POPULATION GENETIC ANALYSIS OF BRAZILIAN PEACH BREEDING GERMPLASM

ABSTRACT Peach has great economic and social importance in Brazil. Diverse sources of germplasm were used to introduce desirable traits in the Brazilian peach breeding pool, composed mainly by local selections and accessions selected from populations developed by the national breeding programs, adapted to subtropical climate, with low chill requirement, as well as accessions introduced from several countries. In this research, we used SSR markers, selected by their high level of polymorphism, to access genetic diversity and population structure of a set composed by 204 peach selected genotypes, based on contrasting phenotypes for valuable traits in peach breeding. A total of 80 alleles were obtained, giving an average of eight alleles per locus. In general, the average value of observed heterozygosity (0.46) was lower than the expected heterozygosity (0.63). STRUCTURE analysis assigned 162 accessions splitted into two subpopulations based mainly on their flesh type: melting (96) and non-melting (66) flesh cultivars. The remaining accessions (42) could not be assigned under the 80% membership coefficient criteria. Genetic variability was greater in melting subpopulation compared to non-melting. Additionally, 55% of the alleles present in the breeding varieties were also present in the founder varieties, indicating that founding clones are well represented in current peach cultivars and advanced selections developed. Overall, this study gives a first insight of the peach genetic variability available and evidence for population differentiation (structure) in this peach panel to be exploited and provides the basis for genome-wide association studies.

摘要 桃在巴西具有重要的经济与社会价值。巴西桃育种种质库主要由适配亚热带气候、需冷量低的本土选育株系、国家育种项目培育种群中筛选的材料，以及从多国引进的种质资源构成，研究人员通过多样化的种质来源为该育种池引入优良性状。本研究选取多态性水平优异的简单序列重复（Simple Sequence Repeat, SSR）标记，针对204份基于桃育种关键性状的差异化表型筛选出的候选基因型群体，开展遗传多样性与种群结构分析。本次研究共获得80个等位基因，平均每个位点包含8个等位基因。总体而言，观测杂合度平均值（0.46）低于预期杂合度（0.63）。STRUCTURE分析将其中162份种质依据果肉类型划分为两个亚群：溶肉质（96份）与非溶肉质（66份）品种。剩余42份种质的隶属系数未达到80%的判定标准，无法归入上述亚群。溶肉质亚群的遗传变异程度高于非溶肉质亚群。此外，当前育种品种中55%的等位基因同样存在于创始种质资源中，表明创始克隆在当前桃栽培品种及后续选育的优系中具有良好的遗传代表性。总体而言，本研究首次揭示了该桃种质群体的遗传变异特征，证实了其种群分化（结构）情况，可为后续育种利用提供依据，并为全基因组关联分析奠定研究基础。