Preliminary Study On The Mechanism Of The Position Effect Of Ginkgo Grafting

Ginkgo biloba L.belongs to the genus ginkgo in the ginkgo family,and integrates medicinal,edible,wood and ornamental values.At present,the excellent varieties of ginkgo are all propagated by grafting methods,but the grafting reproduction has a position effect,the main branches grow diagonally,and there is no obvious trunk.The mechanism of this phenomenon is still unclear.In this study,shoots with good growth conditions in the upper and lower parts of the crown of the real ginkgo tree and the base of the trunk were used as grafting materials.The growth angles of new shoots,related endogenous hormones and regulatory genes were measured and analyzed.The disclosure of the mechanism and the cultivation of ideal plant type ginkgo grafted seedlings provide theoretical basis and technical support.The main results are as follows:?1?The growth of grafted seedlings derived from the base of the trunk of the solid tree is relatively upright,and the angle of new shoot growth is small,while the growth angle of grafted seedlings derived from the scion of the upper and lower crowns of the solid tree is larger.After May,the new shoots of the three grafted seedlings showed upward bending growth,and the greater the base angle,the greater the degree of bending growth.When the grafted seedlings were branched at 60°and 90°,the new shoots showed a greater change in bending growth as the branching angle increased.?2?The content of the growth-promoting hormones IAA and GA₃ on the lower side of the new shoots of the three grafted seedlings was higher than that on the upper side,and the growth speed of the lower side of the new shoots was faster than that on the upper side.The upward growth provides the supporting force,while the grafting seedlings from the base have the largest difference in the content of the upper and lower sides,and the growth is more upright.In addition,the uneven distribution of BR on both sides of the new shoots also participated in regulating the growth direction of the new shoots.At the same time,the content and difference of IAA,GA₃,ZR and BR on the upper and lower sides of the new shoots will change with the branching angle,indicating that IAA,GA₃,ZR and BR are closely related to the Angle development of new shoots of grafted seedlings.?3?The expression of GbLAZY1 in the new shoots of grafted seedlings had a negative correlation with the growth angle of the new shoots.From April to June,the expression level of GbLAZY1 in the new shoot stem segments of the grafted seedlings at the base of the scion source was higher than that of the grafted crowns of the crown of the scion source.At the same time,GbLAZY1 is highly expressed mainly in the stem segment,followed by tip and leaf.After the new shoots of the grafted seedlings were pulled,the expression of GbLAZY1 in all parts of the stem segment was up-regulated,and in June,the expression of GbLAZY1 at the upper end of the new shoots increased with the angle of the shoot.?4?The expression levels of GbLAX1 and GbLAX2 on the upper and lower sides of the new shoots of the three grafted seedlings were higher than those on the upper side,and the difference between the upper and lower sides of the new shoots on the base of the scion source was the highest.Therefore,more IAA was input on the upper and lower sides of the new shoots,and the difference in IAA content between the upper and lower sides of the grafted seedlings at the base of the scion source was the largest.At the same time,there was no significant difference in the expression of GbPIN1 and GbPIN2 between the three grafted seedlings on the upper and lower sides of the new shoots,and the expression of GbPIN1 and GbPIN2 on the lower and upper sides of the grafted seedlings at the base of the scion source was the highest.The content of lateral auxin is higher than that of the upper side,and the new shoot growth of grafted seedlings at the base of the scion source is more upright.The expressions of GbLAX1,GbLAX2 and GbPIN1 and GbPIN2 in the upper and lower sides of the new shoots of the grafted seedlings were upregased to different degrees by the treatment of branch extension.By changing the auxin content in the upper and lower sides of the new shoots,the upward bending growth of the front end of the new shoots was further induced.In summary,the content of IAA and GA₃ on the upper and lower sides of the new shoot is an important factor that affects the different initial growth angles of the new shoot.The change of the extension angle of the new shoot is related to the difference in the contents of IAA,GA₃,ZR and BR on both sides of the new shoot.At the same time,the differential expression of GbLAZY1 and auxin polar transport genes GbLAX1,GbLAX2 and GbPIN1,GbPIN2 are involved in regulating the growth of grafted shoots.