Haploid regeneration system suitable for various genotypes of thin-skinned melons

Cucumis melo ssp. agrestis is a vital crop in the Cucurbitaceae family. Traditional breeding has been the primary method, but prolonged artificial selection has led to a gradual decline in the genetic diversity of thin-skinned melon. Haploid induction system combined with distant hybridization, backcross transfer, gene editing and other breeding techniques can realize germplasm resource innovation, increase genetic diversity of thin-skinned melon, and help thin-skinned melon breeding. This work first established a regeneration system for unfertilized ovules in thin-skinned melons. Based on the regeneration system, experiments were conducted using unfertilized ovules of different genotypes. The results showed that genotype had an impact on the formation of callus tissue, green cells, and bud differentiation in unfertilized ovules. Through validation with eight genotypes of disease-resistant thin-skinned melon, this method exhibits a haploid induction rate of 12.26%, a diploid induction rate of 54.72%, and a tetraploid induction rate of 33.02%. After SSR and SNP molecular marker detection, the obtained haploid plants were resistant to powdery mildew, downy mildew, and frost mold.