Affinity between rootstock and scion: Affinity is the basic condition for successful grafting. The so-called affinity refers to the similarity between rootstock and scion in internal organizational structure, heredity and physiological characteristics, as well as the ability to heal and survive by grafting, and the ability to adapt to each other physiologically after survival. The expression of (1) compatibility: the expression of low compatibility and incompatibility is complex and diverse, mainly including survival after grafting; Poor healing ability and low survival rate; Although the rootstock and both sides of the ear can heal, the grafted buds do not germinate or grow weakly after germination; The healing firmness is poor, it is easy to break and the section is smooth. Hawthorn grafted with apple can heal and grow, but after the second year, the scion is very thick and the rootstock is very thin, and it will soon die. This phenomenon is called early incompatibility. Pterocarya stenoptera grafted with walnut and Quercus variabilis grafted with chestnut grew well at first, which also made walnut bear fruit early. But ten years later, the growth of walnut was gradually blocked, weakened and finally died of premature aging. This phenomenon is called late incompatibility. For example, by dissecting the joint surface of rootstock and scion, we can see the embolic substance, the joint surface is smooth, the rootstock and scion are completely separated, and the tree suddenly breaks. Abnormal growth is characterized by delayed germination, shallower root distribution, smaller crown, early discoloration of leaves in autumn and early defoliation of new shoots, which is characterized by element deficiency. Late incompatibility often occurs in grafting between different genera or species of the same family. Local incompatibility is the incompatibility caused by actual contact between rootstock and scion. Adding an intermediate rootstock with compatible rootstock and scion in the middle will eliminate incompatibility. In this incompatible combination, the mechanical tissue of joints is often fragile, and the connection between cambium and vascular bundle is destroyed. But sometimes there are normal tissue connections, and the joints are still relatively firm. It shows that the anatomical structure of joints is disordered, and nutrients are difficult to transport through joints, leading to root death. The affinity between rhizome and panicle is good, which means that the interface heals well, the plant grows normally, the thickness of rhizome and panicle is the same, there is no tumor on the interface, and the healing trace is difficult to distinguish. The connection between the rootstock and the conductive tissues on both sides of the ear is neat and consistent, with normal effect and long service life.

(2) Factors that determine grafting affinity: Grafting affinity is determined by the differences in coordination of genetic, anatomical, physiological, biochemical and physiological functions formed in the process of plant system development, and is also influenced by viruses. Affinity, affinity is related to the affinity of plant classification. The closer the genetic relationship, the better the genetic relationship, and the strongest the genetic relationship between the same variety or species, such as Fuji apple grafted on Guoguang apple, Yangzhou Zaotian peach grafted on Zaomi flat peach and so on. The affinity between different species of the same genus varies with the types of fruit trees, such as different kinds of apples, different kinds of pears, sweet oranges grafted on lime, peaches grafted on mountain peaches and persimmons grafted on monarch butterflies. The genetic relationship between different genera in the same family is generally small, and grafted fruit trees are often used in production, such as quince grafted pear tree, orange grafted orange, heather grafted loquat and so on. There are also a few incompatibility phenomena between the same genus, such as satsuma mandarin and its lime, European sweet cherry and its wild beans. According to Wang (1996), different varieties of sweet persimmon have obvious differences in rootstock requirements. Most varieties of incomplete sweet persimmons, besides Zen Temple Pill, also have two varieties of complete sweet persimmons, Jiro and Huayusuo, which have strong adaptability to rootstocks and good grafting affinity with Junqianzi or wild persimmons 69 and 56. Completely rich in sweet persimmons, Izu and Matsumoto were born early, and Maekawa Jiro did not get along with Junchiko. According to the distribution rate of standard leaf output C and glucose in the upper and lower parts of the anvil, the radioactivity in the lower part of the anvil is the strongest.

Relationship between radioactivity and affinity below rootstock and panicle junction

No.77 wild persimmon is the second, and Junqianzi is the weakest. Grafting affinity of different ecotypes of the same species is sometimes different. Mengshan sweet tea and Taishan begonia are two ecotypes of Hubei begonia. Mengshan sweet tea is an excellent rootstock of apples in sandy land, but Begonia Taishan has poor affinity with apples, which is manifested by poor germination of grafted buds or their successive death after germination. The genetic relationship between different types in the same area is also different, and the genetic relationship between red begonia and yellow begonia is also significantly different. However, the genetic relationship is not completely consistent, and there are also strong grafting genetic relationships between different genera. For example, the affinity between mandarin oranges and bitter oranges of different genera is good, while the affinity between mandarin oranges and sour oranges of the same genus is poor. Different varieties of the same species grafted on the same rootstock have different affinities, and their affinities also change when rootstocks and scions are exchanged. For example, foreign pears are grafted on quince, Japanese chestnuts are grafted on chestnuts in China, and China plums are grafted on European plums, all of which are completely compatible, and rootstocks and scions are grafted interchangeably, so the affinity is not good.

② The relationship between the affinity of rootstock and scion and anatomical structure. Rootstock and scion adapt to each other in structure, and the tissues are closely connected, which heals the place where the survival process is smooth and has high affinity. If phloem connection is not good, the distribution of nutrients is abnormal; Or the xylem conduit is not well connected, which hinders the transportation of water and minerals; Or after grafting, the parenchyma cells of callus are too weak or impermeable to water at all, which makes the scion lose water and wither; Or the isolation layer between the rootstock and the scion incision is too thick, which can not heal or only heal in a small area, and the connection between the rootstock and the scion is fragile and eventually breaks. The similarity of parenchyma cell size and tissue structure of cambium on both sides of rootstock and scion is one of the important reasons for determining compatibility. Generally, the genetic relationship is inferred by the similarity of the minimum cell size on both sides of rootstock and scion and the compatibility of the growth rate and growth cycle of cambium cells. Rootstock phloem tissue is not jointed, which leads to root death, which is the reason why peach trees grafted on Anna Lee rootstock in Mali are incompatible. The rootstock is not connected with the rootstock cell wall, or only has staggered texture, which is the performance of the incompatible combination of Xiyang pear grafting. In the later incompatibility, black dead cork tissue (black walnut grafted with walnut) or incomplete joint, filled with parenchyma in the middle, poor growth and so on. (Pear grafted on apple rootstock) Often seen.

③ The relationship between compatibility and physiological and biochemical reactions of rootstock and scion, and the differences in absorption, manufacture, metabolism and enzyme activity between rootstock and scion will also cause incompatibility between rootstock and scion. If one side of the rootstock can't produce the enzyme that the other side needs to survive, or produce substances that inhibit or poison the activity of an enzyme of the other side, it will hinder or even interrupt physiological activities. When pear is grafted on quince, the difference of catalase activity between rootstock and spike is small (0. 1 ~ 1.5), and the affinity is good, but the difference is too large (> 1.0), and the affinity is poor. Apple with different combinations of rootstocks and scions had strong affinity when the phloem protein was similar to the enzyme. The osmotic pressure of rootstock also affects affinity. There is no physiological abnormality when rootstocks with high osmotic pressure are grafted with scions with low osmotic pressure. For example, western pears grow well with rootstocks, while autumn pears and bean pears do not perform well because the scions of western pears have high osmotic pressure. The metabolic rate and metabolites of rootstocks and scions also affect affinity. For example, the metabolism of nitrogen and phosphorus in rootstocks and scions is disordered, which leads to protein resistance and death, or resin, tannin or other toxic substances are produced during metabolism, which hinders healing. In the grafting of pear and quince, the cherry glycoside contained in quince root enters the pear scion and decomposes into cyanohydric acid, which can destroy the phloem at the upper part of cambium and interface, hinder the transportation of water and nutrients of rootstock and lead to plant death. Different pear varieties have different abilities to decompose cherry glycosides, so their affinity is different. If the rootstock absorbs too much inorganic salt, which exceeds the tolerance of the scion, the scion will also die. For example, China chestnuts were grafted with Japanese chestnuts, and Japanese chestnuts absorbed too much inorganic salts, which led to incompatibility.

④ The relationship between affinity and virus In the application of new rootstock types and types, many grafts fail to survive or grow poorly or even die after survival, and the seedlings without apomixis are incompatible with many varieties of scions and are highly susceptible because they are very sensitive to scions with viruses; If the rootstock carries the virus, the same scion will resist the rootstock virus and will still die gradually after grafting apomixis scion materials. The above situation shows that the grafting affinity among Malus species has nothing to do with chromosome ploidy difference. Generally, scions are diploid, while apomixis rootstocks are polyploid. For example, Hubei begonia has triploid and tetraploid, and Sikkim begonia is triploid. In production practice, 2 ~ 3 years after apple grafting, some plants become weak, bark cracks, xylem necrosis or pockmark appears, which is a highly infectious disease introduced by virus. Walnut takes black walnut as rootstock, and it produces black line at the joint and dies, which is caused by cherry leaf curl virus. Citrus wilt disease is a devastating virus disease. Sweet orange and some other oranges are grafted on lime. This is because sweet oranges carry viruses and are allergic to viruses. This disease caused South Africa, North America and California to give up lime suitable for local soil conditions as rootstock. When the scion is infected, the disease will not show symptoms. When the virus enters the rhizome, the tissue is necrotic, which hinders the transport of nutrients and causes the plant to die. If the scion is removed, the rootstock will recover even if infected, and other varieties can be grafted in the future. This is the real incompatibility caused by the virus. However, not all people infected with the virus will have incompatibility. Almost all varieties of Japanese satsuma mandarin are infected with the virus, but the rootstock of satsuma mandarin is resistant to the virus, so it is not harmed and grows normally.

(3) Methods to overcome incompatibility. The reason of graft incompatibility has not been fully understood so far, but there are some ways to overcome it in production. When the grafting combination is incompatible, the rootstock can be bridged with the rootstock compatible with the scion, or the seedling rootstock compatible with the scion can be planted beside the plant, and the scion can be butted after survival, so that the seedling rootstock can grow to the root system to maintain the normal growth of the scion variety. Double grafting is a common method to overcome graft incompatibility. If some varieties of western pears are incompatible with each other, the incompatibility can be overcome by selecting the western pears with good compatibility as the intermediate stock for double grafting. For the incompatibility caused by virus, the incompatibility of grafting can be overcome by removing the virus that hinders compatibility in scions and rootstocks. You can also use high temperature virus-free method and shoot tip culture method to virus-free infected rootstocks and scions before grafting.