Enzyme responses of Abutilon theophrasti in an enhanced biocontrol system

摘要

Weak virulence has limited the development of Colletorichum coccodes (Wallr.) Hughes (DAOM 183088) as a bioherbicide for Abutilon theophrasti Medik. (velvetleaf) control. This study examines the role of chemical synergy to suppress host defense mechanisms. Dry weight of A. theophrasti was reduced by treatment with C. coccodes in a tank-mix with 0.25 kg a. i. ha(-1) bentazon more than by the treatment with C. coccodes or bentazon alone, while the effect of a sub-lethal rate of glyphosate was not significant. C. coccodes did not affect phenylalanine ammonia lyase ( PAL) activity in infected leaves of A. theophrasti, whereas PAL activity was significantly inhibited by the presence of bentazon 5 days after treatment. The inhibition was stronger when bentazon was applied alone than when bentazon was applied with C. coccodes. Treatment with glyphosate or a mixture of glyphosate and C. coccodes did not affect PAL activity. Peroxidase activity was strongly induced by C. coccodes treatment and increased over time. Peroxidase activity was not induced by 0.25 kg a. i. ha) 1 bentazon alone. However, when bentazon was applied in combination with C. coccodes, it prevented the activation of peroxidase by C. coccodes infection. Treatment with 0.2 kg a. i. ha(-1) glyphosate did not affect peroxidase activity. These results suggest that these enzymes are involved in the resistance mechanism of A. theophrasti, and the synergistic effect of bentazon on C. coccodes efficacy as a bioherbicide may result from suppressing the activation of these defense-related enzymes.