Analysis on Genetic Diversity of Phenotypic Traits in Rice(Oryza sativa)Core Collection and Its Comprehensive Assessment

Germplasm resources are fundamental in rice breeding and dissecting complex traits.Assessment of genetic diversity benefits the identification of optimal parental combinations to produce segregating offspring with maximum genetic variability,and facilitates the introgression of favorable genes from various germplasm into commercial cultivars.The USDA rice core collection(USDA-RCC)(1 579 rice accessions originated from six continents),was analyzed with 14 phenotypic traits to assess diversity and phenotypically superior rice germplasm.The main results were summarized as follows:(1)Genetic distance of the germplasm from Asia and Africa to that of Oceania was larger.Rice germplasm from Asia,Africa and Oceania had accordingly greater phenotypic and genetic diversities,and genetic diversity of different traits was different among continents.Six traits including kernel length/width(KLW),alkali spreading value(ASC),plant height(PH),kernel width(KW),1000-kernel weight(TKW)and amylose content(AC)had greater genetic diversity.(2)Comprehensive assessment of phenotypic traits was conducted using principal component analysis(PCA)and step regression analysis,demonstrating that the accession PI 392768 from Vietnam had the best comprehensive traits while the accession PI 281760 performed the worst comprehensive traits;AC,HD,PH,lodging,BRC,and HC would be suitable as comprehensive criteria for assessing USDA-RCC germplasm.We suggest these rice germplasm possessing great phenotypic diversity should be widely utilized in breeding programs,moreover,these rice germplasm with farther genetic distance and different comprehensive traits should be appropriately considered for the parental selection.