This study was investigated the effect of immature rhizome production according to harvest times-based treatment method for seed production of Gastrodia elata. The results revealed that when the tuber weight of G. elata harvested in spring (GEHS) was ≥ 100 g, the rate of artificial fertilization, protocorm formation, and immature rhizome formation was 90.9%–94.8%, 3.1%–5.4%, and 10.1%–15.3%, respectively. When G. elata harvested in fall (GEHF) was treated at a low temperature for 4 weeks or more, the rate of artificial fertilization, protocorm formation, and immature rhizome formation was 70.4%–87.6%, 2.2%–2.6%, 8.7%–9.5%, respectively. Therefore, to produce seeds and immature rhizomes, GEHS must have tubers of more than 100 g, whereas GEHF requires breaking dormancy by low-temperature treatment for 4 weeks or more. Compared with those of GEHS, the rate of artificial fertilization, protocorm formation, and immature rhizome formation was lower in GEHF; however, it was higher than those in the natural germination state. Thus, it can be expected that G. elata can be produced throughout the year by ensuring that the seeds and immature rhizomes of G. elata are produced using a constant tuber weight and by breaking dormancy with low temperature treatment.

The immature embryos during seed development were examined to predict the suitable embryos for an efficient regeneration system. Five spring wheat genotypes and five winter wheat genotypes were tested using immature embryos as explants. Spring wheat genotypes showed much higher levels of plant regeneration than those of winter wheat genotypes. The highest frequencies of embryogenesis and regeneration were obtained when embryos at 13-14 days after anthesis (DAA) were used as explant and decreased using embryos at 21-22 DAA during seed development. Significant differences were also found for callus induction and regeneration as affected by immature embryo size. The regeneration efficiency was drastically decreased in spring and winter wheat genotypes when embryos larger than 2.0 mm of length were used. The optimum developmental stage and embryo length for regeneration efficiency were at 13-14 DAA and 1.0-1.5 mm, respectively. The selection of suitable embryos for the high frequencies of embryogenesis and regeneration leads us to efficient genetic improvement of wheat.