Study On Shrink Of SH40 Interstock Apple Seedlings During The Temporary Planting Period

Seedlings are the material base of establishing orchards, and whether their quality is good or not has directly affected the survival rate of building orchards and the period of seedlings recovering, which is closely related to the early high yield of orchards. The apple trees with SH40 interstock possess various advantages, such as their early fruits, excellent fruits quality and strong overwintering ability. Therefore they have been popularized and applied extensively in the northwest regions and the North China. During the production, we find that the interstock segment of SH40 interstock apple seedlings shows shrink and folding phenomena firstly after lifting seedlings, these phenomena could weaken the tree vigor, and even make seedlings died, which could bring serious impact to the production. The study took apple seedlings with SH40 interstock as materials, observed the anatomy and measured the moisture transferring regulation of xylem vessels, the physiological indexes of soluble sugar, soluble protein, free water, bound water, bound water/free water and water potential and so on during the shrink process of seedlings, and explored the shrink reasons and the corresponding measures of the SH40 interstock apple seedlings. The main results were as follows:1. The retention ability of SH40 interstock segment was higher than that of the scions and the crabapple base stocks slightly. Its unit epidermal lenticel density and unit epidermal lenticel area were significantly less than those belong to the scions and the base stocks. Meanwhile, the epidermal transpiration intensity was less than the base anvil stems segment and the scion stems segment significantly. Therefore, the early shrink reason of interstock segment of SH40 interstock apple seedlings had no correlation with its epidermal shrink because of the transpiration.2.The anatomical structure showed that, the periderm thickness of the interstock segment was larger than other parts significantly, which was one of reasons that caused low epidermal transpiration volume. And the differences between the wood departmental area and the skin departmental area of interstock segment and the scion were not significant. The ratio of wood departmental area/ transverse area and wood/bark of interstock segment were less than the scion significantly. The lumen diameter of the interstock segment was larger than the lumen diameter of scions, therefore the unit moisture flow of the interstock segment was slightly higher than that of the scion, when there was water potential difference.3. Moisture migration tests indicated that, the water of SH40 interstock segment could move bi-directionally towards the scions and roots; the roots of seedlings would lose water with the fastest speed when they were exposed in the air, the larger root system, the faster shrink speed of seedlings. The fine roots possessed the fastest shrink speed, which is 2-4 times higher than the thick roots. It only took 3-5 hours for the roots whose diameter were 1-2mm to lose 30% moisture, then the roots would become inactivaty. Therefore, the shrink reason of SH40 interstock segment may be due to prolonged roots exposure in the air, and large amount of water was lost through the root system, transpiration pull formed inside the segment led to moisture moving from interstock to the root system. Besides, the lumen diameter of interstock segment were lager than the scions, which caused water moving rate was faster than those in the scions. Therefore, lacking of timely supplying water for the interstock segment caused their shrink and drape.4.There was a great effect of different shrink degrees on the survival rate of planting seedlings. When the shrink was 15%, the survival rate dropped to 60%; when the shrink was 20%, the survival rate was only 30%. With the increase of shrink degrees, the growth would weaken during the initial stage of planted seedlings. when the shrink reached 20%, long shoot proportion decreased, leafage branches ratio increased, then the tree vigor of seedlings decreased significantly. In the initial period of shrink, the osmotic adjustment substances of soluble sugar and soluble protein in trees would rise, the freedom water reduced, bound water gradually increased and water potential would decrease. However, the contents of soluble sugar and bound water began to decline irreversibly, when the shrink was more than 20%.5. Rehydration tests showed that when the shrink of SH40 interstock seedlings was 10%, the rehydration rate was faster; when the shrink was 15%, interstock and scions could survive thought rehydration; when the shrink was 20%, the rehydration rates of scions and interstock became slow; the shrink rate was more than 20%, water recovery ability had been greatly reduced, then continued to lose water, branches would lose rehydration abilities, even branches could rehydrate, they could not be restored to its original state. Therefore, shrink rate of 20% might be the maximum threshold of shrink to ensure the survival of seedlings.6. Through the protective measures to the roots demonstrated that the roots dipped mud, roots wrapped thin film, and the roots sprayed 40 times polyvinyl alcohol solution could prevent seedlings shrink effectively. Although polyvinyl alcohol 40 times could be able to prevent shrink of seedlings, it would cause a certain extent obstacles for seedlings to absorb water in the latter period, and also affect the survival and growth of seedlings. From an economic point of view, the roots dipped with mud were suitable for large-area applications in production.