effect of metribuzin on kautsky curve and chlorophyll fluorescence parameters in resistant and susceptible junglerice (echinochloa colona) biotypes in the greenhouse conditions

chlorophyll fluorescence induction is a rapid and noninvasive technique for measuring photosynthetic electron transport in plants. chlorophyll fluorescence measurements were performed under greenhouse condition to characterize how the fluorescence induction curves (kautsky curve) and its parameters were affected by metribuzin in susceptible and resistant junglerice (echinochloa colona (l.) link) biotypes. the maximum quantum efficiency of photosystem ii (fv/fm), the relative changes at j step (fvj) and the area between kautsky curve and fm (area) of susceptible biotype were decreased dramatically at 4 hours after spraying. application dose of 100 g ai ha-1 decreased fv/fm, fvj and area about 0.66, 0.07 and 14062, respectively. while, the r-biotypes showed decrease in the fluorescence parameters only at high concentrations of metribuzin; however, response to application rates of metribuzin were different among resistant biotypes. apparently, different resistance mechanisms were existed in the r- biotypes. our results demonstrated that the different measured parameters were different sensitivity to metribuzin treatment. but if we want to choose a parameter which is best suited for field or green house assessment of herbicide efficacy, it could be the maximum quantum efficiency of psii photochemistry. since chlorophyll fluorescence parameters were affected soon after herbicide application, therefore, they could be used as a practical means for assaying herbicide efficacy under green house or probably field conditions.