Monitoring the effects of bentazon, betanal progress and nicosulfuron herbicides on Kautsky curve changes

Background and objectives: A large part of the light is consumed by photosynthesis, and the rest is discharged as heat or fluorescence in plants. The more the plant's photochemical process, the lower the amount of fluorescence. For this reason, chlorophyll fluorescence acts as an internal probe of photosynthesis and is actually a common method in plant physiology. This research aims to investigate whether the changes in the shape of the kautsky curve affected by nicosulfuron, bethanal progress and bentazon herbicides have the ability to prove their site of action.

Materials and methods: This experiment was conducted based on a completely randomized design with 8 replications in 2023 in the Research Greenhouse of the Faculty of Agriculture of Gonbad Kavous University. The treatments included applying the recommended dose of bentazon (Bazagran 48% SL), desmedipham + phenmedipham + ethofumesate (bethanal progress 27.4% EC) in addition to the treatment without herbicide as a control. In the case of nicosulfuron (Cruz 4% OD), a dose of 150% of the recommended dose was also added. Herbicides were applied at the 4-5 leaf stage of Amaranthus retroflexus and the plants were harvested 28 days after spraying (DAS) and their dry weight was measured. Fluorescence meter that emits light with a wavelength of 650 nm and an intensity of 3000 μmol photons per square meter per second measured chlorophyll fluorescence for 10 seconds, from dark adapted leaves for 30 minutes each day at 10:00 a.m.

Results: results showed that the control Kautsky curve had all the stages of a normal Kautsky curve, but in the bentazon treatments, it started to change from the first DAS, and these changes became more obvious in the following days, so that on the fourth and fifth DAS, all its steps disappeared and became a straight line, and the amount of fluorescence also decreased. Nicosulfuron, had no effect on the shape of the Kautsky curve. for betanal progress, the standard form of the curve was disturbed and its steps were lost. Another point is the increase in the amount of chlorophyll fluorescence, which caused a decrease in the upper area of the kautsky curve between the minimum fluorescence (F0) and the maximum point of fluorescence (Fm), known as the Area parameter.

Discussion: Inhibition of photosystem II is the primary effect of two herbicides, bentazon and betanal progress, which was clearly obtained from the shape of the corresponding curves, even the type of proteins involved.

The disappearance of all the steps of the Kautsky curve in bentazon showed that all parts related to the reduction of quinone A and the protein pathway of electron transfer between quinone A and B were disturbed. In the betanal progress, the significant increase in chlorophyll fluorescence along with the fading of some curve steps, including J-I and I-P, caused a decrease in the value of the Area parameter, which indicates the destruction of the plastoquinone pool. While in nicosulfuron, Kautsky's curve was not able to provide enough evidence. The Katsky curve was a good indicator for early detection of the effects of PSII-inhibiting herbicides and determining their site of action, but it is not for nicosulfuron.