Regeneration of double haploid plants from unpollinated ovary cultures of watermelon

Background: Watermelon (Citrullus lanatus), a major fresh fruit, is planted worldwide. Because double haploid plants may be used as parents to shorten watermelon breeding cycle, the present study optimized conditions for regenerating haploid plants from ovaries without pollination.Results: The results revealed that, the 10% sodium hypochlorite sterilized for 10 min is best for ovary enlargement. In addition, a dark culture period of 14 days promoted the ovary enlargement. The MS medium containing 0.5 mg/L NAA, 1.0 mg/L 6-BA and 0.5mg/L KT promoted the embryoid differentiation. The M2 medium containing 0.02 mg/L TDZ, 0.5 mg/L NAA, 0.5 mg/L 6-BA could be used for producing complete plants. The different genotypes affected the embryoid induction. The present study obtained regenerated plants that were established in field. Flow cytometry analyses revealed that the regenerated plants were haploid, diploid or tetraploid plant. The seedlings which were treated with culture medium can increase the chance of chromosome doubling. The SSR marker analyses showed that the diploid and tetraploid plants were homozygous at all six loci tested, indicating that these regenerated plants were double- or tetra-haploid plants.Conclusions: Haploid and homozygous diploid can be obtained through the culture of unpollinated ovary of watermelon, which is an effective way to innovate watermelon germplasm. The present study provides homozygous plants for future watermelon breeding.