Abstract: The previous investigations on occurrence and harmfulness of weedy rice in Jiangsu province showed the province is one of the most serious infestations in China, especially in the central region of Jiangsu province. Hence, in the paper, 33 pairs of co-dominant SSR makers were used to analyse 11 weedy rice populations in central region and other samples in northern and southern regions of this province. Our main objectives were to reveal genetic diversity and analyse the origin of weedy rice. The result showed that the genetic diversity of the 11 populations in central regions of Jiangsu province is He=0.1661, I =0.2872, percentage of polymorphic loci P=87.88%; average number of alleles Na=2.1515; effective number of alleles Ne=1.2887. Among all of 11 populations, the populations collected from Taizhou city had the maximum value of genetic diversity while that from Nantong had the minimum one. Genetic differentiation among regions (1%) was significantly less than among populations (39%) and within populations (60%). Nei’s genetic distance and UPGMA cluster analysis and principle component analysis(PCA) showed that most weedy rice was indica in central and southern regions of Jiangsu Province and a few of japonica in northern regions in the province. All of weedy rice biotypes in central and southern regions did not related with cultivated rice while related with cultivated hybrid indica rice which was ever planted before. Hence, our research results relatively supported the atavistic hypothesis that weedy rice in Jiangsu probably originated from cultivated rice and varieties (accessions) through gene recombination or reverse mutation which produce wild characters. However, the japonica weedy rice in northern regions might be the offspring of the hybrid between cultivated rice and wild rice Ludao.

Key words: Weedy rice, Molecular marker, Genetic diversity, Origin, SSR