The response of tomatoes to atrazine as affected by magnesium and photoperiod Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/v405sd57d

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  • Studies were conducted to determine the nature of the interaction between atrazine (2-chloro-4-ethylamino-6-isopropylaminos- triazine) and magnesium on tomatoes. This interaction was studied under two light regimes: continuous light and a 12-hour photoperiod. Tomato plants were grown in sand cultures at three levels of magnesium fertilization. Four weeks after planting, atrazine was added to the pots containing the plants. The rate of growth of plants grown at the highest magnesium level was much greater than that of those grown at the lowest magnesium level. The high magnesium level helped overcome the toxicity of atrazine. This interaction was more significant under continuous light than under the 12-hour photoperiod. Similar experiments using diuron (3-(3, 4- dichlorophenyl) -1, 1- dimethylurea), linuron (3-(3, 4-dichloropheny1)-1-methoxy-l-methylurea), and bromacil (5-bromo-3-sec-butyl -6-methyluracil) showed that magnesium significantly reduced the toxicity of these herbicides when tomato plants were grown under continuous light conditions. An experiment was conducted to determine the growth responses of tomato plants grown at two levels of magnesium fertilization and two light regimes. Continuous light increased plant dry weight over the 12-hour photoperiod plants for the first 35 days, however, after this time the rate of growth of plants grown under the 12-hour photoperiod was greatest. Continuous light became lethal to tomato plants after about 35 days. This conclusion was based on visual observations. Leaves on plants grown under these conditions began to dry up and fall off. Chlorophyll analysis showed that the chlorophyll content of tomato plants grown under a 12-hour photoperiod was approximately twice that of plants grown under continuous light. The chlorophyll content of tomato plants receiving magnesium was also nearly twice that of plants receiving no magnesium. Two experiments were conducted using an infra-red gas analyzer to measure CO₂ exchange. Each experiment involved two levels of magnesium and four levels of atrazine. These experiments were nearly identical, the only difference being that one was conducted under continuous light and the other was conducted under a 12-hour photoperiod. Atrazine at rates of 1/32 and 1/16 ppm increased respiration when measured at six hours after application but decreased respiration after this period. CO₂ fixation was decreased at all atrazine rates when measured at six hours after application and later. The plants that were treated with atrazine at rates of 1/32 and 1/16 ppm began to recover and fix CO₂ after about 24 hours following herbicide application. Plants receiving high magnesium levels recovered much more rapidly than those receiving no magnesium. These differences in recovery rate between magnesium treatments were observed in both light regimes but were noticeably greater under continuous light than under the 12-hour photoperiod.
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