Exploring quinclorac resistance mechanisms inEchinochloa crus-pavonisfrom China

BACKGROUND Barnyardgrass (Echinochloaspp.) is a global weed in rice fields. Quinclorac is commonly used to control barnyardgrass. However, due to persistent use, quinclorac resistance has evolved. We obtained quinclorac-susceptible (QS) and -resistant (QR1, QR2) lines from the progeny of a single resistantE. crus-pavonisfor a resistance mechanism study. RESULTS Line QR1 exhibited resistance to high quinclorac rates (up to 6400 g ha(-1)), whereas line QR2 exhibited a resistance/susceptibility segregation ratio of 3:1 at the field or lower rates (400, 100 g ha(-1)). Intriguingly, a lower level of(14)C-quinclorac metabolism and hence a higher level of(14)C-quinclorac translocation was observed in QR1 than QS plants. The basal expression levels of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) and ACC oxidase 2 (ACO2) genes did not differ significantly between the QR1 and QS lines. However, more expression ofACSandACOgenes was induced by quinclorac treatment in QS than in QR1. Basal levels of beta-cyanoalanine synthase (beta-CAS) gene expression were similar in QS and QR1 plants, but a greater level of down-regulation was detected in QS than in QR1 plants after quinclorac treatment. CONCLUSION These results indicate QR plants are less responsive to quinclorac than QS plants in terms of up-regulating quinclorac metabolism and ethylene synthesis. Resistance in thisE. crus-pavonisline is likely controlled by a single major gene, involving possibly an alteration in auxin signal perception/transduction to the ethylene biosynthesis pathway. The beta-CAS is unlikely to play a major role in quinclorac resistance in this particular population.

Automated summary

The study on susceptible and resistant lines to quinclorac revealed that the resistant plants showed lower response in terms of up-regulating quinclorac metabolism and ethylene synthesis. The resistance is likely controlled by a single major gene, involving possibly an alteration in auxin signal perception/transduction. The beta-CAS gene is unlikely to play a major role in quinclorac resistance in this specific population.