Bioassay of metalaxyl in plant tissue

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Abstract
SUMMARY: A method for determining the concentration of metalaxyl in methanolic extracts of plant tissue is described. Extracts were applied to filter papers in Petri dishes and covered with small volumes of lima bean agar. The growth of an isolate of Pythium ultimum sensitive to metalaxyl was related to the quantity of fungicide applied. The bioassay could detect quantities as low as 0·025 μg in the filter paper, a sensitivity which was confirmed by using 14C‐metalaxyl. Whilst untreated extracts of lettuce and brassicas were not fungitoxic to the isolate of P. ultimum employed, this was not the case with tobacco and grape‐vine. Hence alternative test organisms may be required before the method can be generally applied to all species.