Studies On Cold Resistance And Its Related Factor Of Young Apple Trees On The SH40Dwarfing Interstocks

Cold resistance was an ability of fruit tree to adapt and resist to the cold climateinfluenced by genetic factor, the environment and the technologies of the culture andmanagement. Studies on cold resistance had important directive to the regionalization offruit tree, productive practices, research and development. The SH40dwarfing rootstockshad become one of important dwarfing interstocks which were concentrated on spreadingin the north of apple-producing areas for its strong resistence to both cold and drought andthe good dwarfing characteristic, but if not well managed, the cold injury of young appletrees on SH40dwarfing interstocks was at higher risk in the north boundary of the applesuitable cultivation area than other areas. Therefore, the study on cold resistance of youngapple trees on the SH40dwarfing rootstocks, especially the study on the related factor ofcold resistance, has an important directive to the culture and management of young appletrees.In order to ascertain the relationship between cold resistance and the annual changesof soluble sugar, starch, soluble protein contents, The seasonal changes and regionaldifference of cold resistance of young apple trees on the SH40dwarfing inter-stocks andsome physiological indexes were studied by electrical resistance method （EL） andelectrochemical impedance spectroscopy （EIS）. Meanwhile, to provide theoreticalguidances and techniques for the scientific management of young apple trees, the effects ofthe tree age, shoot angles and intercropping on cold resistance and some physiologicalindexes in young apple trees also were studied. The main results were as follows:1. The relative electric conductivity of young apple trees on SH40dwarfinginterstocks had increased with the decreasing temperature. The relative electricconductivity of apple shoots declined from summer to next Spring, and there was a trend oftransverse tensile about the curve. But an increasing trend was found in the relative electricconductivity of the next February.2. Electrical impedance spectrum, like a U-type, enlarged with the seasons, while thearc of the next February became smaller than January. The extracellular resistance （re） hadthe same change trend with the low frequency resistance （r₁）. They showed that theresistances （re, r₁） was significantly increased after September and then gradually declinedafter a peak in the next January. The intracellular resistance （ri） and the high frequency resistance （r） had an obvious ascend trend in September and a stable level after that, butthere was another gradual increase until the next January. The relaxation time （τ） decreasedwith decreasing temperature, but the distribution coefficient of the relaxation time （ψ） hadno clear change law. The correlation analysis showed that the cold resistance of youngapple trees on SH40dwarfing interstocks could be evaluated by the change of EISparameters riand re. The cold resistance which was evaluated from the EIS parameters ofapple shoots, such as re, r₁and ri, had a clear correlation with that which was measured bythe EL method in every month, and the methods by re, r₁and ricould evaluate the coldresistance of young apple trees. However, the cold resistance evaluated by the EISparameters was weaker than that measured by EL method, and this characteristic was moresignificance when the stronger cold resistance of the plant was evaluated by the EISparameters or in the periods which the plant had higher cold resistance.3. The cold resistance of young apple trees on the SH40dwarfing interstocks varied insimilar manners, and the cold resistance of different tree ages and varieties was obviousdifference. The semilethal temperature （LT50） of the shoots decreased a little during July tomid-August. Which stabilizes at around7℃to12℃. There was a strongly decreasedafter mid-August, and a slow increasing after the nadir in January. The cold resistance ofone-age and two-age apple trees was weaker than that of four-age apple tree, especiallyduring November this year to January next year in which the differences in semilethaltemperature were as high as6-8℃. The cold resistance of Orin was higher than Fuji,especially during November and January next year. The differences in semilethaltemperature were around2℃.4. The obvious changes of soluble sugar, starch, soluble protein in apple shoots wereassayed from the growing season to the dormancy release period. The soluble sugarcontent maintained at a low level （3%-4%） from the mid-August to the mid-October. Therewas a significant accumulate before December, and the content declined after then. Thecontent of starch increased after the mid-August and attained the highest in mid-October,then gradually decreased and attained the lowest in the next January. The soluble proteincontent accumulated after the mid-August and attained the highest in mid-October, thenmaintained at a high level before the next January and declined after then.5. Comparison with the apple tree of one-age, two-age, the soluble sugar content offour-age apple tree was significantly higher （P<0.01）. The soluble sugar content of one-ageapple tree was significantly lower than that of two-age tree in the mid-October, and therewere no significant difference in other periods. The starch content of one-age apple treewas significantly higher than those of one-age and two-age apple tree in the period of Julyto December, but no significant difference in the next January and February. The starchcontent in shoots showed no significant difference between one-age apple tree and two-ageapple tree in the mid-October, but no significant difference in other periods. The soluble protein content of four-age apple tree was significantly higher than those of one-age andtwo-age apple trees in every month, The soluble protein content in shoots showed nosignificant difference between one-age apple tree and two-age apple tree except forNovember, December and January next year.6. The soluble sugar content of Orin apple trees was significant higher than Fuji appletrees in the mid-July, the mid-August, the mid-November and the following February, butno significant difference in the mid-September and the mid-October. The starch content ofOrin apple trees was significant higher than Fuji apple trees in the course of accumulation,but was lower than Fuji apple tree in course of starch transformation. The starch convertedcompletely in the mid-January, and there were the same starch transformable efficiency inOrin and Fuji apple shoots. The soluble protein content of Orin apple trees was significanthigher than Fuji apple trees in the periods from the mid-September to the next January.7. The cold resistance of the different localities of young apple trees on SH40dwarfing interstocks, which came from the same seedling nursery, was increased with thelatitude increasing, but the degree of increasing was limited. The results indicated that thecold resistance of sanhe Fuji was strongest among four regions of sanhe, shunping,xingtang and neiqiu. The cold resistance of Fuji apple trees, came from shunping region,was better than that in xingtang and neiqiu. The cold resistance of Orin apple trees, camefrom pingquan and sanhe region, was stronger than that in neiqiu region, but there was nosignificant difference between pingquan Orin and sanhe Orin. The contents of solublesugar, starch and soluble protein were coordinated with the cold resistance.8. The cold resistance was significantly enhanced with the increasing age （P<0.01） in0ne-age, two-age and three-age trees, but no significant difference between three-age andfive-age apple trees （P>0.05）. The contents of soluble protein, soluble sugar and starch inthe annual shoots were assayed. The results indicated: the content of soluble proteinobviously increased with the increasing age （P<0.05）, but there was no significantdifference between three-age and five-age apple trees （P>0.05）. The content of solublesugar in three-age apple trees was significantly higher than that in two-age apple trees（P<0.01）, while no significant difference between one-age and two-age apple trees, as wellas between three-age and five-age trees. However, there was no significant difference inthe starch content of trees at different ages （P>0.05）.9. Branch angle affects the cold resistance of young apple trees and the level of somenutritious substances accumulation, such as soluble sugar, starch, soluble protein and so on,but there was still some difference in different apple cultivation area. In Hebei Province,the cold resistance of branch angle80-90°was stronger than that of branch angle40-50°and branch angle110-120°, and in the north of Hebei Province the cold resistance ofbranch angle110-120°was better than that of branch angle40-50°. However, there was nosignificant difference between branch angle40-50°and110-120°in the south-center of Hebei Province. The contents of soluble sugar, starch and soluble protein were coordinatedwith the cold resistance.10. The cold resistance of apple trees in the apple-cowpea intercropping system wassignificantly lower than that of the pure apple tree stand during the winter and beforesprout （P<0.01）. The physiological parameters including soluble sugar, starch and solubleprotein were assayed. The results showed that the soluble sugar and soluble proteincontents in one-year-old apple shoots which intercropped with cowpea were significantlylower than those in the control in the two periods （P<0.05）, and the starch content waslower in the midwinter （P<0.05）, but no significant difference before sprout. Comparedwith clean cultivation, the ratio of the vertical long shoots in intercropping system wassignificantly higher, and the average length of super long shoots and the autumn shootswere much longer, but the diameter of the super long shoots was much smaller.