Optimized shoot regeneration system for the commercial Korean radish 'Jin Ju Dae Pyong'

We have investigated the usefulness of hypocotyl ( cultured on N1B2 medium) and cotyledon explants ( on CR medium: Murashige and Skoog ( MS) medium, 3% sucrose, 20 mum benzylaminopurine, pH 5.8) for the regeneration of shoots of the Korean radish 'Jin Ju Dae Pyong'. The importance of ethylene ( indirectly), polyamines and gelling agent were studied in both media. Although the addition of ethylene-inhibitors and silver nitrate to the culture media were beneficial towards shoot regeneration and agar-based treatments (0.8% w/v) being superior in shoot production compared to agarose treatments (0.4% w/v), both explants responded differently in culture. Hypocotyls cultured in the presence of silver nitrate or aminoethoxyvinylglycine (AVG) regenerated significantly (p < 0.05) more shoots compared to N1B2 medium alone; supplementation of 20 μM AVG to N1B2 medium gave optimal shoot production (40% of explants regenerating shoots). The addition of 10 μM AVG to CR medium produced maximum shoot regeneration from cotyledon explants (60% producing shoots). Plants derived from 3-month-old cultures produced greater seed weights, larger leaves and greater genetic variability ( 50 - 80% of cells having 20 - 40 chromosomes) compared to seed-derived ( 85 - 90% diploid) and plants from 1-month-old cultures ( 78 - 88% diploid). Our results show, that if prolonged culture of explants is avoided, a large number of phenotypically-normal plants can be produced, which in turn, could be utilized in the genetic improvement of radish.