Genetic Variation in a Crossing Population of Camellia oleifera Based on ddRAD Sequencing and Analysis of Association with Fruit Traits

Tea oil is an important high-quality edible oil derived from woody plants. Camellia oleifera is the largest and most widely planted oil-producing plant in the Camellia genus in China, and its seeds are the most important source for obtaining tea oil. In current research, improving the yield and quality of tea oil is the main goal of oil tea genetic breeding. The aim of this study was to investigate the degree of genetic variation in an early crossing population of C. oleifera and identify single nucleotide polymorphisms (SNPs) and genes significantly associated with fruit traits, which can provide a basis for marker-assisted selection and gene editing for achieving trait improvement in the future. In this study, we selected a crossing population of approximately 40-year-old C. oleifera with a total of 330 samples. Then, ddRAD sequencing was used for SNP calling and population genetic analysis, and association analysis was performed on fruit traits measured repeatedly for two consecutive years. The research results indicate that over 8 million high-quality SNPs have been identified, but the vast majority of SNPs occur in intergenic regions. The nucleotide polymorphism of this population is at a low level, and Tajima&rsquo:s D values are mostly greater than 0, indicating that the change in this population was not suitable for the model of central evolution. The population structure analysis shows that the population has seven theoretical sources of genetic material and can be divided into seven groups, and the clustering analysis results support the population structure analysis results. Association analysis identified significant SNPs associated with genes related to the seed number of a single fruit and seed kernel oil content. Our findings provide a basis for molecular breeding and future genetic improvement of cultivated oil tea.