Characteristic Parameters Of Apple Rootstock Vessel Element And Its Relationship With Dwarfing And Drought Resistance

High density planting with dwarfing rootstocks has become the main cultivation form for apple in China for its advantages of high field efficiency,early fruiting,high yield and simple management.Utilization of dwarfing rootstock is one of the methods for dwarfing.Dwarfing rootstock reasonably regulates tree growth potential and promote floral bud development so as to achieve the purpose of early flowering and fruiting,high quality and yield.Northern China lacks of rainfall for the monsoon climate,and rainfall varies between the interannual.The shortage of water resources has become the major influential factors of tree growth,while studies on drought resistance dwarfing rootstocks is inadequate.The rootstocks selection is a time-consuming,laborious work with low work efficiency.Therefore,this study is to provide theoretical basis for the rapid drought and dwarf rootstocks selection through the vessel element characteristic parameters and other indicators.In this experiment,rootstocks with different dwarfing degrees and drought-resistant degrees were used as test materials.The diameter,density,ratio of total area of vessel to xylem,length,width,length of end and tail,and inclination angle of end wall of root vessel molecules of branches and SH lines rootstocks with different lignification degree were studied by dissection and segregation,and the embolism vulnerability of woody branches of different rootstocks was measured to provide basic dwarfing and drought-resistant rootstocks selection.The main results are as follows:1.The root phloem ratio of SH lines rootstock was SH38,SH40,SH29 and SH28 from the largest to the smallest.SH38 and SH40 were identified as dwarfing rootstock and SH28 and SH29 as semi-dwarfing rootstock by the indexes of tree height,trunk diameter and total number of branches of different rootstock grafted varieties.2.The proportion of vessel diameter,area and total area of vessel in xylem of the branch of Begonia octagona was higher than that of dwarf rootstock.The diameter and area of vessel molecular lumen decreased with the increase of dwarfing degrees in M and SH lines,but there was no significant difference in the proportion of total lumen area to xylem.With the increase of dwarfing degree,the area and diameter of vessel molecular lumen decreased,while the density of vessel and the proportion of total lumen area to xylem increased.3.The element length of semi-lignified branches vessel of M and SH dwarf rootstocks was smaller than that of vigrous rootstocks(Malus robusta Rehd).The vessel element length of lignified branches of M and SH dwarf rootstocks was smaller than that of vigrous rootstocks(Malus robusta Rehd).The vessel elements end tail length of lignified branches of M line dwarf rootstocks was smaller than that of vigrous rootstocks(Malus robusta Rehd).The vessel element end wall tilt angle of lignified branches of M and SH dwarfing rootstocks was smaller than that of vigrous rootstocks(Malus robusta Rehd).The element tail length of root vessel of SH rootstock decreased with the increase of dwarfing degree.4.Except MM106 and SH38,the anti-embolism ability of dwarfing rootstocks decreased with the increase of lumen diameter.The maximum hydraulic conductivity of M-rootstock and Crabapple decreased with the increase of dwarfing degrees.Compared with that of SH line and Crabapple,except for the higher hydraulic conductivity of SH40,other rootstocks also conform to the above rules.The water transport rates of SH rootstocks were opposite to the dwarfing degree,that is,the higher the Dwarfing degree is,the lower the transport rate is.5.The area,diameter and total area of vessel in the xylem of rootstocks with strong drought-resistance were lower than those with weak drought-resistance.The density of vessel had no correlation with the degree of drought resistance.The length of vessel increased with the increase of drought resistance,and the diameter of vessel decreased with the increase of drought resistance.In terms of vessel molecular length,there were significant differences between strong drought resistant rootstocks SH40,J1 and medium drought resistant rootstocks,Huang6 and J2,weak drought-resistant rootstocks 24-5 and X3N1.The length of end and tail and the inclination angle of end wall of rootstocks with strong drought resistance were larger than those with weak drought resistance.6.The study on the vulnerability of different drought resistant rootstocks showed that the rootstocks with strong drought resistance had strong anti-embolism ability;Rootstocks with medium drought-resistance and weak drought resistance have poor anti-embolism ability.In terms of maximum water carrying capacity,the maximum water carrying capacity of strong and medium drought-resistant rootstocks increased with the increase of drought resistance.