Resistance Of Amaranthus Retroflexus And Portulaca Oleracea To Glyphosate In Cotton Fields

Amaranlhus retroflexus and Portulaca oleracea are world annual herbs.They are the main broad-leaved weed in cotton, soybean and some crops fields. In our country, they damage to cotton yield seriously, and have been listed as the predominant weeds or regional advantaged weeds in cotton field. Glyphosate is the main pesticide of annual weeds and perennial weeds, which is widely used in cotton filed. With the increase of glyphosate servicing years and dosage, more and more weeds become resistant to glyphosate.In order to investigate the resistance of Amaranthus retroflexus and Portulaca oleracea. to glyphosate,18 collecting sites were selected from the cotton fields of Anhui, Hebei, Henan, Hunan, Shandong, Shaanxi and Xinjiang province, then the level of resistance of these two kinds weed to glyphosate were evaluated by seed bioassay and whole bioassay. According to the results of bioasays, the difference of shikimic acid and chlorophyll content in the Amaranthus retroflexus and Portulaca oleracea were measured by ultraviolet spectrophotometer, and compared the main metabolism enzyme-GSTs between resistant and the susceptible weeds. The results were as follows:The results of seed bioassay and whole bioassay showed that he Amaranthus retroflexus and Portulaca oleracea from different collecting sites had different levels of resistance to glyphosate, and the two detection methods showed the same resistant tendency. Amaranthus retroflexus and Portulaca oleracea from the collecting site of Xi’an, Shaanxi Province and Shule, Xinjiang Province were most susceptible to glyphosate, respectively. The resistant level of Amaranthus retroflexus from the collecting site of Quzhou county, Hebei Province was the highest, which reach to 6.872, and The resistant level of Portulaca oleracea were all low, and the highest was only 2.414.On the basis of Amaranthus retroflexus and Portulaca oleracea whole plant bioassay, setting the glyphosate spraying dosage was higher than their highest ED50, respectively 18 g-hm^-2 and 90 g-hm^-2. The content changes of shiikimic acid, chlorophyll and the activity of GSTs between resistant and susceptible were measured after glyphosate treatment. The Amaranthus retroflexus and Portulaca oleracea shikimic acid content increased gradually, and the lower resistant of Amaranthus retroflexus and Portulacaoleracea shikimic acid accumulation was generally higher than the higher resistant plants. Their chlorophyll a, chlorophyll b and total chlorophyll content were decreased gradually, and the lower resistant plants were decreased much more than the higher resistant pants. The GSTs activity of resistant and susceptible Amaranthus retroflexus and Portulaca oleracea reached their highest in fifth days after glyphosate treatment. But compared with the untreated plant, the GSTs activity was no significant difference, and the relative activity was only 1.03, which suggested the GSTs activity was irrelevant with the generation of resistant.