Genetic diversity of winter wheat in Shaanxi province, China, and other common wheat germplasm pools

Cultivated Chinese wheat germplasm has been a valuable genetic resource in international plant breeding. Landraces endemic to China are a genetic resource that is distinct from other wheat germplasm. Patterns of genetic diversity among cultivated Chinese accessions and relationship to other germplasm pools are unknown, despite the proven value and potential novelty. The objective of this work was to determine the level of genetic diversity within improved Chinese germplasm in the context of several other wheat germplasm pools.We analyzed a set of improved accessions cultivated from the 1940s to the 1990s in Shaanxi province, China, using six simple sequence repeat (SSR)primer pairs and 30 restriction fragment length polymorphism - probe enzyme combinations (RFLP-PEC)previously used to characterize 21 geographically based germplasm pools. Shaanxi germplasm consists of three groups based on foreign introductions from Italy, Australia, Denmark, and Russia. There was a decrease in genetic diversity among Shaanxi accessions cultivated in the 1970s and 1980s to the 1990s, and accession classifications based on primary decade of cultivation were found to be significantly undifferentiated. The analysis of the mean genetic distance among 22 geographically based pools of germplasm suggests several regions are significantly undifferentiated. A vast majority of the total amount of variation was found within pools; therefore, pools appear to be largely differentiated based on small differences in band relative frequency and few if any unique bands. Previous studies have identified some Chinese landrace pools as morphologically and genetically unique. The Shaanxi pool does not have the same unique morphological or genetic features, nor is it more similar to the landrace pools than other improved germplasm pools.