, shows strong resistance to this disease and is cross-compatible with cultivated asparagus, the genetic basis of this resistance remains unclear. In this study, we used BC1 populations from interspecific crosses between A. officinalis and A. kiusianus to dissect stem blight resistance inheritance and identify markers suitable for marker-assisted selection. Disease severity was evaluated using P. asparagi inoculation, and RAD sequencing was used to construct a linkage map and perform QTL analysis. Segregation patterns suggested that resistance was controlled by major genes and polygenic factors which depended on the cross combination. A major QTL was detected on chromosome 1 and SNP_PRK showed a significant association (LOD > 3). A dCAPS marker derived from SNP_PRK was associated with resistance, with approximately 80% of individuals carrying the associated genotype showing resistance. CAPS marker PR1 distinguished the same genotype classes and produced results consistent with those obtained using PRK in the evaluated materials. PR1 may therefore facilitate resistant individual selection in breeding programs.