| Phoebe bournei is a valuable tree widely cultivated for its nice timber and beautiful outlook throughout southern China,which is enlisted for valuable tree and national stocking plantations in China.Poor rooting is a common problem for the propagation of sapling of P.bournei by cuttings,tissue culture,and air layering so far,which detering propagation efficiency of superior sapling selected in young stand and establishment of clonal seed orchards.To screen out the effects of air-layering seasons,branch grades and wound position,growth regulators,medium types,medium wrapping material,and water supply on the rooting effect of 6-year-old branches in P.bournei,research was conducted by employing randomly complete block design or completely randomized block design.The purpose is to explore factors and their levels to improve rooting rate and survival rate after transplanting for sapling layers by air-layering in P.bournei,the results are as follows:(1)Spring and summer are the best seasonsfor air layering.Rooting ratesfor branches air-layered both in spring and summerare significantly higher than that in autumn or winterwhen branches are air-layered for 3 months,but not significantly differentwhen branches are air-layered for 6 months.Sois root effect index when branches are air-layered.It is concluded that the air-layered branches in spring or summer root within 3 months,which is 3months shorter than those in autumn and winter.(2)First-order branches are the best branches for air layering and their bases are the best place to be wounded for air layering of P.bournei.Index of rooting rate,number of roots,the total length of first-order roots,and transplanting survival rate of the first-order branches are the biggest,which are 53.33%,8.28,56.29 cm,and 80%respectively.The interaction is not significant between branch order and wound place.The rooting rate of first-order branch air-layered is 64.3%,which is significantly higher than that of the second-order branch(49.37%).Except for the average root length and average root thickness,other rooting indicators and transplanting survival rate of branches wounded in the base are significantly better than those of branches wounded in its middle.The rooting effect is similar between first-order branches and second-order branches if they are wounded at the base,but the first-order branches had better rooting effect.(3)1000 mg/L of naphthalene acetic acid(NAA)or ABT1~#rooting powder is suitable for the air layering of P.bournei.For single root stimulator,NAA is obtained to be the optimum auxin for rooting of air-layered branches for samplings of P.bournei and the branches treated with 1000 mg/L have the highest rooting rate of 54.67%.For ABT1~#rooting powder consisted of IBA and NAA,1000 mg/L was the optimal concentration,and the maximum first-order root length and root biomass of the air-layered branches treated at the concentration are better than the control.It is concluded NAA or ABT1~#rooting powder is recommended to apply at the level of 1000 mg/L in air layering for saplings of P.bournei.(4)The subsoil and coco coir 1:1 mixed medium or subsoil is the suitable substrate for the air layering of P.bournei.Root effect indexes of the three treatments with subsoil,subsoil,and coco coir 1:1 mixed substrate and peat-only medium are higher,which respectively were 1.33,1.44,and 1.72.The average root thickness and survival rate of the branch treated with subsoil and coco coir 1:1 mixed medium and subsoil were significantly better than those treated with peat only.It is concluded subsoil or 1:1 mixed medium of subsoil and coco coir is more suitable as the medium of P bournei.(5)The transparent packaging material can be used in the air layering of P.bournei.The root system in the soil lives in a dark environment,and some studies show that darkness is good for root growth.Our study results show that the rooting index,root length,and root diameter of air layered branches wrapped with black opaque plastic cups were not significantly different from those wrapped with colorless transparent plastic cups.Therefore,rooting is not influenced by the transparent of the wrapping material in P.bournei.Layers are found whether rooting directly to be transplanted if packaging materials are transparent,and non-transparent material is difficult to observe directly whether layers are rooting.It is concluded that transparent material is suitable to be wrapping material for medium.(6)Watering is not essential forbranches air-layered.The total length of the first root,average root diameter,root effect index,root biomass index rooting status of air layered branches watered once a month and without water were significantly higher than the once half a month,while the differences between once a month and without watering didn’t reach a significant level.The total length of the first root and root number total of air-layered branches in without water were significantly higher than once a month treatment,and the root biomass was significantly lower than that treatment of once a month.The root effect index of air-layered branches watered once a month was not significantly different from without water.It was concluded the substrate didn’t need the water supply or watered once a month.In summary,the rooting rate and survival rate after transplanting will improve effectively for sapling layers in P.bournei by manipulating factoes mentioned above.The method is considered to improve the efficiency to propagate ramets of superior saplings selected on growth performance in young stands,the duration is reduced for genetic testing and and establishment of clonal seed orchard in P.bournei.It is concluded that the results are significant for the breeding of new varieties and the application of elite seed in the cultivation of P.bournei. |
