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Abstract Guitang 46 is an excellent sugarcane variety bred by the Sugarcane Research Institute of Guangxi Academy of Agricultural Sciences under the "Five-Nursery" breeding program through regional trials and production experiments， which exhibits high yield， stable yield， and various excellent characters such as medium maturing， high sucrose content， good ratoon ability， more effective stems， uniform growth and strong resistance to smut. Moreover， Guitang 46 has strong lodging resistance and good defoliation ability， which is suitable for both mechanical management and harvesting， and manual operations. Therefore， Guitang 46 is a new variety with high promotion potential. In June 2015， Guitang 46 was approved by Guangxi Crop Variety Approval Committee[GSZ2015001]. At present， Guitang 46 has been cultivated within a certain area.
Key words Sugarcane； Guitang 46； Breeding； Evaluation
Guangxi is a sucrose production base of in China. Sucrose industry is a traditional pillar industry in Guangxi[1]， involving more than 50 counties and cities with a population of about 20 million. It is an important industry for increasing peasants’ income and stabilizing social employment. At present， sugarcane cultivation has become one of the important anti-poverty measures in Guangxi[2]. However， the high-cost and inefficient sugarcane industry under manual operation conditions in the cultivation region is facing major challenges such as labor shortage and rising labor costs， thereby affecting farmer’s income and industrial development[2-3]. In addition， the sugarcane cultivation area is gradually reduced due to increasing cultivation area of other crops such as banana and citrus. How to reduce the production cost and increase the income of sugarcane growers has become a problem that must be solved in the sustainable development of sugarcane industry in Guangxi. Sugarcane varieties are the key factors of sucrose production. Improving and updating sugarcane varieties is the most economical and effective measure to develop sucrose production. Practice has proved that the improvement of sugarcane varieties exerts significant effects on the development of sucrose industry. All the major sucrose producing countries in the world attach great importance to the innovation of new sugarcane varieties and regard the improvement of sugarcane varieties as one of the most important measures to improve sugarcane yield and increase sucrose amount. The continuous upgrading of sugarcane varieties is the premise of steady development of sucrose industry[4-5]. Therefore， breeding new sugarcane varieties suitable for mechanical harvesting with high yield， stable yield， good ratoon ability， strong lodging resistance to meet the needs of sugarcane growers and sucrose producers and gradually improve the monoculture condition of sugarcane varieties in this area is very important to the development of sugarcane industry in Guangxi[6-7]. Breeding Process
Parental combinations
Yuetang 85-177， the female parent， has excellent characters such as good growth potential， high yield， moderate sucrose content， straight shape， medium and large stems， and good ratoon ability， which is suitable for sugarcane cultivation region with good water and fertilizer conditions. ROC25， the male parent， exhibits medium maturing， high sucrose content and good ratoon ability. The pedigree chart of Guitang 46 was shown in Fig. 1.
Breeding process
The breeding of Guitang 46 was conducted under the "Five-Nursery" breeding program with local cultivar ROC22 as a control. In September 2005， the Sugarcane Research Institute of Guangxi Academy of Agricultural Sciences prepared the hybrid combination plan and sugarcane hybridization was carried out by the Hainan Sugarcane Breeding Farm of Guangzhou Sugarcane Research Institute. In 2006， the hybrid combination was sown to breed sugarcane seedlings. In 2006-2009， new-planting and ratooning experiments were carried out in the hybrid nursery， selection nursery and identification nursery in the production base of Jinsui Agricultural Development Co.， Ltd.， Natong Town， Longan County. In 2009-2010， 1-year new-planting and 1-year ratooning experiments were carried out in the Nanning Sugarcane Experimental Field of Sugarcane Research Institute of Guangxi Academy of Agricultural Sciences and the Youyi Branch of Guangxi Agricultural Cultivation State-owned Jinguang Farm for comparison of preparatory varieties. In 2010-2012， 3-year new-planting and 2-year ratooning comparative trials were carried out in the Nanning Sugarcane Experimental Field of Sugarcane Research Institute of Guangxi Academy of Agricultural Sciences. In 2013-2014， 2-year new-planting and 1-year ratooning regional trials and 1-year new-planting production experiments were carried out in Nanning， Liuzhou， Hechi， Baise and Longzhou with 11 experimental lines including Liucheng 05-136， Guitang 03-3005， Guitang 05-3626 and Guitang 06-1721.
During hybridization of the combination Yuetang 85-177 × ROC25， one excellent sugarcane variety （Guitang 46） was finally obtained from 3 266 seedlings planted in the hybrid nursery， with a final selection rate of 0.03%. Guitang 46 exhibited good performance in the selection nursery with strong lodging resistance， medium and large stems， more effective stems and good defoliation ability. In the identification nursery and later breeding stages， Guitang 46 showed outstanding cane yield， rare diseases and pests and strong ratoon ability. In the selection nursery and identification nursery， field brix of Guitang 46 was 0.70% and 0.72% （absolute value） higher than that of ROC22， respectively； in the preparatory comparison nursery and comparison nursery， sucrose content of Guitang 46 was 0.47% and 0.41% （absolute value） higher than that of ROC22， respectively； cane yield of Guitang 46 was 98.73-109.25 t/hm2 in various nurseries， which was 11.44%-19.16% higher than that of ROC22； sucrose yield of Guitang 46 was 15.65-17.33 t/hm2 in various nurseries， which was 19.03%-22.32% higher than that of ROC22. Results and Analysis
Main agronomic traits and resistance
Guitang 46 exhibited good agronomic traits， remarkable plant height， medium and large stems. In the regional trials conducted in Guangxi during 2013-2014， the plant height of Guitang 46 was 313 cm； the stem diameter was 2.68 cm； emergence rate and tillering rate were 59.1% and 46.7%， respectively； the ratooning rate was 118.4%； the number of effective stems was 69.16 thousand plants/hm2， which was 8.66% higher than that of the control； the number of effective stems of ratoon cane （67.28 thousand plants/hm2） exhibited obvious advantages compared with the control， which was 17.73% higher than that of the control. Moreover， Guitang 46 exhibited significantly stronger lodging resistance than the control. Guitang 46 also had excellent disease resistance， of which the incidence of smut （1.13%） was significantly lower than that of the control （5.52%）.
Main economic traits
Cane yield and sucrose yield
The cane yield and sucrose yield of Guitang 46 were obviously superior to that of ROC22， which ranked first in the regional trials conducted in Guangxi. Specifically， after 2-year new-planting， average cane yield （119.57 t/hm2） and ratoon cane yield （109.41 t/hm2） were improved by 18.61% and 24.04% compared with the control， respectively. After 2-year new-planting and 1-year ratooning， average cane yield （114.48 t/hm2） was improved by 21.14% compared with the control； average sucrose yield reached 16.49t/hm2， which was improved by 22.50% compared with the control； sucrose yield of ratoon cane reached 15.84 t/hm2， which was improved by 25.71% compared with the control. During the production experiments conduced in 2014， average cane yield reached 101.31 t/hm2， which was improved by 9.36% compared with the control， ranking the second.
Sucrose content
Guitang 46 exhibited medium maturing and high sucrose content. In the regional trials conducted in Guangxi during 2013-2014， average sucrose content of new-planted cane reached 14.33%， which was 0.13% （absolute value） higher than that of the control； average sucrose content of ratoon cane reached 14.48%， which was 0.19% （absolute value） higher than that of the control. After 2-year new-planting and 1-year ratooning， average sucrose content reached 14.40%， which was 0.16% （absolute value） higher than that of the control. Sucrose content of Guitang 46 was higher than that of the control except that of new-planted cane in January and February， 2014. Ratoon ability
Guitang 46 emerged early with high emergence rate. In multi-point regional trials， average emergence rate reached 118.4%. The ratoon cane seedlings were sturdy with good growth. In the five spots of regional trials conducted in Guangxi， both cane yield and sucrose yield were improved compared with the control， indicating that Guitang 46 had strong ratoon ability.
Morphological characteristics
Guitang 46 exhibited tall plant type， straight shape， uniform growth， moderate and large stems and cylindrical stems， which was yellow before exposure and light brownish red to yellow-green after exposure. Moreover， Guitang 46 had smooth stem epidermis， moderate internode length， fewer wax powders， more effective stems and good defoliation ability， which could be automatically defoliated to the upper part. Guitang 46 had round or triangular buds with medium bud size； bud base was apart from leaf scar； bud tips were hairy and longer than the growing band； bud ditch was obvious and relatively long. The leaves were dark green， thick， wide and long with more wax powders on the sheaths. The leaf sheaths were short， green and slightly red. The inner auricles were lanceolate and the outer auricles exhibited transitional shape. In addition， there were a few short hair group 57， which could easily fall off.
Cultivation Techniques
Guitang 46 is suitable for cultivation in arid and paddy fields with loose soil and moderate or high fertility.
Due to good defoliation ability and easy exposure of sugarcane buds of Guitang 46， the freshness of canes should be retained during planting； canes should be planted within 15 days after harvest； moreover， the mid-upper buds wrapped by sugarcane leaves should be selected as canes to improve the germination rate and cane quality. In addition， sufficient base fertilizer should be applied early； nitrogen， phosphorus and potassium fertilizers should be applied in combination； organic and inorganic fertilizers should be applied in combination. The row spacing was 0.9-1.2 m. The number of effective buds per ha was 105 000. The width of furrows for sowing was 10-20 cm. Early earthing should be performed appropriately. Ineffective tillering should be controlled at late stages. After planting， plastic mulching can significantly increase sugarcane yield. During the growth， sugarcane growers should pay attention to the prevention and treatment of diseases， insects and grass damage， especially rat disaster in sugarcane cultivation regions with high rat density. Timely furrowing and stubble loosening should be carried out for ratoon canes. In sugarcane cultivation regions under moderate or higher levels of management， the time of ratooning can be prolonged appropriately to 3-4 years. Common herbicides （including Diuron） are safe to Guitang 46 and can be used effectively within the safe concentration range according to the introductions. However， the nozzle should be suppressed as possible to avoid spraying on seedlings during weeding with herbicides after sugarcane bud planting.
Conclusion and Discussion
Guangxi， as the largest sugarcane production area in China with the highest sucrose yield， has played a crucial role in the development of sucrose industry in China. Guitang 46 has huge advantages compared with ROC22 in cane yield per unit area and sucrose yield， especially in ratoon cane， which is in line with the urgent need to increase yield per unit area in this area. Guitang 46 exhibits various excellent characters such as medium maturing， high sucrose content， good ratoon ability， more effective stems， uniform growth， solid stems， strong lodging resistance and good defoliation ability， which is suitable for both mechanical management and harvesting， and manual operations. Guitang 46 is an excellent variety for sugarcane growers and sucrose producers， which is conducive to improving the variety structure and enhancing farmers’ income and sucrose producers’ benefit by using appropriate cultivation techniques and strengthening publicity and promotion， thereby exhibiting broad application prospects.
Since Guitang 46 was approved by Guangxi Crop Variety Approval Committee[GSZ2015001]in 2015， its demonstration area has reached 13 333 hm2 within two years in sugarcane cultivation regions in Guangxi. Currently， Guitang 46 is popular with sugarcane growers with a shortage of canes and good popularization potential.
Agricultural Biotechnology2018
References
[1] LI YR， YANG LT， TAN HW， et al. Development and progress of sugarcane farming technologies in Guangxi， China[J]. Journal of Southern Agriculture， 2014， 45（10）：1770-1775.（in Chinese）
[2] DENG YS. In-depth improving the pillar position of food industry in Guangxi[J]. Guangxi Economy， 2010， （Z1）：26-29.（in Chinese）
[3] YANG RZ， LIANG Q， GUI YY， et al. Impact on stubble seedling of mechanical harvesting and crosses screening for rolling resistance[J]. Southwest China Journal of Agricultural Sciences， 2014， 27（5）：2195-2202.（in Chinese）
[4] CHEN RK. Theory and Practice of Modern Sugarcane Breeding[M]. Beijing： China Agriculture Press， 2003， 2-5，13.（in Chinese）
[5] XU JY， CHEN CJ， ZHONG J， et al. New discussion about the concept of the sugarcane crop breeding and introduce the seed[J]. Guangxi Sugarcane & Canesugar， 2005， （2）：3-7.（in Chinese）
[6] ZHANG RH， HE H， ZHANG GM， et al. Breeding of new sugarcane variety Guitang 29 with high ratoon ability[J]. Sugar Crops of China， 2011， 32（1）：1-4.（in Chinese）
[7] WANG LW， LIAO JX， YAN F， et al. Breeding of new high-yield， high-sugar and lodging-resistant sugarcane variety Guitang 42 and its high-yield cultivation technique[J]. Journal of Southern Agriculture， 2015， （8）：1361-1366.（in Chinese
Key words Sugarcane； Guitang 46； Breeding； Evaluation
Guangxi is a sucrose production base of in China. Sucrose industry is a traditional pillar industry in Guangxi[1]， involving more than 50 counties and cities with a population of about 20 million. It is an important industry for increasing peasants’ income and stabilizing social employment. At present， sugarcane cultivation has become one of the important anti-poverty measures in Guangxi[2]. However， the high-cost and inefficient sugarcane industry under manual operation conditions in the cultivation region is facing major challenges such as labor shortage and rising labor costs， thereby affecting farmer’s income and industrial development[2-3]. In addition， the sugarcane cultivation area is gradually reduced due to increasing cultivation area of other crops such as banana and citrus. How to reduce the production cost and increase the income of sugarcane growers has become a problem that must be solved in the sustainable development of sugarcane industry in Guangxi. Sugarcane varieties are the key factors of sucrose production. Improving and updating sugarcane varieties is the most economical and effective measure to develop sucrose production. Practice has proved that the improvement of sugarcane varieties exerts significant effects on the development of sucrose industry. All the major sucrose producing countries in the world attach great importance to the innovation of new sugarcane varieties and regard the improvement of sugarcane varieties as one of the most important measures to improve sugarcane yield and increase sucrose amount. The continuous upgrading of sugarcane varieties is the premise of steady development of sucrose industry[4-5]. Therefore， breeding new sugarcane varieties suitable for mechanical harvesting with high yield， stable yield， good ratoon ability， strong lodging resistance to meet the needs of sugarcane growers and sucrose producers and gradually improve the monoculture condition of sugarcane varieties in this area is very important to the development of sugarcane industry in Guangxi[6-7]. Breeding Process
Parental combinations
Yuetang 85-177， the female parent， has excellent characters such as good growth potential， high yield， moderate sucrose content， straight shape， medium and large stems， and good ratoon ability， which is suitable for sugarcane cultivation region with good water and fertilizer conditions. ROC25， the male parent， exhibits medium maturing， high sucrose content and good ratoon ability. The pedigree chart of Guitang 46 was shown in Fig. 1.
Breeding process
The breeding of Guitang 46 was conducted under the "Five-Nursery" breeding program with local cultivar ROC22 as a control. In September 2005， the Sugarcane Research Institute of Guangxi Academy of Agricultural Sciences prepared the hybrid combination plan and sugarcane hybridization was carried out by the Hainan Sugarcane Breeding Farm of Guangzhou Sugarcane Research Institute. In 2006， the hybrid combination was sown to breed sugarcane seedlings. In 2006-2009， new-planting and ratooning experiments were carried out in the hybrid nursery， selection nursery and identification nursery in the production base of Jinsui Agricultural Development Co.， Ltd.， Natong Town， Longan County. In 2009-2010， 1-year new-planting and 1-year ratooning experiments were carried out in the Nanning Sugarcane Experimental Field of Sugarcane Research Institute of Guangxi Academy of Agricultural Sciences and the Youyi Branch of Guangxi Agricultural Cultivation State-owned Jinguang Farm for comparison of preparatory varieties. In 2010-2012， 3-year new-planting and 2-year ratooning comparative trials were carried out in the Nanning Sugarcane Experimental Field of Sugarcane Research Institute of Guangxi Academy of Agricultural Sciences. In 2013-2014， 2-year new-planting and 1-year ratooning regional trials and 1-year new-planting production experiments were carried out in Nanning， Liuzhou， Hechi， Baise and Longzhou with 11 experimental lines including Liucheng 05-136， Guitang 03-3005， Guitang 05-3626 and Guitang 06-1721.
During hybridization of the combination Yuetang 85-177 × ROC25， one excellent sugarcane variety （Guitang 46） was finally obtained from 3 266 seedlings planted in the hybrid nursery， with a final selection rate of 0.03%. Guitang 46 exhibited good performance in the selection nursery with strong lodging resistance， medium and large stems， more effective stems and good defoliation ability. In the identification nursery and later breeding stages， Guitang 46 showed outstanding cane yield， rare diseases and pests and strong ratoon ability. In the selection nursery and identification nursery， field brix of Guitang 46 was 0.70% and 0.72% （absolute value） higher than that of ROC22， respectively； in the preparatory comparison nursery and comparison nursery， sucrose content of Guitang 46 was 0.47% and 0.41% （absolute value） higher than that of ROC22， respectively； cane yield of Guitang 46 was 98.73-109.25 t/hm2 in various nurseries， which was 11.44%-19.16% higher than that of ROC22； sucrose yield of Guitang 46 was 15.65-17.33 t/hm2 in various nurseries， which was 19.03%-22.32% higher than that of ROC22. Results and Analysis
Main agronomic traits and resistance
Guitang 46 exhibited good agronomic traits， remarkable plant height， medium and large stems. In the regional trials conducted in Guangxi during 2013-2014， the plant height of Guitang 46 was 313 cm； the stem diameter was 2.68 cm； emergence rate and tillering rate were 59.1% and 46.7%， respectively； the ratooning rate was 118.4%； the number of effective stems was 69.16 thousand plants/hm2， which was 8.66% higher than that of the control； the number of effective stems of ratoon cane （67.28 thousand plants/hm2） exhibited obvious advantages compared with the control， which was 17.73% higher than that of the control. Moreover， Guitang 46 exhibited significantly stronger lodging resistance than the control. Guitang 46 also had excellent disease resistance， of which the incidence of smut （1.13%） was significantly lower than that of the control （5.52%）.
Main economic traits
Cane yield and sucrose yield
The cane yield and sucrose yield of Guitang 46 were obviously superior to that of ROC22， which ranked first in the regional trials conducted in Guangxi. Specifically， after 2-year new-planting， average cane yield （119.57 t/hm2） and ratoon cane yield （109.41 t/hm2） were improved by 18.61% and 24.04% compared with the control， respectively. After 2-year new-planting and 1-year ratooning， average cane yield （114.48 t/hm2） was improved by 21.14% compared with the control； average sucrose yield reached 16.49t/hm2， which was improved by 22.50% compared with the control； sucrose yield of ratoon cane reached 15.84 t/hm2， which was improved by 25.71% compared with the control. During the production experiments conduced in 2014， average cane yield reached 101.31 t/hm2， which was improved by 9.36% compared with the control， ranking the second.
Sucrose content
Guitang 46 exhibited medium maturing and high sucrose content. In the regional trials conducted in Guangxi during 2013-2014， average sucrose content of new-planted cane reached 14.33%， which was 0.13% （absolute value） higher than that of the control； average sucrose content of ratoon cane reached 14.48%， which was 0.19% （absolute value） higher than that of the control. After 2-year new-planting and 1-year ratooning， average sucrose content reached 14.40%， which was 0.16% （absolute value） higher than that of the control. Sucrose content of Guitang 46 was higher than that of the control except that of new-planted cane in January and February， 2014. Ratoon ability
Guitang 46 emerged early with high emergence rate. In multi-point regional trials， average emergence rate reached 118.4%. The ratoon cane seedlings were sturdy with good growth. In the five spots of regional trials conducted in Guangxi， both cane yield and sucrose yield were improved compared with the control， indicating that Guitang 46 had strong ratoon ability.
Morphological characteristics
Guitang 46 exhibited tall plant type， straight shape， uniform growth， moderate and large stems and cylindrical stems， which was yellow before exposure and light brownish red to yellow-green after exposure. Moreover， Guitang 46 had smooth stem epidermis， moderate internode length， fewer wax powders， more effective stems and good defoliation ability， which could be automatically defoliated to the upper part. Guitang 46 had round or triangular buds with medium bud size； bud base was apart from leaf scar； bud tips were hairy and longer than the growing band； bud ditch was obvious and relatively long. The leaves were dark green， thick， wide and long with more wax powders on the sheaths. The leaf sheaths were short， green and slightly red. The inner auricles were lanceolate and the outer auricles exhibited transitional shape. In addition， there were a few short hair group 57， which could easily fall off.
Cultivation Techniques
Guitang 46 is suitable for cultivation in arid and paddy fields with loose soil and moderate or high fertility.
Due to good defoliation ability and easy exposure of sugarcane buds of Guitang 46， the freshness of canes should be retained during planting； canes should be planted within 15 days after harvest； moreover， the mid-upper buds wrapped by sugarcane leaves should be selected as canes to improve the germination rate and cane quality. In addition， sufficient base fertilizer should be applied early； nitrogen， phosphorus and potassium fertilizers should be applied in combination； organic and inorganic fertilizers should be applied in combination. The row spacing was 0.9-1.2 m. The number of effective buds per ha was 105 000. The width of furrows for sowing was 10-20 cm. Early earthing should be performed appropriately. Ineffective tillering should be controlled at late stages. After planting， plastic mulching can significantly increase sugarcane yield. During the growth， sugarcane growers should pay attention to the prevention and treatment of diseases， insects and grass damage， especially rat disaster in sugarcane cultivation regions with high rat density. Timely furrowing and stubble loosening should be carried out for ratoon canes. In sugarcane cultivation regions under moderate or higher levels of management， the time of ratooning can be prolonged appropriately to 3-4 years. Common herbicides （including Diuron） are safe to Guitang 46 and can be used effectively within the safe concentration range according to the introductions. However， the nozzle should be suppressed as possible to avoid spraying on seedlings during weeding with herbicides after sugarcane bud planting.
Conclusion and Discussion
Guangxi， as the largest sugarcane production area in China with the highest sucrose yield， has played a crucial role in the development of sucrose industry in China. Guitang 46 has huge advantages compared with ROC22 in cane yield per unit area and sucrose yield， especially in ratoon cane， which is in line with the urgent need to increase yield per unit area in this area. Guitang 46 exhibits various excellent characters such as medium maturing， high sucrose content， good ratoon ability， more effective stems， uniform growth， solid stems， strong lodging resistance and good defoliation ability， which is suitable for both mechanical management and harvesting， and manual operations. Guitang 46 is an excellent variety for sugarcane growers and sucrose producers， which is conducive to improving the variety structure and enhancing farmers’ income and sucrose producers’ benefit by using appropriate cultivation techniques and strengthening publicity and promotion， thereby exhibiting broad application prospects.
Since Guitang 46 was approved by Guangxi Crop Variety Approval Committee[GSZ2015001]in 2015， its demonstration area has reached 13 333 hm2 within two years in sugarcane cultivation regions in Guangxi. Currently， Guitang 46 is popular with sugarcane growers with a shortage of canes and good popularization potential.
Agricultural Biotechnology2018
References
[1] LI YR， YANG LT， TAN HW， et al. Development and progress of sugarcane farming technologies in Guangxi， China[J]. Journal of Southern Agriculture， 2014， 45（10）：1770-1775.（in Chinese）
[2] DENG YS. In-depth improving the pillar position of food industry in Guangxi[J]. Guangxi Economy， 2010， （Z1）：26-29.（in Chinese）
[3] YANG RZ， LIANG Q， GUI YY， et al. Impact on stubble seedling of mechanical harvesting and crosses screening for rolling resistance[J]. Southwest China Journal of Agricultural Sciences， 2014， 27（5）：2195-2202.（in Chinese）
[4] CHEN RK. Theory and Practice of Modern Sugarcane Breeding[M]. Beijing： China Agriculture Press， 2003， 2-5，13.（in Chinese）
[5] XU JY， CHEN CJ， ZHONG J， et al. New discussion about the concept of the sugarcane crop breeding and introduce the seed[J]. Guangxi Sugarcane & Canesugar， 2005， （2）：3-7.（in Chinese）
[6] ZHANG RH， HE H， ZHANG GM， et al. Breeding of new sugarcane variety Guitang 29 with high ratoon ability[J]. Sugar Crops of China， 2011， 32（1）：1-4.（in Chinese）
[7] WANG LW， LIAO JX， YAN F， et al. Breeding of new high-yield， high-sugar and lodging-resistant sugarcane variety Guitang 42 and its high-yield cultivation technique[J]. Journal of Southern Agriculture， 2015， （8）：1361-1366.（in Chinese