Study On The Tolerant Mechanism Of Acalypha Australis L. To Glyphosate

Glyphosate is an excellent herbicide widely used in the world. Due to its extensive use, inevitably causing the development of resisitant and tolerant weed populations and increasing the difficulty of weed control. Acalypha australis L. is a major field weed, and it is found that this species hard to be controlled by glyphosate in previous field experiments. In this study, the method of comparative biology were used to study the biology, physiology and biochemical indicators of Acalypha australis L. and other sensitive weed species after glyphosate application, including the shikimate accumulation, photosynthesis, evaporation, epicuticular wax layer, glyphosate absorption and EPSPS activity of the species. Then the main results are as follows:1. The results of whole plant bioassay showed that A. australis expressed high tolerance to glyphosate. The ED50 of different populations of A. australis spread from 717.28 g a.i./hm2~1013.66 g a.i./hm2, which are higher than the Pharbitis purpurea L., Calystegia hederacea Wall., Chenopodium album L., Eleusine indica L., and Amaranthus retroflexus L. No significant differences were found among the populations of A. australis in glyphosate. The plant height of A. australis had a great impact on its sensitivity to glyphosate. The ED50 of A. australis were 711.38 g a.i./ hm2~2762.64 g a.i./ hm2 when the plant were 3~17cm in height. A. australis became more tolerant to glyphosate in the mature stage. 2. After glyphosate application at rate of 1230 g a.i./hm2, the highest shikimate accumulation of A. australis, Chenopodium album L. and Amaranthus retroflexus L. were 1247.19μg/g, 1400.65μg/g and 858.66μg/g respectively, which showed no significant correlation with glyphosate tolarance of three weed species. However glyphosate tolerance of weed species showed significantly correlated with the ratio of treated one to its blank control in shikimate accumulation at the same sampling time.The ratio of the tolerant weed species was much lower than the sensitive species. 3. The chlorophyll fluorescence parameters and sucrose of A. australis and A. retroflexus showed no significant changes after glyphosate application, but net photosynthesis and transpiration rate of A.retroflexus had declined significantly. The stability of photosynthesis and transpiration rate of A. australis after glyphosate application was also a reason of glyphosate tolerance. 4. Without glyphosate, the EPSPS activity of A. australis and A.retroflexus were 0.55 U and 0.26 U mg-1 protein respectively. The ED50 of EPSPS of A. australis and A.retroflexus were 4.37μM and 0.49μM treated with glyphosate in vitro condition. The EPSPS of A. australis showed a significant natural tolerance to glyphosate comparing to A.retroflexus. 5. The absorption of glyphosate in leaves of A. australis and A.retroflexus were 60.30% and 54.68%, 65.81% and 77.33%,71.99% and 82.82%, at the rates of 4g a.i./L, 2g a.i./L and 1g a.i./L, respectively, 48 h after application. The highest glyphosate concentration in nearby leaves above the treated leaves in A. australis and A.retroflexus were 9.35 mg/kg and 13.09 mg/kg after spot application of glyphosate at 2g a.i./L, indicating that lower glyphosate concentration in the leaves of A. australis may led to glyphosate tolerance.The results of the experiment provides evidence of glyphosate tolerant mechanism of A. australis and will facilitate glyphosate reduction application technology.