Spreading Pathway Of Weedy Rice In The Northeastern China

The three provinces in the northeastern China is an important grain production base and which is also the main rice producing areas in China. Its perennial rice planting area accounts for about 50% of the total japonica’s area in China.The proportion of the three provinces in the country’s total japonica rice output is also rising, has risen to 45.60% in 2010. Its rice total production reached 28.7 million tons, accounting for 28.8% of the country’s rice production. The three northeastern provinces are also a very important high-quality grain production bases. Their market price is higher than hybrid rices’3～5 times. Since 2000, the weedy rices in the northeastern China gradually occured harmful. They are not only harmful to rice yield, but also affect the quality of rice. In order to protect our country’s food security, we need to carry out the control work on the weedy rices in the northeastern China.Current research for the weedy rices in the northeastern China mainly focus on morphology, physiology and genetic relationship on individual provinces.For weedy rice control work, first we need to kown the occurrence and infestation of weedy rice in whole northeastern China. Then we need to kown that how many weedy rice ecotypes have and the identifications of weedy rices and cultivated rice. Finally we discuss recent origin of weedy rices if they are occurred independently or mutual transmission so that we can find some relevant prevention and control measures.We do the following research based on that we collected a total of 23 kinds of types of 274 control sample after four years. (1) We investigating 240 sites of Northeastern China in order to understand the occurrence and infestation of weedy rice in the Northeastern China; (2) 138 accession of weedy rice samples collected in 14 cities of the three northeastern provinces were cultivated in homogeneous plantations, and 38 biology traits during vegetative and reproductive growth stage were observed and measured in order to differentiate the weedy rice groups in the northeastern China and reveal the morphological differences of weedy rice and cultivated rice in the various periods. (3) 32 pairs of codominant markers were used for genetic structure analysis include 384 individuals with 19 populations in the northeastern China in order to find that the weedy rice in the northeastern China were occurred independently or mutual transmission. (4) 38 morphological characters and 32 pairs of co-dominant markers were used for discussing recent origin of weedy rice in the northeastern China with 19 weedy rice populations and 23 kinds of types of 274 control samples.Occurrence and infestation investigation of weedy rice in the northeastern China shows, through the 240 sites of weedy rice investigation in the northeastern China, the comprehensive infestation index for every province is followed by Liaoning Province (0.4220), Heilongjiang (0.3733), Jilin Province (0.2171). Correlation analysis showed that the comprehensive infestation index for every province had significant positive correlation (r= 0.417, P= 0.043) with Relative ratio of Per Capita Net Income of Rural Households by Region and Relative effective Irrigated Area. And it also had a highly significant positive correlation (r= 0.515, P= 0.010) with Total Relative Agricultural Machinery Power. Occurrence frequency of weedy rice in the northeastern China had a highly significant positive correlation (r= 0.873, P= 0.000) with Relative ratio of Per Capita Net Income of Rural Households by Region, Total Relative Agricultural Machinery Power and Relative effective Irrigated Area. These shows that the reduction of rural land labor inputs is an important factor in weedy rice’s increasing infestation. And increased mechanization accelerated propagation velocity of weedy rice.Classification and identification of characteristics of weedy rice in the northeastern China reveal that we can divide 4 weedy rice groups by the UPGMA (unweighted pair-group method with arithmetic means) dendrogram which was clustered by 138 weedy rice’s 38 biology traits during vegetative and reproductive growth stage. The first group (I) are mainly composed of Liaoning weedy rice. The main features of vegetative stage was strong tillering, shorter plant height in seedling stage and higher plant height after transplantin 60 days; the main features of reproductive stage was weak shattering, late heading, long ear length of main panicle, more effective panicles and more compact panicle type. The second group (Ⅱ) are mainly composed of Liaoning weedy rice. The main features of vegetative stage was stronger tillering, slow seedling growth, higher plant height after transplanting 30 days and 60 days; the main features of reproductive stage was strong shattering, short awn, late heading, late, less effective panicles and drooping flag leaf type.The third group (III) are mainly composed of Heilongjiang weedy rice. The main features of vegetative stage was weak tillering, higher plant height in seedling and after transplanting 60 days; The main features of reproductive stage was long awn, early heading, short ear length of main panicle, precocious, erect flag leaf type and their flag leaf is short and narrow. The fourth group (IV) are mainly composed of Jilin weedy rice. The main features of vegetative stage was weak tillering and shorter plant height; The main features of reproductive stage was short ear length of main panicle, less effective panicles, early heading and erect flag leaf type. ANOVA (analysis of variance) of weedy rice and cultivated rice in the northeastern China based on 38 biology traits showed that weedy rice in the northeastern China had significant variation with cultivated rice in pericarp color, effective panicles and leaf type. And it had no significant variation in other traits. The study on the morphological index and classification of weedy rice and cultivated rice in the northeastern China may provide theoretical basis for identification, prevention and control of weedy rice.The research of spreading pathway of weedy rice in the northeastern China showed that the genetic diversity of the 19 populations in the northeastern China is He=0.1523, Shannon index (I)=0.2743, Gene flow (Num)=0.2664, outcrossing rate (t) is 0.0372. AMOVA (Analysis of molecular variance) showed that genetic differentiation among regions (2%) was significantly less than among populations (39%) and within populations (59%). STRUCTURE genetic structure analysis showed that weedy rices in the northeastern China can be divided into three categories, while weedy rices of three provinces were mixed. The result is similar to AMOVA analysis. MANTEL Test analysis showed that 19 weedy rice populations in the northeastern China was no significant correlation (R2= 0.0034, P= 0.269) with their geographic distance. Further UPGMA (unweighted pair-group method with arithmetic means) cluster analysis of weedy rice in the northeastern China based on 38 biology traits and 32 pairs of co-dominant markers showed that all weedy rices can be divided into four groups. Two groups were composed of Weedy Rice in Liaoning Province and the other two groups were mixed by weedy rices of the three provinces. The result of principle component analysis (PC A) based on 38 biology traits and 32 pairs of co-dominant markers also showed similar results. In conclusion, this study suggests that weedy rices in the northeastern China were not occurred independently in every provinces but spread from Liaoning province to Heilongjiang and Jilin provinces.Finally, we discussed the recent origin of the weedy rices in the northeastern China by UPGMA cluster analysis with 19 weedy rice populations and 23 kinds of types of 274 control samples based on 32 pairs of co-dominant markers. The result showed that the weedy rices in the northeastern China had a closer parental relationship with Anhui and Jiangsu ancient weedy rice (Lu Dao and Tang Dao) and the weedy rice in South Korea. Meanwhile, they were distant with the cultivated rice collected from the sample field, conventional rice, wild rice, indica rice and so on. STRUCTURE genetic structure analysis and UPGMA cluster analysis had similar results above. In conclusion, these results revealed that the weedy rices in the northeastern China may not be originated from local cultivated rice. The results were different from common views which thought weedy rices in the northeastern China were originated from local cultivated rice.