Growth responses of Pinto bean and alfalfa to sublethal fluoride concentrations

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Abstract
Empirical observations of several species of plants fumigated with fluoride during a 10-year period have shown these to grow more rapidly than non-fumigated control plants. The present study was initiated to determine quantitatively the validity of these observations on Pinto bean (Phaseolus vulgaris L. var. Pinto) and alfalfa (Medicago sativa L.). When plants were fumigated with fluoride, growth was accelerated and internode development was conspicuously greater than in control plants. Fresh and dry plant weights were positively correlated with increasing fluoride content of the leaves. Statistically significant correlation coefficients of 0.91 and 0.98 were calculated between fluoride content and fresh and dry weights, respectively. When fluoride content exceeded approximately 200 p.p.m., weights decreased below those of the controls. Leaf chlorosis did not develop until foliar fluoride concentrations exceeded approximately 500 p.p.m.Fluoride sometimes stimulated growth of alfalfa plants but results were inconsistent and no statistically significant relation existed between foliar fluorides content and plant weights. However, dry weight of plants analyzing over 500 p.p.m. fluoride was only 63% that of the control plants despite the absence of any chlorosis or necrosis.

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