| Sugarcane(Saccharum spp.)belongs to Saccharum genus of Gramineae family;is a C4 plant with high photosynthetic efficiency and high biological yield.Sugarcane provides raw materials for sugar and alcohol production.Sugarcane cross breeding is the most important method for breeding new varieties.The breeding efficiency can be improved by studying the selection technique for parents,combinations and clones.Cold resistance is the important characteristic of a sugarcane variety.Low temperature disasters lead to large economic losses,selection and application of varieties with strong cold resistance are important for reducing loss.As for sugarcane resistance breeding,yield is a selection character during early stage of five nursery system.In the present study,parent selection,combination formulation,family selection technique at seedling stage,clone selection technique in advanced nurseries,cold resistance evaluation for variety and identification with cold resistance gene were carried out.The objectives were to select lines with high yield and high sucrose content by comprehensive selection technique,then to evaluate the lines with cold resistance based on field performance,physiological characteristics and molecular bases,and ultimately to provide theoretical basis and reference for breeding elite varieties with high yield,high sucrose content and strong cold resistance.The main results obtained were as follows.1.The experiment were conducted with 70 female parents,51 male parents and 134 combinations.At seedling stage,agronomic characters,brix and yield were investigated,and the combining ability for female parents,male parents and combinations were analyzed.The result showed that ROC11,CP70-1133,CP72-1210,HoCP94-806,ZZ92-126,GT92-66,ROC24,GT93-102,GT00-122,and ZZ93-88 as female parents had high general combining ability of brix weight per stool and could be used as high yield and high sugar parents.YT91-976,YR05-649,YT96-86,ROC11,CP84-1198,YR05-872,CP82-1592,ROC26,YR05-628,and YR99-113 as male parents had high general combining ability of brix weight per stool and could be used as high yield and high sugar parents in the future.ROC25xYR05-649,ROC11×YT91-976,YT91-976xROC11,CP70-1133×GT92-66,CP72-1210×ROC22,GT00-122×YT91-976,HoCP94-806xROC25,ROC26xROC22,GT92-66xCP84-1198,and ZZ92-126xCP84-1198 had high special combining ability of brix weight per stool.2.Agronomic characters,brix and yield characters of 134 hybridized combinations were genetically analyzed,and the families were evaluated by comprehensive index method.The results showed that there were highly significant differences among the families in both traits.Stalk height,stalk diameter,stalk number per stool in plant crop had higher level of broad-sense heritability,genetic variation coefficient and relative genetic advance than those in ratoon crop.Analysis of phenotypic and genotypic correlation showed that weight per stool was significantly correlated with brix weight per stool.Nineteen elite families were selected based on comprehensive index method,and weight per stool and brix weight per stool showed greater genetic gain.3.Agronomic characters,processing quality characters and yield characters in 27 new lines and 2 control varieties were genetically analyzed in variety comparison trial,and the clones were evaluated by comprehensive index method.The results showed that there were significant or highly significant differences among the investigated traits except for the rate of dead heart seedling.Millable stalks per hectare(MSH),tonnage of cane per hectare(TCH),tonnage of sugar per hectare(TSH)and tons of total fermentable sugar per hectare(TFSH)showed relatively higher in both genetic variation coefficient and broad-sense heritability,but plant height,stalk diameter,and brix exhibited relatively lower in both genetic variation coefficient and broad-sense heritability.Analysis of correlation showed that MSH was significantly correlated with TCH,TSH and TFSH.Thirteen elite lines were selected by index selection,Among which,8 new lines showed that the averages of TSH and TFSH in both plant and ratoon cane were higher than those in 2 control varieties.The results indicated that higher rate of genetic gains can be obtained by index selection method,which can be applied for evaluation of sugar and energy cane varieties.4.In order to explore the correlations between changes of photosynthetic characteristics and cold tolerance and use photosynthetic parameters to identified sugarcane genotypes,7 lines with good comprehensive characters in field and 2 main cultivars were employed in prior variety comparison trial,the changes of chilling injury index,chlorophyll content and photosynthetic parameters were examined under low temperature stress at seedling stage.The result showed that chilling injury index was continually increased with the prolonging of low temperature treatment,the chlorophyll content in all the sugarcane genotypes were continually decreased.There were significant differences in net photosynthetic rate and stomatal conductance between control and low-temperature treatment.The Fv/Fm,ΦPS Ⅱ,Fv’/Fm’,qP and ETR were decreased obviously,but Fo,Fs and qNP were increased after the low temperature treatment.The correlation coefficients between Fv/Fm,Fv’/Fm’,ΦPS Ⅱ and chilling injury indexes were higher than 0.800,which suggested that chlorophyll content,photosynthetic parameters and chlorophyll fluorescence parameters could be used as the indexes of cold tolerance identification in sugarcane.The Subordinate fuzzy function was used to evaluate comprehensively cold resistence,which results showed that GT08-1092、GT08-1180、GT08-297 had better cold resistance than ROC22.Chlorophyll fluorescence parameters could be applied as indexes in sugarcane breeding,and their measurements are fast,easy,accurate and without damage on plant.5.In order to screen genes for cold resistance,RNA-sequencing was adopted in this study.GT08-1180 and ROC22 were used for cold stress treatment and normal temperature treatment(control),and differentially expressed genes(DEGs)were analyzed from the gene expression profile.The results showed that a total of 382.68 million clean reads with the whole base number of 57.41 G were produced.360404 transcripts and 183515 unigenes were obtained after de novo assembly.All unigenes were annotated in NR,NT,KOG/COG,Swiss-Prot,PFAM,KEGG and GO,and 110021 uni genes were functionally annotated in at least one database.There were 16145 and 20317 DEGs found in the cold stress treatment and control in GT08-1180 and ROC22 respectively.13113 DEGs were found common in both GT08-1180 and ROC22,7204 DEGs only in ROC22,and 3032 DEGs only in GT08-1180.There were more up-regulated DEGs than down-regulated DEGs in both GT08-1180 and ROC22.The result of gene ontology enrichment analysis showed that all DEGs in GT08-1180 were divided into 20,20 and 14 function groupsin biological processes,cellular components and molecular function categories,respectively.All DEGs in ROC22 were divided into 20,20 and 14 function groups in the 3 categories respectively.The result of KEGG enrichment analysis showed that all DEGs in both GT08-1180 and ROC22 were divided into 121 pathways.The result of GO enrichment analysis of DEGs in both GT08-1180 and ROC22 showed that they had common sub-groups of differentially expressed genes related to cold stress response,membrane and photosynthesis,which indicated that both GT08-1180 and ROC22 performed the same in stress responses,membrane damage and photosynthesis decrease under cold stress.ROC22 showed more enrichment in DEGs related to synthesis and transfer of organic substances,and transporter protease.GT08-1180 showed more enrichment in DEGs related to DNA integration、RNA polymerase、ADP binding and metabolic enzymes. |
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