Study Of Biological Characters On Triploid And Diploid Dioscorea Zingiberensis Plantlet

Dioscorea zingiberensis C.H.Wright,known as yellow ginger, is an important source plant for steroidhormone medicines. It is largely planted in Hubei, Shanxi, Henan, Hunan and other regions. The resourceof wild D.zingiberensis is being in exhaustion due to over-harvest in the past years and thus plantingbecomes the main source of this medicinal plant. However, some problems are present during planting suchas serious degeneration of quantity and decline of diosgenin content. Polyploid plants have some goodcharacteristics such as high production, high resistance to various diseases, etc. and thus can be aconsideration for breeding variety of Dioscorea zingiberensis with high yield, good quality and highresistance combined with tissue culture technology. In our previous study, triploid plantlets were obtainedby using endosperm cultivation technology. In this study, rapid propagation, dedifferention, diosgenincontent and resistance to diseases under different light intensity were compared between diploid andtriploid plantlets to evaluate their growth characteristics and provide theoretical basis for development ofnew varieties.The following main results were obtained:1. The suitable medium for plantlet rapid propagation were obtained by screening. The medium fordiploid and triploid plantlets was MS+6-BA2mg·L-1+NAA0.2mg·L-1and MS+6-BA1.5mg·L-1+NAA0.1mg·L-1, respectively. Both reproductive cycles were30d and the propagation coefficient was5.50and4.50,respectively.2. The suitable medium for plantlet rooting was selected. Rooting culture medium suitable for diploidand triploid plantlets was1/2MS+IBA0.3mg·L-1+Ce(NO13)35mg·L-and1/2MS+NAA0.3mg·L-1+Ce(NO3)310mg·L-1, respectively. Both rooting cycle were45d. Rrooting rate for diploid and triploidplantlets was98.75%and93.65%, and the root number was16.10and18.50, respectively.3. Callus induction, growth characteristics, soluble sugar and protein contents were investigated indiploid and triploid plantlets. The results indicated that the induction effects in stem were better than in leaffor both diploid and triploid; however, whether stems or leaves as explant, callus was easier to be inducedin diploid plantes than in triploid plantlets. The best media for diploid and triploid stems callus induction were same: MS+2,4-D1.5mg·L-1+6-BA1.0mg·L-1and induction rate was100%and80%, respectively;The best leaf callus induction medium for diploid and triploid was MS+2,4-D1.0mg·L-1+6-BA0.5mg·L-1and MS+2,4-D1.5mg·L-1+6-BA0.5mg·L-1, and the induction rate was93.75%and56.25%, respectively.Both growth curves of diploid and triploid callus showed "S" types in which diploid callus grew faster thantriploid callus with3days earlier of delay period and the exponential growth phase. In their growth periods,soluble sugar contents showed double peaks and soluble protein contents showed a single peak.4. Diosgenin contents in stems, leaves and callus in diploid and triploid plantlets were determined. Theresults indicated that diosgenin contents in leaves in diploid and triploid plantlets were2.876%and4.073%, respectively with an increase amplitude of41.61%in triploid plantlets; Diosgenin contents in stems indiploid and triploid plantlets were0and1.496%, respectively; Diosgenin contents in callus in diploid andtriploid plantlets were0.679%and1.676%, respectively, with an increase amplitude of146.91%intriploid plantlets.5. Some physiological and biochemical indexes of diploid and triploid plantlets were determinedunder different light intensity (750lx,2000lx and3200lx).(1) Soluble sugar and protein contents,chlorophyll a, chlorophyll b, carotenoid and chlorophyll content were highest at the light intensity of2000lx t. and were always higher in triploid plantlets than in diploid plantlets under each treatment;(2) Thecontents of O2·－, MDA and relative conductivity were lowest under the light intensity of2000lx, the valuesin triploid plantlets were lower than iin diploid plantlets in the above treatment;(3) SOD and PODactivities were highest under2000lx light intensity with higher values in triploid plantlets leaves, whichsuggested that triploid plantlets might have stronger resistance than diploid plantlets.