| Marker-assisted selection(MAS)is one of main techniques,which can greatly accelerate the process and improve the efficiency of plant breeding,but it depends on the data of molecular genetic diversity,especially on the research based on target genes and the development of linked marker to target genes.Sucrose content is one of the most important characters,which closely related to the sucrose metabolism genes.In cultivation,cold stress is an important factor that affects the growth of sugarcane.For above,TRAP marker was occupied to study on the genetic diversity of thirtythree important sugarcane clones,including some main cultivars,recent released varieties and some germplasms introduced abroad recently.The total of six genes related to sucrose metabolism were selected as target genes and were used to design the anchored primers for pairing with nine arbitrary primers.The six genes contain five key genes involved in sucrose metabolism in sugarcane,and one gene reported to play an important role in the character of cold tolerance of sugarcane.In total,there were 90 primer combinations and thirty-four combinations of primers were screened to produce clear banding patterns and polymorphisms.The result showed that a total of 579 bands were scored with the 34 pairs of primed screened,of which 288 taking 49.74%in total were polymorphisms.Thus,the polymorphism results from combinations of forward fixed and arbitrary primers reflected that the exonic regions outside the open reading frames(ORFs)of sugarcane genes have a very high mutation rate and diversity.The cluster analyses using UPGMA revealed a narrow genetic diversity among the entries with genetic distance(GD)ranging from 0.26 to 0.63.At the GD level of 0.52,33 sugarcane clones were divided into four groups and the target-genes in 'ROC' series cultivars had a small dissimilarity coefficient.Therefore,the cluster analysis based on TRAP analysis with six target-genes can reflect the variation degree of key genes in sucrose metabolism,in 33 sugarcane clones used in this study,while can't contribute completely to parentage grouping of the 33 clones.At the same time,some special germplasms were found.Therefore,the data from the TRAP analysis can enhance the accumulation of basic data of parent selection and combination configuration and help in high-sucrose and cold-tolerance breeding practice.In this study,genetic diversity analysis was also conducted in another 28 sugarcane clones by 17 primer combinations.The 28 samples set included parents and their hybrid progenies,of which the differences of sucrose content character is relatively obvious.In other words,they are high-sucrose content and low-sucrose content individual.A total of 170 bands were scored and among them 64.12%ie.109 were polymorphisms. Cluster analysis showed that the genetic distance(GD),based on the diversity of the target genes,ranges from 0.12 to 0.80.The results of TRAP analysis on the 28 sugarcane genotypes can't completely grouping these genotypes according to their pedigree records,as in some cases full and half siblings failed to cluster together. However,in this cluster analysis,it was observed to have an order distribution of high sucrose content clones and low sucrose content clones to some extent.And thus,it can provide the practical and theoretical foundation for the establishment of the sucrose trait evaluation in marker-assisted selection.Furthermore,it can also be concluded from this study that TRAP marker technique have many other merits,such as good repeatability, high efficiency,and easy operation,which suggests its great potential applicability in sugarcane classification,important trait marker etc.The results of this study have an important theoretical and practical value.
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