Study On The Resistance Of Echinochloa Crusgalli Var. Zelayensis To Quinclorac In Paddy Rice

Echinochloa crusgalli var. zelayensis, one of the most noxious weeds in paddy fields of Jiangsu, Anhui and Shanghai in China, was chosen as a main research object in this paper. The susceptibility of E. crusgalli var. zelayensis to quinclorac were investigated by the seed bioassay and whole-plant bioassay experiments which were also carried out to evaluate the multiple resistance levels of quinclorac-resistant E. crusgalli var. zelayensis. Based on the observed quantified responses of the ethylene biosynthesis and antioxidase activities in five biotypes (JNX-S, JZD-R, JTJ-R, Jcw-R and Ssx-R) with different susceptibility levels, the potential mechanisms of quinclorac resistance in E. crusgalli var. zelayensis were explored. Available techniques used for chemical control of quinclorac-resistant E. crusgalli var. zelayensis were studied in laboratory. The results were as follows:Similar results were obtained by the seed bioassay and whole-plant bioassay experiments about the quinclorac susceptibility of E. crusgalli var. zelayensis which were collected from different paddy fields of Jiangsu, Anhui and Shanghai in China. Both of the methods showed that the JNX-S biotype was denominated as the susceptible biotype with the lowest ED50value. The Ssx-R, Jcw-R, JTJ-R and JZD-R biotypes were resistant to quinclorac, with their ED50ratios123.07,41.21,21.96and5.34in the seed bioassay experiment, and66.88,9.68,6.20and3.32in the whole-plant bioassay experiment, respectively, denominating these four biotypes as resistant biotypes with resistance levels ranked as SSX-R> Jcw-R> JTJ-R> JZD-R.The results of mulitiple resistance revealed that the susceptibility of the Ssx-R biotype to butachlor and thiobencarb was decreasing, with the ED50ratios2.69and2.25, respectively. And all of the ED50ratios of the Ssx-R biotype to other herbicides were less than2.00, showing that on mulitiple resistance were obtained.The study of the connection between ethylene biosynthesis and quinclorac resistance revealed increases in quinclorac-stimulated levels of ethylene and1-aminocyclo-propane-1-carboxylic acid (ACC) and activities of ACC synthase and ACC oxidase in E. crusgalli var. zelayensis, and higher resistance level, less increases. The study of the connection between antioxidase activities and quinclorac resistance revealed that the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX) and glutathione reductase (GR) increased first and decreased later in susceptible and low resistant biotypes, while less significant difference was found in high resistant biotypes. It is suggested that resistance to quinclorac in E. crusgalli var. zelayensis involved at least two mechanisms:(1) inhibition in the ethylene response pathway;(2) enhanced the antioxidase activities, which should enable quinclorac-induced oxidative damage elimination.Two optimum formulation were screened out to control quinclorac-resistant E. crusgalli var. zelayensis in rice fields by Gowing’s method and isoble method, which were cyhalofop-butyl to penoxsulam (ratio of5:1) and metamifop to anilofos (ration of1:3). The pot-spraying experiments showed that the mixture of cyhalofop-butyl and penoxsulam got the general effect over90%against E. crusgalli var. zelayensis, Leptochloa chinensis and Eclipta prostrata, and the mixture of metamifop and anilofos inhibited E. crusgalli var. zelayensis, L. chinensis and Cyperus difformis in water-seeded rice; while, the effects significantly decreased in dry-seeded rice. The study on the safety of rice revealed that both of the two mixtures were safe to rice.