Investigation of Tree Structure Parameters of Highquality and Highyielding Yshaped Pear Orchards

Shuwei WEI Shaomin WANG Ran DONG Kun RAN Hongwei WANG

Abstract In order to study reasonable tree structure parameters of Yshaped pear orchards in natural conditions and at management technical level of Taiюan area， the tree structure and population structure of highquality and highyielding Yshaped pear orchards were investigated. The results showed that when the yield of Yshaped ‘Oshu’ was 2 550 kg/667 m2 in the early fully fruiting period， the quantity of the branches per 667 m2 was about 54 000， and the number of short branches was the largest， accounting for 80.1% of total number of branches， followed by middle branches， long branches and developmental branches. As the yield of Yshaped ‘Qiuyue’ was 2 875 kg/667 m2 in the early fully fruiting period， the quantity of the branches per 667 m2 was 51 000， and the number of short branches was the largest， accounting for 75.6% of total number of branches， followed by middle branches， long branches and developmental branches. When the yield of Yshaped ‘Niitaka’ was 3 000 kg/667 m2 in the early fully fruiting period， the quantity of the branches per 667 m2 was 43 000， and the number of short branches was the largest， accounting for 82.0% of total number of branches， followed by long branches， middle branches and developmental branches.

Key words Pear; Y shape; Highquality and highyielding; Tree structure parameters

China is a big pear producing country， where the planting area of pear trees and the yield of pear fruit ranks first in the world[1]. The tree structure and population structure of fruit trees are the main factors influencing the yield and quality of fruit in a orchard. The Yshaped pruning of pear trees， a pruning technique developed by Department of Fruit Trees， Korea Horticulture Experimental Station， is applicable to close planting[2]， with  characteristics of rapid formation of crown， obtaining high yield in early stage and facilitating orchard management and mechanized operation. At present， some orchards with Yshaped cultivation have appeared in some main pear producing areas in Shandong， but as a new technology， Yshaped cultivation still has a problem of unreasonable tree structure during the demonstration and promotion process. In this paper， the tree structure of highquality and highyielding Yshaped pear orchards in Tianpinghu experimental and demonstration base of Shandong Institute of Pomology was investigated to study reasonable tree structure parameters and then provide a scientific basis for further exploration of efficient pruning technology of pear trees.

Materials and Methods

General situation of the surveyed orchards

From 2015 to 2016， three highquality and highyielding varieties of pear （‘Qiuyue’， ‘Niitaka’ and ‘Oshu’） were investigated in the pear orchards of Tianpinghu experimental and demonstration base of Shandong Institute of Pomology. The three varieties had Yshaped trees. They were planted in 2009， and the distances between rows and plants were 4.7 m≠1.0 m. In 2015， the average yield of the three varieties per 667 m2 was 2 550， 2 875 and 3 000 kg respectively， and and more than 90% of fruits had good quality.

Survey content and method

Survey content

Tree structure was investigated from aspects of tree height， trunk height， trunk girth， crown diameter， number of backbone branches， number of main branches， distribution characteristics， angle of main branches， tree vigor， tree shape and growth of new shoots.

Survey method

Ten representative trees were randomly selected from each variety for investigation. Tree height was measured with a benchmark. Trunk height， which is the height from the ground to the first main branch， was measured with a tape measure. Trunk girth was measured with a tape measure 20 cm away from the ground. Crown diameter was measured with a tape measure， including the northsouth and eastwest length of crown. For growth of new shoots， 30 peripheral branches of canopy were randomly selected from each tree to measure their length with a tape measure， and the average length of the peripheral branches were calculated[3]. The average area of a single leaf and the area of leaves per plant were calculated as follows：

leaf area=leaf length≠leaf width/2

leaf area index=（number of leaves per plant≠area of a single leaf）≤projection area of crown per plant

Results and Analysis

Basic situation of pear trees

Seen from Table 1， the average tree height of the three varieties was 242-300 cm， and it reduced obviously， which is convenient for production and operation. The height of the Yshaped pear trees was less than the line spacing， and the crown base of the adjacent two rows of trees in the growing season had sufficient direct sunlight every day.

The trunk height of the three varieties was 40-61 cm， averaging 49.3 cm. The dwarfed trunk is good for wind protection and the transportation and exchange of nutrients and water between the underground part and overground part. Moreover， the canopy expanded rapidly， and trunk girth increased rapidly; they fruited early， and the yield was high. However， too dwarfed trunk was easy to cause close canopy to affect the ventilation and light transmission of the orchards and increase the difficulty of ground management in the orchards （Table 1）.

The eastwest and northsouth crown diameter of the three varieties were 256-312 and 134-160 cm respectively. The number of backbone branches per plant was 8-11， and the number of main branches was two. The angle of main branches was around 45°. The branches were distributed in a plane， and the light transmittance was large; the utilization rate of light energy was high， and the crown is moderate in size （Table 1）.

Quantity and constitution of branches

The appropriate amount of branches is the basis for the robustness， high quality and high yield of trees. Studies have shown that under good management conditions， the quantity of branches of apple trees in the early fruiting stage to the fully fruiting stage was positively correlated with the yield; in the fully fruiting stage， the yield did not increase with the increase of number of branches and leaf area index[2].

As shown in Table 2， the number of branches per plant of the three varieties was 292-382， namely 43 138-54 205 per 667 m2. The proportion of each type of branches was reasonable， and the quantity of short branches was the largest， followed by medium branches and long branches， while the quantity of developmental branches was the smallest， that is， there were only 2-8 developmental branches per plant.

In order to achieve high and stable yield， pear trees should not only have suitable quantities of branches， but also maintain appropriate proportions of long， medium and short branches. If there are too many long branches， vegetative growth of the trees is strong， and it is not easy to form flower buds， so the yield is low. If there are too few long branches and too many medium and short branches， although it is easy to form flower buds， trees are weak， and flowers and fruits are easy to fall， so the yield is not high[3]. According to the proportions of various branches of highquality and highyielding Yshaped pear trees， the order of various types of branches are as follows： short branches>middle branches>long branches>developmental branches.

Growth situation of new shoots and leaves

According to Table 3， the number of new shoots per plant of the three varieties ranged from 84 to 101， and the length was 24.7-27.5 cm. The area of a single leaf was 30.29-36.02 cm2， and the area of leaves per plant was 5.11-8.96 m2. That is， the quantity of new shoots per 667 m2 was 11 915.46-14 326.96， and the number of leaves per 667 m2 was 239 841.78-265 715.41， while the area of leaves per 667 m2 was 724.85-1 270.98 m2.

The three varieties had strong ability to branch and large quantities of new shoots and leaves. During the management process， attention should be paid to sparse branches， and a good crown structure should be cultivated to prevent the canopy from being too tight and avoid canopy closure， affecting ventilation and light transmission and reducing fruit yield and quality. At the same time， the picking of long branches should be performed timely， or girdling， bud notching and other treatments can be conducted to prevent prosperous growth， promote flower bud differentiation， improve fruit setting rate and fruit quality.

Conclusions

When the yield of Yshaped ‘Oshu’ was 2 550 kg/667 m2 in the early fully fruiting period， the quantity of the branches per 667 m2 was about 54 000， and the ratio between long branches， middle branches and short branches was 3.1≥13.0≥80.1. As the yield of Yshaped ‘Qiuyue’ was 2 875 kg/667 m2 in the early fully fruiting period， the quantity of the branches per 667 m2 was around 51 000， and the ratio between long branches， middle branches and short branches was 2.5≥18.3≥75.6. When the yield of Yshaped ‘Niitaka’ was 3 000 kg/667 m2 in the early fully fruiting period， the quantity of the branches per 667 m2 was about 43 000， and the ratio between long branches， middle branches and short branches was 3.9≥7.2≥82.0.

References

[1]ZHANG SL， ZHOU YH. Development trend and suggestion of pear industry in 2012[J]. China Fruit News. 2012， 29（2）： 25-27. （in Chinese）.

[2]JIN SN， CUI DG， LI B， et al. Techniques for applying "Y" tree form to solidplanted pear tree[J]. Deciduous Fruits， 2005（6）： 35-37. （in Chinese）.

[3]MA SW， XIA GH， SONG SW， et al. Study on the tree structure of highyielding apple in Funan mountainous area[J]. Journal of Henan Agricultural Sciences， 1994（7）： 29-31. （in Chinese）.