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1. Harbin Research Institute of Forestry Machinery, State Forestry Administration, Harbin 150086, China; 2. Forestry New Technology Research Institute, Chinese Academy of Forestry, Beijing 100091, China; 3. Forestry Equipment Engineering Technology Research Center, State Forestry Administration, Harbin 150086, China

Abstract The current cultivation of apple trees mainly relies on grafted seedlings to achieve seedling regeneration of apple trees. The commonly used splice grafting, V-shaped grafting and tongue grafting mostly use plastic film for fixation and sealing. After one year, the wrapped plastic film needs to be removed to avoid affecting the growth of the seedlings. This paper introduces a brand new grafting technology which uses tongue grafting iron nails for fixation and growth fixation wax for sealing (SDRG). The process of mechanized grafting for apple nursery stock is determined, and the fixation and sealing problems with the grafting parts of seedlings are solved. The technology is characterized by quick speed, high efficiency, improved seedling survival rate lower labor cost and great significance to the promotion of industrialized nursery and mechanized grafting.

Key words Grafting, Fixation with iron nails, Process program, Industrialized nursery

1 Introduction

According to statistics, in 2017, the planting area of fruit trees in China was more than 13 million ha, and the output was nearly 130 million t, of which the planting area of apple exceeded 2.22 million ha and the output was 38.5 million t, ranking first in the world[1]. Compared with food production, fruit and vegetable cultivation is labor-intensive industry. The number of fruit trees regenerated in the orchard is huge each year. The application of grafted seedlings for fruit tree renewal is currently the most commonly used technical means. Therefore, the number of grafted seedlings required is huge. It requires completing a large number of grafting tasks during an effective grafting period, taking time and effort. The survival rate is not high[2-4]. In order to reduce the labor intensity of apple planting farmers, save labor costs, and improve production efficiency and economic efficiency, a fast and efficient grafting technology is introduced in this paper. It is of important practical significance to promote the industrialized nursery and mechanized production of fruit trees[5-8].

2 Overview of advantages and process of grafting

The cultivation of fine fruit trees by grafting has the following advantages. First, it helps to maintain and develop excellent traits to maintain the excellent heredity. Second, it helps to achieve early harvest and high yield. If grafting is used, fruit trees will generally bloom in the second year after grafting and enter the full fruiting period in the third year. Third, the grafted varieties use dwarf varieties, promoting the dwarfing of fruit trees, facilitating mechanized operations and production management, enhancing the adaptability of seedlings, and improving the quality of fruit. Fourth, it helps to update the variety. With the development of science and technology, the scientific research units are constantly cultivating new and excellent varieties. It is necessary to update the original old varieties and develop them into new varieties with high yield, high quality and strong anti-viral ability. Fifth, it helps to improve the adaptability of fruit trees.

The existing domestic and foreign fruit tree grafting methods, such as splice grafting method, V-shaped grafting method and tongue grafting method, mostly use plastic film wrapping to fix and seal, which is time consuming and laborious. After one year, the plastic film wrapped needs to be removed to prevent plastic film from affecting the growth of grafted seedlings. Due to the difference in the diameter of stock and scion, the grafting method that uses plastic film to fix and seal is difficult to realize mechanized mass production in the future, only suitable for manual work. Targeting at the large demand for grafted seedlings of apple by China’s orchards in the spring and autumn, a new grafting method is needed to solve the sealing and fixation problems of the grafting joints, improve the survival rate, facilitate future mechanization operations and mass production, and reduce labor demand.

3 Apple grafting test and analysis

The grafting process test was carried out in April 2018. Three commonly used grafting methods, V-shaped grafting method, tongue grafting method and splice grafting method were selected for test.Malusbaccata(Linn.) Borkh. (Rosaceae:Malus), is a common deciduous semi-evergreen tree in the northeast, with extremely strong cold tolerance. It was used as the rootstock. High-quality apple seedlings were selected as the scion seedlings. The grafting program and test results are shown in Table 1.

As shown in Table 1, three grafting methods, V-shaped grafting, tongue grafting and splice grafting were selected in this test. Adhesive tape, iron wire and iron nail were used for fixation. In all the treatment groups, grafting wax was used for sealing. Thus, 11 groups of 2018 grafting texts were performed. The grafted seedlings were then incubated at room temperature (Fig.1). After one month, the number of germinations was counted and the germination rate was calculated (Table 1).

Taking facilitating mechanized production into account, the grafting program that used tongue grafting iron nails for fixation and growth fixation wax for sealing (SDRG) was finally determined as the optimal. The process of the optimal grafting program was as follows: (i) chamfering the scion seedling at an angle of 20°; (ii) chamfering the rootstock seedling at an angle of 20°; (iii) splicing the rootstock and scion seedlings; (iv) fixing the rootstock and scion seedlings with a iron nail in diameter of 1 mm; (v) immersing quickly the fixed rootstock and scion seedlings in melted grafting wax (about 70℃) to make the grafting joint and the top of the rootstock seedling completely waxed; (vi) immersing quickly the waxed rootstock and grafting joint into water (about 20℃) to cool and fix the grafting wax (Fig.2).

Table1Designofappleseedlinggraftingtest

No.Grafting dateObservation timeGrafting methodFixation modeAmount graftedAmount germinatedGermination rate∥%1April 27, 2018May 29, 2018TJ-LAdhesive tape181477.782April 27, 2018May 29, 2018TD-LIron nail181055.563April 27, 2018May 29, 2018TT-LIron wire1818100.004April 27, 2018May 29, 2018SJ-LAdhesive tape181055.565April 27, 2018May 29, 2018VT-LIron wire1818100.006April 27, 2018May 29, 2018ST-LIron wire181477.787April 27, 2018May 29, 2018SD-LIron nail201050.008April 28, 2018May 29, 2018SDRIron nail201050.009April 28, 2018May 29, 2018SDRGIron nail2020100.0010April 28, 2018May 29, 2018SDGIron nail20840.0011April 28, 2018May 29, 2018STRGIron wire201890.00

Note: TJ-L, splice grafting adhesive tape for fixation and wax for sealing; TD-L, splice grafting iron nail for fixation and wax for sealing; TT-L, splice grafting iron wire for fixation and wax for sealing; SJ-L, tongue grafting adhesive tape for fixation and wax for sealing; VT-L, V-shaped grafting iron wire for fixation and wax for sealing; ST-L, tongue grafting iron wire for fixation and wax for sealing; SD-L, tongue grafting iron nail for fixation and wax for sealing; SDR, tongue grafting iron nail for fixation and growth wax for sealing; SDRG, tongue grafting iron nail for fixation and growth fixation wax for sealing; SDG, tongue grafting iron nail for fixation and fixation wax for sealing; STRG, tongue grafting iron wire for fixation and growth fixation wax for sealing.

Fig.1Processofmechanizedgraftingofappleseedlings

Fig.2Mechanizedgraftingtestofappleseedlings

4 Conclusions

In the past, grafting methods almost always pay attention to the fixation of rootstock and scion seedlings. Various cutting methods are time consuming and laborious. Plastic film is generally used to wrap grafting joints, thereby achieving the sealing effect and preventing water loss. After the growing season, the plastic film also needs to be removed manually to prevent plastic film from affecting the growth of seedlings. The most important thing is that the traditional grafting process cannot achieve mechanization and factory production. In the grafting process studied in this paper, the cutting of the rootstock and scion seedlings is simple, fixation with iron nails is easy to be mechanized (using air nailer), and sealing with wax is easy to operate with good sealing. With the growth of seedlings, wax will naturally fall off. Compared with the traditional process, the manual secondary unsealing workload is eliminated. This process is very suitable for mechanized production.