The Growth Characteristics And Mechanism Of Tolerance To Glyphosate Of Alligator Weed (Alternanthera Philoxeroides) Under High Manganese Stress

Alligator weed, Alternanthera philoxeroides (Mart.) Griseb., is one of the most invasive alien weeds in China. The experiments were conducted to study the growth characteristics and glyphosate tolerance of alligator weed under high manganese (Mn) condition, which is the basis of alligator weed control and glyphosate high efficiency used in high Mn area.1. On 120 days after 0.31mM (middle Mn) and 2.45mM (high Mn) treatments in hydroponic system, the Mn content in alligator weed leaves were 7.09 and 16.81 times more than that of 0.0091mM Mn treatment (the control and normal Mn level, 2.65mg/g), respectively. The Mn content in alligator weed in high Mn treatment extracted by ethanol, deionized water, sodium chloride, acetic acid and hydrochloric acid solution were 10.32, 23.30, 22.41, 63.94 and 11.84 times more than that of the control, respectively. In high Mn condition, the Mn was exsisted primarily in sodium chloride and ethanol extractable binding form alligator weed, and Mn content for the two binding forms was more than 85% of the total Mn.The results indicated that chelate compounding of Mn with high affinity ligands might be one of the mechanisms that leading alligator weed tolerance to Mn. Considering the increasing of the hydro-soluble Mn in the weed which is antagonistic to glyphosate in high Mn condition, maybe this is one of the major mechanisms that causing alligator weed tolerance to glyphosate in high Mn environment.2. Twenty days after Mn addition of 8～128 mg/kg in the soil, the branch numbers of alligator weed were significantly increased by 22.57%～48.31% compared to that of the control (4.43 per plant), the length of longest stems were significantly increased by 16.60%～19.87% compared to that of the control (23.85 cm), and the total rhizomes numbers were significantly increased by 29.87%～47.40% compared to that of the control (1.54 per plant), the dry weight of the weed were significantly increased by 22.45%～27.00%, as compared to that of the control (0.23 g), respectively. The leaves areas were also more than that of the control in 32¹28 mg/kg Mn addition treatment. The results indicated that the growth and propagation of alligator weed were stimulated when the Mn content in soil was increased, and this might be one of the major reasons leading to the extend of infection of the weed in acidic soil environment.3. Twenty one days after glyphosate application in dosage of 68, 102 and 136 g ae/hm², respectively, the alligator weed fresh weight reduction (FWR) declined by 27.39%, 24.57% and 30.06% , respectively, in treatment of Mn 128 mg/kg addition in the soil compared to that of the control,. The dry weight reduction of the plant were declined by 9.54%,34.37% and 36.37% , respectively, in Mn 128 mg/kg addition treatment compared to that of the control. Alligator weed showed remarkably tolerant to glyphosate under high Mn condition in the soil4. The difference of EPSPS activity in different Mn concentration treatments in hydroponic system in the weed was little. The EPSPS activity in three Mn concentration treatments were declined after glyphosate application in dosage of 68 g ae/hm², with the relatively big reductions in the control. Between 2 to 6 days after glyphosate application, EPSPS activity in high Mn treatment were 1.22¹.39 times more than that of the control. In middle and high Mn treatments, the IC₅₀ (the concentration with 50% activity inhibition) value of glyphosate to EPSPS in vitro were 1.35 and 2.43 times more than that of the control(36.60μmol/L). The results indicated that the susceptibility of EPSPS to glyphosate was declined under high Mn.5. In Middle Mn treatments, GSTs activity and GSH content of alligator weed leaves were almost same to that of conctrol, but declined by 26.63% and 26.33% compared to that of the control(1.007 mmol/min·mg,0.056 mg/g)in high Mn treatments. The GSTs activity and GSH content of alligator weed in the three Mn level treatments were increased after glyphosate (68 g ae/hm²) application, and 4 days after glyphosate application the GSTs activity in normal, middle and high Mn treatment were 1.64, 1.63 and 1.71 times more than that without glyphosate application, respectively and GSH content were 1.36,1.40 and 1.47 times more than that without glyphosate application. The results indicated that the tolerance of alligator weed to glyphosate under high Mn treatment may be not correlated with GSTs activity and GSH content.6. The FWR of glyphosate (68 g ae/hm²) to alligator weed were 80.63%, 68.11% and 57.80% under normal,middle and high Mn treatment, respectively. The FWR for treatment of mixture of piperonyl butoxide (PBO, 800 g ai/hm²) and glyphosate in normal, middle and high Mn treatments were increased by 12.57%,19.89% and 35.49%, respectively, compared to that of glyphosate treatment alone. Considering the susceptibility increasment of alligator weed to glyphosate in the condition of cyt P450 inhibition under high Mn treatment, maybe difference of cyt P450 activity in different Mn level is one of the fators that causing alligator weed tolerant to glyphosate.