A Double Mutation in the ALS Gene Confers a High Level of Resistance to Mesosulfuron-Methyl in Shepherd's-Purse.

Shepherd's-purse (Capsella bursa-pastoris), a globally distributed noxious weed species often found in wheat, has evolved resistance to ALS-inhibiting herbicides mainly due to single mutations in the ALS gene. In the present study, dose-response bioassays showed that a shepherd's-purse population (R), collected from Xinghua, Jiangsu Province, China, had high level of resistance to the ALS-inhibiting herbicide, mesosulfuron-methyl (800-fold), and even much higher resistance levels to other reported ALS-inhibiting herbicides, tribenuron-methyl (1313-fold), bensulfuron-methyl (969-fold) and penoxsulam (613-fold). Sequencing of the open reading frame of the ALS gene revealed a double ALS gene mutation (Pro197-Ser plus Trp574-Leu) conferring the high resistance in the R plants. Docking analysis of the ALS protein and mesosulfuron-methyl predicts that the two amino acid substitutions in the R samples reduces the binding energy to the herbicide by decreasing the hydrogen bonds (H-bonds) and other interactions, thus endowing resistance to ALS-inhibiting herbicides. These results demonstrate that the double ALS mutation confers high resistance levels to ALS-inhibiting herbicides. To our knowledge, this is the first evidence of the double ALS mutation in shepherd's-purse endowing ALS-inhibiting herbicide resistance.

Long-Distance Wind Dispersal Drives Population Range Expansion of Solidago canadensis.

Canada goldenrod (Solidago canadensis L.) is a serious invasive alien plant species that exerts negative effects on natural and agricultural ecosystems in China. Few studies have addressed the dispersal of S. canadensis to explain how it rapidly spreads to large areas over long distances. Here, we quantify the dispersal of S. canadensis via wind by capturing in situ-stained diaspores. The diaspores were trapped and counted along 11 radiating transects from the center of a dispersal source. Solidago canadensis diaspores could be dispersed in all directions from the source, traveling longer distances and in greater amounts in the downwind direction than the upwind one. With a source including about 58 million diaspores and a wind speed at Beaufort scale 4, the dispersal distance in the prevailing wind direction (PWD) was at least 2000 m. Diaspores shattered at a rate of approximately 3% daily with the common wind speed of scale 4, indicating that dispersal could last for more than a month. A mechanistic model was used to fit the dispersal curve along the PWD. Although the model slightly underestimated long-distance dispersal, it still demonstrated the potential of long-distance dispersal with great source strength. Wind-dispersed diaspores to new areas persisted over winter and were able to form new plants at a density of about 2 plants per m2 at 500 m away from the source. Further experiments showed that the dispersed amount of S. canadensis diaspores was significantly positively correlated with the temperature and wind speed, but significantly negatively correlated with relative humidity, which indicated that, during a day, the maximum dispersal usually occurred in the afternoon when the temperature was the highest and the relative humidity the lowest. In addition, for an already existent population patch, the patch range can expand 2-4 m per year, mainly depending on the seedlings recruited from the rhizomes. These results provide insights into the long-distance dispersal of S. canadensis by wind and its effects on the range expansion process.