Abstract

MOLINA-VARGAS, Luis Federico  and  MELO-MARTINEZ, Sandra Esperanza. Importance of the statistical method applied to calculate the EC₅₀ and EC₉₅ of some isothiocyanates evaluated against Rhizoctonia solani Kühn. Agron. colomb. [online]. 2010, vol.28, n.2, pp.235-244. ISSN 0120-9965.

Framed in the evaluation of the effect of some isothiocyanates (ITC) on the growth of Rhizoctonia solani Kühn, the present research also studied whether the applied statistical method determines significant differences in the values of the Median (EC₅₀) and 95 (EC₉₅) effective concentrations of these compounds. For this purpose, we conducted an in vitro experiment in which said values were calculated by different statistical methods. In vitro efficacy against R. solani AG-3 was tested of allyl isothiocyanate (AITC), benzyl isothiocyanate (BITC), phenyl isothiocyanate (PITC), phenethyl isothiocyanate (PEITC) and methyl isothiocyanate (MITC). Under constant shaking we prepared stock solutions by mixing ITC with methanol as solvent, to get concentrations of 0.0, 0.01, 0.1, 1.0, and 10%, corresponding to the different studied treatments; each of which consisted in the addition of 50 mL of one of these solutions to the experimental units. The latter were Petri dishes containing potato-dextrose-agar medium (PDA) and mycelium of R. solani AG-3. These containers were then sealed with two layers of parafilm and incubated at room temperature. Digital pictures were taken to obtain the colony areas using MapMaker 3.5^® software, 72 and 144 hours after the treatments were applied. The Median (EC₅₀) and 95 (EC₉₅) effective concentrations were calculated through linear and non-linear (Gompertz, logistic, and polynomial models) regressions, as well as probit analysis. The values obtained through the latter were found to be considerably different from the actual ones, which in turn coincided with those found by means of linear regressions. All of ITC at 10% concentration were completely inhibitory, with the exception of PEITC. Whereas BITC was fungistatic up to twenty one days after the treatments were applied, PITC, AITC, and MITC had a longer fungistatic effect, even one year after treatment application.

Keywords : Gompertz; logistic; polinomic; Probit; regressions.

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