Effect of optimal stage of female gametophyte and heat treatment on in vitro gynogenesis induction in cucumber (Cucumis sativus L.)

Gynogenic plants of pickling cucumber were successfully produced by in vitro culture from unpollinated ovules. Haploids and spontaneous doubled haploids originated directly through embryogenesis. The cucumber ovaries were placed on induction media containing thidiazuron and cultured in the dark for 2-5 days, at 24degreesC, 28degreesC or 35degreesC. After induction, the material was transferred to regeneration media containing a-naphthaleneacetic acid and 6-benzylaminopurine. Results from the regeneration test indicated that the heat treatment increased the efficiency of gynogenesis in the optimal developmental stage of the female gametophyte. The highest number of embryos occurred following the 35degreesC induction treatment. The maximum frequency of gynogenesis was 18.4%, while maximum plant regeneration was 7.1%. The flow cytometry analysis showed that 87.7% of the regenerants were haploid. On the basis of histological studies carried out on the female gametophyte, the best developmental stage for haploid induction seems to be the cellularization stage of embryo-sac formation, when the nuclei are already in position, the membranes have sometimes developed, and the cells are quite uniform in shape and structure.