Quinclorac Resistance in Echinochloa crus-galli from China

Over the past decade, there has been a productive collaboration between AHRI and Chinese researchers. Scholarships from the China Scholarship Council have enabled young Chinese university assistant Professors (Lecturers) to come to AHRI each for one year to work principally with AHRI researchers Drs Yu Qin and Heping Han. Dr Qiong Peng came to AHRI for one year to study Chinese Echinochloa populations resistant to the rice-selective auxinic herbicide quinclorac. This paper documents two Echinochloa populations as being very highly resistant to quinclorac. She found that quinclorac resistance in these Echinochloa populations is not due to differential quinclorac uptake, translocation or metabolism. Anyone who works on the mechanistic basis of auxinic herbicide resistance knows that this is a very difficult research area, given the cascade of changes that auxinic herbicides cause in plants. Further molecular work is required to identify the mechanistic basis of quinclorac resistance.

Abstract

Echinochloa crus-galli is a major weed in rice fields in China, and quinclorac has been long used for its control. Over-reliance of quinclorac has resulted in quinclorac resistance in E. crus-galli.

Two resistant (R) E. crus-galli populations from Hunan, China were confirmed to be at least 78-fold more resistant to quinclorac than the susceptible (S) population. No difference in foliar uptake of 14C-labelled quinclorac was detected between the R and S plants. However, a higher level of 14C translocation and a lower level of quinclorac metabolism were found in the R plants. Basal and induced expression levels of β-cyanoalanine synthase (β-CAS) gene and β-CAS activity were not significantly different between the R and S plants. However, the induction expression of 1-aminocyclopropane-1-carboxylic acid oxidase (ACO1) gene by quinclorac treatment was evident in the S plants but not in the R plants.

Quinclorac resistance in the two resistant E. crus-galli populations was not likely to be related to foliar uptake, translocation or metabolism of quinclorac, nor to cyanide detoxification via β-CAS. Thus, target-site based quinclorac signal reception and transduction and regulation of the ethylene synthesis pathway should be the focus for further research.