Section 2 Control the growth of summer shoots

1. Branch growth

The citrus bud is covered by several pieces of undeveloped fleshy first leaves. Each leaf axil of the first leaves has a bud and several latent buds, so several new shoots can often sprout on a node. Using this feature, manually erase the first sprouted shoots, which can promote the germination of more new shoots. A few days after the elongation of the new shoots of citrus stopped, the apex of the tender shoots could fall off automatically, which is called the phenomenon of "self-cutting" of the top buds. Therefore, citrus shoots have no terminal buds, only lateral buds. Citrus buds are divided into leaf buds and flower buds. Leaf buds only sprout branches, while flower buds can not only sprout branches, but also blossom and bear fruit. Citrus shoots can be divided into spring, summer, autumn and winter shoots according to the occurrence period. Spring shoots generally sprout from February to April and are important branches in the year. Spring shoots can be divided into flowering branches and vegetative branches due to their different properties. After flowering, flowering and fruiting at the top or leaf vein. The vegetative branch has only leaves and no flowers. It mainly produces nutrients. After development, it can become the fruiting mother branch of the next year. Therefore, the development of spring shoots affects the yield of the year; Summer shoots sprout from May to July. They grow vigorously in high temperature and rainy season. The branches are thick and long, and the leaves are large and thick. Summer shoots sprout irregularly under natural growth. When summer shoots sprout in large numbers, they often compete with young fruits for nutrients, which aggravates physiological fruit drop. Therefore, in addition to expanding the use of young trees to fill the crown, production should control summer shoots more; The autumn shoots are harvested in batches from August to October. The growth potential is stronger than spring shoots and weaker than summer shoots, and the leaf size is between spring and summer shoots. Young trees and early fruit trees have a large number of autumn shoots. The robust autumn shoots are excellent bearing mother branches with good flower quality and reliable fruit setting. In order to increase the number of flowering and fruiting in the next year, the measures of wiping out summer buds and promoting the release of autumn shoots were adopted in cultivation; In areas and years with warm winter, winter shoots can be sprouted around November, but the number is small, and it is not easy to ripen, and the low temperature is often affected by freezing. Some winter shoots can bloom in the next year, but the flowers and fruits fall seriously. Winter shoots have no use value in production, and should be pruned more.

2. Technical measures to control the growth of summer shoots

(1) Spraying paclobutrazol with a concentration of 250~1000mg/L on the leaves of citrus during the summer shoot occurrence period can shorten the summer shoot by 50%~75%, shorten the internode, slightly reduce the number of summer shoots, increase the summer leaves, increase the fruit setting rate by 2%~4%, increase the yield by 6%~48%, thin the peel, and increase the edible rate. When applied in production, the concentration of satsuma mandarin is 750 mg/L, Ponkan mandarin is 1000 mg/L, and local early is 500 mg/L. Tong Changhua et al. (1987) advanced the spraying period to the end of spring shoot elongation, which had a more significant effect on inhibiting the occurrence and elongation of summer shoots and improving fruit setting rate and yield. The sugar orange fruit-bearing trees were sprayed with 500 times of liquid once at the second physiological fruit fall (when the summer shoots were about to be pulled out), and the second time every 20 days. PP333 was sprayed on the tree crown, and the germination amount of the summer shoots was 35%~37% of that of the control sprayed with water. When the spraying concentration of dark orange is 250~750mg/L before the occurrence of summer shoots, the summer shoots can be shortened by 11%~26%, and the inhibition effect will be strengthened with the increase of the application concentration, without affecting the fruit development and quality. The application of paclobutrazol with a concentration of 1000mg/L can make the "generation" of potted plants grow slowly and robustly, and can inhibit the growth of roots, meeting the requirements of potted plants. Mei Zhengmin et al. (2009) suggested that the effect of the use of penicillin 500mg/L+paclobutrazol 700mg/L in production was better when the new shoot length was about 2cm, and the number of drug use should not exceed two times a year.

(2) During the summer shoot emergence period of the 3-year-old Weizhang satsuma mandarin, the number of summer shoots of the former is only 65.8%~86.9% of the control, the branches are shortened, the fruit setting rate is increased by 5.1%~5.6%, and the yield is increased by 40%~50% when the concentration is 2000~4000 mg/L or the concentration is 500~1000 mg/L of the water solution of chlormequat is sprayed at the rhizosphere of each plant; The number of hair shoots of the latter decreased by 1-2%, the fruit setting rate increased by 1.4%~3.3%, and the yield increased by about 10%. The fruit quality is the same as the control. However, the fruit irrigated with 1000mg/L chlormequat aqueous solution in the rhizosphere is orange-red, bright and pleasing to the eye, and full of luster.

Section 3 Flower and fruit thinning

1. Flower and fruit thinning mechanism

Too many arboreal flowers and fruits consume the nutrition of the tree, inhibit the growth of new shoots, form large and small years, make the tree weak, and even die due to too many fruits. Artificial fruit thinning is adopted, with large labor consumption and high cost. Y. Kamuro et al. (1982) found that the ethylene content in the leaves of satsuma mandarin rose after spraying indole ester, which suggested that during the physiological fruit fall of citrus, spraying indole ester could promote the occurrence of ethylene, thus accelerating the formation of separation layer and promoting fruit fall. Compared with NAA and ethephon, the amount of ethylene produced by indole ester is less than that produced by NAA and ethephon, but the duration of ethylene production is longer, which is consistent with the late and longer peak of young fruit abscission reported by Shi Xuegen after spraying indole ester (Wang Yangjie et al., 1995).

2. Technical measures for chemical flower and fruit thinning

(1) Naphthylacetic acid is used for fruit thinning of satsuma mandarin. It is generally effective to spray wine 20~30 days after blooming. In areas where the temperature rises quickly in spring and flowering is relatively early, it is better to spray wine 20 days after blooming, and on the contrary, it is better to spray wine 30 days after blooming. The application concentration is 200 mg/L. When the amount of fruit set is very large and the temperature is low, the concentration of alcohol that can be sprayed is 300mg/L. Spraying at the above concentration and time can maintain the leaf-fruit ratio of satsuma mandarin at (20~25): 1, reaching the degree of artificial fruit thinning. (2) Indole ester The common concentration of indole ester is 100-200 mg/L, and it is ideal to spray it 30~50 days after full bloom, among which local early and early maturing satsuma mandarin is 30 days after full bloom, and common satsuma mandarin is 40~50 days after full bloom. One week after spraying, a large number of small fruits turn yellow and fall off. The peak period of fruit falling lasts for 5~10 days, and the fruit falling period lasts for about 2~3 weeks. It can make the mature fruit uniform in size, reduce the peeling, color early for 5~9 days, increase the sugar content, and improve the content of amino acids in the fruit. The removal rate of satsuma mandarin, local early and ponkan mandarin can reach 20%~60%. Generally, the smaller the fruit diameter is, the easier it is to be removed. With the increase of the fruit diameter, the removal rate gradually decreases. However, orange trees with extremely weak growth, more flowers, more fruits, smaller fruit shape or excessive growth and less flowers are not suitable for application. In addition, it is not allowed to increase the concentration of liquid medicine at will to avoid excessive fruit thinning.

Section IV Control of flower amount

1. Flower bud differentiation

Most citrus species in subtropical areas undergo flower bud differentiation before and after fruit ripening in winter and before sprouting in the spring of the next year, but the same variety also differs in the same place due to year, tree age, nutritional status, tree vigor, fruit status, etc. In addition, on the same plant, spring shoots differentiated earlier, followed by autumn shoots and summer shoots; The short shoots differentiated earlier than the long shoots; The bud at the base of the long branch is earlier than the bud at the top. For example, in Chongqing, Huang Huibai et al. (1991) observed that the flower induction period of Dark Orange was from the end of September to the end of October; Liu Zhongxiao et al. (1984) reported that the induction period of orange flowers in Fulingxia was from early September to mid-October. In central China, Wenzhou mandarin oranges in Yichang, Hubei Province began to undergo flower bud differentiation in late December (Chen Jiezhong, 2003). Citrus flowering is a complex physiological and biochemical process affected by many internal and external factors. It is not only the accumulation of nutrients, the dynamic changes of hormones, but also controlled by genetic genes. Citrus is a perennial woody plant, which is greatly affected by external factors. Some accidental factors can stop the flower bud differentiation process. Low temperature and drought promote the transformation of citrus tree physiology to the direction conducive to flower bud differentiation. Circular peeling can cause the same physiological changes as water control treatment, and has a significant effect on promoting flower bud differentiation. Ringing increased the RNA content and RNA/DNA ratio in shoots of Miyagawa satsuma mandarin and dark orange (Huang Huibai et al., 1991) during flower bud breeding, and promoted flower bud initiation. Spraying GA3 decreased the RNA/DNA ratio and inhibited flower bud initiation; Defoliation inhibits flower bud breeding, has no effect on the DNA content and GA level of shoot tip, but reduces the RNA content and IAA level of shoot tip, and delays the accumulation of ABA and CTK (Li Xingjun et al., 2002). In autumn and winter, paclobutrazol treatment inhibited GA synthesis and nutrient growth of citrus branches and leaves, increased carbohydrate level and promoted flower bud differentiation.

Citrus flower bud differentiation is closely related to plant hormones. Bangerth believes that cytokinin (CTK) plays a role in promoting flower bud development. At the stage of citrus flower bud differentiation, the level of cytokinin in citrus flower bud gradually increased and reached a higher level at the early stage of morphological differentiation. Gibberellin (GA) is the main flower inhibiting hormone (Li Jinxue et al., 2012). GA is the main inhibitor of flower formation in most fruit trees. External application of GA can counteract the effect of ring cutting on flower formation. The content of GA1, GA19 and GA30 in the vegetative branches and leaves of satsuma mandarin also showed a peak. During the flower bud differentiation of satsuma mandarin, the content of GA in big branches decreased continuously during the whole flower bud induction period. Gold-schmidt et al. analyzed the content of endogenous hormones in mixed branches, vegetative branches and pure flower bud branches of lemon tree, and found that the level of GA in vegetative branches was higher, while that in pure flower bud branches was lower. Citrus bears less fruit in the early year. Through ring cutting, water control and flower promotion, the flower bud differentiation of citrus was significantly promoted, and the content of GA in the branches during the physiological differentiation of flower buds was reduced. Abscisic acid (ABA) may play different roles in different stages of flower bud differentiation. Ruan Yongling and others found that ABA was at a low level in the flower bud induction stage and had the effect of inhibiting flower bud differentiation, while rising to a higher level during the formation of flower primordium had the effect of promoting flower bud differentiation. ABA can obviously stop the vegetative growth of citrus trees, and may indirectly affect flower bud breeding. Kojema et al. believed that ABA promoted the flower bud breeding of satsuma mandarin because ABA could counteract the effect of GA3, increase the concentration of sugar in the vacuole of citrus bud, and increase the strength of the pool. When people have studied the relationship between citrus flower bud inoculation and hormones for a long time, they found that flower bud inoculation is a comprehensive result of the interaction of various hormones in time and space (Li Jinxue et al., 2012).

2. Technical measures for regulating flower amount

The plant growth regulators that can effectively promote the differentiation and formation of citrus flower buds include chlormequat, paclobutrazol, nucleotides, etc. Growth substances induce the flowering of citrus seedlings, and it is only possible for young trees to develop through sexual stage; The effect of application on adult trees is significant only at the physiological differentiation stage of flower buds. After the physiological differentiation stage, application has some effects, but the effect is not significant.

(1) Increase the amount of flowers

① The nine-year-old seedlings of broad-skinned citrus, Satsuma mandarin, were sprayed with 2000 mg/L chlormequat or 2000~4000 mg/L butyrylhydrazide in the middle of September, and the flower amount in the following year increased by 118%~242% respectively. From September 15 to January 25, spraying 50mg/L of nucleotides every 10 days for satsuma mandarin in the initial fruit stage can increase the number of flower bud differentiation in the next year. The spraying effect in the middle of November is better, and the number of flower bud differentiation is nearly doubled. Tong Changhua et al. (1989) proved that spraying paclobutrazol before the physiological differentiation stage of flower buds can significantly promote flower formation, among which the appropriate concentration of satsuma mandarin is 700mg/L, and Ponkan mandarin is 1000mg/L; Spraying 200 mg/L cytokinin at the stage of flower bud morphological differentiation can also significantly promote the development of flower organs and increase the amount of flowers in the next year. From November to December, when the autumn shoots ripen, the granulated orange will be sprayed with 500 times of 15% paclobutrazol once, which has obvious flower promoting effect (Mao Shunhua et al., 2008). ② Qin Xuannan et al. (1994), a lemon species, sprayed paclobutrazol at the concentration of 300~400mg/L twice on the tree crown from late October to early November before the flower bud differentiation of Yulike lemon, which can significantly promote the proportion of flowering and normal flowers, and has certain effects on improving the fruit setting rate, cold resistance and reducing the abnormal defoliation rate in winter. In addition, in the middle and late August, spray BTOA (benzothiazole oxyacetate) twice in succession, which can promote the autumn flowers of Eurek lemon. CCM, butyrylhydrazide and MH-30 can also promote the differentiation of lemon flower buds. ③ Golden orange Golden orange blossoms many times a year and bears many fruits. Among them, the first "early dormant flower" accounts for about 80% of the annual fruit yield, and the fruit is large and high-quality, with significant economic benefits. If the concentration of paclobutrazol or butyrylhydrazide was 1000 mg/L or 3000 mg/L at the beginning of the first shoot germination, the "early dormant flowers" after the use of paclobutrazol increased by 10 times, and the "late dormant flowers" of the second shoot were significantly reduced. Although the total amount of flowers decreased, the economic benefits were extremely significant. On the contrary, Bejiu (Bs) has reduced "early summer flowers" and increased "late summer flowers", with insignificant economic benefits.

(2) The experiment of reducing the amount of flowers showed that the effective period of gibberellin inhibiting the flower bud differentiation of Voringxia orange was the critical period of flower bud differentiation, that is, the physiological differentiation period (September) to the morphological differentiation period (November). The effect of advance or delay decreased. The appropriate concentration of spraying was 100-200 mg/L. In addition, the effect of flower inhibition in the next year is closely related to the fruit load in the current year, that is, the effect of flower inhibition is significant when the fruit is abundant in the current year, and on the contrary, it is relatively weak. From November to January of the next year, Shamoti sweet orange is sprayed with gibberellin with a concentration of 200 mg/L, once every two weeks. If it is sprayed to the end of December, it will not blossom in the next year, and if it is sprayed to the beginning of December, it will still blossom in the next year, but the flowering period will be delayed. The effect of inhibiting flower growth of satsuma mandarin by spraying gibberellin 100mg/L in January was significant. Clementine red orange was sprayed with the same concentration as satsuma mandarin in December, and the flower amount in the next year decreased by 75%. After spraying gibberellin to control the flowers, the spring shoots and leafy fruit-bearing branches in the next year increased significantly and grew vigorously. It should be used with caution in areas with severe late spring cold.

The article is from the book "Application of plant growth regulators in fruit trees", and the content is for reference only.