Phytotoxicity index

The values obtained for each parameter examined can be transposed into phytotoxicity classes each parameter is used to classify the substrate in a given phytotoxicity class. A classification system was developed for the parameters studied on Phaseohts vulgaris cv. Limburgse vroege and is presented in Table 6-4. The phytotoxicity index for a given substrate represents the mean value of the toxicity class numbers obtained for each parameter separately. 

The sensitivity of plants to mercury compounds are different. In general, the fungitoxic concentration does not harm the seeds and bulbs of the plants the therapeutic index of mercury compounds for seed treatment is therefore satisfactory. Potato seed is an exception because it is susceptible to many species. However, only aryl mercury compounds are suitable for foliage application, and these only in the case of certain plants or in certain stages of development. Thus, phenylmercury acetate or chloride are not phytotoxic to apple trees in the prebloom period. Arylmercury compounds are not phytotoxic to the rice plant at all. Phytotoxicity is mainly caused primarily by mercury vapours formed on the reduction of mercury compounds (Hitchcock and Zimmermann, 1957). According to Lee et at. (1973), mercury compounds inhibit the biochemical reactions of the electron transport of photosynthesis, depending on the pH value and on the concentration. 

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