WO2024172301A1 - Early satsuma mandarin variety, early yein, and breeding method thereof - Google Patents

Abstract

The present invention relates to a new mutant Satsuma mandarin variety, early Yein, more specifically to a new citrus variety obtained by irradiating branches and buds of early Satsuma mandarins (Citrus unshiu Marc. cv. Miyagawa-wase) with gamma rays, grafting, and then asexually breeding. Differences from the Satsuma mandarins are evident in the sugar content, thickness of the skin, color and firmness, and the like, and the fruit can withstand being stored. Thus, the present invention is a new variety with high economic value and is expected to be a significant contributor in raising the profit of citrus-growing farms.

Description

Yeinjosang, a variant of the early-ripening-onju citrus variety, and its breeding method

Cross-reference to related applications

This application claims the benefit of priority to Korean Patent Application No. 2023-0020990, filed February 16, 2023, the contents of which are incorporated herein by reference in their entirety.

The present invention relates to a new mutant citrus variety, “Yejinjosang,” and more specifically, to a new citrus variety obtained by grafting and vegetatively propagating a branch bud of Citrus unshiu Marc. cv. Miyagawa-wase after irradiating it with gamma rays.

Tangerines are a representative crop that ranks first or second in terms of production value among fruit crops in Korea, depending on the year of production. However, unlike other fruit crops, tangerines are produced only in Jeju Island.

Among the commercially cultivated citrus varieties, the satsuma mandarin is a variety that can be cultivated at the lowest temperatures, which are an annual average temperature of 15℃ or higher and a winter minimum temperature of -7℃ or higher. In addition, it is difficult to cultivate in subtropical regions where the winter minimum temperature is high because coloring does not occur properly and the taste is bland. The development of mandarin varieties that have no seeds and have thin skins that are easy to peel, like the satsuma mandarin, is the goal of citrus breeding in Western countries including the United States.

The early-ripening satsuma mandarin, Gungcheonjosang, is the most widely cultivated variety in Jeju Island. It is native to Fukuoka Prefecture, Japan, and was developed in 1925 after a mutation in the branch of the traditional satsuma mandarin was discovered. This lineage was introduced to Korea and is now cultivated as a representative early-ripening satsuma mandarin. The second most widely cultivated variety, Heungjinjosang, is a variety created from a mutation in the branch of Gungcheonjosang.

The proportion of the cultivation area of Onju tangerines, including Gungcheon Jo-sang, is very high, at over 90% of the total tangerine cultivation area (Statistics Korea, KREI Agricultural Outlook 2015). Most of the tangerines produced are consumed for eating, and some of the tangerines that are not of a commercial size are consumed for processing purposes such as juice.

Accordingly, it is necessary to develop varieties that are not only useful for reproduction but can also be grown for ornamental purposes, and have improved storage properties, making them highly economically viable.

In addition, since most of the current domestic citrus varieties are varieties introduced from Japan, there is an urgent need to develop new domestic citrus varieties, and thus, the development and cultivation of high-quality new citrus varieties is actively underway.

Although the Onjumikan does not form seeds, seeds can be obtained through artificial crossbreeding with seed-forming parent plants. However, since the seeds are polyembryonic and pollen is hardly formed, it is very difficult to develop new varieties through crossbreeding. In addition, it is expected that the possibility of developing varieties with better traits than the varieties currently being cultivated is low.

Accordingly, mutation breeding research using radiation is being actively conducted in countries such as the United States, Israel, and Japan (US registered patent USPP08378; Nucleus., 2000, 37(1-2):107-112). Through mutation breeding research using radiation, varieties exhibiting traits such as seedlessness, color variation, and peeling ease are being developed and distributed to the field.

Radiation mutation breeding technology is a technology that irradiates plant seeds or seedlings to induce genetic or chromosomal mutations, selects mutants with superior traits in subsequent generations, and develops new genetic resources through a genetic fixation process.

Using this technology, the frequency of mutations that occur at a low frequency in nature can be increased through radiation stimulation, and unlike genetic modification technology that artificially inserts foreign genes, this technology has been proven to be safe, and is being used to improve food crops such as rice and soybeans and to develop new varieties of flowers and fruits.

[Prior art literature]

[Patent Document] Korean Patent No. 10-1922110 (announced on November 27, 2018)

The purpose of the present invention is to provide a new variety of citrus plant having improved fruit storage properties due to increased sugar content and hardness by using an artificial mutation breeding method using gamma irradiation.

In order to achieve the above object, a mutant citrus plant named Yeonginjosang according to one embodiment of the present invention is bred by irradiating gamma rays to a bud of a branch of C. unshiu Marc. cv. Miyagawa-wase, grafting the gamma-ray-irradiated bud to induce a branch, selecting a mutant with a changed fruit shape, collecting the branch bud, and grafting the collected branch bud onto a rootstock, or is an early-maturing citrus plant (hereinafter referred to as “Yeinjosang”) that is stably asexually propagated by grafting the branch bud of the bred mutant plant onto a rootstock, and has the following characteristics: i) the pericarp is orange with a reddish tint, ii) the pericarp is thicker than that of the Gungcheonjosang fruit, iii) the fruit hardness is higher than that of the Gungcheonjosang fruit, and iv) the fruit sugar content and acidity are higher than those of the Gungcheonjosang fruit.

Specifically, the above-mentioned early warning signs may have the following characteristics:

a) Fruit diameter: 50 to 60 mm;

b) Fruit transverse diameter: 55 to 70 mm;

c) Overweight: 90 to 130 g;

d) Peel thickness: 2.5 to 4.5 mm;

e) Fruit sugar content: 9.0 to 12 Brix;

f) Acidity: 0.75 to 1.0 wt%;

g) Hardness: 1200 to 1400 g;

h) Peel color: orange with a strong red tint;

i) Propagation method: Asexual propagation through grafting.

According to another embodiment of the present invention, a citrus fruit is harvested from a mutant citrus plant named Yeinjosang described above.

According to another embodiment of the present invention, a method for breeding a mutant citrus plant named Yeonjosaeng comprises the steps of: 1) irradiating the buds of early-maturing branches with gamma rays; 2) grafting the buds irradiated with gamma rays in step 1) to induce branches, and then selecting mutants with changed fruit shapes and collecting buds of the branches; 3) grafting the buds of the mutant branches selected and collected in step 2) onto a rootstock to grow them; The present invention provides a method for breeding an early-maturing citrus plant having the characteristics of i) a red pericarp, ii) a thick pericarp, iii) high fruit firmness, and iv) high fruit sugar content, and which is stably asexually propagated and exhibits the following characteristics; a) fruit diameter: 50 to 60 mm; b) fruit transverse diameter: 55 to 70 mm; c) fruit weight: 90 to 130 g; d) Peel thickness: 2.5 to 4.5 mm; e) Fruit sugar content: 9.0 to 12 Brix; f) Acidity: 0.75 to 1.0 wt%; g) Hardness: 1200 to 1400 g; h) Peel color: orange with strong red tint; i) Propagation method: Vegetative propagation by grafting.

A method for breeding a mutant citrus plant named Yeinjosang according to another embodiment of the present invention may include a step of vegetatively propagating by grafting branch buds of a bred mutant citrus tree onto a rootstock.

The term "early-maturing satsuma mandarin" in the present invention refers to an early-maturing satsuma mandarin, and the " Citrus unshiu Marc. cv. Miysagawa-wase" of the present invention is a citrus variety that is native to Fukuoka Prefecture, Japan, and was bred after discovering that a branch has mutated from a traditional common satsuma mandarin, and is a representative early-maturing satsuma mandarin that is also widely cultivated in Korea.

The term "grafting" in the present invention refers to an artificial cultivation technique of cutting and connecting a part of the tissue of the same plant or a different plant to create a single plant, and is a method of producing a grafted seedling by attaching a bud or a stem with buds (scion; the upper part of the graft, scion) to a stem with roots or roots (the lower part of the graft, rootstock). Through grafting, the rootstock and scion adhere to each other through the cambium layer of the scion and are connected by vascular bundles and connecting bundles to grow into a complete plant. Depending on whether the scion is a branch, bud, or new shoot, it is divided into branch grafting, bud grafting, and pure grafting, and depending on the method of cutting a branch and grafting it onto the rootstock, branch grafting is divided into cut grafting, cleft grafting, side grafting, and top grafting. Although not limited thereto, in the present invention, grafting is preferably performed through a high-point or a low-point, and the specific grafting method can be performed by a conventional method well known to those skilled in the art.

In addition, in the present invention, although not limited thereto, a mature tree of the comparative variety of the present invention, Gungcheonjosang, can be used as a rootstock, and a tangerine tree used as a rootstock for tangerine trees can also be used.

In the present invention, the term "unsexual propagation" is the same as asexual reproduction, and refers to a method in which an individual forms a new individual on their own without the need for a male or female. Asexual reproduction occurs when a gamete created from an individual becomes a new individual on its own. It refers to all propagation methods other than seed propagation (sexual reproduction), and is not limited thereto, but in the present invention, it is preferable to adopt an asexual propagation method through grafting.

Hereinafter, the present invention will be described in more detail.

The inventors of the present invention introduced a breeding technique for inducing mutations in the most actively cultivated variety, Jo-saeng Onju Gungcheon Jo-saeng, and bred a new mutant citrus plant, Jo-saeng Onju, which has changes in the shape and composition of the citrus, thereby completing the present invention.

Specifically, the inventors of the present invention have made great efforts to develop a high-quality Onju citrus variety with the goal of diversifying citrus varieties, and as a result, they have introduced radiation mutation breeding technology to 'Gungcheon Jo-sang', an early-maturing Onju that has the largest cultivation area in Korea, that is, is most actively cultivated, and have bred a new early-maturing Onju citrus variety that exhibits changed fruit characteristics and improved storability, thereby completing the present invention.

The present invention provides a mutant citrus plant named "Yeinjosang" having changed fruit characteristics and improved storability, citrus fruits thereof, and a method for breeding the citrus plant.

The description in this specification, which indicates the characteristics of the mutant citrus plant such as the weight, size, peel thickness, sugar content, acidity, and peel color of the fruit as well as the water content of the plant, should be interpreted in consideration of the fact that some changes may appear in the characteristics of the plant within a range that can be generally recognized due to the characteristics of the plant or the asexual plant itself, and should not be interpreted as unreasonably limiting the characteristics of the mutant citrus plant named "Yeinjo-saeng" described in this specification, nor shall the scope of the rights of the present invention be limited thereby.

When the mutant citrus plant named "Yejinjosung" of the present invention is cultivated by its breeding method or asexual propagation method, depending on the conditions such as the cultivation region, cultivation location, climate, soil, weather, and whether it is cultivated in a greenhouse, not only the characteristics of the plant itself such as tree growth but also the weight, size, peel thickness, sugar content, acidity, peel color, fruit shape, etc. of the fruit may show some differences, and the characteristics of the fruit may also show some differences depending on the age of the plant. If these differences are caused by external factors rather than the characteristics of the variety itself and can be interpreted as changes in characteristics that may appear in the same plant variety due to changes in the environment, etc., they are interpreted as being included in the scope of the rights of the present invention despite such differences.

The description of the examples of the mutant citrus plant named "Yeinjo-saeng" of the present invention is based on field cultivation in the environment of Jeju Special Self-Governing Province, Republic of Korea, where breeding took place, unless otherwise specifically stated.

In order to achieve the above object, the fruit of a mutant citrus plant named as Yeinjosang according to one embodiment of the present invention is a type of early maturing citrus, and has the following characteristics: i) the peel is red, ii) the peel is thick, iii) the fruit is hard, and iv) the fruit has high sugar content.

The fruits of the above-mentioned early-ripening variety, iv) have similar characteristics to those of the early-ripening variety in terms of tree growth, flowering period, coloring period of the pericarp, and harvest period, but v) have the characteristic that the hardness of the pericarp is increased compared to that of the early-ripening variety, vi) have the characteristic that the collapse of the epidermal cells in the mature fruit tends to be delayed compared to that of the early-ripening variety, and vii) have the characteristic of excellent storability of the fruit.

The above-mentioned early-ripening fruit also has the following characteristics: viii) the fruit size is somewhat larger than that of the early-ripening fruit of Gungcheon; ix) the thickness of the pericarp is somewhat thicker than that of the early-ripening fruit of Gungcheon; x) the fruit firmness is high; and xi) the fruit sugar content is somewhat high.

The general characteristics of the above-mentioned early-ripening fruits are as follows:

a) Fruit diameter: 50 to 60 mm; b) Fruit transverse diameter: 55 to 70 mm; c) Fruit weight: 90 to 130 g; d) Pericarp thickness: 2.5 to 4.5 mm; e) Fruit sugar content: 9.0 to 12 Brix; f) Acidity: 0.75 to 1.0 wt%; g) Firmness: 1200 to 1400 g; h) Pericarp color: orange with strong red tint; i) Propagation method: Vegetative propagation by grafting.

In addition, the tree age, flowering period, peel coloring period, and harvest period of the early-maturing citrus tree are generally similar to those of the early-maturing citrus tree.

In addition, the leaves of the Japanese maple have the following characteristics compared to those of the Japanese maple: i) longer blade length, ii) shorter blade width, iii) more concave blade cross-section, iv) stronger blade rolling, and v) longer petioles.

Additionally, the general characteristics of the leaves of the yew tree are as follows:

1) Blade length: 100 to 118 mm; 2) Blade width: 2.6 to 4.0 mm; 3) Blade cross-section: severely concave; 4) Blade curl: strong; 5) Blade surface ridges: absent or weak; 6) Blade greenness: dark; 7) Blade margin undulation: absent or weak; 8) Blade margin notch: blunt serrated; 9) Blade top shape: acute; 10) Blade apex groove: absent; and 11) Petiole length: 16 to 29 mm;

However, these characteristics may differ somewhat depending on factors such as weather and environment, and the scope of the rights of the present invention is not limited due to such differences.

Considering the characteristics of the fruit shape and fruit tree described above, the early maturing citrus of the present invention has higher sugar content and acidity than the widely cultivated Gungcheon early maturing citrus, so it can be cultivated for raw consumption, and can also be utilized as food and processing materials therefor. In addition, the hardness of the fruit is high, so the fruit storage capacity is excellent, and it can contribute to increasing the income of citrus farms.

The above-mentioned new variety of Onju tangerine, Yeinjosang, has similar fruit characteristics at maturity to Gungcheonjosang, with skin coloring occurring in late November to early December. However, this characteristic can vary depending on climate, soil, environment, cultivation method, fruit size, and age.

The above-mentioned early-ripening variety is bred by irradiating the buds of an early-ripening variety of a Gungcheon branch with gamma rays, grafting the irradiated buds onto a mature tree to induce branches, selecting mutants with changed fruit shapes, collecting buds of the branches, and grafting the buds of the collected branches onto a stock, or by grafting the buds of the branches of the bred mutant plant onto a stock to stably propagate asexually.

The gamma-ray irradiation performed on the branch bud of the above C. unshiu Marc. cv. Miyagawa-wase can be performed by irradiating the bud with gamma-rays of cobalt-60 at a dose of about 60 Gray (about 0.6 rad), and specifically, the step 1) can be performed by irradiating the bud of the branch of C. unshiu Marc. cv. Miyagawa-wase with gamma-rays (γ-rays) of ⁶⁰ Co at a dose of about 60 Gy at a distance of about 0.63 m from the radiation source for about 22 hours.

The above grafting can be carried out using various rootstocks of citrus trees such as Gungcheonjo-saeng, Tangja, or Swingle, but is not limited thereto, and any rootstock capable of stably asexually propagating a mutant citrus tree named Yeoninjo-saeng can be applied as the rootstock used in the present invention.

In addition, in the present invention, the grafting in steps 1) and 3) need not be performed on the same type of stock. For example, the grafting in step 1) can be performed on a mature tree of the early-growing family, and the grafting in step 3) can be performed on a mature tree of the early-growing family or a Chinese juniper tree.

According to another embodiment of the present invention, a citrus fruit is harvested from a mutant citrus plant named Yeinjosang described above.

The early maturing mutant citrus fruit “Yeinjosang” of the present invention differs from Gungcheonjosang in fruit traits such as sugar content, peel thickness and color, and fruit hardness, and has excellent fruit storability, so it has high economic value and is therefore expected to greatly contribute to increasing the income of citrus fruit farms.

Figure 1 is a photograph comparing the top part of the fruit (top), the side part of the fruit, the back part of the fruit (bottom), the cross-section, and the longitudinal section of the fruit of Gungcheonjo-saeng (A) and the fruit of a mutant citrus named Yeinjo-saeng bred according to the present invention (B).

Figure 2 is a photograph comparing the leaves of a Gungcheonjo-saeng tree (A) and the leaves of a mutant citrus tree named Yeinjo-saeng bred according to the present invention (B).

Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[ Example 1] Mutant citrus breeding using radiation

In the present invention, the most widely cultivated 'Gungcheonjosang' in Jeju Island was selected as a breeding experimental material, and accordingly, 5 kg of branches of the Onju tangerine 'Gungcheonjosang' were distributed by the Jeju Special Self-Governing Province Agricultural Research and Extension Services and used. At this time, the branches of 'Gungcheonjosang' for inducing mutations in the eyes by radiation exposure were used after collecting scions in early to mid-February, and were stored in a 4°C refrigerator for 3 months until the grafting period, which was mid-April to early May, and then used.

The buds of the Gungcheonjo-saeng branches, donated by Jeju Special Self-Governing Province Agricultural Research and Extension Services, were irradiated with gamma rays using the cobalt-60 ( ⁶⁰ CO) irradiation facility (source C-188, Nordion International Ltd., Canada) of the Jeju National University Radiation Applied Science Research Institute (now the Atomic Energy Research Institute), to induce mutations. These were then grafted onto the adult Gungcheonjo-saeng trees through high grafting. Cultivation and management were performed according to conventional methods.

Specifically, in April 2006, mutations were induced by gamma-ray irradiation on the buds of Gungcheonjosaeng branches using the cobalt-60 ( ⁶⁰ CO) irradiation facility of the Radiation Application Science Research Institute of Jeju National University. At this time, the gamma-ray irradiation was performed under the condition of treating the buds of Gungcheonjosaeng branches with about 60 Gy of gamma rays for about 22 hours at a distance of 0.63 m from the radiation source. The buds of Gungcheonjosaeng branches in which mutations were induced by the gamma-ray irradiation were grafted onto Gungcheonjosaeng mature trees using a rootstock, at the citrus packaging facility of Jeju National University's Research and Practice Center, and then the branches were induced and selected by examining their traits. At this time, a total of 913 scions were grafted, and the germination rate was examined two months after grafting, and the result was 71.6% (total 654 scions).

After first selecting branches showing mutant traits from branches grafted onto Gungcheon early-maturing mature trees, scions were collected from the selected branches, and in April 2008, branches of Gungcheon early-maturing trees in the citrus field of Jeju National University's Subtropical Agriculture and Life Science Research Institute (Topyeong-dong, Seogwipo-si) were removed. After grafting multiple scions with one mutant trait per tree to induce branches, it was investigated whether the mutant traits were maintained to select mutant branches. In addition, the fruits set from each mutant branch were harvested in late November to early December every year from 2012 to 2022, and their fruit weight and diameter, pericarp thickness, sugar content and acidity, and fruit color changes were measured.

The weight was measured to the nearest 0.1 g using an electronic indicating scale (CAS Co., Ltd., Korea). The longitudinal and transverse diameters were measured to the nearest 0.1 mm using a digital caliper (Mitutoyo Corporation, Japan).

After measuring the fruit size and weight, the juice of the fruit was collected. The sugar content and acidity were measured using an acidity analyzer NH-2000 (HORIBA, Japan), and about 4 to 5 mL of juice was injected with a syringe according to the device user manual to measure the sugar content and acidity.

The color change was measured using a colorimeter (Chroma meter CR-400, Minolta) to measure the color of mutant fruits showing color change.

Changes in the shape of the fruit were observed with the naked eye, and additional observations of changes in the peel were performed at the cellular level using a microscope (Nikon microphto type 114).

From the branches selected in this way, mutant branch buds were collected again and grafted onto the adult trees of Gungcheonjosang and the rootstock of Tangja (purchased from a nurseryman) to induce the fruiting of citrus fruits.

[ Example 2] Early bloomer Characterization of mutant citrus fruits

1) Comparison of general characteristics

The characteristics of the citrus fruits produced in Example 1 above were investigated in 2021 and 2022 by comparing the general characteristics of the fruit tree and the general characteristics of the citrus fruits with those of the early maturing citrus fruits.

Specifically, the mutant citrus fruits grown in the above Example 1 were found to have similar characteristics to the Gungcheon early maturing citrus fruits commonly grown in Jeju in terms of leaf color, flowering period, tree vigor, etc., as shown in Table 1 below.

Varieties Wash bloom Pericarp pigmentation Harvest time Early spring in the palace middle May 10th - 20th Late November Late November to mid-December Tow truck middle May 10th - 20th Late November Late November to mid-December

2) Comparison of fruit characteristics

In the mutant citrus named Yeinjosaeng and its parent, Gungcheonjosaeng, which were bred according to Example 1 of the present invention, photographs of the top part of the fruit (top), the side part of the fruit, the back part of the fruit (bottom), and the cross-section are shown in Figure 1 (A: Gungcheonjosaeng; B: Yeinjosaeng).

In addition, the mutant citrus fruits grown in Example 1 above were harvested in early to mid-December over two years from 2021 to 2022, which bloomed between May 10 and 20 (field-grown in Donghong-dong, Seogwipo-si, Jeju Special Self-Governing Province), and their traits were investigated, and the results are summarized in Table 2 below. The traits of the leaves were investigated, and the results are summarized in Table 3 below.

Table 2 below shows the characteristics of the Gungcheon early maturing (control) and mutant citrus early maturing varieties, and Table 3 below shows the characteristics of the Gungcheon early maturing (control) leaves and mutant citrus early maturing leaves.

Referring to Table 2 and Fig. 1, it was confirmed that the mutant citrus, Yeinjosang, bred in Example 1, differs from its parent, Gungcheonjosang, in fruit characteristics. In particular, as shown in Fig. 1, it was confirmed that there was a large difference in the color of the peel. Compared to Gungcheonjosang, Yeinjosang shows an orange color with a strong red color, which is also confirmed by the fact that the a value of Yeinjosang was measured higher in the colorimeter presented in Table 2, and it seems that it can be developed as an ornamental citrus due to these fruit characteristics. In addition, as can be confirmed in the longitudinal cross-section photograph (the last photograph), both Gungcheonjosang and Yeinjosang have the morphological characteristic of a large transverse diameter, but the longitudinal cross-section shape of Gungcheonjosang is closer to an oval, whereas Yeinjosang is closer to a circle (i.e., the difference between the longitudinal and transverse diameters is greater for Gungcheonjosang).

In addition, the fruits of early-ripening Yeinjo-sang maintain the changed form of the fruit shape described above from the young fruits that have set until early December when they mature, and when compared to early-ripening Gungcheon-sang, the harvest period of early-ripening Yeinjo-sang is similar, but the color of the peel is clearly different.

In addition, it can be seen that the hardness of the fruits of early-ripening Yeinjosaeng is significantly increased compared to early-ripening Gungcheonjosaeng, and thus the fruit storage capacity is also increased.

In addition, as shown in Table 2 above, it was confirmed that although the fruit of the mutant citrus fruit, Yeinjo-saeng, which was bred in Example 1, had differences in phenotypes depending on the climate (precipitation, amount of sunlight, etc.) of the year of investigation, the characteristic phenotypes of the fruit were stably maintained.

In addition, referring to Table 3 and Figure 2 above, it can be confirmed that the leaves of the early-ripening ...

The early maturing method of the present invention is different from the early maturing method of the present invention and has high economic value due to its superior fruit storage properties, and thus can greatly contribute to increasing the income of citrus farms.

Claims (6)

1) A step of irradiating the bud of a branch of Citrus unshiu Marc. cv. Miyagawa-wase with gamma rays (γ-rays) of ⁶⁰ Co; 2) A step of grafting the buds irradiated with gamma rays in the above step 1) onto the stock to induce branches, and then selecting mutants with changed fruit characteristics compared to the early maturing ones and collecting the buds of the branches; and 3) A step of grafting and growing the buds of mutant branches selected and collected in step 2) onto a rootstock; A method for breeding a new variety of mutant citrus plant, named Yeinjosang, which is stably asexually propagated and exhibits the following characteristics: The fruits of early childhood education are a) Fruit diameter: 50 to 60 mm; b) Fruit transverse diameter: 55 to 70 mm; c) Overweight: 90 to 130 g; d) Peel thickness: 2.5 to 4.5 mm; e) Fruit sugar content: 9.0 to 12 Brix; f) Acidity: 0.75 to 1.0 wt%; g) Hardness: 1200 to 1400 g; h) Peel color: orange with a strong red tint; and i) Propagation method: Asexual propagation through grafting, having all the characteristics selected from the group consisting of; The early-maturing citrus tree, j) Flowering period: Early May to mid-May; k) Peel coloring period: mid-November to late November; and l) Harvest season: late November to mid-December; Have all the characteristics selected from the group consisting of In the first paragraph, A method for breeding a new variety of mutant citrus plant named Yeinjo-saeng, wherein the step of irradiating with gamma rays (γ-rays) of ⁶⁰ Co in the above step 1) is performed for 22 hours at a distance of 0.63 m from a radiation source with an irradiation dose of 60 Gy. In the first paragraph, The leaves of the towpathway tree, A method for breeding a new variety of a mutant citrus plant named Yeonjosang, which has all the characteristics selected from the group consisting of: 1) blade length: 100 to 118 mm; 2) blade width: 2.6 to 4.0 mm; 3) blade cross-section: severely concave; 4) blade curl: strong; 5) blade surface ridge: absent or weak; 6) blade greenness: dark; 7) blade margin wavyness: absent or weak; 8) blade margin notch: blunt serrated; 9) blade top shape: acute; 10) blade apical groove: none; and 11) petiole length: 16 to 29 mm. In the first paragraph, A method for breeding a mutant citrus plant, a new variety named Yeinjosang, which includes a step of asexually propagating by grafting the buds of branches of the mutant plant bred in the above step 3) onto a rootstock. A new variety of citrus plant, named Yeinjosang, bred by the method of any one of claims 1 to 4. Citrus fruits harvested from a mutant citrus plant of the fifth paragraph.

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