Genetic Diversity And Association Analysis Of Molecular Markers With Important Traits Of Superior Clones In Salix Spp.

Willow is recognized as general term of Salix and Chosenia which are members of the Salicaceae family. The genus Salix comprises more than 520 species, of which there are 257 species, 122 varietas and 33 formas in China. Willow is apt to hybridize across species as well as across genera under natural conditions, and has abundant genetic diversity. There are trees which reach up to 20 meters above, as well as shrubs which are as low as 15-30 centimeters. Willow are used for forest protection, soil and water conservation, forest landscape and timber. To be noticed, as a result of rapid growth and high biomass yields, many species can be used as important resource for biofuels. However, only about 10 species such as Salix alba L., S. matsudana Koidz and S. babylonica L. are most commonly in the research and application of agroforestry. Since it is still lack of varieties with high ornamental value and biomass, the needs of modern production in Salix are difficult to meet.Traditional cross-breeding is time-consuming and inefficiency. While marker assisted selection is an efficient breeding technique used to track and select the target traits by genetic markers linked with phenotypic traits. This system is particularly beneficial for willow with complex genetic background and time-consuming breeding cycle to accelerate the breeding process. Previously, molecular markers have been successfully used in the willow research, including the classification, variety identification, genetic diversity, and genetic relatedness. However, there are few researches refer to association analysis of important traits by molecular markers in the willow.In this study, population structure of Salix germplasm resources was analyzed, based on variation of characteristics of morphological, photosynthetic and biomass, and genotype through scanning Salix using 26 SSRs and 10 AFLPs. Then association analysis between markers and important traits were performed in order to find critical markers related to these traits. The main conclusions were as follows:There were few differences between the same clones in these traits. However, the variation of these traits of Salix spp. was significant and specific. Modified rectangular hyperbola model was the optimality model used to estimate photosynthetic light-response curve parameters in Salix comparing the results fitted by three models, amd 50 clones were divided into four types based on the fitting parameters. According to the growth curve, it was considered that Logistic model could be used to fit growth curve, which divided the growth into three stages. And the fast growing stage was the most important stage. In addition, it was showed that 50 clones were divided into 3 phenological types according to the result of principle component analysis, which were long-growing period type, short-growing period type and middle-growing period type.26 SSRs and 10 AFLPs were selected from reported markers using four different clones. The way using two molecular markers with high resolution and good repeatability was preciser for Salix to analyze the genetic diversity, which could be helpful to avoid deviation caused by using single molecular marker. This genetic study showed that the genetic diversity of Salix was high and the same as the study of phenotype. And the Salix germplasm resources did not show strong group differentiation, their population structure was weak.The results of association analysis and multiple test showed that there were some associations, of which there were 22 SSR markers associated with 16 morphological traits, 3 SSR markers associated with 2 light response characteristic parameters and 11 SSR markers associated with 9 biomass traits. And there were 10 AFLP markers associated with 25 morphological traits, 7 AFLP markers associated with 3 light response characteristic parameters and 10 AFLP markers associated with 8 biomass traits. These markers is expected to be used for selection and excavation of superior clones in Salix spp. in the future.This study ascertain the genetic variation and diversity from several aspects, and found some markers related to these traits. And this system provides a new way to analysis complex traits, and plays a fundamental role in selecting new variety, excavating early advantages and cloning related genes controlled excellent traits in Salix spp..