Abstract
Chlorophyll fluorescence analysis is a simple and rapid method for detecting herbicide effects after a short time following their application in photosynthetic apparatus in plants. Chlorophyll fluorescence measurements were carried out against two broad of weeds to describe how the Kautsky curve and its parameters were affected by herbicides. Desmedipham + phenmedipham + ethofumesate changed the chlorophyll fluorescence induction curve at all time intervals except four hours after spring (HAS) in Amaranthus retroflexus L. and at all doses of Portulaca oleracea L. 4 HAS. In contrast, chlorophyll fluorescence inhibition was evident by chloridazon at doses of 650 and 325 g a.i. ha-1 in P. oleracea and A. retroflexus respectively, for all time intervals. Furthermore, chlorophyll fluorescence decays only occurred by clopyralid in A. retroflexus at the highest dose. A biomass effective dose (ED50 and/or ED90) based on log-logistic dose-response curves for A. retroflexus were considerably higher than that of P. oleracea. The maximum quantum efficiency (FV/Fm) was stable, whereas the relative changes at the J step (Fvj) and area (the area between the Kautsky curve and the maximum fluorescence (Fm)) was more sensitive to all three herbicides. There was a relatively good correlation between fluorescence parameters taken 24 hours after the spraying and the dry matter taken three weeks later, for both species under study.
Highlights
Light energy absorbed by leaf chlorophyll molecules, if not used in a photosynthetic pathway, is dissipated as heat or re-emitted as fluorescence
The ED50 and ED90 values of desmedipham + phenmedipham + ethofumesate were lower than chloridazon and clopyralid for A. retroflexus and P. oleracea at the cotyledon stage revealed that desmedipham + phenmedipham + ethofumesate were potent compared to other herbicides
We may recommend using desmedipham + phenmedipham + ethofumesate, which may show a better performance for weed control in sugar beet instead of chloridazon and clopyralid
Summary
Light energy absorbed by leaf chlorophyll molecules, if not used in a photosynthetic pathway, is dissipated as heat or re-emitted as fluorescence. These three processes take place in competition, and any rise in the efficiency of one will result in a decline in the yield of others (Maxwel and Johnson, 2000). An increase in the amounts of chlorophyll fluorescence emission is created with an illumination of 650 nm wavelength of healthy dark-adapted leaves with some trait phases. These phases primarily indicate photochemical events relevant to PSII (Govindjee, 1995). Three phases are found discovered on the O, J, I and P steps and depicted as follows: The O-J phase, complete reduction of the primary electron acceptor QA of PSII
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