Propanil resistance in sprangletop (Leptochloa chinensis [L.] Nees) caused by enhanced propanil detoxification

The current study was conducted to elucidate the resistance mechanism of leptochloa chinensis by comparing the difference in metabolism,aryl acylamidase activity,and chlorophyll fluorescence between the propanil-resistant (r) and the propanil-susceptible (s) biotypes of l. chinensis,using 4-week old seedlings. the concentration of propanil in the leaf and culm extracts of the r and s biotypes was found to increase after propanil treatment. the concentration of propanil in the leaf and culm extracts of the s biotype at 48 h was 12.23 and 5.49 μg ml-1,respectively. however,a lower concentration of propanil was observed in the r biotype,compared to that in the s biotype. no residue of 3,4-dichloroaniline was observed in the s biotype. in contrast the residue of 3,4-dichloroaniline was detected in the leaf and culm extracts of the r biotype. the level of aryl acylamidase in the leaf tissue extracts of the r biotype was ~211% higher than that in the s biotype. the fluorescence studies showed that propanil inhibited the quantum efficiency of photosystem ii in both the r and s biotypes after 2 h of incubation. however,when the leaf discs were transferred and incubated in deionized water for 48 h,the quantum efficiency increased in the r biotype but decreased in the s biotype. the results of the study suggest that propanil metabolism,enhanced by aryl acylamidase activity,is the most likely factor conferring the mechanism of propanil resistance in l. chinensis plants at the 4-week growth stage.