Breeding Technology of Sunflower Inbred Lines with Four Generations in One Year

Wei DUAN Shengli LIU Yantao LIU Peng WANG Hongye DONG Zengshuai LYU

Abstract   The breeding technology of sunflower inbred lines with four generations in one year was explored through the research on the biological characteristics of sunflower itself and the breeding status of sunflower inbred lines using the young embryo culture technology， the greenhouse seedling technology and field test planting， based on sunflower field breeding and planting combined with greenhouse planting. The reasonable selection of planting sites as the core of the breeding technology of sunflower inbred lines with four generations in one year is a guarantee. Embryos can be taken 7-10 d after pollination to enter the next generation of cultivation， thus shortening the generational cultivation cycle. The establishment of a breeding method of sunflower inbred lines with four generations in one year reduces the cost of breeding and has a practical role and significance for the field of sunflower inbred line breeding technologies.

Key words   Sunflower; Inbred line; Four generations in one year; Breeding technology

Purpose and Significance

The key to the success or failure of breeding lies in the parents， and the lack of parent resources is a major bottleneck restricting sunflower breeding. Chinas sunflower variety resources and inbred line materials for combining three-line hybrids are relatively scarce， and have a narrow genetic base and weak combining advantages. The sunflower germplasm resource innovation technology is lagging behind. It mainly uses wild sunflower resources，  local  varieties and existing backbone inbred lines to breed inbred lines with high quality， disease resistance， and wide adaptability， while the use of wild sunflower often has problems such as self- incompatibility  and difficulty in conservation. In terms of breeding methods， due to limited light and heat resources in the north， the breeding materials can only be planted for one generation， and then winter propagation is conducted in Hainan to achieve the existing propagation model with two generations a year for sunflower inbred lines. Therefore， it takes at least 3 years to breed a new sunflower inbred line. The long breeding cycle of new varieties leads to a slow process of breeding sunflower varieties. Therefore， accelerating the utilization of excellent sunflower resources and the breeding of excellent sunflower inbred lines with excellent characters， disease resistance and high combining ability is of great significance to the enrichment of the genetic population of sunflower breeding. New edible sunflower varieties with outstanding dominant traits and excellent comprehensive traits can be selected through the creation of high-quality， disease-resistant， and stress-resistant sunflower germplasm resources， so that the international competitiveness of Chinas sunflower industry can be improved through the industrialization of improved varieties.

Since the utilization of sunflower germplasm resources and the innovative breeding of inbred lines are the basis for the breeding of sunflower hybrids， only by cultivating inbred lines with excellent characters， disease resistance and high combining ability can excellent three-line hybrids be combined. Each generation of sunflower needs to go from sowing to harvest， and this cycle is generally 100 to 120 d， and requires at least an effective accumulated temperature≥5 ℃ equal to or greater than 1 900 ℃  [1] . It is of great practical significance to achieve the goal of the breeding technology of sunflower inbred lines with four generations in one year.

Breeding Technology of Sunflower Inbred Lines with Four Generation in One Year

The first generation of spring sowing and propagation in Shihezi， Xinjiang

Sunflower inbred lines and their sources： 60 early-generation inbred lines 001-060 and 60 stable inbred lines 1001-1060 of sunflower were provided by Crop Research Institute， Xinjiang  Academy  of Agricultural Sciences.

According to the conditions of insufficient light and heat resources in the north， the light and heat resources required for the growth of inbred lines are mainly supplemented by raising seedlings in greenhouses. Seeds were sown in Spring in Shihezi， Xinjiang （the selection standard for spring sowing and propagation sites were based on the effective accumulated temperature≥5 ℃ equal to or greater than 1 900 ℃ within 110 d from the date of sowing）. The seedlings were raised in pots in a greenhouse in the first ten days of March， and transplanted to the propagation test field after 30-35 d. Irrigation， fertilization， and fine management were carried out to ensure that the seedlings were uniform and strong. When plants flowered in early May， single plants were bagged for pollination， and 10 d after pollination， embryos were artificially taken for inoculation and culture， which meant the completion of the first generation.

The second generation of summer sowing and propagation in Shihezi， Xinjiang

Summer sowing was carried out in Shihezi， Xinjiang （the selection standard of the propagation site for summer sowing is based on the effective accumulated temperature≥5 ℃ equal to or greater than 1 900 ℃ within 100 d from the date of embryo collection and inoculation）. At the end of May， the embryos were artificially taken and cultured， and inoculated into pots with a diameter of  10 cm  with the seedling-raising matrix as the culture soil. The plants were cultured in a greenhouse while keeping sufficient under the pots， and the upper part was shaded by a sunshade net. The cotyledons were expanded on the 8  th  d， and the plants were transplanted into fields in a greenhouse after 25-30 d to ensure sufficient water and fertilizers. The plants flowered and were bagged and pollinated at the end of July. Before harvesting， the maturity period， seed setting rate， stress resistance and disease resistance of sunflower inbred lines were investigated. At the end of August and the beginning of September， the second generation was completed by cutting the discs， inserting the discs for drying， cleaning， and bagging.

After sunflower reached physiological maturity， it should be harvested， cleaned and dried in time according to weather conditions to prevent the loss of breeding materials. Direct manual threshing was performed according to different materials in the test sites， which could not only prevent the mixing of materials， but also had good ventilation performance and short drying time.

After harvesting， the residual film should be promptly removed from the film-covered fields to purify the farmland and  avoid  plastic film pollution. The diseased plant residues were removed， and the diseased plants were timely taken out of the fields in time， and burned or buried deeply to prevent the bacteria from overwintering in the soil and bring diseases to the crops in the coming year.

The third generation of southern propagation added in  Hainan

The selection standard of the site for generation-added southern propagation was based on the effective accumulated temperature≥5 ℃ equal to or greater than 1 900 ℃ within 110 d from the date of sowing. In Sanya， Hainan， the harvested seeds of the second generation were raised in a greenhouse at the end of September. After 20 d， they were transplanted to the southern propagation fields. For sunflower planting in Hainan， ridge planting is conducive to the extension of the root system of taproot crops and the prevention of lodging. In case of heavy rain， it is conducive to drainage and prevention of waterlogging from affecting the normal growth of plants. Laying film is beneficial to increasing ground temperature， preventing topsoil from hardening， improving air permeability of loam， and burying weeds. Timely irrigation， fertilization and careful management can ensure that the seedlings are healthy and strong  [2] . It is necessary to rationally irrigate and  fertilize  according to the weather， moisture content and seedling situation under the principle of small amount and many times， no water at the bottom of ditches， preventing fertilizer leakage， and maintaining ground temperature. With more water， the ground temperature and the soil oxygen content decrease， which is not conducive to root growth. The plants flowered， and were bagged and pollinated at the end of November. The embryos were artificially taken for inoculation and cultured 10 d after pollination， and the third generation was completed.

The fourth generation of propagation added in the south

The selection standard of the site for generation-added southern propagation was based on the effective accumulated temperature≥5 ℃ equal to or greater than 1 900 ℃ within 100 d from the date of embryo collection and inoculation. In mid-December， the embryos were artificially taken and cultured， and inoculated into pots with a diameter of 10 cm using the seedling-raising matrix as the culture soil. The plants were cultured in a pergola while keeping sufficient under the pots， and the upper part was shaded by a sunshade net. The cotyledons were expanded from the 6  th  to the 8  th  d， and the plants were transplanted into fields after 25-30 d. The fields for southern propagation should be land with medium and high soil fertility， and have not undergone continuous cropping. The fields should not be low-lying and flood-prone plots. Intertillage should be strengthened， and it should be wide intertillage and deep intertillage under the premise of not hurting or burying the seedlings， so as to achieve better weeding and ground temperature-improving effects. Weeds should be removed artificially to eliminate weeds and reduce the ineffective consumption of nutrients and water.

Attention should be paid to the investigation of pests and diseases， and timely control them. Pests are mostly manifested as direct feeding， resulting in a reduction in the number of florets. Diseases are mostly manifested as affecting leaf photosynthesis or the absorption and transportation of nutrients and water， resulting in malnutrition of plants and failure of normal formation and growth of florets. It is necessary to timely control pests （cotton bollworms， sunflower borers，  etc. ） and prevent and control the occurrence and development of diseases （downy mildew， rust， sclerotinia， white rust）. In the critical period before the breeding material is bagged， chemical control is carried out by spraying 5% beta-cypermethrin EC 800 times dilution and 40% chlorpyrifos EC 800 times dilution.

In late January of the following year， the plants flowers and were bagged and pollinated， and artificial pollination should be carried out 2 to 3 d after flowering， and then once every 3 d， for a total of 2 to 3 times. It is best to perform pollination in the morning after the dew has fallen. After sunflowers bloom， water must not be lacking， and the principle of "seeing the dryness and seeing the wetness" should be followed to promote large and more grains， so as to achieve high yield and high quality. It is recommended not to irrigate in the late stage of maturity， because it will cause excessive humidity in the field and easily induce sclerotinia.

The maturation period， seed setting rate， stress resistance and disease resistance of sunflower inbred lines were investigated before harvest. In mid-to-late February， the discs were cut， inserted into the stalks for drying， cleaned， and bagged  [4] ， and the harvested seeds were transported back to Shihezi， Xinjiang in early March， which meant the completion of the fourth generation.

The discs are inserted upwards in Shihezi， Xinjiang， generally， and it is recommended to insert them obliquely in Sanya area to avoid moldy seeds caused by rainy weather.

Application results

According to the above method from 2005 to 2006， the sunflower sterile line BH4-m241434A was selected and bred for 8 consecutive generations， and the sterile rate reached 100%. The inbred line is the sterile line of Shikui AR9-9293.

The sunflower restorer line RR1-61421 was selected through consecutive generation adding of 7 generations from 2005 to 2006， and a stable restorer line XX5-IV14111 was formed， with a restoring ability of 100%. The inbred line is the restorer line of Shikui AR9-9293.

In January 2015， the Shikui variety AR9-9293 was approved by the National Sunflower Variety Approval Committee， with the approval number Guopinjiankui 2015005 and the certificate number 2015-1-93  [3] .

Conclusions

The reasonable selection of planting sites as the core of the breeding technology of sunflower inbred lines with four generations in one year is a guarantee. It takes about 170 d to achieve two generations of planting in northern China， and about 150 d to  achieve  two generations of planting in Sanya， Hainan. The technology well connects the two generations of planting in northern China with the two generations of planting in Sanya， Hainan， realizing four generations of planting in one year.

The breeding technology of sunflower inbred lines with four generations in one year overcomes the shortcoming of the long breeding cycle of the current sunflower inbred lines， improves the breeding methods with improved breeding efficiency， and can realize the breeding of a new sunflower inbred line within one year. It obviously shortens the breeding process of sunflower inbred line generations， and has great economic value in the field of sunflower inbred line breeding technologies.

The breeding technology of sunflower inbred lines with four generations in one year has the advantages of short cultivation period， low cost and easy operation. It solves the problems of long cultivation period and high price of sunflower inbred lines in the traditional breeding process. The technology can breed a new sunflower inbred line in a short time， so that the breeding process of sunflower inbred line generations is greatly improved， and the production cost is reduced while increasing the profit obviously.

References

[1]  DUAN W， LIU SL， CHEN YC，  et al.  Research on the breeding technology of three generations for one year in sunflower inbred line[J]. Heilongjiang Agricultural Sciences， 2015（10）： 189-191. （in Chinese）.

[2] YANG T， LI HH， LIU WJ，  et al.  Cultivation and management technology of oil sunflower in southern generation-adding propagation[J]. Xinjiang Farm Research of Science and Technology， 2014（8）： 14-15. （in Chinese）.

[3] LIU SL， LIU YT， WANG P，  et al.  Breeding and cultivation techniques of edible sunflower variety AR9-9293[J]. Agricultural Science & Technology， 2017， 18（9）： 1642-1644. （in Chinese）.

[4] DUAN W， LIU WJ. A simple cleaning equipment for sunflower seeds[P]. China， ZL201320359039.3， 2013-11-20. （in Chinese）.

Editor： Yingzhi GUANG   Proofreader： Xinxiu ZHU