Study On The Genetic Diversity And Origin Of The Weedy Rice In Jiangsu And Hainan Province

As direct-seeding cultivation has been widely applied in rice production areas, weedy rice becomes one of the most harmful weeds in the paddy field in recent years. Weedy rice shares shattering and seed dormancy character with weeds. At present, Weedy rice found nationwide varied largely in morphological characters. The classification standard on weedy rice has not yet established so that weedy rice may not be identified. On the contrary on various characteristics, in some area the genetic diversity index of weedy rice based on genetic markers is very low. So it is necessary to analyse the genetic diversity and relationship between weedy rice populations collected from different cultivated areas at larger geographical scale in order to reveal the genetic structure as well as origin and evolution of weedy rice. This may have important theoretical and practical significance in weedy rice study and control.The investigations on weedy rice occurrence and infestation in the main rice production areas of Jiangsu and Hainan Proviences were conducted in the autumn of 2006 to 2010.915 accessions of weedy rice specimen and seed samples were collected. These include 720 individuals with 38 populations in Jiangsu and 195 individuals with 11 population in Henan. In addition, cultivated rice samples were collected in the occurred fields. Then, the seeds were planted in the experiment farm of Nanjing Agricultural University in Jiangpu district, Nanjing. Young leaves were collected for DNA extract from seedlings of each individual respectively. The genetic diversity, differation structure of weedy rice populations and the origin were analyzed with selected 33 pairs of rice genetic SSR markers including 30 pairs of nuclear genome markers and 2 pairs of mitochondrial genome makers and 1 chloroplast genome maker.The result showed that the genetic diversity of the 38 populations of weedy rice in central regions of Jiangsu provience had He=0.1998,1=0.3554, percentage of polymorphic P=93.94%; average number of alleles Na=2.7273; effective number of alleles Ne=1.3523. Among all of the 38 populations, the populations collected from Yanjiang rice cultivation region had the maximum value of genetic diversity while Lixiahe rice cultivation region was the minimum. Genetic differentiation among regions(3%) was significantly less than among populations(52%) and within populations(45%). UPGMA cluster analysis and principle component analysis(PCA) based on Nei’s genetic distance showed weedy rice in all six rice cultivation regions almost was indica. All of weedy rice biotypes did not related with cultivated rice which are currently grown but related with hybrid rice which were ever planted before and currently cultivated indica rice. Analyzing genetical structure differentiation of 38 populations and relationship with cultivated rice and wild rice using the STRUCTURE Software exhibited similar resultes with cluster analysis. Optimum K=4 was determined. All of weedy rice biotypes in Jiangsu province closely related with currently cultivated hybrid rice, indica rice and parents of hybrid rice which were ever planted while did not relate with japonica rice, Ludao and wild rice. Hence, our research supports 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.Hainan Provience is another place where weedy rice invaded seriously. Based on the analysis of 33 pairs of co-dominant SSR makers, the 11 weedy rice populations in Hainan Provience.demonstrated its own characteristics. The genetic diversity of the 11 populations in Hainan Provience is higher than Jiangsu, He=0.2619,I=0.4439,percentage of polymorphic P=93.94%; average number of alleles Na=2.6061; effective number of alleles Ne=1.5003. Among all of the 11 populations, Qiongzhou had the maximum value of genetic diversity while Lingshil had the minimum. Genetic differentiation among regions(18%) which is higher than Jiangsu, and the differentiation among populations is 36) and within populations is 46%, which suggests that these may have different origins. UPGMA cluster analysis and principle component analysis(PCA) based on Nei’s genetic distance showed most of weedy rice in Hainan Provience was indica and had close relationship with local cultivated rice. The results also showed the weedy rice in Hainan have distant relationship with wild rice and typical cultivated japonica rice. The anlysis of STRUCTURE also confirmed this as well, and all the 11 populations can be divided into 3 groups. Besides the analysis of PCA and STRUCTURE also showed one sample in Hainan is similar to wild rice. Hence, our research results relatively support the atavistic hypothesis that weedy rice in Hainan probably originated from cultivated rice and varieties (accessions) through gene recombination or reverse mutation which produce wild characters. At the same time, we do not exclude the possibility that the trend and potential of wild rice introgress into weedy rice population.