Resistance Of Digitaria Sanguinalis To Glyphosate In Cotton Fields

Crab grass (Digitaria sanguinalis) is an annual gramineous weed commonly seen in dry land. It is distributed across China, mainly damaging such crops as Gossypium, Sorghum bicolor Moench, Triticum aestivum and Glycine max Merr. With its high occurrence and great damage in fields, it is one of the top ten vicious weeds in China, which does great harm to the production of crops in China. According to the survey on the history of herbicides used in cotton field, glyphosate is often applied to control and remove annual weeds in recent years. The experiment was applied three methods, including seed bioassay, whole plant assay and grade of symptoms to access the resistance of twenty one Digitaria sanguinalis populations from twenty counties in four provinces to glyphosate, including Hunan, Anhui, Henan and Jiangxi. The ultraviolet spectrophotometry was used to test the change of shikimic acid, GSTs energy of four species after applying glyphosate, as well as the change of chlorophyll content of two species after the treatment of glyphosate. In order to delay the occurrence of resistant weeds and provide theoretical foundation for the control of resistant weeds. The results of experiment are as follows:The measurement of the resistance of Digitaria sanguinalis using seed bioassay indicated that: The population from Wenqiao was the most sensitive to glyphosate. Comparing with it, the relative resistance index of Anzhang population was the highest, being 5.320, while the relative resistance index of other populations remained 1.019-5.320.The result of whole plant assay indicates that:Similarly, Wenqiao population from Jiangxi province are the most sensitive to glyphosate. The relative resistance index of Anzhang population from Hunan province is the highest, being 7.637. With the Junqiao population from Jiangxi province as the relative sensitive species, the relative resistance index of other populations are 1.031?7.637. The results measuring by whole plant assay and by seed bioassay are roughly the same. While the overall resistance index is higher than the result measuring by seed bioassay.The result of grade of symptoms indicated that after treating the twenty one populations with glyphosate for fourteen days, the plants showed various symptoms, among which only one population with medium resistance to glyphosate grew well in comparison with other populations. The sensitive population nearly wilted, with more than 95% leaves dead.In terms of the physiological biochemistry, it was tested that the change of shikimic acid accumulated and GSTs energy of a relative sensitive population and three relative resistant populations after treating glyphosate for zero, one, three, five, seven and nine days by using spectrophotometry, as well as the change of chlorophyll content of Wenqiao population and Anzhang population. The shikimic acid accumulated suggested that the accumulation of three relative resistant populations is lower than that of relative sensitive population from Wenqiao within zero to nine days. The change of GST energy of four populations was not obvious. There were little differences among populations. This might have nothing to do with the resistance of Digitaria sanguinalis to glyphosate. The content of chlorophyll a, chlorophyll b and the total content of chlorophyll of Wenqiao population and Anzhang population gradually decreased as time changes. But the decrease in chlorophyll of sensitive population was more obvious than that of resistant popalations.