Pointed gourd (Trichosanthes dioica Roxb.) (2n = 2x = 22) is a dioecious cucurbit vegetable and green fruit that is edible after cooking. Consumers prefer to consume seedless or less-seeded fruit because seeds are unpalatable due to their hard coats. Therefore, the cross compatibility between the diploid and induced tetraploid will be helpful for seedless or less-seeded fruit production. Thus, the present study was conducted using mature seeds that were immersed in 0.05%, 0.1%, and 0.5% colchicine for 24, 48, and 72 h to induce tetraploids. These tetraploids were used as parents (male or female) in the inter-ploidy and intra-ploidy crosses. A flow cytometric analysis confirmed the induction of three tetraploids at 0.5% colchicine for 48 and 72 h soaking periods. Among these, two (2) females and one (1) male were differentiated after flower initiation. Crossing between the tetraploid’s maternal and diploid paternal parent (4x × 2x), which were revealed to be compatible, resulted in a similar fruit set rate and shape as those of the diploid. In addition, a seed number of 4x × 2x produced fruits that were drastically reduced to 1.8 seeds per fruit, whereas the natural diploid fruits had 26.4 seeds per fruit. These findings suggest that colchicine-induced tetraploid females are important genetic resources for less-seeded fruit production. The genetic stability of tetraploid clones can easily and effectively be maintained by vine cutting for advanced uses.

Stem blight, caused by Phomopsis asparagi, is the most serious disease of asparagus (Asparagus officinalis L.) cultivation in warm regions of east and southeast Asia including Japan. Although Asparagus kiusianus, a wild species endemic to Japan, shows strong resistance 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 the inheritance of stem blight resistance and identify markers suitable for marker-assisted selection. Disease severity was evaluated by 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 depending on the cross combination. A major QTL was detected on chromosome 1, and SNP_PRK showed significant association (LOD > 3). A dCAPS marker derived from SNP_PRK identified resistant individuals, with about 80% of heterozygotes showing resistance. CAPS marker PR1 discriminated susceptible, resistant, and heterozygous genotypes, and its genotyping results for all three genotypes were identical to those obtained with PRK. This marker may therefore provide a useful basis for selecting resistant lines in breeding programs.

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.