DIRECT SHOOT FORMATION AND PLANT-REGENERATION FROM COTYLEDON EXPLANTSOF RAPID-CYCLING BRASSICA-RAPA

An in vitro culture system for direct shoot regeneration from cotyledo n explants of rapid-cycling Brassica rapa was developed. Cotyledons fr om 3-d-old seedlings, when cultured on Murashige and Skoog (MS) medium supplemented with 20 mu M N-6-benzyladenine (BA) and 2 mu M alpha-nap hthaleneacetic acid (NAA), regenerated shoots directly at a frequency of 20%. The addition of 2 mu M aminoethoxyvinylglycine (AVG) to this m edium increased shoot regeneration to 33%, but silver nitrate drastica lly inhibited shoot regeneration. Shoot regeneration occurred directly , at the petiolar cut ends of cotyledonary explants, between 10 to 17 d in culture. The highest percentage of regeneration (33%) was obtaine d from 3-d-old seedlings. NAA was the most effective auxin for root in duction and development, with 49% of shoots producing roots after 2 wk on medium containing 1.0 mu M NAA. Regenerated plantlets were grown t o maturity in pots containing peat moss and vermiculite (1:1). These p lants were morphologically normal and fertile. With this protocol, ove r 100 independently derived, flowering R-0 plants were obtained from 4 0 regenerating cotyledonary explants within 40 d after culture initiat ion.