Production and identification of melon double haploid induced by wide hybridization between melon and cucumber

Parthenogenesis is an important way for melon (Cucumis melo L.) haploid production, but difficulties remain in low induction rate, embryo rescue, and chromosome doubling. Wide hybridization of Gramineae crops can directly obtain maternal haploids without embryo rescue and then form double haploids by chromosome doubling. However, this method has not been applied to the melon. To broaden the double haploid creation pathway in melon, seven cross combinations of the genus Cucumis were used for wide hybridization. After pollination, the ovary was treated with forchlorfenuron and thidiazuron to promote embryonic development and chromosome doubling. Results demonstrated that the fruit setting rate was 67.67–84.00%. However, most of the fruits were parthenocarpic (empty seeds), and only one fruit from the combination of BPC-4 (C. melo ‘baipicui’) × YPJ-6 (C. sativus L.) obtained 3 mature seeds. After the 3 seeds germinated, only one seed developed into a plant. Then, the plant (F₁) was selfed and obtained F₂ and F₃. Chromosome counts showed that F₂ was diploid (2n = 2x = 24). Compared to BPC-4, the visible variation of compact on botanical traits appeared in F₂ and F₃ and was uniform in population among F₂ and F₃. 27 SSR polymorphic markers demonstrated that the maternal origin of gene locus and homozygosity of the F₂ hybrid plants. Genome resequencing analysis showed that the F₂ genomes were further purified by 0.24% compared to BPC-4. Therefore, the hybrid offsprings were double haploid. In conclusion, we are the first to induce a melon double haploid by wide hybridization.