A low-position bridging method for restoring fruit bearing on citrus Huanglongbing trees

Abstract

The present invention discloses a low-position bridging method for restoring fruit bearing on citrus Huanglongbing trees. A new rootstock planted in the field and resistant to citrus Huanglongbing is bridged to a citrus tree with the disease, and the necrotic rootstock is replaced with a rootstock variety resistant to citrus Huanglongbing. Since citrus plants planted for many years become sick and their root systems become necrotic, resulting in a serious decrease in the fruit bearing rate, the low-position bridging technology can restore the normal fruit bearing of the plants one year after the successful low-position rootstock replacement, helping growers to make up for their losses.

Description

Technical Field

[0001] The invention belongs to the technical field of citrus rejuvenation grafting, and particularly relates to a low-position bridging method capable of restoring normal fruit bearing production of citrus Huanglongbing diseased trees. Background Art

[0002] Citrus Huanglongbing is a devastating disease of the citrus industry, caused by Candidatus Liberibacterasiaticus (CLas). Since CLas is a nutritionally deficient bacterium, it has not yet been cultivated in pure in vitro culture, resulting in the failure to develop effective drugs for prevention and treatment. When Huanglongbing bacteria infect citrus plants, the plants will undergo a stress response, causing abnormal starch metabolism, starch accumulation in the sieve tubes, blocking the sieve tubes of the phloem, and reducing the plant's ability to transport nutrients downward. The photosynthetic products produced by the leaves cannot be supplied to the roots, the roots become starved, and the roots will die in large numbers in the later stages. In the later stages of the disease, necrosis of the citrus root system will further affect the plant's absorption of various nutrients and water, ultimately leading to symptoms such as chlorosis, mottled chlorosis, dead fruit, fruit drop, and red nose fruit.

[0003] The current scientific prevention and control strategy of citrus Huanglongbing is to use virus-free seedlings, dig up diseased trees, and kill psyllids. In reality, many orchards cannot strictly enforce the management level or are difficult to implement, especially in orchards that have been infected on a large scale and have a certain amount of fruit bearing. Farmers often cannot cut down diseased trees on a large scale. Therefore, in the past, farmers tended to inject antibiotics into the plants at high pressure to ensure that the diseased plants resumed fruit bearing, but many years of high-pressure injection will also cause the diseased plants to eventually die due to damage to the tree. Summary of the invention

[0004] The purpose of the present invention is to overcome the problem that trees infected with Huanglongbing cannot bear fruit normally. Through the low-position bridging rootstock replacement technology, that is, a new rootstock planted in the ground is grafted onto a diseased citrus tree to replace the necrotic rootstock. This technology can enhance the adaptability of the diseased plants to the environment, restore the tree vigor, save the diseased trees, extend the fruiting period of the diseased trees, and retain the excellent varieties of the original citrus trees.

[0005] The low-position bridging method for restoring fruit bearing on citrus Huanglongbing trees of the present invention is to bridge a new rootstock planted in the field and resistant to citrus Huanglongbing to the diseased citrus tree, and replace the necrotic rootstock with a rootstock variety resistant to citrus Huanglongbing.

[0006] Preferably, the rootstocks resistant to Huanglongbing are hybrid varieties of pomelo.

[0007] Preferably, the rootstock of the pomelo hybrid variety is a 2-year-old container seedling with an average ground diameter of 2.0 cm and a seedling height of 700-900 cm.

[0008] Citrus pomelo hybrids have the advantages of rapid growth, sturdy stems, and high affinity for different citrus varieties. By grafting diseased trees at a low position, they can grow rapidly while ensuring the survival rate of the graft.

[0009] Preferably, the method comprises the following steps:

[0010] S1. Choose a season with sufficient water for the planting of anvils;

[0011] S2. Treat the root system of the rootstock seedling before grafting, use rooting powder to "dip the roots", remove weeds and soil from the root of the fruit tree, and use a hoe to dig a hole with the same depth as the seedling to be planted;

[0012] S3. Select a location about 10 cm above the ground as the scion point, and cut the skin of the fruit tree with two cuts, one vertical and one horizontal;

[0013] S4. Make a 30-45° bevel cut on the top of the stock and a 20° bevel cut on the back.

[0014] S5. Insert the top of the rootstock into the opening of the trunk and fix it, then wrap it with plastic film to seal it, so as to reduce the evaporation of water from the xylem of the cambium and prevent rainwater from seeping into the wound and causing fungal infection.

[0015] Preferably, the season with sufficient moisture is from April to September in the south.

[0016] Under the technical conditions of killing citrus psyllids, we carried out the process of dynamic zeroing diseased trees. We invented a low-position rootstock replacement cultivation technology for productive orchards to ensure normal production of fruit farmers and recover the losses caused by Huanglongbing. Therefore, the patent of this invention screened out the type of rootstock that is resistant to Huanglongbing and grows fast, and based on the dynamic law of plant growth and the growth and production benefits of citrus after different treatments in different time periods, we then created a low-position bridge rootstock replacement technology that can restore the fruit bearing of citrus Huanglongbing trees.

[0017] Compared with the existing cultivation technology, the present invention has the following beneficial effects:

[0018] (1) After citrus plants have been planted for many years and become sick, their root systems become necrotic, which causes a serious drop in the fruit-bearing rate. Through the low-position bridging technology, the plants can be restored to normal fruiting one year after a successful low-position rootstock replacement, helping growers to make up for their losses.

[0019] (2) The rootstock variety selected in the present invention is a hybrid variety of pomelo, which has good resistance to Huanglongbing disease and high affinity with a variety of citrus varieties, and can be widely used for low-position bridging of different citrus varieties.

[0020] (3) Another rootstock variety selected by the present invention is red lemon and red orange, which have the advantages of fast growth rate and well-developed root system and can be widely used for low-position bridging of different citrus trees to achieve the purpose of rapid rootstock replacement.

[0021] (4) Due to damage caused by citrus foot rot, longhorn beetles and other pests, gum flow at the root neck or branches, and mechanical operation injuries, this method can be used to repair the damaged parts of the branches and trunks by bridging, so that the tree can be restored to health.

[0022] (5) The cultivation measures provided by the present invention can meet the needs of resuming production in orchards with severe or mild diseases, are highly operational, and are suitable for popularization and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 .Schematic diagram of low-level bridging technology;

[0024] Figure 2 .Growth of citrus fruits one year after low-position bridging;

[0025] Figure 3 .Differences in tree parameters (tree height, crown width and number of fruits) of Sugar Mandarin oranges at different stages before and after low-position rootstock replacement (citrus pomelo hybrid). Note: The native fruit trees are 8-year-old Sugar Mandarin oranges. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below in conjunction with specific embodiments. The given examples are only for illustrating the present invention, but not for limiting the scope of the present invention.

[0027] Embodiment 1:

[0028] From October 1, 2020 to December 1, 2021, the disease resistance of different rootstocks to citrus Huanglongbing was evaluated at the citrus planting experimental base of Zhongkai University of Agriculture and Engineering.

[0029] The rootstock materials tested in this study were five hybrids of the genus Citrus aurantium, including Citrus aurantium tangerine, Citrus aurantium pulcherrima, Citrus aurantium serrata, Citrus aurantium truncatum (a hybrid with Citrus aurantium as the female parent and Citrus aurantium as the male parent, Citrus aurantium being sour orange (Citrus×aurantium Engl.)).

[0030] Grafting method Figure 1 As shown, the details are as follows:

[0031] Twenty rootstocks of each variety were planted in the experimental garden for standby use. The test scions were collected from Conghua District, Guangzhou in October 2020, with typical symptoms of Huanglongbing, and the results of quantitative PCR test were positive (HLB test CT value was 24-25).

[0032] S1. Choose a season with sufficient water (the rainy season in the south is generally from April to September) for rootstocking;

[0033] S2. Treat the root system of the rootstock seedling before grafting, use rooting powder to "dip the roots", remove weeds and soil from the root of the fruit tree, and use a hoe to dig a hole with the same depth as the seedling to be planted;

[0034] S3. Cut the test scion into 10 cm (including 2 to 3 buds) long segments, select two branches about 10 cm above the ground and graft one scion each, and make two cuts, one vertical and one horizontal, to open the fruit tree's skin.

[0035] S4. Make a 30-45° bevel cut on the top of the stock and a 20° bevel cut on the back.

[0036] S5. Insert the top of the rootstock into the opening of the trunk and fix it. Wrap it with plastic film and seal it to reduce the evaporation of water from the xylem of the cambium and prevent rainwater from seeping into the wound and causing fungal infection. Graft 10 plants of each rootstock variety.

[0037] The results showed that the hybrid pomelo showed no symptoms of Huanglongbing at 3 months after grafting, while those at 9 and 12 months after grafting showed mild symptoms of Huanglongbing ( Figure 2 ), and the disease course index was the lowest (Table 1).

[0038] Table 1. Disease index of different rootstocks

[0039]

[0040] Note: Disease index = ∑ (number of diseased leaves at each level × representative value at each level) (total number of leaves surveyed / × highest representative value). The symptoms of Huanglongbing on the new shoots of the rootstock were surveyed once at 3, 6 and 9 months after grafting, and 5 leaves were surveyed each time. According to the proportion of the yellowing or mottled area of ​​the leaves to the whole leaf (SI), they were divided into 4 levels: no symptoms for level 1; 0≤SI≤1 / 3 for level 2; 1 / 3≤SI≤2 for level 3; 2 / 3≤SI for level 4.

[0041] Example 2

[0042] From April 1, 2021 to April 1, 2023, the tolerant rootstock (2-year-old pomelo hybrid as rootstock + red lemon seedling as scion, low-position bridging according to the method of Example 1) was carried out at the citrus planting test base in Lantang Town, Zijin. The tree indicators were significantly improved, showing that the tree vigor was enhanced and the fruiting rate was significantly improved (see Figure 3 ).

Claims

1. A low-position bridging method for restoring fruit bearing on citrus Huanglongbing trees, characterized in that: The new rootstocks planted in the field that are resistant to citrus Huanglongbing will be bridged to the diseased citrus trees, and the dead rootstocks will be replaced with rootstock varieties that are resistant to citrus Huanglongbing. The new rootstock resistant to citrus Huanglongbing disease is a hybrid variety of pomelo, which is a hybrid with Shatian pomelo as the female parent and Citrus aurantium as the male parent.

2. The low-position bridging method according to claim 1, characterized in that: The pomelo hybrid variety has a rootstock tree age of 2-year-old container seedlings, an average ground diameter of 2.0 cm, and a seedling height of 700-900 cm.

3. The low-position bridging method according to claim 1, characterized in that: The following steps are involved: S1. Choose a season with sufficient water for the planting; S2. Treat the root system of the rootstock seedling before grafting, "dip the roots" with rooting powder, remove weeds and soil from the root of the fruit tree, and dig a hole with a hoe to the same depth as the seedling; S3. Select a location about 10 cm above the ground as the grafting point, and cut the tree's skin with two cuts, one vertical and one horizontal; S4. Make a 30-45° bevel cut on the top of the stock and a 20° bevel cut on the back. S5. Insert the top of the rootstock into the opening of the trunk and fix it, then wrap it with plastic film to seal it to reduce the evaporation of water from the xylem of the cambium and prevent rainwater from seeping into the wound and causing fungal infection.

4. The low-position bridging method according to claim 3, characterized in that: The season with sufficient water is from April to September in the south.

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