Study On Dwarfing Cultivation Techniques Of Magnolia Wufengensis

Magnolia wufengensis is a deciduous tree of Magnolia from Magnoliaceae,discovered in 2004.With beautiful crown shape and beautiful flowers,it is an excellent afforestation and flowering tree species.In the past few years,the seedling industrial development of this species has emerged and rapidly grown up,but its application is still limited to outdoor greening due to tall tree shape.In order to further enhance the ornamental and economic value and open the indoor seedling supply market,it is urgent to study its dwarfing technique.Magnolia wufengensis ’jiaohong 2’ grafted seedlings were used as experimental materials to study the effects of spraying different concentrations of morphactin(CFM)and different pruning methods on the morphology,resistance physiology and endogenous hormone indexes of seedlings under field and greenhouse conditions.The cultivation method of Magnolia wufengensis with good dwarf effect provides a preliminary technical basis for the cultivation of Magnolia wufengensis indoor flower bonsai.The results are mainly as follows:In the field,the seedlings were sprayed by five concentrations(0,50 mg·L-1,100 mg·L-1,200 mg·L-1 and 300 mg·L-1)of the morphactin.The results showed that:The best concentration is 200 mg·L-1,with the plant height(58.8 cm)and the intemode length(6.55 cm)were respectively descended to 39.1%and 71.6%of the control at the end of the first year.At the end of the second year,these seedlings were still dwarfed,with the diameter(15.40 mm),plant height(105.1 cm)and height diameter ratio were respectively reduced to 67.5%,51.9%and 71.7%of the control,and the first lateral branch number reached 7.7 per meter,115.4%of the control.In the second year,the inhibitory effect of the first year spraying on height growth was decreased and the additional dwarfing measures are supposed to be considered.In addition,the morphactin spraying produced a trunk refinement effect,resulting in that stem diameter(15.40 mm)decreased to only 67.6%of the control at the end of the second year.Besides,The sprayed seedlings responded to the growth stress by increasing the POD activity and soluble protein content of leaves,and maintained MDA content at the control level,indicated that the membrane system was not damaged,and the resistance of the seedlings was enhanced.Sprayed seedlings controlled the growth potential mainly by increasing ABA content to reduce GA3/ABA,ZT/ABA and(GA3+IAA+ZT)/ABA,while ZT content also decreased at highest concentration(300 mg·L-1),and thus cutting down ZT/ABA,enhancing IAA/ZT,inherently responsible for less lateral branches.In the field,only spraying 200 mg·L-1 morphactin in the first year(A),only 1/4 pruning in the second year(B)and "pruning based on spraying(both A and B)" were carried out.The results showed that:1/4 pruning in the second year maintained the dwarf crown shape induced by 200 mg·L-1 morphactin with higher level of coarse growth and side branch number.As the optimal treatment,the stem diameter(18.64 mm),plant height(103.5 cm),high stem ratio of "pruning based on spraying"treatment were respectively 83.6%,51.1%and 60.1%of the control,showing 9.2 first branches per meter(137.8%of the control).As for physiological responses,POD activity and soluble protein content of "pruning based on spraying" treatment kept higher than the control,while MDA content maintained the same,indicating that the membrane system was not damaged,and the resistance of the seedlings was enhanced.Besides,the contents of GA3,IAA and ZT declined and ABA content rose up.Hormone content ratios of GA3/ABA,IAA/ABA、ZT/ABA,(GA3+IAA+ZT)/ABA and IAA/ZT were decreased to the lowest among these treatments,thus inhibiting the top advantage and promoting lateral growth.In the greenhouse,the potted seedlings were sprayed by five concentrations(0,25 mg·L-1,50 mg·L-1,75 mg·L-1 and 100 mg·L-1)of morphactin,and the results showed that:with the optimal concentration of 75 mg·L-1,the seedlings diameter(7.74 mm)show no significant difference with the control,while height(42.2 cm)and height diameter ratio respectively decreased to 76.1%and 85.1%,with 9.7 first branches per meter,124.8%of the control.Besides,the morphactin spraying enhanced SOD activity,POD activity,soluble sugar content and soluble protein content of seedlings,showing enhanced stress resistance.However,MDA content of the leaves from the highest concentration(100 mg·L-1)group significantly increased in two months,indicating serious membrane damage.Under the morphactin treatment,the GA3 content descended while the ABA and ZT content enhanced.Besides,the ratios of GA3/ABA,(GA3+IAA+ZT)/ABA,IAA/ZT were reduced and ZT/ABA enhanced,which indicated apical growth inhibition and collateral growth promotion effectsIn the greenhouse,different pruning methods(control,topping,1/3 pruning)were carried out for potted seedlings.The results declared that:the best dwarfing effect was showed in the topping pruning treatment.The seedling diameter(6.32 mm)was similar to the control,while the height(34.3cm)was only 77.2%of the control.And the seedlings grew 10.2 first branches and 136.1cm branches in each meter of height,respectively 151.4%and 137.0%of the control.Under the topping pruning condition,the SOD activity,POD activity,soluble sugar and protein contents of seedlings firstly increased and then decreased to cope with mechanical damage,so that the MDA content of leaves remained at the normal level.After topping,GA3 and IAA content of leaves decreased,and the contents of ZT and ABA increased,which reduced GA3/ABA,IAA/ABA,(GA3+IAA+ZT)/ABA and IAA/ZT and enhanced ZT/ABA,thus controlling the top growth and motivating side branchesIn summary of those experiments,the best treatment for field dwarfing cultivation of Magnolia wufengensis is spraying 200 mg·L-1 morphactin in the first year after grafted,and then pruning a quarter length of shoots in the second year,while the best dwarfing treatment for greenhouse pot is spraying with 75 mg·L-1 morphactin or topping pruning in the second year after grafted.