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Salt stress reduces the yield and quality of rice. It is of great significance to screen out salt-tolerant varieties for the development and utilization of saline land. The study was carried out on 114 rice varieties; first, seven varieties were selected and treated with different salt concentrations (0, 50, 85, 120, 155, 190, 225 mM), and seven traits, including germination energy, germination capacity, shoot length, root length, root number, plant fresh weight, and seedling vigor index, were measured. The salt concentration at which the sodium chloride injury index was 50% of the control was considered the optimal salt concentration. Second, 114 rice germplasms were carried out under an optimal salt concentration (120 mM). Then, principal component analysis, fuzzy function analysis, stepwise regression analysis, correlation analysis, and systematic cluster analysis were carried out on each parameter. There was a significant correlation between each parameter and the D-value, and the correlation coefficient between the seedling vigor index and D-value was the highest. D-value = − 0.272 + 1.335 × STI − SVI + 0.549 × STI − RN − 0.617 × STI-RL + 0.073 × STI − GE, R2 = 0.986. Using this equation, the sodium chloride tolerance of rice in the germination experiment could be quickly identified. This study showed that the seedling vigor index was a reliable parameter to identify the salinity tolerance of rice varieties. Five groups were obtained by classification at a Euclidean distance of 5. There were 8 highly salt-tolerant cultivars, 23 salt-tolerant cultivars, 42 cultivars with moderate salt tolerance, 33 salt-sensitive cultivars, and 8 highly salt-sensitive cultivars. In this study, we found that Riguang was the most salt-tolerant rice variety, and Xiangxuejing15 was the most salt-sensitive variety.

Weedy rice (Oryza sativa L.) severely decreases the grain yield and profitability of rice is one of the most significant problems in the majority of rice fields worldwide. Few reports focus on the dispersal of weedy rice, especially how it rapidly spreads to large areas and long distances. Here, we quantify for the first time the within-and between-field dispersal of weedy rice associated with combine harvesting operations. We randomly sampled 31 combine harvesters to determine where and how much weedy rice seeds remained on the machines at three locations in Jiangsu Province, China. Based on the sampling results, the field area over which weedy rice seeds were retained on the combine harvester during harvesting was estimated to assess the within-field dispersibility of weedy rice seeds remaining in the harvesters. A tracking experiment was also carried out by tracing the distribution of weedy rice seeds along harvest trails, to estimate the dispersal of weedy rice seeds within the field being harvested. Weedy rice seeds remained in the harvest pocket, on the pedrail, and the metal plate of the combine harvester. On average, more than 5000 weedy rice seeds which were 22.80% of remaining grains could potentially be transported into adjacent fields by the combine after each rice field infested with weedy rice had been harvested. Of the statistical models compared, a double exponential model simulating the variation in seed retention predicted that weedy rice seeds remaining on the metal plate could be dispersed over 6473.91 m 2 or 3236.96 m into the next field during the harvesting operation. Within the field, the number of fallen weedy rice seeds and their dispersal distance were positively correlated to weedy rice panicle density with the combine dispersing most of seeds away from their mother plant thus creating new weed patches. Therefore, fields that were severely infested with weedy rice should be harvested cautiously and separately and seed remaining in a harvester should be avoided to prevent intra-and inter-field, and even cross-regional dispersal of weedy rice.

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BACKGROUND:It remains an open question if the long-term application of single chemical herbicides would inevitably lead to increased weed populations and result in out-of-control weeds. The annual dynamics of weed seed bank responses to different weeding measures (chemical herbicide, hand weeding and no weeding) in rice-wheat cropping systems were compared to observe the succession of weed communities under different weed selection pressures for 17 years. RESULTS:In unweeded rice-wheat cropping plots, the initially dominant broadleaf weeds were overtaken by grasses and eventually by sedges, while in plots subjected to chemical herbicide or hand weeding, broadleaf weeds remained dominant followed by grasses. The rice-wheat cropping system favoured the spread of paddy weed species; weeding had little effect on the composition of the dominant rice weeds but greatly influenced that of wheat weeds. Total seed density tended to decrease in both weeded and unweeded plots, but the species density and composition of the seed banks differed among plots treated differently. Weeding slightly increased weed species diversity and decreased weed community evenness and dominance in the first several years, but this scenario could have negative consequences in the long term; however, without weeding, stronger interspecific competition led to a decrease in weed species diversity whereas weed community evenness and dominance increased.CONCLUSION: Long-term and repeated application of pre-emergence chemical herbicides and hand weeding had similar effects on the weed community dynamics, indicating that exclusive application of pre-emergence herbicide could maintain the weed community at a durable relatively low infestation level.