Research Of Establishment Of Early Evaluation System For Ratooning Of Sugarcane Varieties

Sugarcane is the main sugar crop in China and its sugar production accounts for 85%of the total sugar production in China.Ratoon sugarcane is a kind of sugarcane planting mode which produces sugarcane by using their underground sugarcane stools after harvesting the newly planted sugarcane.The mode save more seeds,labor and time than planting new-planted sugarcane.Ratooning is the important production character of sugarcane,which plays an important role in sugarcane planting efficiency.The ability of sugarcane ratooning mainly depends on variety,soil environment,management measures and production level,and the influence of variety difference is the most.The production value of sugarcane varieties is directly determined by their ability of ratooning.However,there is no early screening system for sugarcane varieties at present.Therefore,12sugarcane varieties,including main varieties and new varieties are selected as experimental materials.By harvesting treatment,the growth of ratooning was simulated and the content of hormones,enzymes and expression of related genes in early stage were analyzed.Compare the indexes of early ratooning the indexes of yield and production benefit in mature stage of different varieties.The results are as follows:1.Changes of main endogenous hormones content related to ratooning of sugarcane with harvesting:Indoleacetic acid（IAA）content in leaves,stems and roots of sugarcane were higher before harvesting.After harvesting to re-germinating,the content of IAA increased in a lower level or increase until the 20^th day and then began to decline.In the whole detection period,the content of IAA in leaves was the highest,followed by that are stems and the least are roots.The response time of different parts of different varieties to harvesting was different.Combined with subsequent field data analysis,it was found that the IAA content in the leaves and stems of the strong ratooning varieties continued to decrease for a long time.The content of IAA in roots of cultivars with strong ratooning increased for a long time due to auxin polar transport.Abscisic acid（ABA）content in stems and roots after harvesting was lower than that under normal growth condition.ABA content in leaves was higher than that in stems and roots,because the response to harvesting treatment was more intense.The content of gibberellin（GA₃）in leaves,stems and roots was low.GA₃ content in leaves and roots increased after harvesting,and the increase amplitude was different among different varieties.The content of GA₃ in stems of strong ratooning varieties would decrease.2.Changes of main enzyme activities related to ratooning of sugarcane with harvesting:The superoxide dismutase（SOD）activity in leaves responds strongly to harvesting treatment.Moreover,SOD activity in the leaves of sugarcane varieties with strong ratooning decreased significantly after harvesting,because SOD activity was inhibited by the consumption of organic matter in the germination of ratooning seedlings,and then increased with the growth of seedlings into adult plants.The peroxidase（POD）activity in the leaves of strong ratooning varieties decreased after harvesting,but increased with the germination and growth of the seedlings,and the POD activity was the strongest on the 20^th day.Respiration and photosynthesis also increased with the increase of POD enzyme activity.POD activity in stems and roots began to rise on the 10^th day,indicating that the stems and roots had strong antioxidant capacity to avoid the damage caused by harvesting.The content of malondialdehyde（MDA）in leaves,stems and roots was low.3.The endogenous hormones IAA,ABA and GA₃ all responded to harvesting treatment.The contents of IAA and ABA in leaves were significantly different from those in roots and stems.Among the key enzymes,ratooning was related to POD activity in leaves.4.Combined with the yield data of 12 sugarcane varieties for two consecutive years,It was found that performance of quality and yield characters of sugarcane varieties would deteriorate with the increase of root years.The correlation degree of field traits and physiological and biochemical indexes of ratooning in the first season was high.After harvesting,ABA content was positively correlated with stalk diameter,SOD activity was negatively correlated with cane yield,POD activity was negatively correlated with sucrose content.High ABA content,low SOD activity and low POD activity after harvesting can be used as screening indexes for strong ratooning in sugarcane seedling stage.5.Based on the results of correlation analysis,8 traits including IAA,ABA,GA₃,SOD,POD,stem diameter,yield and sucrose content were selected with strong correlation to comprehensively evaluate the ratooning of 12 varieties.The results showed that Zhongfu 1 and Zhongtang 3 had strong ratooning;Guitang 42,Guitang 58,Zhongtang 17,Guinanya 14-6210 followed;Zhongtang 6,Guitang 44,Zhongtang 19,Zhongtang 1,Guitang 55 and Guiliu 05136 were slightly weak,which were in line with the previous production investigation and evaluation.6.The differential expression analysis of tiller genes Sc TB1 and Sc CCD8 in different organizations of sugarcane was conducted in 12 varieties,and it was found that Sc TB1was highly expressed in stems and roots,but relatively lower before harvesting.The expression of Sc CCD8 gene in leaves after harvesting was higher than before.In this research,we used harvesting treatment for different varieties at seedling stage to simulate the growth of ratooning.Then,we carried out a comparative analysis of the early evaluation indexes and the harvest yield indexes at maturity stage.We screened out the indexes that the content of ABA,SOD and POD after harvesting can be used to evaluate the ratooning ability of sugarcane varieties.The expression of sugarcane tiller gene Sc TB1 and sugarcane monolactone biosynthesis gene Sc CCD8 are different in different sugarcane varieties.Further studies are needed on the physiological and biochemical molecular mechanism between ratooning ability difference,endogenous hormone content,enzyme activity and gene expression of sugarcane varieties,so as to establish a molecular index system for the evaluation of sugarcane varieties’ratooning.The research and theoretical basis of the technology and method of sugarcane variety breeding are offered.