The importance of determining the autumn shoot as the main fruiting mother branch of longan

Longan and other subtropical evergreen fruit trees have new shoots every year, which shoot 4-5 times a year in Fuzhou area, spring shoot 1-2 times, autumn shoot 1-2 times, winter shoot less, only a large number of winter shoots are produced in warm winter climate. According to the observation of adult longan trees in Wulongling and Youtan by Golden Pine (1962), the number of autumn shoots is more and common, accounting for 33.02% of the total shoots. However, if there is little or no fruit in that year, the number of spring and summer shoots is more, with an average of 23.99% in spring shoots, 43.03% in summer shoots (including Xiayan autumn shoots) and 22.98% in autumn shoots. The shoot length of spring shoot was the longest (average 9.87 cm), followed by autumn shoot (7.61 cm) and summer shoot (6.67 cm). According to the observation in Sichuan, there are more spring shoots and the least autumn shoots.

The germination rate of longan treetop is higher, but the branch-forming ability is lower. The shoot of longan usually extends at the top of the full shoot, so 2-4 years after planting, attention should be paid to shaping and pruning, short extension of branches, so as to facilitate the rapid expansion of the crown. At the initial stage of shoot germination, the scales covered by the bud began to release, and the color of the bud changed from yellowish brown to yellowish green. 5-10 days after germination, the leaflets on the first leaf of the new shoot began to spread, and in the early stage of shoot germination (about 15 days), the increase of length and thickness was the most obvious, and then showed in the thickening and enrichment of the shoot. A new shoot from the beginning to the leaf light green, fast 15 days, slow 30 days, from light green to dark green to germination, fast 20 days, slow 45 days. Therefore, complete a shoot cycle, fast 50 days, slow 80 days. The average shoot cycle was 60 days in spring, 50 days in summer and 45-50 days in autumn, and the winter shoot did not turn green for a long time. Different shoots complete the establishment of a growth cycle days, which provides a scientific basis for the formulation of cultivation measures, such as fertilization, pest control, spraying or ring peeling treatment to control winter shoot emergence.

There are four kinds of longan shoots: spring shoot, summer shoot, autumn shoot and winter shoot. The criteria for the division of the shoot of each branch: if 70% of 80% of the branches in the crown of the tree in a month pull out a tender shoot with a length of 1-2 cm, it is defined as the shoot drawn in that month, such as the spring shoot from February to April (early spring shoot in February, spring shoot in March, late spring shoot in April), and summer shoot from May to July (early summer shoot in May, summer shoot in June, late summer shoot in July). The autumn shoots are from August to October (early autumn shoots in August, autumn shoots in September and late autumn shoots in October), and winter shoots from November to January (early winter shoots in November, winter shoots in December and late winter shoots in January). The above criteria are helpful to eliminate the confusion in the discrimination of shoot types and provide a basis for phenological observation of shoot occurrence period.

The main results are as follows: 1) Spring shoots are usually extracted from autumn shoots or postharvest autumn shoots and old branches that did not develop into spikes last year. Spring shoots germinate sooner or later related to air temperature and varieties. Fuzhou district germinates around late January. Warm or early-maturing varieties such as Bayi early, red shell, etc., spring shoots germinate as early as late December, spring shoots grow vigorously from mid-February to mid-March, and most spring shoots stop elongating in mid-April. It is basically mature in late April. As a result, the number of spring shoots of trees is small, but the trees with few or a large number of flower spikes in the same year have more and more spring shoot growth. Because of the low temperature, long growing period and weak growth potential, it is difficult to form a good fruiting mother branch in the following year, but the emergence of spring shoots plays an important role in improving longan photosynthesis, increasing nutrient accumulation and promoting summer shoots, and then extend autumn shoots. Therefore, the spring shoot is an important basic branch of longan.

2) the summer shoots are generally drawn from the spring shoots of the same year or from the fruit-picking branches and old branches that did not germinate last year. From the first ten days of May to the last ten days of July, the summer shoots have 1 or 2 times of emergence, the first peak of summer shoots is in the first half of May, and the number of growth is relatively small, and the second peak is from the middle of June to the middle of July, when the temperature is high and the rainfall is sufficient. The young and strong trees with good management level will reproduce from the top of the summer shoots that germinated early in mid-late July to form the second summer shoots. The emergence of summer shoots is closely related to the amount of fruit in the current year and the level of management. if there are many fruits in that year, a large amount of nutrients are consumed in fruit development, so there are few summer shoots, and vice versa. Plants with moderate results, such as strengthening fertilizer and water management, can produce more summer shoots on shoots that do not bear fruit. Summer shoots grow sturdily and have a large number of leaves, which is usually an important basic shoot for extending autumn shoots. Therefore, the number and strength of summer shoots play a significant role in increasing the number of autumn shoots, increasing fruit and reducing fruit drop in the later stage. Strengthening the application of pre-flowering fertilizer, properly thinning the cultivation and management of flower and fruit ears, and promoting a large number of summer shoots are important basic shoots to slow down and overcome the annual fruit of longan and obtain stable yield. But the trees with more fruit are less likely to shoot in summer.

3) there are mainly two kinds of autumn shoots: one is the autumn shoot that extends the basic branch of summer shoot (commonly known as Xiayan autumn shoot). This kind of autumn shoot germinates early and strong, and it is the main fruiting mother branch in the coming year. The other is the postharvest autumn shoots with axillary buds at the top of the mother branches after fruit harvest, early-maturing longan varieties and longan producing areas in southern China. If irrigation and water conservancy facilities are available, and pre-harvest fertilizer can be fully applied in time, most of the postharvest autumn shoots that can be harvested twice can also become good fruiting mother shoots. However, if there is fertilizer but no water supply, the weak growth of postharvest autumn shoots will be difficult to become good fruiting mother branches. Strengthening agricultural measures and cultivating a sufficient number of strong autumn shoots is an important key to the high yield of longan every year.

4) the correct judgment of winter shoot should be determined from the period of flower bud differentiation of longan. Before entering the physiological differentiation of flower bud, the new shoot which is not mature and can not carry out flower bud morphological differentiation is called winter shoot. In Fuzhou, longan entered the physiological differentiation of flower buds in December, so the new shoots germinated from November to December were winter shoots. The emergence of winter shoots is related to the temperature and moisture in winter. under the condition of warm and rainy winter, it is easy to sprout winter shoots. The growth of winter shoot is slow, the branch is thin and weak, and it is easy to freeze if it is not full. At the same time, winter shoot growth consumes a lot of nutrients accumulated in trees, so winter shoot germination is disadvantageous to flower bud differentiation in the following year. Therefore, in cultivation, fertilizer and water, root cutting, girdling and growth regulators are often used to avoid the emergence of winter shoots, so as to adjust the contradiction between vegetative growth and reproductive growth, so as to achieve the goal of high yield and high quality.

It is determined that the autumn shoots of longan from August to October are autumn shoots. The adult fruiting trees of middle and late mature varieties generally draw only one postharvest autumn shoot. The young fruiting trees germinate and grow from late August to early September after fruit harvest, but the climate is suitable, the water and fertilizer is sufficient and the trees are strong. Autumn shoots will be produced for the second time in mid-late October, and young fruit trees of early-maturing varieties generally produce autumn shoots twice, the first from early August to early September and the second from late September to early November. Therefore, the mid-late-maturing varieties should release autumn shoots once from late August to early September to control the germination of the second autumn shoots, and for those young fruiting trees with strong trees, it is necessary to strengthen management and release autumn shoots twice to prevent winter shoots from sprouting; for early-maturing varieties, autumn shoots should be released twice, that is, autumn shoots should be released twice in early August and late September to early October.

Pruning and clearing the garden at the right time, if the autumn shoot longan fruit tree is not pruned and allowed to grow naturally, its branch growth may appear as follows: branches are clustered, delicate and overlapping; some branches grow excessively, overlord branches protrude, but some branches are difficult to grow and the position is empty; the strength of each branch group is unbalanced, and the crown is difficult to be full and complete. For this reason, through pruning, cutting off dead branches, weak branches, overlapping branches, disease and insect branches, long branches, etc., to control the number of branches, in order to concentrate nutrients, promote the healthy growth of new shoots, and cultivate a good hemispherical crown. Adult fruiting trees, such as those with more fruit, weak tree potential and neat autumn shoots planned for one time, can be pruned a little later to retain more leaves, which is beneficial to the restoration of tree potential, and can be carried out when the branches begin to sprout new shoots after fruit harvest (from late August to early September). If there are few fruits in that year, the trees are strong, the conditions of fertilizer and water are good, and the autumn shoots are planned to be planted twice, they should be pruned immediately after fruit harvest to promote the early germination of autumn shoots. For young fruiting trees, if they have sufficient fertilizer and water and can produce autumn shoots twice after fruit harvest, they should be pruned sooner rather than later, and they should also be pruned immediately after fruit harvest; for trees that hang too many fruits and grow weakly in that year, their leaves should be retained as far as possible after fruit harvesting, so as to prevent the decline caused by sun exposure to the trunk, and then prune when the leaves of autumn shoots turn green. At the same time, the orchard was cleared with pruning to remove harmful weeds, dead branches and fallen leaves in the orchard, bury or burn them, and then spray the mixture of carbendazim and dichlorvos 1000 times once to keep the orchard clean, prevent weeds from competing with fruit trees for fertilizer, water and glory, reduce the damage of diseases and insect pests, and promote the early germination of new shoots.

The annual shoot of longan contains two sections with different functions: fruiting mother branch and basal branch. The fruiting mother branch refers to the last new shoot on the annual shoot, which grows well and can blossom and bear fruit in the next year, which is called the fruiting mother branch, and the vegetative branch below the fruiting mother branch (spring and summer shoot) is called the basic branch of the fruiting mother branch. It is a conceptual mistake in our longan producing area to regard the whole branch of the mass saying "Xiayan Autumn shoot" as a good fruiting mother branch, because exactly speaking, the summer shoot is the basic branch, and its extended autumn shoot is the real fruiting mother branch. In recent years, Guangdong and Guangxi emphasize the promotion of secondary postharvest autumn shoots as fruiting mother shoots, so that the first postharvest autumn shoots, including spring and summer shoots, are called fruiting mother shoots, and the second postharvest autumn shoots are fruiting mother shoots. This is conceptually the same as the division of parent branch units proposed by Lu Meiying (1997). The autumn shoot is mainly extracted from the terminal bud of the vegetative base branch or from the axillary bud of the fruiting mother branch after fruit harvest. The autumn shoots extracted from vegetative shoots (that is, spring and summer shoots) have the best quality, and the flower and fruit setting are the best. According to Chen Wenxun (1964), the panicle rate of autumn shoot extracted from vegetative branches is 40.0%, and that of postharvest autumn shoots is 23.0%. At the same time, good fruiting mother shoots must be two-stage shoots, that is, on the basis of vegetative shoots, then extend autumn fruiting mother shoots. However, the postharvest autumn shoots or late harvested autumn shoots are difficult to become good fruiting mother branches. Dormant buds from perennial branches in summer shoots or high-yielding years can also form fruiting mother branches, but this is rare. Because mature summer shoots must be extended to produce autumn shoots; in terms of the time to complete a shooting period, summer shoots are 50 days. If summer shoots are pulled out in July, under normal management conditions, autumn shoots are usually extended in September. Therefore, it is very important for longan to formulate high-yield and high-quality cultivation measures to establish the concept of autumn shoot as the main fruiting mother branch of longan.