CONCLUSIONS 
In vitro fungicide tests are extensively used in the 
initial evaluation of potentially valuable fungicides. 
In recent years these tests have provided valuable in- 
formation on the toxicity of various chemical structures 
and their modes of action against fungi. 
The methods of testing to determine the fungi- 
toxicity of chemicals are extremely varied and are 
constantly changing. This probably means that an 
acceptable method that can be universally used as a 
standard procedure is yet to be developed. The pro- 
cedures for fungicide testing should be quick, easy, 
and simple and the results should be reliable, re- 
producible, and usable. 
In vitro fungicide tests are used not only to deter- 
mine fungitoxicity of test chemicals but also range 
and degree of susceptibility of fungi, deposition and 
redistribution of fungicides, stability to resist chemical 
change, tenacity to resist rainfall and wind, and per- 
sistence to resist other degrading elements. The re- 
sults from these in vitro tests often will explain why 
a fungicide performed well or poorly in the field, 
When a varied group of in vitro tests are per- 
formed in the laboratory, the candidate fungicides 
most likely to give satisfactory protection to plants 
will be selected for continued greenhouse and field 
testing. Not all of the complex chemical and en- 
vironmental conditions of disease development can be 
reproduced either in the laboratory or the greenhouse. 
The introduction of plants or plant parts into in vitro 
tests does more closely approach natural conditions, 
and the use of these techniques will probably increase 
in the future. 
At present there are no practical substitutes for in 
vitro tests for the initial screening of candidate fungi- 
cides. Thus these tests are invaluable as one of a 
series of steps required in the evaluation of fungicides, 
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