Efficient induction of gynogenesis through unfertilized ovary culture with winter squash (Cucurbita maxima Duch.) and pumpkin (Cucurbita moschata Duch.)

Gynogenesis induction through unfertilized ovary/ovule culture is an effective way to accelerate breeding schemes by obtaining homozygous materials in a brief period, and great progress has been made with cucurbitaceous crops in recent years. However, limited studies are available for Cucurbita plants, especially winter squash (Cucurbita maxima) and pumpkin(Cucurbita moschata). Unfertilized ovary culture was conducted in this study with 13 Cucurbita lines (nine winter squash, three pumpkin, and one winter squash/pumpkin hybrid). First, we evaluated the effects of genotype and induction media on unfertilized ovary cultures. The results showed that the induction rates of both embryo-like structures (ELSs) and plantlets induction rates varied with lines in the same culture condition and different lines had different optimum induction media. Eight of the 13 Cucurbita lines produced ELSs successfully. The highest ELS and plantlet induction rates were 39.67 ELSs and 10.18 plantlets per 100 ovary slices, respectively, and were obtained in I-3 media with 1.0 mg L-1 6-benzylaminopurine (6-BA) in the L-13 line. The ploidy level of 59 regenerated plants was determined by flow cytometry, and the results demonstrated that 18.64 % were haploid, 3.40 % were haploid-diploid, 32.20 % were diploid, and 45.76 % were tetraploid. Second, we calculated the effects of genotype, induction media, and their interaction on ELS induction for the first time by a two-way ANOVA. We found that both genotype and induction media have significant effects on ELS induction, but their interaction played a more important role. Third, we domesticated and transplanted a part of the regenerated plants and conducted self-cross and character observation. Finally, we found one line, that had a smaller lumen and fewer seeds compared with donor fruits. In conclusion, these findings might provide an important reference for future research regarding gynogenesis induction and accelerate the application of unfertilized ovary/ovule culture in Cucurbita breeding.