Studying the Effect of Mesosulfuron Methyl + iodosulfuron Methyl on Chlorophyll Fluorescence Parameters of Phalaris Minor

  Measuring of chlorophyll fluorescence is a nondestructive and sensitive way to give important information about photosynthesis apparatus. Fluorescence spectrum is different from the absorbed one by chlorophyll and it has higher wave length so the fluorescence yield could be measured by exposing a leaf with a defined wave length of light and then quantifying the higher reflected wave. The purpose of this experiment was to make comparison among chlorophyll fluorescence important parameters for early prediction of destructive effects of mesosulfuron methyl + iodosulfuron methyl before revealing the symptoms of Phalaris minor. A greenhouse experiment with five replications and six treatment based on completely randomized design was conducted to evaluate the chlorophyll fluorescence parameters of Phalaris minor sprayed by mesosulfuron methyl + iodosulfuron methyl up to seven days after spraying.Herbicide doses were 18, 12, 8, 5.3 and 3.5 g a. i./ha with an untreated treatment as control. Herbicide was applied at three leaf stage of Phalaris minor with MATABI elegance plus sprayer equipped by tee-jet 8001 nozzle at 300 kpa pressure. Fluorescence measurements were conducted by Handy PEA fluorimeter that flashes a wave length of 650 nm at 300 μ mol/m2.s intensity during 10 seconds on dark adapted leaf one day after spraying at 10 a.m. every day until seven days after spraying. The results indicated that Fv/Fm and Area parameters showed slow response to mesosulfuron methyl + iodosulfuron methyl application whereas Fvj and PI showed a fast reaction. Approximately from the first day after spraying the two mentioned parameters drastic reduction happened which was more intense but with bigger standard errors in PI compared to Fvj. with an increase in mesosulfuron methyl + iodosulfuron methyl dose both PI and Fvj parameters were decreased. It could be concluded that these two parameters show special sensitivity to the mesosulfuron methyl + iodosulfuron methyl application and before the symptoms of the herbicide appears, they give a picture of physiological destructive effects of the herbicide.Whereas the Fvj parameters during all seven days after spraying shows a steady reduction with low standard errors, PI index shows reduction with higher standard errors which make the Fvj parameters more reliable. The two Fv/Fm and Area which were repeatedly reported as a sensitive factor to the stresses at this experiment were not appropriate indices. The common dose response methods of herbicide can be replaced by chlorophyll fluorescence measurements and it can offer fast, accurate, and an important information about herbicide efficiency very fast and accurate