The Resistance Of Baryardgrass (Echinochloa Crusgalli(L.) Beauv.) To Quinclorac

Barnyardgrass [Echinochloa crusgalli (L.) Beauv] is the most troublesome weed in rice in China. Quinclorac is one of the most excellent herbicides for barnyardgrass control in the rice field with good safety, high efficacy and low price. The occurrence of barnyardgrass resistance to quinclorac constitutes a major thread in rice yield safety. It is very necessary to confirm barnyardgrass resistance level and its mechanism to quinclorac, in order to effectively control barnyardgrass and prolong the lifespan of quinclorac in practice. Barnyardgrass seeds were collected from rice field of Hunan, Zhejiang and Jiangsu provinces The sensitivity of Barnyardgrass to Quinclorac was determined by pot planting experiments in the greenhouse, its resistant level and mechanism were also conducted. The results were obtained as followings.1. The resistance of Barnyardgrass to quinclorac were determined by using pot planting method for42populations of barnyardgrass, which were collected from the rice regions around middle and lower area of Yangtze river of China during2008to2011. The results showed that higher resistance levels were observed in two biotypes of barnyardgrass from Zhihukou Town in Yiyang County (R1) and Wangcheng County (R2), Hunan Province, and the resistance indexes were21.84and32.31fold, respectively. There were less resistance levels (1.12-7.32fold) in other populations of barnyardgrass in other rice regions of Hunan, Jiangsu and Zhejiang Province. R1and R2biotype were harvested and were conducted by whole plant experiments in potted in the greenhouse next year. The results revealed that the two biotypes still showed high level resistance level, Which suggested that the resistance of barnyardgrass could be inherited.2. The1-aminocyclopropane-1-carboxylate synthase (ACS) activities in two resistance biotypes of barnyardgrass (R1and R2) were inhibited significantly which was lower than that in sensitive biotype (S) at1st day after treated by quinclorac, the two RIs were0.49and0.56fold compared with the contemporary control, respectively. Both of them increased slightly at2nd days and were still lower than that in the control; however they decreased slowly to0.34-and0.35-fold relative to the control at4th days The β-cyanoalanine (β-CAS) activities in R1and R2of barnyardgrass increased significantly after treated by quinclorac; the maximum were observed at5th days, which were1.80and2.05-fold, compared with the control respectively.3. DNA sequence of barnyardgrass ACS gene was amplified, cloned and compared between resistant and susceptible biotype. The length ACS gene were987nucleotides which was approximately translated into329amino acids. The amino acids sequences of the susceptible and resistant biotypes were consistent. No mutations were found in the resistant biotypes of R1and R2.4. Under the condition of the non-competition, The plant height, the weight of the plant aerial part, the root length, the root weight and the breadth of leaf of sensitive biotype barnyardgrass is better than that of two resistant biotypes. Different biotypes were not significantly different from the number leaf of Barnyardgrass.5. Pot planting experiments in the greenhouse and field experiments were conducted to other six herbicides to control barnyardgrass, which are penoxsulam, bispyribac-sodium, pyribenzoxim, flucetosulfuron, Metamifop, cyhalofop-butyl. The reults showed that the six herbicides could effectively control barnyardgrass and did not show any across-resistance with Quinclorac. All of them gave very good barnyardgrass control.6. The different herbicides combinations were used to control the resistance weed in direct seeding rice fields in the region of Dongting Lake in2009-2011. The results showed that barnyardgrass were resistant to quinclorac in the area, which only provided53.1%of barnyardgrass plant density control and65.5%of barnyardgrass plant fresh weight control. The three combination herbicides of1,2,3gave excellent control effect to resistance barnyardgrass and its population.The control effect was more than90%to the weed in two years experiments. The three combination herbicides were used with ring application form in different years and to avoid or delay appearing of new resistance weeds. So that the three combination herbicides should be extension promoting in direct seeding rice area of Dongting Lake.