Analysis of factors affecting the survival rate of pecan grafting
1 Grafting impact factor
1.1 Grafting time The time of pecan grafting varies according to the method of grafting, and the time chosen is also different. Generally starting from the spring, that is, March and April, if the grafting time is too early, it will lead to a low survival rate, if the grafting time is too late, it will lead to no germination or incomplete growth in the year of budding, and it is difficult to overwinter. Generally choose in the spring equinox to Qingming time, the local nursery choose to graft in mid-March, at this time the temperature is suitable, the temperature is constant, there is no obvious temperature change, the precipitation is sufficient, the sunlight exposure is also more suitable, the hickory tree is in the one-leaf stage, the plant circulation is fast, the growth rate after grafting is also accelerated, the physiological activity of the tree is exuberant, the rootstock injury flow is less, which is conducive to the healing of the rootstock.
1.2 Planting soil Quality Pecans have slightly different soil requirements for different varieties during grafting, and generally need to be planted in places where the soil is loose and breathable, the soil is fertile, and the nutrient supply in the soil is sufficient. Before grafting, according to the law of plant growth, the soil is sorted out, generally in the early spring, deep ploughing of the land will be refined, and soil fertilization, so that it has sufficient base fertilizer to supply pecan growth, and the soil sterilization treatment, increase the ventilation and ventilation performance of the soil, especially for the saplings ready to graft, should be fertilized and watered according to the terrain, slope, soil fertility, climatic conditions and tree growth status.
1.3 Quality factors of rootstock and scion Rootstock and scion are the decisive factors for the quality of grafting and the survival rate of pecans, whether in time, climate or grafting technology and other factors, it must be based on the quality of the grafted rootstock and scion. Therefore, special attention should be paid when selecting these two basic conditions. First, rootstock selection. Hickory grafted rootstock is currently mostly selected american thin-shell pecan seedlings or local pecan seedlings, rootstock seedlings require the thickness of the stem to be more than 1cm, the seedlings grow strong, no diseases and insect pests, smooth grafting sites; second, spike selection, collection and storage. First of all, the mother hickory tree that collects spikes should choose a mature tree with robust tree strength, full germination, light pests and diseases, strong affinity and excellent fruit quality. Secondly, the collection of panicles needs to select the developing branches of the year on the periphery of the ear mother tree, can not choose fruit branches, and requires the shoots on the spikes to be full, and the scion should be cut at any time on the spikes when grafting; third, the time of the collection of the spikes should not be too early or too late, generally collected in 1 to 2 months, after the collection must be timely sealing of the shears, and according to the type, thickness and thickness of the classification and bundling, generally 30 to 50 a bundle. After bundling, it is sealed in a plastic bag or wrapped with plastic wrap, placed at a low temperature for preservation, and the general temperature is controlled below 5 ° C, and the humidity is about 70%; fourth, the grafted variety is selected. For grafted varieties, we should try to choose varieties with good seeds or good fruit quality, high yield and stable yield, disease and insect resistance, cold and drought resistance.
1.4 Plant planting density Due to the large amount of nutrient supply required during the grafting process, each plant must have a certain growth space. At the same time, the planting density directly affects the ventilation and ventilation performance, the degree of closure, the incidence of diseases and insect pests, etc. of the seedlings in the seedling field, so the planting density of the seedlings in the nursery also directly affects the survival rate of grafting. Generally, it is advisable to colonize or keep 8 000 to 10 000 trees/667 m2 rootstock seedlings.
1.5 Water supply factors When rootstocking, the first task after filling the soil is to water the root water, and this watering must be watered thoroughly, so that it is in full contact with the soil, while strengthening the circulation of sap in the tree body and enhancing growth and healing ability. Water management in the grafting process is also very important, because in the grafting process to promote the healing of the incision through the circulation of sap, the sap is sufficient, the nutrient supply is comprehensive, the faster the healing speed of the grafting incision, the faster the growth rate of the branches, especially in the more arid and less precipitation areas and seasons, the soil moisture and the growth of seedlings should be observed in time to replenish fertilizer. Fertilizer water should be checked regularly during the process of survival rate check, and if drought is encountered, water can be replenished for 10 to 15 days to facilitate the germination of ear buds.
2 Grafting methods and techniques
2.1 Grafting method The grafting method used by pecans should be selected according to the variety of pecans on the one hand, and on the other hand, it should be combined with its growth and planting environment. Depending on the time of grafting, there are different grafting methods for different varieties of grafting. At present, the production of pecan grafting seedlings can choose to graft nutrient bag seedlings and graft bare root seedlings, and the grafting method generally adopts cutting. (1) Grafting seedlings. There are two ways to graft seedlings, the first is to graft nutrient bag seedlings, that is, the prepared nutrient soil is loaded into a non-woven nutrition bag, and then sown or transplanted in the bag to cultivate rootstock seedlings. The survival rate of this grafting and seedling method is relatively high, generally more than 95%, and the time for seedlings to go up the mountain for afforestation is also extended, and the root system is intact. The second is grafting bare root seedlings, that is, in the process of transplanting rootstock seedlings, the root system does not carry soil, this plant has lower resistance and weak adaptability in the initial growth process, but as it grows gradually, the vitality is gradually vigorous and grows more rapidly, but the survival rate is less than the first way. (2) Grafting method: cutting. After years of practice, pecan grafting adopts this grafting method with strong practical operability and high survival rate. The main steps are: the rootstock retains 5cm shear, the scion is cut into a wedge shape, the long cutting surface is cut into 3 to 4cm, the cutting layer is slightly thinner, not exceeding the center of the pulp, the short cutting surface is controlled at about 1cm, and the scion shear retains 2 buds. When grafting, the rootstock first has a knife back- and slightly cut off with xylem, the length of the incision is slightly shorter than the long cutting surface of the scion, and then insert the scion, pay attention to the whiteness when inserting the scion, align the formation layer, and finally be sure to wrap it tightly with a special plastic belt for grafting.
2.2 Grafting technology In the process of grafting, we should pay attention to several technical essentials. First, the grafting speed should be fast, avoid letting the incision touch other items, do not let the scion stay in the air for a long time, and the scion cutting should also be used with the collection, on the one hand, to reduce the threat of pests and diseases, on the other hand, to reduce water loss. Second, pay attention to the early stage of pecan grafting must pay attention to avoid injury flow, otherwise the survival rate is reduced, and the rootstock should be injured and released water 2 to 3 days before the rootstock grafting or released water in the rhizosphere in time after grafting to reduce the impact of injury flow on the survival rate. At the same time, it is also necessary to do a good job of water control and de-germination work after receiving, and often check whether the joint is waterlogged within 2 weeks after the connection, and if there is water accumulation, it should be injured and released in time. After the grafting, the tillers should be erased in time to prevent nutrient consumption and help the healing of the grafting site. Third, according to different conditions, choose the appropriate grafting period and method, the grafting tool should be sharp, and the cutting surface should be kept smooth. The anvil panicle formation layer should be aligned, and the anvil should be aligned on one side when the thickness of the anvil is inconsistent. Fourth, after the end of the grafting, it must be tied tightly with a plastic film with good air permeability, and ensure that the interface is straight, flat and aligned to prevent water loss, and if it is found that the strap affects the growth of the branches, it should be lifted in time. When lashing, it can be fixed with a small wooden stick to play a role in preventing wind blowing and folding.
3 Post-grafting management factors
After grafting of pecans, there are a series of post-grafting management work such as patching, removal of germination, anvil cutting, unbundling, heartbreaking, shading, cold protection and disease prevention, which are all factors that affect the survival rate of grafting. If the early grafting growth is successful, and the management of it is relaxed in the later stage, it will still lead to a decline in the survival rate. Therefore, it is first necessary to check regularly and make up for those who have not survived in time to improve the survival rate. Then de-germination is carried out, and the buds on the rootstock are removed to promote the growth of the buds, and the time can be controlled at about 10 to 15 days. When the grafted new shoots grow to more than 5 cm, the plastic film should be untangled to avoid the growth of the grafted branches. When the new shoots grow to more than 30 cm, in order to ensure the safety of the plant overwintering, it should be hearthed, and at the same time, wintering and cold protection should be carried out. Measures such as plastic film wrapping can be selected; followed by the control of pests and diseases, and strengthening pest control is also an important factor in improving the survival rate. 2 different varieties of pecara are grafted, and in the process of grafting, they may be exposed to bacteria, insect eggs, etc., while rootstocks have low resistance in the process of growth and repair, so they are very susceptible to diseases and insect pests. The most common pests and diseases of hickory are: hickory blight, hickory branch blight, hickory red leaf spot, hickory aphid and Tianshe moth (green worm), etc., which occur in different growth periods. At the same time, the grafting of 2 varieties of plants will make the plants produce unsuitable performance or carry the diseases and insect pests that are prone to both, so it must be prevented in advance, and the chemical and physical control according to the growth stage and the diseases and insect pests that are prone to occur will often achieve the effect of doubling the results with half the effort.