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Abstract [Objectives] This study was conducted to improve the propagation efficiency of Gardenia jasminoides Ellis and improve the quality of plantlets.
[Methods]A G. jasminoides cutting experiment was carried out with three different cuttage modes and two cutting treatment methods， and the rooting time， rooting rate， root amount and plantlet growth were measured and analyzed.
[Results] The three-dimensional cutting model of CL1 could not only shorten the nursery cycle and promote root development， but also effectively improve the quality of plantlets and increase the yield of plantlets per unit area. It is an ideal way to improve the quality and efficiency of cutting plantlets.
[Conclusions]This study has a positive role in promoting the healthy development of the nursery stock industry.
Key words Gardenia jasminoides Ellis; Three-dimensional cuttage; Rooting; Growth
Received： May 5， 2021 Accepted： July 7， 2021
Supported by Changsha Science and Technology Planning Project （kq1801028）; Major Landmark Innovation Demonstration Project （2019XK2002）.
Yan YANG （1980-）， female， P. R. China， associate researcher， devoted to research about forest tree breeding， cultivation and application.
*Corresponding author.
Gardenia jasminoides Ellis is an evergreen shrub belonging to the Gardenia genus in the Rubiaceae family. It has green leaves， pleasant floral fragrance， and orange-red festive fruit color. It is the first choice for landscaping and garden viewing. The fragrance of gardenia is refreshing， and the tender and refreshing flesh is a rare raw material for essential oils， drinks， dishes and pastries. It is also an ideal source of nectar. The fruit contains geniposide， crocin， squalene and other active ingredients that are beneficial to the human body. The fruit oil is rich in unsaturated fatty acids. The natural pigments extracted from the fruit， gardenia yellow and gardenia blue， can also be used as food pigments and handicraft dyeing pigments. Meanwhile， the fruits， leaves and roots of G. jasminoides can be used as medicine， with high nutritional value and health care functions， and are good products for human body conditioning and nourishment[1-4]. It can be seen that G. jasminoides has the usages of "medicine， food and appreciation"， high ecological， economic and social value， and great application potential in the fields of medicine， food， agriculture， and cosmetics.
G. jasminoides is mostly reproduced by seeds， but due to the unstable germination rate of seed reproduction， the production of seedlings is affected by the season and the seedlings from seed breeding are prone to variability. And the excellent traits of the female parent are difficult to maintain， while asexual reproduction makes up for such deficiency[5]. Cuttage， as a kind of asexual reproduction， can not only maintain excellent target traits， but also do not need to consider the cumbersome selection and cultivation of rootstocks， nor are they restricted by seasons and breeding locations compared with grafting reproduction methods. It is an ideal way of asexual reproduction for G. jasminoides[6]. At present， the cutting propagation of G. jasminoides mostly uses field cuttings and nutrient cup and plantlet plate cuttings[7-10]. Although field cuttings are simple to operate， they are easily affected by external conditions. Seedling raising is seasonal， and root system development is generally delayed and rooting is uneven due to the influence of ground temperature. Although nutrient cup cuttings can make up for the shortcomings of field cuttings， it takes up more space than field cuttings and cannot make full use of the three-dimensional space， and the cost of raising plantlets is relatively high. However， three-dimensional cuttings not only ensure the good quality of seedlings and efficient breeding， but also increase the yield of plantlets in a limited area， reduce the impact of ground temperature on the rooting of plantlets， increase the air permeability of the seedling substrate， and improve the quality of plantlets. It can be seen that three-dimensional cuttage will become a new way for the sustainable development of the agricultural and forestry seedling industry in the future， and will play a positive role in promoting the healthy development of the seedling industry. Materials and Methods
General situation of experimental field
The test site is located in the nursery of the experimental forest farm of Hunan Academy of Forestry （113°01′30″ east longitude， 28°06′40″ north latitude）. It has a humid subtropical monsoon climate with an average annual temperature of about 17 ℃ and an average annual rainfall of 1 411.4 mm. The annual frost-free period is 272 d. The soil type is red soil， and the soil layer is deep. The soil has a pH value between 4.5 and 5.5， and slightly acidic.
Experimental materials
According to the cultivation objective， 3 to 5 year-old seed trees that healthy and free of diseases and pests were selected， and the semi-lignified branches or twigs in the middle of the crown on the sun-facing side were used as cuttings.
Experimental methods
Cutting treatment
The branches were cut into stems of about 10 cm， leaving 2 to 3 leaves on each stem， and the lower part of each stem was cut into a horseshoe shape with branch shears to increase the adsorption area of nutrients and rooting agent. The lower parts of the cut stems were aligned and arranged according to 30 stems per bundle into bundles， which were tied with rubber bands and kept moisturized， and put in a moist and cool place for later use.
Three-dimensional cutting device production and substrate treatment
A PVC pipe with an inner diameter of 40 mm （wall thickness 2 mm） was cut into segments 50 cm long. Then， a punching tool was used to drill holes along the lines corresponding to the four points of the "cross" of the PVC pipe. Each hole was 5 mm wide， 10 mm long， and the hole spacing on each straight line was 40 mm. A roll of white non-woven fabric weighing 20 g and 10 m in length was taken and cut and sewn into cylinders 70 cm in length and 25 cm in diameter， for later use.
The cutting substrate adopted the optimal substrate ratio （peat soil∶perlite∶yellow heart soil=2∶1∶1） obtained from the previous experiment. The PVC tubes were put into the sewn non-woven fabric cylinders， and the cutting substrate was filled between each PVC tube and corresponding non-woven fabric cylinder with the PVC tube as a center. And watering was performed while filling to form a substrate cylinder with the PVC tube as the central axis. A layer of round-hole nursery sponge 2 cm in thickness was wrapped on the periphery of each substrate cylinder for moisturizing， and the lower end of each substrate cylinder was fixed in a container filled with sand. Finally， the substrate was sprayed with 0.05% potassium permanganate solution until it was drenched to the bottom to achieve the purpose of disinfecting the substrate cylinders. Experimental design
In this study， we used the screened cutting substrate of G. jasminoides. with flat cuttings as a control， two three-dimensional cutting methods were set up. The specific treatment methods are shown in Table 1.
Management after cuttage
The three cutting treatments were all implemented in a greenhouse， and an automatic intermittent spray system was adopted. Nutrient management and sterilization and disease prevention were implemented using conventional management methods.
Data investigation and statistics
Through regular tracking and measurement， the rooting time of plantlets was recorded， and the rooting rate of plantlets in different treatments was recorded after 40 d. After 180 d， the plantlet height and ground diameter were measured， and the yield of plantlets per unit area， root length and root number were also counted or measured. Each of the above measured indexes was the average of three replicates.
The survey data were processed by Excel 2016， and histograms were made combining with the results of variance analysis performed in SPSS 18.0.
Results and Analysis
Effects of different cutting treatments on rooting time and rooting rate of plantlets
Rooting time and rooting rate are key indicators for evaluating the effect of forestry cuttage. In this study， the rooting time and rooting rate of different cutting treatments of G. jasminoides were calculated， as shown in Fig. 1. Through comparison and analysis， it could be seen that the rooting time of the three cutting treatments was quite different. The rooting time of the control treatment （CK） was the latest， and the rooting took place gradually about 25 d after insertion. The rooting of treatment 1 （CL1） and treatment 2 （CL2） were both earlier， and the cuttings began to root about 19 d after insertion. In terms of rooting rate， there were no significant differences in the rooting rate between the three cutting treatments， and the rooting rate reached more than 93%. Among them， the average rooting rate of CL1 was the highest， reaching 98.43%， and the average rooting rates of CL2 and the CK were respectively 95.37% and 93.07%. Based on the above， it could be seen that CL1 had the best effect among the three cutting treatments. It not only rooted early （it only took about 18 d for rooting）， but also had a high rooting rate.
Agricultural Biotechnology2021
Effects of different cutting treatments on the growth of plantlets The growth of seedlings included seedling height and ground diameter， which represented whether different cutting treatments could promote the growth of seedlings. Based on the statistics of seedling height and ground diameter on different cutting treatments （Fig. 2）， it was found that there were certain differences in plantlet height and ground diameter between the three cutting treatments， among which CL1 had the highest plantlet height （14.03 cm） and the largest ground diameter （2.98 mm）， CL2 showed the plantlet height and ground diameter ranking second， at 12.67 cm and 2.57 mm， respectively， and the CK exhibited the smallest plantlet height and ground diameter， at 12.57 cm and 2.01 mm， respectively. It could be seen that in the three cutting treatments， CL1 had a better promoting effect on the growth of cutting plantlets.
Effects of different cutting treatments on plantlet root length and rooting quantity
Through observation and determination （Fig. 3）， it could be seen that the root length and the amount of G. jasminoides cuttings were significantly different between the three cutting treatments， and the order of root length from small to large was CK （3.61 cm）， CL2 （5.58 cm） and CL1 （9.84 cm）. The average root length of CL1 was 2.7 times that of the CK. The root amounts of the three treatments were CK （10）， CL2 （20） and CL1 （38） sequentially in descending order. The root amount of CL1 was 3.8 times that of the CK. It could be seen that the root growth of G. jasminoides cuttings in cutting treatment 1 （CL1） was the best.
Effects of different cutting treatments on the yield of plantlets per unit area
Cutting plantlet raising is an efficient way of raising plantlets， which can cultivate a large number of high-quality plantlets in a limited space. In this study， the yield of plantlets per unit area was compared among the three cutting treatments， so as to screen out the best treatment for raising G. jasminoides plantlets （Fig. 4）. It can be seen from Fig. 4 that the average yield of plantlets per unit area differed greatly among the three cutting treatments. The treatment with the largest average yield of plantlets per unit area was CL1 （686.56 plants/m2）， followed by CL2 （656.93 plants/m2）， and the smallest value was in treatment CK （273.26 plants/m2）. The yield of plantlets per unit area of CL1 was 2.5 times that of the CK.
Conclusions and Discussion
On the basis of the existing substrate ratio， a comparison of the cutting effects of plane cuttings （CK） and three-dimensional cuttings （CL1 and CL2） was carried out， and the following conclusions were preliminarily drawn： three-dimensional cuttage significantly promoted plantlet rooting， root development and plantlet growth; and for the same three-dimensional cuttage， different cutting treatments also showed great differences in the rooting and growth of plantlets， and specifically， the seedlings of CL1 had the best rooting and the largest growth， as well as the largest yield of plantlet per unit area. Obviously， the important factors affecting the rooting and growth of cuttings are the rooting agent used and cutting substrate-related conditions[8]， and the cutting mode that promotes the sustainable and efficient development of plantlet production is three-dimensional cuttage. Many studies believe that rooting agents can achieve rooting of cuttings by adjusting the dynamic balance between the contents of rooting inhibitory substances and promoting substances in cuttings[11-14]. In this study， we used commercially available rooting powder （CK and CL2） and willow twig extract as rooting agent （CL1） to compare the cutting effect of G. jasminoides. It was found that the G. jasminoides cuttings treated with willow twig extract rooted early， and showed a large amount of roots and the best plantlet growth， which might be due to the willow twig extract contained salicylic acid and aspirin that can induce and promote plant rooting. The active ingredients are not only rich in nutrition but also have a bactericidal effect， and they can improve the microenvironment of cutting roots， facilitate the formation of cutting root primordia， and ensure the survival rate of plantlets[15-18]. Furthermore， the pretreatment of CL1 used a mixture of vitamin C and potassium dihydrogen phosphate （1∶1） for soaking. In addition to promoting root differentiation， both vitamin C and potassium dihydrogen phosphate can also improve cutting resistance， promote seedling growth， increase the biomass of a single plant and improve the quality of seedlings， thereby providing energy and nutrients for the rooting of cuttings and the growth of seedlings[19，20].
Cutting substrates play an extremely important role in cutting propagation. Different placement forms of the same cutting substrate also show great differences in the rooting of cuttings and the growth of plantlets， and the air permeability of substrates is the key to the rooting of cuttings and the growth of plantlets[21]. In this study， the cutting effect was the best in treatment CL1. Because it used three-dimensional substrate cylinders， which were supported by a plastic tube with holes in the center and equipped with a spray head， it could not only ensure the uniform moisture retention of the substrate， but also further increased the permeability of the substrate， which could deliver oxygen to the root tip in time， further activate root enzyme activity， and promote root growth. Therefore， the root growth of CL1 was the best， with an average root length of 9.84 cm and the largest amount of roots （38 roots）. In terms of substrate placement， three-dimensional cuttings could better promote the respiration of the substrate， thereby improving the oxygen circulation of the substrate and improving the quality of plantlet. Raising plantlets with cuttings is not restricted by seasons， and if we can save production land in addition to saving time， it can be said to have the best of both worlds. In this study， the three-dimensional cuttage model CL1 not only had a large growth of plantlets （the height of the plantlets increased by 11.61% compared with the CK， and the ground diameter increased by 48.26% compared with the CK）， but also the yield of plantlets per unit area was large， which was 2.5 times that of the CK. The three-dimensional cuttage model can not only make up for insufficient plantlets raised in the field， but also improve the quality and efficiency of raising plantlets with cuttings. It is an ideal way for plantlet breeding at present.
References
[1] YANG Y， TANG YX， TANG J， et al. Fruit active ingredients and agronomic traits relations of edible and medicinal plant Gardenia jasminoides[J]. Journal of Central South University of Forestry & Technology， 2019， 39（1）： 15-19. （in Chinese）
[2] YANG Y， KUANG D， TANG J， et al. Comparisons of main agronomic characters and interrelationships of edible and medicinal plant Gardenia jasminoides[J]. Nonwood Forest Research， 2016， 34（4）： 134-137. （in Chinese）
[3] RAO GC， HE H， DENG ZW. Techniques for high-yield cultivation and industrialization of Gardenia jasminoides Ellis[J]. Nonwood Forest Research， 2008（2）： 105-111. （in Chinese）
[4] QI YJ， GU JQ， WANG L， et al. Research progress on the functional components of Gardenia jasminoides Ellis[J]. Science and Technology of Food Industry， 2013， 34（14）： 363-369. （in Chinese）
[5] GU S， LUO GM， ZHU YY， et al. Optimization of seed germination and detection of germination inhibitors in gardenia fruits[J]. Journal of Southern Agriculture， 2014， 45（3）： 376-382. （in Chinese）
[6] WANG YF， ZHANG XH， CHEN QH， et al. Breeding new resource of Gardenia jasminoides var. radicans through cutting[J]. Subtropical Agriculture Research， 2020， 16（2）： 94-99. （in Chinese）
[7] WU KG. Study on container plantlet raising of Gardenia jasminoides Ellis Fenguan No. 1 by tender branch cuttings seedlings[J]. Forestry Prospect and Design， 2017， 37（2）： 87-89， 93. （in Chinese）
[8] LI J， YIN CM， LI JA， et al. The key techniques in cutting propagation of Gardenia jasminoides[J]. South China Forestry Science， 2017， 45（2）： 20-23. （in Chinese）
[9] CHEN YP. Effect of rooting agent and substrate treatment on rooting of Gardenia jasminoides[J]. Fujian Science & Technology of Tropical Crops， 2014， 39（2）： 12-14. （in Chinese） [10] MA JM. Study on the influence of different substrates on hardwood cuttings of Gardenia[J]. Modern Agriculture， 2013（4）： 15. （in Chinese）
[11] COPES DL， MANDEL NL. Effects of IBA and NAA treatments on rooting douglas-fir stem cutting[J]. New Forests， 2000（20）： 249-257.
[12] AMINAH H， DICK J MC P， LEAKEY RRB， et al. Effect ofindole butyric acid （IBA） on stem cuttings of Shorea leprosula[J]. Forest Ecology and anagement.1995（72）： 199-206.
[13] YU LL， QIAO RF， JI KX. Effect of different exogenous hormones on changes of endogenous hormones in hybrid tulip tree during rooting process[J]. Journal of Northeast Forestry University， 2007， 35（9）： 24-26. （in Chinese）
[14] ANDREIA H， EDUARDO NC， ELIZABETH O， et al. Effect of plant growth regulators in the rooting of Pinus cuttings[J]. Brazilian Archives of Biology and Technology， 2006（49）： 189-196.
[15] NIU HD， WANG MR. Effect of willow branch liquid on rooting of grape cuttings[J]. China Fruits， 1991（2）： 48-49. （in Chinese）
[16] CHANG YP. Physiological effects of salicylic acid and its application in fruit preservation[J]. Northern Horticulture， 2008（5）： 69-71. （in Chinese）
[17] MENG XJ， DI K， DING GH. Progress of study on the physiological role of salicylic acid in plant[J]. Chinese Agricultural Science Bulletin， 2010， 26（15）： 207-214. （in Chinese）
[18] LIU LL， GU X， ZHAO YL. The physiological effects of salicylic acid on breeding stem section of dehydrated virus potato[J]. Acta Agriculturae Boreali-occidentalis Sinica， 2003（2）： 48-50. （in Chinese）
[19] WU YC， HE BB， XUE SX， et al. Research progress on preparation and application of potassium dihydrogen phosphate[J]. Phosphate & Compound Fertilizer， 2017， 32（2）： 30-34. （in Chinese）
[20] LIU YH， YU L， WANG RZ， et al. Role of ascorbic acid in plant growth and development and its deficient mutants in higher plants[J]. Plant Physiology Communications， 201 47（9）： 847-854. （in Chinese）
[21] OU YH. Physiological basis of forest tree cultivation[M]. Shanghai： Shanghai Science and Technology Press， 1987. （in Chinese）
[Methods]A G. jasminoides cutting experiment was carried out with three different cuttage modes and two cutting treatment methods， and the rooting time， rooting rate， root amount and plantlet growth were measured and analyzed.
[Results] The three-dimensional cutting model of CL1 could not only shorten the nursery cycle and promote root development， but also effectively improve the quality of plantlets and increase the yield of plantlets per unit area. It is an ideal way to improve the quality and efficiency of cutting plantlets.
[Conclusions]This study has a positive role in promoting the healthy development of the nursery stock industry.
Key words Gardenia jasminoides Ellis; Three-dimensional cuttage; Rooting; Growth
Received： May 5， 2021 Accepted： July 7， 2021
Supported by Changsha Science and Technology Planning Project （kq1801028）; Major Landmark Innovation Demonstration Project （2019XK2002）.
Yan YANG （1980-）， female， P. R. China， associate researcher， devoted to research about forest tree breeding， cultivation and application.
*Corresponding author.
Gardenia jasminoides Ellis is an evergreen shrub belonging to the Gardenia genus in the Rubiaceae family. It has green leaves， pleasant floral fragrance， and orange-red festive fruit color. It is the first choice for landscaping and garden viewing. The fragrance of gardenia is refreshing， and the tender and refreshing flesh is a rare raw material for essential oils， drinks， dishes and pastries. It is also an ideal source of nectar. The fruit contains geniposide， crocin， squalene and other active ingredients that are beneficial to the human body. The fruit oil is rich in unsaturated fatty acids. The natural pigments extracted from the fruit， gardenia yellow and gardenia blue， can also be used as food pigments and handicraft dyeing pigments. Meanwhile， the fruits， leaves and roots of G. jasminoides can be used as medicine， with high nutritional value and health care functions， and are good products for human body conditioning and nourishment[1-4]. It can be seen that G. jasminoides has the usages of "medicine， food and appreciation"， high ecological， economic and social value， and great application potential in the fields of medicine， food， agriculture， and cosmetics.
G. jasminoides is mostly reproduced by seeds， but due to the unstable germination rate of seed reproduction， the production of seedlings is affected by the season and the seedlings from seed breeding are prone to variability. And the excellent traits of the female parent are difficult to maintain， while asexual reproduction makes up for such deficiency[5]. Cuttage， as a kind of asexual reproduction， can not only maintain excellent target traits， but also do not need to consider the cumbersome selection and cultivation of rootstocks， nor are they restricted by seasons and breeding locations compared with grafting reproduction methods. It is an ideal way of asexual reproduction for G. jasminoides[6]. At present， the cutting propagation of G. jasminoides mostly uses field cuttings and nutrient cup and plantlet plate cuttings[7-10]. Although field cuttings are simple to operate， they are easily affected by external conditions. Seedling raising is seasonal， and root system development is generally delayed and rooting is uneven due to the influence of ground temperature. Although nutrient cup cuttings can make up for the shortcomings of field cuttings， it takes up more space than field cuttings and cannot make full use of the three-dimensional space， and the cost of raising plantlets is relatively high. However， three-dimensional cuttings not only ensure the good quality of seedlings and efficient breeding， but also increase the yield of plantlets in a limited area， reduce the impact of ground temperature on the rooting of plantlets， increase the air permeability of the seedling substrate， and improve the quality of plantlets. It can be seen that three-dimensional cuttage will become a new way for the sustainable development of the agricultural and forestry seedling industry in the future， and will play a positive role in promoting the healthy development of the seedling industry. Materials and Methods
General situation of experimental field
The test site is located in the nursery of the experimental forest farm of Hunan Academy of Forestry （113°01′30″ east longitude， 28°06′40″ north latitude）. It has a humid subtropical monsoon climate with an average annual temperature of about 17 ℃ and an average annual rainfall of 1 411.4 mm. The annual frost-free period is 272 d. The soil type is red soil， and the soil layer is deep. The soil has a pH value between 4.5 and 5.5， and slightly acidic.
Experimental materials
According to the cultivation objective， 3 to 5 year-old seed trees that healthy and free of diseases and pests were selected， and the semi-lignified branches or twigs in the middle of the crown on the sun-facing side were used as cuttings.
Experimental methods
Cutting treatment
The branches were cut into stems of about 10 cm， leaving 2 to 3 leaves on each stem， and the lower part of each stem was cut into a horseshoe shape with branch shears to increase the adsorption area of nutrients and rooting agent. The lower parts of the cut stems were aligned and arranged according to 30 stems per bundle into bundles， which were tied with rubber bands and kept moisturized， and put in a moist and cool place for later use.
Three-dimensional cutting device production and substrate treatment
A PVC pipe with an inner diameter of 40 mm （wall thickness 2 mm） was cut into segments 50 cm long. Then， a punching tool was used to drill holes along the lines corresponding to the four points of the "cross" of the PVC pipe. Each hole was 5 mm wide， 10 mm long， and the hole spacing on each straight line was 40 mm. A roll of white non-woven fabric weighing 20 g and 10 m in length was taken and cut and sewn into cylinders 70 cm in length and 25 cm in diameter， for later use.
The cutting substrate adopted the optimal substrate ratio （peat soil∶perlite∶yellow heart soil=2∶1∶1） obtained from the previous experiment. The PVC tubes were put into the sewn non-woven fabric cylinders， and the cutting substrate was filled between each PVC tube and corresponding non-woven fabric cylinder with the PVC tube as a center. And watering was performed while filling to form a substrate cylinder with the PVC tube as the central axis. A layer of round-hole nursery sponge 2 cm in thickness was wrapped on the periphery of each substrate cylinder for moisturizing， and the lower end of each substrate cylinder was fixed in a container filled with sand. Finally， the substrate was sprayed with 0.05% potassium permanganate solution until it was drenched to the bottom to achieve the purpose of disinfecting the substrate cylinders. Experimental design
In this study， we used the screened cutting substrate of G. jasminoides. with flat cuttings as a control， two three-dimensional cutting methods were set up. The specific treatment methods are shown in Table 1.
Management after cuttage
The three cutting treatments were all implemented in a greenhouse， and an automatic intermittent spray system was adopted. Nutrient management and sterilization and disease prevention were implemented using conventional management methods.
Data investigation and statistics
Through regular tracking and measurement， the rooting time of plantlets was recorded， and the rooting rate of plantlets in different treatments was recorded after 40 d. After 180 d， the plantlet height and ground diameter were measured， and the yield of plantlets per unit area， root length and root number were also counted or measured. Each of the above measured indexes was the average of three replicates.
The survey data were processed by Excel 2016， and histograms were made combining with the results of variance analysis performed in SPSS 18.0.
Results and Analysis
Effects of different cutting treatments on rooting time and rooting rate of plantlets
Rooting time and rooting rate are key indicators for evaluating the effect of forestry cuttage. In this study， the rooting time and rooting rate of different cutting treatments of G. jasminoides were calculated， as shown in Fig. 1. Through comparison and analysis， it could be seen that the rooting time of the three cutting treatments was quite different. The rooting time of the control treatment （CK） was the latest， and the rooting took place gradually about 25 d after insertion. The rooting of treatment 1 （CL1） and treatment 2 （CL2） were both earlier， and the cuttings began to root about 19 d after insertion. In terms of rooting rate， there were no significant differences in the rooting rate between the three cutting treatments， and the rooting rate reached more than 93%. Among them， the average rooting rate of CL1 was the highest， reaching 98.43%， and the average rooting rates of CL2 and the CK were respectively 95.37% and 93.07%. Based on the above， it could be seen that CL1 had the best effect among the three cutting treatments. It not only rooted early （it only took about 18 d for rooting）， but also had a high rooting rate.
Agricultural Biotechnology2021
Effects of different cutting treatments on the growth of plantlets The growth of seedlings included seedling height and ground diameter， which represented whether different cutting treatments could promote the growth of seedlings. Based on the statistics of seedling height and ground diameter on different cutting treatments （Fig. 2）， it was found that there were certain differences in plantlet height and ground diameter between the three cutting treatments， among which CL1 had the highest plantlet height （14.03 cm） and the largest ground diameter （2.98 mm）， CL2 showed the plantlet height and ground diameter ranking second， at 12.67 cm and 2.57 mm， respectively， and the CK exhibited the smallest plantlet height and ground diameter， at 12.57 cm and 2.01 mm， respectively. It could be seen that in the three cutting treatments， CL1 had a better promoting effect on the growth of cutting plantlets.
Effects of different cutting treatments on plantlet root length and rooting quantity
Through observation and determination （Fig. 3）， it could be seen that the root length and the amount of G. jasminoides cuttings were significantly different between the three cutting treatments， and the order of root length from small to large was CK （3.61 cm）， CL2 （5.58 cm） and CL1 （9.84 cm）. The average root length of CL1 was 2.7 times that of the CK. The root amounts of the three treatments were CK （10）， CL2 （20） and CL1 （38） sequentially in descending order. The root amount of CL1 was 3.8 times that of the CK. It could be seen that the root growth of G. jasminoides cuttings in cutting treatment 1 （CL1） was the best.
Effects of different cutting treatments on the yield of plantlets per unit area
Cutting plantlet raising is an efficient way of raising plantlets， which can cultivate a large number of high-quality plantlets in a limited space. In this study， the yield of plantlets per unit area was compared among the three cutting treatments， so as to screen out the best treatment for raising G. jasminoides plantlets （Fig. 4）. It can be seen from Fig. 4 that the average yield of plantlets per unit area differed greatly among the three cutting treatments. The treatment with the largest average yield of plantlets per unit area was CL1 （686.56 plants/m2）， followed by CL2 （656.93 plants/m2）， and the smallest value was in treatment CK （273.26 plants/m2）. The yield of plantlets per unit area of CL1 was 2.5 times that of the CK.
Conclusions and Discussion
On the basis of the existing substrate ratio， a comparison of the cutting effects of plane cuttings （CK） and three-dimensional cuttings （CL1 and CL2） was carried out， and the following conclusions were preliminarily drawn： three-dimensional cuttage significantly promoted plantlet rooting， root development and plantlet growth; and for the same three-dimensional cuttage， different cutting treatments also showed great differences in the rooting and growth of plantlets， and specifically， the seedlings of CL1 had the best rooting and the largest growth， as well as the largest yield of plantlet per unit area. Obviously， the important factors affecting the rooting and growth of cuttings are the rooting agent used and cutting substrate-related conditions[8]， and the cutting mode that promotes the sustainable and efficient development of plantlet production is three-dimensional cuttage. Many studies believe that rooting agents can achieve rooting of cuttings by adjusting the dynamic balance between the contents of rooting inhibitory substances and promoting substances in cuttings[11-14]. In this study， we used commercially available rooting powder （CK and CL2） and willow twig extract as rooting agent （CL1） to compare the cutting effect of G. jasminoides. It was found that the G. jasminoides cuttings treated with willow twig extract rooted early， and showed a large amount of roots and the best plantlet growth， which might be due to the willow twig extract contained salicylic acid and aspirin that can induce and promote plant rooting. The active ingredients are not only rich in nutrition but also have a bactericidal effect， and they can improve the microenvironment of cutting roots， facilitate the formation of cutting root primordia， and ensure the survival rate of plantlets[15-18]. Furthermore， the pretreatment of CL1 used a mixture of vitamin C and potassium dihydrogen phosphate （1∶1） for soaking. In addition to promoting root differentiation， both vitamin C and potassium dihydrogen phosphate can also improve cutting resistance， promote seedling growth， increase the biomass of a single plant and improve the quality of seedlings， thereby providing energy and nutrients for the rooting of cuttings and the growth of seedlings[19，20].
Cutting substrates play an extremely important role in cutting propagation. Different placement forms of the same cutting substrate also show great differences in the rooting of cuttings and the growth of plantlets， and the air permeability of substrates is the key to the rooting of cuttings and the growth of plantlets[21]. In this study， the cutting effect was the best in treatment CL1. Because it used three-dimensional substrate cylinders， which were supported by a plastic tube with holes in the center and equipped with a spray head， it could not only ensure the uniform moisture retention of the substrate， but also further increased the permeability of the substrate， which could deliver oxygen to the root tip in time， further activate root enzyme activity， and promote root growth. Therefore， the root growth of CL1 was the best， with an average root length of 9.84 cm and the largest amount of roots （38 roots）. In terms of substrate placement， three-dimensional cuttings could better promote the respiration of the substrate， thereby improving the oxygen circulation of the substrate and improving the quality of plantlet. Raising plantlets with cuttings is not restricted by seasons， and if we can save production land in addition to saving time， it can be said to have the best of both worlds. In this study， the three-dimensional cuttage model CL1 not only had a large growth of plantlets （the height of the plantlets increased by 11.61% compared with the CK， and the ground diameter increased by 48.26% compared with the CK）， but also the yield of plantlets per unit area was large， which was 2.5 times that of the CK. The three-dimensional cuttage model can not only make up for insufficient plantlets raised in the field， but also improve the quality and efficiency of raising plantlets with cuttings. It is an ideal way for plantlet breeding at present.
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