论文部分内容阅读
Abstract This study was conducted to investigate the effects of different vine cuttings and provide a fast method for production of highquality sweet potato seedlings. With short vine type ‘Ganshu No.2’ as an experiment material， biological characteristics of sweet potato seedlings were investigated by setting three vine sections （the inglenode section， dualnode section and threenode top bud section） using three kinds of substrates （red soil， leaf mould and pond sludge）. The results showed that the dualnode vine section plus leaf mould treatment sprouted earliest （3 d） with the highest survival rate（86.6%）， root number （9.2 roots） and the longest root length（5.9 cm）， compared with other treatments. Therefore， dualnode vine section plus leaf mould plug seedling raising has the characteristics of short sprouting time， high survival rate and low cost. The method could provide seedlings in a short period （20 d）， improves sweet potato propagation coefficient and is worth extending and applying.
Key words Ganshu No. 2; Vine; Singlenode section; Dualnode section; Threenode top bud section; Plug seedling production
Sweet potato （Ipomoea batatas Lam.） is an annual herb in Convolvulaceae， also known as Fanshu， Hongtiao， Shanyu and Digua. It has a planting history longer than 400 years in China， with the characteristics of high yield， wide application， strong adaptability and good nutrition. Sweet potato is an important raw material for food， animal husbandry， medical and energy industries. In recent years， the annual average planting area has reached 4 500 000 hm 2， accounting for about 45.0% of the planting area of sweet potato in the world， and its yield accounts for 80% of the total yield in the world. Sweet potato is the fourth main food crop in China ranking only next to rice， wheat and maize[1-3]. At present， with the development of economy and the improvement of peoples living standard， the breeding of sweet potato has entered a multiuse development age， and a batch of highstarch[4-6]， highanthocyanin[7-9]， highcarotene[10-12] and fresheating fruit type sweet potato[13-16] varieties have been widely applied. Sweet potato is a kind of asexually propagated crop， and potato pieces and potato vines are both propagation means. In production， seedlings are mainly obtained by raising seedlings from seed potato in most areas of China. Therefore， seedling breeding is the key link in production， as well as the basis for realizing high yield of sweet potato[17]. Planting method and the selection of stem sections greatly influence the growth and yield of sweet potato[18]. ‘Ganshu No. 2’ is a new fruit type of sweet potato cultivar bred by Red Soil Institute of Jiangxi Province in recent years[19]. This variety has large and uniform tubers which are fusiform， smooth without recess and have orange flesh. The tubers have high sugar content， and taste sweet and crisp， but they could be injured easily and are not resistant to storage at a lower temperature compared with ordinary sweet potato due to relatively higher water content in production， transportation and storage. In north Jiangxi rural area， improper measures would cause seed decay during seedling propagation from seed potato， producing seedlings from potato tuber has the disadvantages of slow germination， slow growth， short vine （with average length of 60 cm at maturation stage） and low propagation coefficient （3-5 seedlings from single tuber）， and there are reasons causing long seedling providing time， which restricts largescale production and popularization of the variety and simultaneously increases sowing quantity for raising seedlings and postpones transplanting date. Especially， in hilly red upland soil without irrigation condition， survival rate of cuttings decreases due to missing rainy season， resulting in decline of yield and quality due to insufficient density and not enough growth period. At present， it is difficult to supply seed sweet potato and seedlings through largescale enterprise marketing due to restricted storage and sale condition， seed supply channels are in chaos， and the extending speed of good varieties is also very low， which also influences the extension of special sweet potato varieties and the play of high yield potential. In this study， directing at problems in propagation of ‘Ganshu No. 2’ seedlings and combining with upland planting characteristics in red soil area， a seedling raising experiment was carried out by singlenode， dualnode and threenode top bud seedling raising methods according to the cultivars characteristics of more vine nodes， short internodes （internodes at the base part and branching section having a length of 10-15 mm） and more branches using maturer vines cut from the first batch of spring seedlings （raised from seed potato）， during which different substrates were used， and occurrence of auxiliary buds， growth and rooting of sweet potato vines were observed and recorded， aiming at providing a scientific basis for rapid seedling propagation of sweet potato cultivar ‘Ganshu No. 2’.
Materials and Methods Experimental materials
The experiment was carried out on March 15， 2016. Smooth and healthy tubers of ‘Ganshu No. 2’ free of diseases and damage were selected as seed potato after winter storage. Tubers with a weight of 200-300 g were transferred to a coated steelframe greenhouse， where furrowing and arrangement of tubers were performed to breed seedlings. Meanwhile， heat and moisture preservation was well done. On May 15， when the seedlings had grown to 20-30 cm， strong vines with full nodes， no injury on axillary buds and short and uniform internodes were cut off for later use. Seedlingraising trays： XS162（9×18） polystyrene plastic trays （540 mm×280 mm×45 mm） were selected. The trays were mainly filled with following substrate materials： local red soil easy to collect （0-20 cm arable layer of red upland）， leaf mould （nutrient soil prepared by collecting rotten leaves and mixed with soil through stacking and fermentation） and pond sludge （dry sludge collected from pond at dry season）.
Experimental design
The experiment was set with three vine sections： A1： singlenode vine section （sweet potato vines at mature section were cut into sections with one node as a unit which was reserved with half leaf）， A2： dualnode vine section （sweet potato vines at mature section were cut into sections with two nodes as a unit， each node of which was reserved with half leaf）， and A3： threenode top bud section （terminal buds of sweet potato vines were relatively tenderer than other stem nodes， so two nodes of each terminal bud were planted into substrate with leaves removed， and the top bud and the 1st leaf from top were reserved）. The plug trays were plastic trays （540 mm×280 mm×45 mm） with 162 holes. Because the 50 holes at the edge lose water easily due to external influences， so they were only filled with substrate， but not planted with sweet potato seedlings， and the remaining inner 112 holes were planted with sweet potato seedlings according to one plant per hole. Three medium treatments were designed： B1： red soil， B2： leaf mould， and B3： pond sludge. The three kinds of vine sections were planted in the three kinds of substrates， forming 9 treatments， each of which included three plug trays， which were planted with vine sections according to one seedling per pole， 336 seedlings in total， i.e.， there were three replicates. Randomized block arrangement was adopted.
Experimental methods
The seedling raising experiment was carried out in A plastic steel greenhouse of Red Soil Institute of Jiangxi Province. The three kinds of substrates were pulverized at first and sprayed with 50% carbendazim WP， followed by stirring uniformly. The substrates were filled into plug trays and flatly placed on field. The cut vine sections were planted into the substrates. The singlenode section was inserted with the main stem covered and the half leaf kept outside; the dualnode vine section was planted with one node in soil and the other node carrying the half leaf outside; and the top bud section was inserted with two nodes entering soil and other parts in the air. After planting， the soil was compacted with hands， so that the substrate surface was flush with or lower than hole surface. And the soil was irrigated thoroughly by atomization. The diurnal temperature ranged from 25 to 35 ℃ in the greenhouse， and the relative humidity was maintained in the range of 70%-90% artificially. Water was supplemented every three days. Data of biological characteristics including seedling growth and days for sprouting were collected. Survival rates of seedlings in various treatments were investigated， as well as outgrowth of auxiliary buds， leaf number， seedling height and rooting， on June 3， i.e.， 20 d after planting. Data processing
Three replicates of each treatment were investigated， and average survival rate was calculated according to survived plants in each treatment. The data were processed with Excel 2007 and DPS v 7.05.
Results and Analysis
Comparison on biological traits in ‘Ganshu No. 2’ among different vine sections and different seedling raising methods
‘Ganshu No. 2’ was planted according to different vine sections and different substrates， and the biological traits during the growth process of each treatment were analyzed 20 d later （Table 1）. For the singlenode section， there were no remarkable differences in days for sprouting among the three substrate treatments， and specifically， sprouting was firstly observed in leaf mould， at the time of 6 d， followed by pond sludge， at 6.3 d， and last in red soil， at 6.7 d. As to the dualnode vine section， there were no significant differences in days for sprouting among the three soil treatments， and specifically， sprouting happened firstly in leaf mould， at 3 d， and later in pond sludge and red soil， not exceeding 4 d. In the case of the threenode bud section， there were very significant differences in days for sprouting among the three soil treatments， and specifically， it needed the shortest time， 5.3 d in the leaf mould treatment， 6.0 d in the pond sludge treatment， and the longest time， 6.0 d in the red soil treatment. In the aspect of leaf number， there were no significant differences among the three soil treatments for the singlenode vine section， which had most leaves in leaf mould， 5.7 leaves， followed by pond sludge， 5.3 leaves， and fewest leaves in red soil， 5.0 leaves. Among the three soil treatments of the dualnode section， there was a very significant difference between the leaf mould and pond sludge treatments， and a significant difference between the red soil and pond sludge treatments， and leaf numbers of the three treatments ranked as leaf mould （8.7 leaves）>red soil （8.3 leaves）>pond sludge （7.3 leaves）. Among the three soil treatments of the top bud section， the leaf mould treatment had no significant difference from the pond sludge treatment， but a very significant difference from the red soil treatment， and the leaf numbers of the three treatments ranked as leaf mould （7.7 leaves）>pond sludge （7.0 leaves）>red soil （6.3 leaves）. In terms of seedling length， among the three soil treatments， the leaf mould treatment had no significant difference from the pond sludge treatment， but a significant difference from the red soil treatment， and there was a significant difference between the red soil and pond sludge treatments. And the seedling lengths of the three treatments ranked as leaf mould （5.1 cm）>pond sludge （4.9 cm）>red soil （4.3 cm）. Among the three soil treatments of the dualnode section， the leaf mould treatment had very significant differences from other two treatments， while there was no significant difference between the red soil and pond sludge treatments. And the seedling lengths of the three treatments ranked as leaf mould （7.3 cm）>pond sludge （6.6 cm）>red soil （6.4 cm）. Among the three soil treatments of the top bud section， the leaf mould treatment had very significant differences from other two soil treatments， while there was no significant difference between the red soil and pond sludge treatments. And the seedling lengths of the three treatments ranked as leaf mould （7.2 cm）>pond sludge （6.5 cm）>red soil （6.1 cm）. Different uppercase and lowercase letters in the same column indicate significant differences at 0.01 and 0.05 levels， respectively， similarly hereinafter.
As shown in Table 1， it could be seen from the overall comparison of the nine treatments formed by the three vine sections and three substrates that the dualnode vine section had very significant differences in days for sprouting from the singlenode and threenode top bud sections， and the section sprouted 2-4 d earlier than other treatments overall， indicating that adopting dualnode vine section could promote early growth and produce the desired result faster. As to leaf number， the dualnode vine section also had the advantage of early growth and showed more leaves， 2-3 leaves more than the singlenode vine section and 1-2 leaves more than the threenode top bud section， suggesting that the dualnode section absorbed fertilizer better and grew faster. In the case of seedling growth， the dualnode vine sections were about 2 cm longer than the singlenode vine section and closer to the top bud section， which was mainly because the threenode section had already got larger length at the time of planting.
Comparison on survival rate of ‘Ganshu No. 2’ among different vine sections and different seedling raising methods
In seedling propagation， improvement of survival rate and shortening of seedling raising time generally serve as important indices for fast seedling propagation from vines of sweet potato[20]. It could be seen from Table 2 that the singlenode vine section of ‘Ganshu No. 2’ had a seedling survival rate in the range of 18.8%-25.6% in the three kinds of substrates， which was generally lower. The survival rate was relatively higher in leaf mould （only 25.6%）， followed by pond sludge （20.2%）， and the lowest in red soil （18.8%）. The dualnode section showed a survival rate of 78.6%-86.0% in the three kinds of substrates. The survival rate was the highest in leaf mould （86.0%） which was very significantly different from red soil （78.6%）， and the pond sludge treatment exhibited a survival rate of 81.0%， which ranked the second. The threenode top bud section had a survival rate in the range of 45.8%-51.2% in the three kinds of substrates. The survival rates of the three soil treatments ranked as leaf mould （51.2%）>pond sludge （48.2%）>red soil （45.8%）. It could be seen from the nine treatments in Table 2 overall that the survival rates ranked as dualnode vine section>threenode top bud section>singlenode vine section， and the quality of seedlings raised in various substrates was in order of leaf mould>pond sludge>red soil. Agricultural Biotechnology2018
The fast formation of roots after sweet potato planting is the basis for ensuring survival of potato seedlings and tuber formation， so the growth and development of roots at seedling stage plays an important role in the whole life cycle of sweet potato[21]. However， root number of potato seedlings is related to soil nutrient， moisture， oxygen and some trace elements in addition to the maturity of potato vines. The root number of the singlenode vine section of ‘Ganshu No. 2’ was compared among the three kinds of substrates， as shown in Table 3. Specifically， the leaf mould treatment had a very significant difference from the red soil treatment， and a significant difference from the pond sludge， and the root numbers of the three treatments ranked as leaf mould （5.3 roots）>pond sludge （4.5 roots）>red soil（4.0 root）. The comparison on the root number of the dualnode vine section of ‘Ganshu No. 2’ showed that the leaf mould treatment was very significantly different from the red soil and pond sludge treatments， and there was a significant difference between the red soil and pond sludge treatments. And the root numbers of the three soil treatments were in order of leaf mould （9.2 roots）>pond sludge （8.1 roots）>red soil （7.3 roots）. The comparison on the root number of the threenode top bud section showed that the leaf mould treatment had a very significant difference from the red soil treatment， and a significant difference from the pond sludge treatment. And the root numbers of the three soil treatments ranked as leaf mould （7.5 roots）>pond sludge （6.7 roots）>red soil （6.4 roots）.
The same as other crops， the growth rate of roots in sweet potato seedlings is also an important indicator for evaluating the vitality of potato seedlings at seedling stage， while the supply of nutrients and water in cultivated soil matrix is the key to root development. As shown in Table 4， the root length of ‘Ganshu No. 2’ raised from the singlenode vine section was compared among the three substrate treatments. There was a very significant difference between the leaf mould and red soil treatments， which had no big differences from the pond sludge treatment， and the root lengths of the three soil treatments were in order of leaf mould （3.2 cm）>pond sludge （2.7 cm）>red soil （2.4 cm）. The comparison on root length of ‘Ganshu No. 2’ raised from the dualnode vine section showed that the leaf mould treatment had very significant differences from the red soil and pond sludge treatments， and there was also a significant difference between the red soil and pond sludge treatment. And the root lengths of the three substrate treatments were in order of leaf mould （5.9 cm）>pond sludge （4.9 cm）>red soil （4.4 cm）. The comparison on root length of ‘Ganshu No. 2’ raised from the top bud vine section showed that the leaf mould treatment had very significant differences from the red soil and pond sludge treatments which were not significantly different from each other. And the root lengths of the three substrate treatments were in order of leaf mould （4.3 cm）>pond sludge （3.4 cm）>red soil （3.0 cm）. Conclusions
Differences in seedling raising performance between different vine sections of ‘Ganshu No. 2’
The experimental results showed that under the same soil substrate and time condition， it could be seen from comparison on days for sprouting， leaf number， seedling length， survival rate， root number and root length that the dualnode section is the best， and the threenode top bud section and the singlenode vine section also could grow into seedlings， but have the disadvantages of longer sprouting time and relatively lower survival rate， which are not beneficial to fast propagation， cost saving and efficiency improvement.
Selection of substrate for raising plug seedlings
The results of the same section in the three kinds of substrates showed that leaf mould with better soil physical and chemical properties having higher organic matter content as plug tray substrate could create an overall better growth condition than pond sludge and red soil， and is more beneficial to early and fast growth.
Discussion
In this study， sweet potato vines were cut into singlenode， dualnode and threenode top bud sections， for seedling raising in plug trays using three kinds of substrates （red soil， leaf mould and pond sludge） commonly used in agricultural areas in northern and central Jiangxi Province. The results showed that selecting dualnode vine section and leaf mould for raising seedlings could achieve the best effect. The technique has the advantages of strong operability， simple facility， short seeding raising time， high seedling rate and low cost. In largescale sweet potato cultivation， this method could provide a large quantity of seedlings in a short period， and not only could save a large quantity of seed potato， but also could improve seedling propagation efficiency. Wang et al.[22] have developed mature technique for raising sweet potato seedlings from the dualnode vine section. The key to this technique is the selection of mature vine section and proper substrate， and under corresponding temperature and humidity conditions， nodes of sweet potato cuttings could develop roots and axillary buds in a short period through the supply of nutrients， which leads to early and fast growth of sweet potato seedlings， thereby realizing the purpose of fast seedling propagation.
The materials for raising seedlings were vines of short vine type sweet potato cultivar ‘Ganshu No. 2’ bred by Red Soil Institute of Jiangxi Province. The vines were obtained through seedling raising under proper temperature and humidity in coated steel frame greenhouses. Because the cultivar has the characteristics of few sprouted seedlings， short vines and internodes and more nodes during seedling raising， a large quantity of seed potato is needed when seedlings are raised from seed potato and directly planted in field production， while according to the characteristic of more nodes， propagating seedlings by cuttage with vines cut to short sections following seedling raising using seed potato could supply appreciable quantity of seedlings in a short period. When selecting different vine sections for raising seedlings， the survival rate differed greatly due to differences in vine maturity， and ranked as singlenode vine section The ultimate goal of fast sweet potato seedling raising is to serve production， i.e.， to realize high yield and high efficiency through scientific and rational cultivation and effective management to achieve. At present， conventional sweet potato seedling raising is still adopted in production， which means to provide seedlings using stored seed potato through seeding and pregermination by natural warming measures such as covering seedbed with plastic film， plastic film mulching and cultivation in vinyl house or artificial warming method such as heated bed， fermentation hotbed and electric hotbed， all of which effectively solve the problem of demand for sweet potato seedlings， but have the need for certain quantity of seed potato with the disadvantages of low propagation coefficient， high planting cost， long seedling period， late tuberization， poor drought resistance and weak growth vigor. However， top bud seedlings with roots wrapped with soil obtained through vine plug seedling raising， as independent growth individuals， have multiple advantages of self improvement and overcoming natural condition in field transplanting. For instance， Guo et al.[23] found that top bud seedlings with roots grew earlier and faster than ordinary seedlings raised with 2-3 sections from top. Specifically， 31 d after transplanting， main vines of top bud seedlings with roots were 14.8-17.6 cm longer than ordinary seedlings raised with 2-3 sections from top; there were also more side vines （1.4-2.5 more）， with a length increased by 1.3-4.6 cm; and tubers formed earlier and more， with smooth intact skin， resulting in a yield increase of 24%-30%. In red soil dryland with insufficient fertilizer and water conditions， top bud seedlings with root raised with plug trays not only have the advantages of strong drought resistance and fertilizerretaining capacity， but also could safely get through recovery stage in a short period， which means a higher survival rate which ensures stable and high sweet potato yield.
References
[1] WANG LJ， WANG Q， WEN QB. Development situation of sweet potato industry in China[J]. Grain Processing， 2008， 33（1）： 13-15. （in Chinese）
[2] MA DF， LI Q， CAO QH， et al. Development and prospect of sweetpotato industry and its technologies in China[J]. Jiangsu Journal of Agricultural Sciences， 2012， 28（5）： 969-973. （in Chinese）
[3] HUANG YM， LU SQ， LI YQ， et al. Current exploitation and development prospect of sweet potato[J]. Guangxi Agricultural Sciences， 2008， 39（5）： 696-699. （in Chinese） [4] XIN GS， LIN ZJ， HAN JJ， et al. Studies on the breeding and mulching cultivation of ‘Yanshu 24’ with high yield and high starch[J]. Chinese Agricultural Science Bulletin， 2013， 29（21）： 72-77. （in Chinese）
[5] LI Q， LI XY， XIE YP， et al. Breeding and yield formation of a new sweetpotato cultivar Xushu 26 with high starch content and disease resistance[J]. Journal of Plant Genetic Resources， 2010， 11（5）： 654-658. （in Chinese）
[6] JIE Q， ZHANG G， DU DY， et al. Breeding and cultivation techniques of a new sweet potato cultivar ‘Langyanshu 6’ with high yield and good quality[J]. Journal of Agriculture， 2016， 6（1）： 25-27. （in Chinese）
[7] LIAO FQ. Compared experiment in new sweet potato varieties with high content of cyanidin[J]. Journal of Anhui Agricultural Sciences， 2005， 33（12）： 2252， 2273. （in Chinese）
[8] XIE YZ， YIN QH， QIU RL. Study and utilization of sweetpotato with high anthocyanin[J]. Rain Fed Crops， 2004， 24（1）： 23-25. （in Chinese）
[9] HOU M， ZHANG YG， LIU YJ， et al. Study on yield and quality traits of new sweetpotato cultivars Xuzishu No. 4 with high anthocyanin content J]. Southwest China Journal of Agricultural Sciences， 2015， 28（5）： 1895-1898. （in Chinese）
[10] YU CZ， FU WZ， HE WZ， et al. Breeding of a high yield， fine quality， high βcarotene content sweet potato， Quanshu No.10[J]. Fujian Journal of Agricultural Sciences， 2013， 28（5）： 448-451.
[11] WU ZS， FANG QS， FENG SH， et al. Breeding of highquality highcarotene new sweetpotato variety Pushu 25[J]. Guangdong Agricultural Sciences， 2005（5）： 25-26. （in Chinese）
[12] WANG X， LI Q， ZHANG YG， et al. Breeding and Cultivation Techniques of A New Sweetpotato Variety Xuyushu 35 with High Carotene Content[J]. Hubei Agricultural Sciences， 2016， 55（24）： 6381-6384. （in Chinese）
[13] TANG YB， LIU JR， ZHU XY， et al. Planting performance and cultivation technology of fruit type sweetpotato ‘Sushu 13’[J]. Chinese Horticulture Abstracts， 2011， 6： 191，175. （in Chinese）
[14] HUANG TB. Study on integrated cultivation technique for hilly red soil upland new fruit type sweetpotato cultivar Ganshu No. 2[D]. Nanchang： Jiangxi Agricultural University， 2013. （in Chinese）
[15] FAN XP， LIU JF. New special sweetpotato variety： Fruit type sweet potato "extremely earlymaturing No. 2"[J]. Gansu Agriculture， 2005（11）： 205.
[16] ZENG B， LI QF， ZHANG L， et al. Advances in Integrated Utilization of Multifunction Fruit Type of Sweet Potato[J]. Hunan Agricultural Sciences，2013（23）：101-103. （in Chinese） [17] WANG YX， XIAO LZ. Industrialized operation of sweet potato industry[M]. Beijing： JinDun Publishing House， 2008： 37-40. （in Chinese）
[18] ZHANG LM， MA DF. Main cultivation mode of sweet potato in China[M]. Beijing：China Agricultural Science and Technology Press， 2012： 1-170. （in Chinese）
[19] XIAO GB， YE C， YU XC， et al. Breeding and cultivation techniques of sweet potato new variety Ganshu No.2[J]. Acta Agriculturae Jiangxi， 2011， 23（4）： 17-19. （in Chinese）
[20] LI MF. Prime report on rapid propagation technique for sweet potato seedlings using floating culture system[J]. Guangxi Agricultural Sciences， 2011， 42（4）： 395-398. （in Chinese）
[21] DU ZH， WANG BQ， XIE BT， et al. Research progress on effects of drought and agronomic measures on root growth and development of sweet potato at seedling stage[J]. Shandong Agricultural Sciences， 2013， 45（11）： 142-144. （in Chinese）
[22] WANG ZR， YAN Z， YE BW， et al. Plug seedlingraising technique of doublenode tender bud of sweet potato[J]. Fujian Agricultural Science and Technology， 2013， 8： 16-17. （in Chinese）
[23] GUO SG， YANG LM， WU WM， et al. Sweet potato cultivation applying root apical seedling technique[J]. Fujian Journal of Agricultural Sciences， 2011， 26（4）： 567-571. （in Chinese）
Key words Ganshu No. 2; Vine; Singlenode section; Dualnode section; Threenode top bud section; Plug seedling production
Sweet potato （Ipomoea batatas Lam.） is an annual herb in Convolvulaceae， also known as Fanshu， Hongtiao， Shanyu and Digua. It has a planting history longer than 400 years in China， with the characteristics of high yield， wide application， strong adaptability and good nutrition. Sweet potato is an important raw material for food， animal husbandry， medical and energy industries. In recent years， the annual average planting area has reached 4 500 000 hm 2， accounting for about 45.0% of the planting area of sweet potato in the world， and its yield accounts for 80% of the total yield in the world. Sweet potato is the fourth main food crop in China ranking only next to rice， wheat and maize[1-3]. At present， with the development of economy and the improvement of peoples living standard， the breeding of sweet potato has entered a multiuse development age， and a batch of highstarch[4-6]， highanthocyanin[7-9]， highcarotene[10-12] and fresheating fruit type sweet potato[13-16] varieties have been widely applied. Sweet potato is a kind of asexually propagated crop， and potato pieces and potato vines are both propagation means. In production， seedlings are mainly obtained by raising seedlings from seed potato in most areas of China. Therefore， seedling breeding is the key link in production， as well as the basis for realizing high yield of sweet potato[17]. Planting method and the selection of stem sections greatly influence the growth and yield of sweet potato[18]. ‘Ganshu No. 2’ is a new fruit type of sweet potato cultivar bred by Red Soil Institute of Jiangxi Province in recent years[19]. This variety has large and uniform tubers which are fusiform， smooth without recess and have orange flesh. The tubers have high sugar content， and taste sweet and crisp， but they could be injured easily and are not resistant to storage at a lower temperature compared with ordinary sweet potato due to relatively higher water content in production， transportation and storage. In north Jiangxi rural area， improper measures would cause seed decay during seedling propagation from seed potato， producing seedlings from potato tuber has the disadvantages of slow germination， slow growth， short vine （with average length of 60 cm at maturation stage） and low propagation coefficient （3-5 seedlings from single tuber）， and there are reasons causing long seedling providing time， which restricts largescale production and popularization of the variety and simultaneously increases sowing quantity for raising seedlings and postpones transplanting date. Especially， in hilly red upland soil without irrigation condition， survival rate of cuttings decreases due to missing rainy season， resulting in decline of yield and quality due to insufficient density and not enough growth period. At present， it is difficult to supply seed sweet potato and seedlings through largescale enterprise marketing due to restricted storage and sale condition， seed supply channels are in chaos， and the extending speed of good varieties is also very low， which also influences the extension of special sweet potato varieties and the play of high yield potential. In this study， directing at problems in propagation of ‘Ganshu No. 2’ seedlings and combining with upland planting characteristics in red soil area， a seedling raising experiment was carried out by singlenode， dualnode and threenode top bud seedling raising methods according to the cultivars characteristics of more vine nodes， short internodes （internodes at the base part and branching section having a length of 10-15 mm） and more branches using maturer vines cut from the first batch of spring seedlings （raised from seed potato）， during which different substrates were used， and occurrence of auxiliary buds， growth and rooting of sweet potato vines were observed and recorded， aiming at providing a scientific basis for rapid seedling propagation of sweet potato cultivar ‘Ganshu No. 2’.
Materials and Methods Experimental materials
The experiment was carried out on March 15， 2016. Smooth and healthy tubers of ‘Ganshu No. 2’ free of diseases and damage were selected as seed potato after winter storage. Tubers with a weight of 200-300 g were transferred to a coated steelframe greenhouse， where furrowing and arrangement of tubers were performed to breed seedlings. Meanwhile， heat and moisture preservation was well done. On May 15， when the seedlings had grown to 20-30 cm， strong vines with full nodes， no injury on axillary buds and short and uniform internodes were cut off for later use. Seedlingraising trays： XS162（9×18） polystyrene plastic trays （540 mm×280 mm×45 mm） were selected. The trays were mainly filled with following substrate materials： local red soil easy to collect （0-20 cm arable layer of red upland）， leaf mould （nutrient soil prepared by collecting rotten leaves and mixed with soil through stacking and fermentation） and pond sludge （dry sludge collected from pond at dry season）.
Experimental design
The experiment was set with three vine sections： A1： singlenode vine section （sweet potato vines at mature section were cut into sections with one node as a unit which was reserved with half leaf）， A2： dualnode vine section （sweet potato vines at mature section were cut into sections with two nodes as a unit， each node of which was reserved with half leaf）， and A3： threenode top bud section （terminal buds of sweet potato vines were relatively tenderer than other stem nodes， so two nodes of each terminal bud were planted into substrate with leaves removed， and the top bud and the 1st leaf from top were reserved）. The plug trays were plastic trays （540 mm×280 mm×45 mm） with 162 holes. Because the 50 holes at the edge lose water easily due to external influences， so they were only filled with substrate， but not planted with sweet potato seedlings， and the remaining inner 112 holes were planted with sweet potato seedlings according to one plant per hole. Three medium treatments were designed： B1： red soil， B2： leaf mould， and B3： pond sludge. The three kinds of vine sections were planted in the three kinds of substrates， forming 9 treatments， each of which included three plug trays， which were planted with vine sections according to one seedling per pole， 336 seedlings in total， i.e.， there were three replicates. Randomized block arrangement was adopted.
Experimental methods
The seedling raising experiment was carried out in A plastic steel greenhouse of Red Soil Institute of Jiangxi Province. The three kinds of substrates were pulverized at first and sprayed with 50% carbendazim WP， followed by stirring uniformly. The substrates were filled into plug trays and flatly placed on field. The cut vine sections were planted into the substrates. The singlenode section was inserted with the main stem covered and the half leaf kept outside; the dualnode vine section was planted with one node in soil and the other node carrying the half leaf outside; and the top bud section was inserted with two nodes entering soil and other parts in the air. After planting， the soil was compacted with hands， so that the substrate surface was flush with or lower than hole surface. And the soil was irrigated thoroughly by atomization. The diurnal temperature ranged from 25 to 35 ℃ in the greenhouse， and the relative humidity was maintained in the range of 70%-90% artificially. Water was supplemented every three days. Data of biological characteristics including seedling growth and days for sprouting were collected. Survival rates of seedlings in various treatments were investigated， as well as outgrowth of auxiliary buds， leaf number， seedling height and rooting， on June 3， i.e.， 20 d after planting. Data processing
Three replicates of each treatment were investigated， and average survival rate was calculated according to survived plants in each treatment. The data were processed with Excel 2007 and DPS v 7.05.
Results and Analysis
Comparison on biological traits in ‘Ganshu No. 2’ among different vine sections and different seedling raising methods
‘Ganshu No. 2’ was planted according to different vine sections and different substrates， and the biological traits during the growth process of each treatment were analyzed 20 d later （Table 1）. For the singlenode section， there were no remarkable differences in days for sprouting among the three substrate treatments， and specifically， sprouting was firstly observed in leaf mould， at the time of 6 d， followed by pond sludge， at 6.3 d， and last in red soil， at 6.7 d. As to the dualnode vine section， there were no significant differences in days for sprouting among the three soil treatments， and specifically， sprouting happened firstly in leaf mould， at 3 d， and later in pond sludge and red soil， not exceeding 4 d. In the case of the threenode bud section， there were very significant differences in days for sprouting among the three soil treatments， and specifically， it needed the shortest time， 5.3 d in the leaf mould treatment， 6.0 d in the pond sludge treatment， and the longest time， 6.0 d in the red soil treatment. In the aspect of leaf number， there were no significant differences among the three soil treatments for the singlenode vine section， which had most leaves in leaf mould， 5.7 leaves， followed by pond sludge， 5.3 leaves， and fewest leaves in red soil， 5.0 leaves. Among the three soil treatments of the dualnode section， there was a very significant difference between the leaf mould and pond sludge treatments， and a significant difference between the red soil and pond sludge treatments， and leaf numbers of the three treatments ranked as leaf mould （8.7 leaves）>red soil （8.3 leaves）>pond sludge （7.3 leaves）. Among the three soil treatments of the top bud section， the leaf mould treatment had no significant difference from the pond sludge treatment， but a very significant difference from the red soil treatment， and the leaf numbers of the three treatments ranked as leaf mould （7.7 leaves）>pond sludge （7.0 leaves）>red soil （6.3 leaves）. In terms of seedling length， among the three soil treatments， the leaf mould treatment had no significant difference from the pond sludge treatment， but a significant difference from the red soil treatment， and there was a significant difference between the red soil and pond sludge treatments. And the seedling lengths of the three treatments ranked as leaf mould （5.1 cm）>pond sludge （4.9 cm）>red soil （4.3 cm）. Among the three soil treatments of the dualnode section， the leaf mould treatment had very significant differences from other two treatments， while there was no significant difference between the red soil and pond sludge treatments. And the seedling lengths of the three treatments ranked as leaf mould （7.3 cm）>pond sludge （6.6 cm）>red soil （6.4 cm）. Among the three soil treatments of the top bud section， the leaf mould treatment had very significant differences from other two soil treatments， while there was no significant difference between the red soil and pond sludge treatments. And the seedling lengths of the three treatments ranked as leaf mould （7.2 cm）>pond sludge （6.5 cm）>red soil （6.1 cm）. Different uppercase and lowercase letters in the same column indicate significant differences at 0.01 and 0.05 levels， respectively， similarly hereinafter.
As shown in Table 1， it could be seen from the overall comparison of the nine treatments formed by the three vine sections and three substrates that the dualnode vine section had very significant differences in days for sprouting from the singlenode and threenode top bud sections， and the section sprouted 2-4 d earlier than other treatments overall， indicating that adopting dualnode vine section could promote early growth and produce the desired result faster. As to leaf number， the dualnode vine section also had the advantage of early growth and showed more leaves， 2-3 leaves more than the singlenode vine section and 1-2 leaves more than the threenode top bud section， suggesting that the dualnode section absorbed fertilizer better and grew faster. In the case of seedling growth， the dualnode vine sections were about 2 cm longer than the singlenode vine section and closer to the top bud section， which was mainly because the threenode section had already got larger length at the time of planting.
Comparison on survival rate of ‘Ganshu No. 2’ among different vine sections and different seedling raising methods
In seedling propagation， improvement of survival rate and shortening of seedling raising time generally serve as important indices for fast seedling propagation from vines of sweet potato[20]. It could be seen from Table 2 that the singlenode vine section of ‘Ganshu No. 2’ had a seedling survival rate in the range of 18.8%-25.6% in the three kinds of substrates， which was generally lower. The survival rate was relatively higher in leaf mould （only 25.6%）， followed by pond sludge （20.2%）， and the lowest in red soil （18.8%）. The dualnode section showed a survival rate of 78.6%-86.0% in the three kinds of substrates. The survival rate was the highest in leaf mould （86.0%） which was very significantly different from red soil （78.6%）， and the pond sludge treatment exhibited a survival rate of 81.0%， which ranked the second. The threenode top bud section had a survival rate in the range of 45.8%-51.2% in the three kinds of substrates. The survival rates of the three soil treatments ranked as leaf mould （51.2%）>pond sludge （48.2%）>red soil （45.8%）. It could be seen from the nine treatments in Table 2 overall that the survival rates ranked as dualnode vine section>threenode top bud section>singlenode vine section， and the quality of seedlings raised in various substrates was in order of leaf mould>pond sludge>red soil. Agricultural Biotechnology2018
The fast formation of roots after sweet potato planting is the basis for ensuring survival of potato seedlings and tuber formation， so the growth and development of roots at seedling stage plays an important role in the whole life cycle of sweet potato[21]. However， root number of potato seedlings is related to soil nutrient， moisture， oxygen and some trace elements in addition to the maturity of potato vines. The root number of the singlenode vine section of ‘Ganshu No. 2’ was compared among the three kinds of substrates， as shown in Table 3. Specifically， the leaf mould treatment had a very significant difference from the red soil treatment， and a significant difference from the pond sludge， and the root numbers of the three treatments ranked as leaf mould （5.3 roots）>pond sludge （4.5 roots）>red soil（4.0 root）. The comparison on the root number of the dualnode vine section of ‘Ganshu No. 2’ showed that the leaf mould treatment was very significantly different from the red soil and pond sludge treatments， and there was a significant difference between the red soil and pond sludge treatments. And the root numbers of the three soil treatments were in order of leaf mould （9.2 roots）>pond sludge （8.1 roots）>red soil （7.3 roots）. The comparison on the root number of the threenode top bud section showed that the leaf mould treatment had a very significant difference from the red soil treatment， and a significant difference from the pond sludge treatment. And the root numbers of the three soil treatments ranked as leaf mould （7.5 roots）>pond sludge （6.7 roots）>red soil （6.4 roots）.
The same as other crops， the growth rate of roots in sweet potato seedlings is also an important indicator for evaluating the vitality of potato seedlings at seedling stage， while the supply of nutrients and water in cultivated soil matrix is the key to root development. As shown in Table 4， the root length of ‘Ganshu No. 2’ raised from the singlenode vine section was compared among the three substrate treatments. There was a very significant difference between the leaf mould and red soil treatments， which had no big differences from the pond sludge treatment， and the root lengths of the three soil treatments were in order of leaf mould （3.2 cm）>pond sludge （2.7 cm）>red soil （2.4 cm）. The comparison on root length of ‘Ganshu No. 2’ raised from the dualnode vine section showed that the leaf mould treatment had very significant differences from the red soil and pond sludge treatments， and there was also a significant difference between the red soil and pond sludge treatment. And the root lengths of the three substrate treatments were in order of leaf mould （5.9 cm）>pond sludge （4.9 cm）>red soil （4.4 cm）. The comparison on root length of ‘Ganshu No. 2’ raised from the top bud vine section showed that the leaf mould treatment had very significant differences from the red soil and pond sludge treatments which were not significantly different from each other. And the root lengths of the three substrate treatments were in order of leaf mould （4.3 cm）>pond sludge （3.4 cm）>red soil （3.0 cm）. Conclusions
Differences in seedling raising performance between different vine sections of ‘Ganshu No. 2’
The experimental results showed that under the same soil substrate and time condition， it could be seen from comparison on days for sprouting， leaf number， seedling length， survival rate， root number and root length that the dualnode section is the best， and the threenode top bud section and the singlenode vine section also could grow into seedlings， but have the disadvantages of longer sprouting time and relatively lower survival rate， which are not beneficial to fast propagation， cost saving and efficiency improvement.
Selection of substrate for raising plug seedlings
The results of the same section in the three kinds of substrates showed that leaf mould with better soil physical and chemical properties having higher organic matter content as plug tray substrate could create an overall better growth condition than pond sludge and red soil， and is more beneficial to early and fast growth.
Discussion
In this study， sweet potato vines were cut into singlenode， dualnode and threenode top bud sections， for seedling raising in plug trays using three kinds of substrates （red soil， leaf mould and pond sludge） commonly used in agricultural areas in northern and central Jiangxi Province. The results showed that selecting dualnode vine section and leaf mould for raising seedlings could achieve the best effect. The technique has the advantages of strong operability， simple facility， short seeding raising time， high seedling rate and low cost. In largescale sweet potato cultivation， this method could provide a large quantity of seedlings in a short period， and not only could save a large quantity of seed potato， but also could improve seedling propagation efficiency. Wang et al.[22] have developed mature technique for raising sweet potato seedlings from the dualnode vine section. The key to this technique is the selection of mature vine section and proper substrate， and under corresponding temperature and humidity conditions， nodes of sweet potato cuttings could develop roots and axillary buds in a short period through the supply of nutrients， which leads to early and fast growth of sweet potato seedlings， thereby realizing the purpose of fast seedling propagation.
The materials for raising seedlings were vines of short vine type sweet potato cultivar ‘Ganshu No. 2’ bred by Red Soil Institute of Jiangxi Province. The vines were obtained through seedling raising under proper temperature and humidity in coated steel frame greenhouses. Because the cultivar has the characteristics of few sprouted seedlings， short vines and internodes and more nodes during seedling raising， a large quantity of seed potato is needed when seedlings are raised from seed potato and directly planted in field production， while according to the characteristic of more nodes， propagating seedlings by cuttage with vines cut to short sections following seedling raising using seed potato could supply appreciable quantity of seedlings in a short period. When selecting different vine sections for raising seedlings， the survival rate differed greatly due to differences in vine maturity， and ranked as singlenode vine section The ultimate goal of fast sweet potato seedling raising is to serve production， i.e.， to realize high yield and high efficiency through scientific and rational cultivation and effective management to achieve. At present， conventional sweet potato seedling raising is still adopted in production， which means to provide seedlings using stored seed potato through seeding and pregermination by natural warming measures such as covering seedbed with plastic film， plastic film mulching and cultivation in vinyl house or artificial warming method such as heated bed， fermentation hotbed and electric hotbed， all of which effectively solve the problem of demand for sweet potato seedlings， but have the need for certain quantity of seed potato with the disadvantages of low propagation coefficient， high planting cost， long seedling period， late tuberization， poor drought resistance and weak growth vigor. However， top bud seedlings with roots wrapped with soil obtained through vine plug seedling raising， as independent growth individuals， have multiple advantages of self improvement and overcoming natural condition in field transplanting. For instance， Guo et al.[23] found that top bud seedlings with roots grew earlier and faster than ordinary seedlings raised with 2-3 sections from top. Specifically， 31 d after transplanting， main vines of top bud seedlings with roots were 14.8-17.6 cm longer than ordinary seedlings raised with 2-3 sections from top; there were also more side vines （1.4-2.5 more）， with a length increased by 1.3-4.6 cm; and tubers formed earlier and more， with smooth intact skin， resulting in a yield increase of 24%-30%. In red soil dryland with insufficient fertilizer and water conditions， top bud seedlings with root raised with plug trays not only have the advantages of strong drought resistance and fertilizerretaining capacity， but also could safely get through recovery stage in a short period， which means a higher survival rate which ensures stable and high sweet potato yield.
References
[1] WANG LJ， WANG Q， WEN QB. Development situation of sweet potato industry in China[J]. Grain Processing， 2008， 33（1）： 13-15. （in Chinese）
[2] MA DF， LI Q， CAO QH， et al. Development and prospect of sweetpotato industry and its technologies in China[J]. Jiangsu Journal of Agricultural Sciences， 2012， 28（5）： 969-973. （in Chinese）
[3] HUANG YM， LU SQ， LI YQ， et al. Current exploitation and development prospect of sweet potato[J]. Guangxi Agricultural Sciences， 2008， 39（5）： 696-699. （in Chinese） [4] XIN GS， LIN ZJ， HAN JJ， et al. Studies on the breeding and mulching cultivation of ‘Yanshu 24’ with high yield and high starch[J]. Chinese Agricultural Science Bulletin， 2013， 29（21）： 72-77. （in Chinese）
[5] LI Q， LI XY， XIE YP， et al. Breeding and yield formation of a new sweetpotato cultivar Xushu 26 with high starch content and disease resistance[J]. Journal of Plant Genetic Resources， 2010， 11（5）： 654-658. （in Chinese）
[6] JIE Q， ZHANG G， DU DY， et al. Breeding and cultivation techniques of a new sweet potato cultivar ‘Langyanshu 6’ with high yield and good quality[J]. Journal of Agriculture， 2016， 6（1）： 25-27. （in Chinese）
[7] LIAO FQ. Compared experiment in new sweet potato varieties with high content of cyanidin[J]. Journal of Anhui Agricultural Sciences， 2005， 33（12）： 2252， 2273. （in Chinese）
[8] XIE YZ， YIN QH， QIU RL. Study and utilization of sweetpotato with high anthocyanin[J]. Rain Fed Crops， 2004， 24（1）： 23-25. （in Chinese）
[9] HOU M， ZHANG YG， LIU YJ， et al. Study on yield and quality traits of new sweetpotato cultivars Xuzishu No. 4 with high anthocyanin content J]. Southwest China Journal of Agricultural Sciences， 2015， 28（5）： 1895-1898. （in Chinese）
[10] YU CZ， FU WZ， HE WZ， et al. Breeding of a high yield， fine quality， high βcarotene content sweet potato， Quanshu No.10[J]. Fujian Journal of Agricultural Sciences， 2013， 28（5）： 448-451.
[11] WU ZS， FANG QS， FENG SH， et al. Breeding of highquality highcarotene new sweetpotato variety Pushu 25[J]. Guangdong Agricultural Sciences， 2005（5）： 25-26. （in Chinese）
[12] WANG X， LI Q， ZHANG YG， et al. Breeding and Cultivation Techniques of A New Sweetpotato Variety Xuyushu 35 with High Carotene Content[J]. Hubei Agricultural Sciences， 2016， 55（24）： 6381-6384. （in Chinese）
[13] TANG YB， LIU JR， ZHU XY， et al. Planting performance and cultivation technology of fruit type sweetpotato ‘Sushu 13’[J]. Chinese Horticulture Abstracts， 2011， 6： 191，175. （in Chinese）
[14] HUANG TB. Study on integrated cultivation technique for hilly red soil upland new fruit type sweetpotato cultivar Ganshu No. 2[D]. Nanchang： Jiangxi Agricultural University， 2013. （in Chinese）
[15] FAN XP， LIU JF. New special sweetpotato variety： Fruit type sweet potato "extremely earlymaturing No. 2"[J]. Gansu Agriculture， 2005（11）： 205.
[16] ZENG B， LI QF， ZHANG L， et al. Advances in Integrated Utilization of Multifunction Fruit Type of Sweet Potato[J]. Hunan Agricultural Sciences，2013（23）：101-103. （in Chinese） [17] WANG YX， XIAO LZ. Industrialized operation of sweet potato industry[M]. Beijing： JinDun Publishing House， 2008： 37-40. （in Chinese）
[18] ZHANG LM， MA DF. Main cultivation mode of sweet potato in China[M]. Beijing：China Agricultural Science and Technology Press， 2012： 1-170. （in Chinese）
[19] XIAO GB， YE C， YU XC， et al. Breeding and cultivation techniques of sweet potato new variety Ganshu No.2[J]. Acta Agriculturae Jiangxi， 2011， 23（4）： 17-19. （in Chinese）
[20] LI MF. Prime report on rapid propagation technique for sweet potato seedlings using floating culture system[J]. Guangxi Agricultural Sciences， 2011， 42（4）： 395-398. （in Chinese）
[21] DU ZH， WANG BQ， XIE BT， et al. Research progress on effects of drought and agronomic measures on root growth and development of sweet potato at seedling stage[J]. Shandong Agricultural Sciences， 2013， 45（11）： 142-144. （in Chinese）
[22] WANG ZR， YAN Z， YE BW， et al. Plug seedlingraising technique of doublenode tender bud of sweet potato[J]. Fujian Agricultural Science and Technology， 2013， 8： 16-17. （in Chinese）
[23] GUO SG， YANG LM， WU WM， et al. Sweet potato cultivation applying root apical seedling technique[J]. Fujian Journal of Agricultural Sciences， 2011， 26（4）： 567-571. （in Chinese）