Abstract: Substantial genetic variation is found in weedy rice (Oryza sativa f. spontanea Roshev.) populations from different rice-planting regions with the change of farming styles. To determine the association of such genetic variation with rice farming changes is critical for understanding the adaptive evolution of weedy rice. We studied weedy-rice specific novel single nucleotide polymorphisms (SNPs) by genome-wide comparison between DNA sequences of weedy and cultivated rice, in addition to polymerase chain reaction fingerprinting at 22 selected novel SNP loci in weedy rice populations. A great number of novel SNPs were identified across the weedy rice genome. High frequencies of the novel SNPs were determined at the 22 selected loci, although with considerable variation among weedy rice populations in different rice-planting regions. The highest frequency (∼57%) of novel SNPs was identified in weedy rice populations from Jiangsu that experienced the most dramatic changes in rice farming styles, including the shift from transplanting to direct seeding, and from indica to japonica varieties. The lowest frequency (∼29%) was detected in weedy rice populations from Northeast China, where rice farming has undergone relatively less change. The association between frequencies of novel SNPs in weedy rice populations and the extent of changes in rice farming styles suggests the critical role of adaptive mutation and accumulation of the mutation influenced by human activities in the rapid evolution of weedy rice.

Key words: adaptive evolution, change of farming practice, genome sequence, human influence, novel mutant, weed