Glyphosate effect on growth and aflatoxin B1 production by Aspergillus flavus strains isolated from soil.

BARBERIS C.L.; CARRANZA M.C.; BERGESIO M.V.; FERNÁNDEZ- JURI M.G.,; MAGNOLI A.P.,; MONGE M.P.,; DALCERO A.M; CHIACCHIERA S.M.; MAGNOLI C.E,

Rotterdam

Congreso; The World Mycotoxin Forum IUPAC, 7th Conference of the world Mycotoxin Forum and XIIIth IUPAC International Symposium on Mycotoxins and Phycotoxins; 2012

The use of agricultural pesticides as increased during the past years for insect, pest and dideases control in Argentina. Glyphosate has been reported as a toxicological and environmental safe herbicide, the potential non-target effects of glyphosate on soil microorganisms are still a topic of much concern amongst stakeholders in soil conservation. The aim of the present study was to evaluate the effect of glyphosate on (i) lag phase (ii) growth rate and iii) aflatoxin B production of A. flavus strains on corn meal extract agar under different environmental conditions. Four strains of A. flavus isolated from soil destined to corn crop were used (AFS 54, AFS 56, AFS 57 and AFS 63). CMEA was used at 3%. The aW of the basic medium was adjusted to 0.98, 0.95 and 0.93 with the addition of glycerol, after autoclaved, different levels of glyphosate (0.5, 1.0, 1.5, 2.0, 5.0 and 10 mM) were added. The plates were centrally needle-inoculated and incubated for 28 days at 25ºC. Two diameters of the colony at right angles to each other were daily measured. The radius of the colony was plotted against time, and a linear regression was applied in order to obtain the growth rate. The lag phase was obtained by extrapolation of this line to the x axis. At 14, 21 and 28 days, three agar plugs were removed from different points of the colony and extracted with l of chloroform, the mixture was agitated, the chloroform extract was taken and injected into the HPLC. In the control treatments there was an increase in the lag phase and a decrease on growth rate when aW decreased for all strains assayed. The lag phase show a further increased at highest concentrations of glyphosate. A significant increase in growth rate was observed from 0.5 mM of herbicide at 0.93 and 0.95 aW. At 0.5 mM and 0.98 aW, the glyphosate not affected significantly the growth, over 2.0 mM, AFS 56 and AFS 57 showed and significant increase on growth rate, the same fact was observed for AFS 54 and AFS 63, now over 5 mM of glyphosate. The optimum aW level for AFB1 production was 0.98 and 7 days of incubation, resulting 0.95 and 0.93 in a reduction in the level of toxin produced. AFB1 production was slightly influenced by the presence of different glyphosate concentrations at all aW and times of incubations assayed. These results showed that glyphosate could significant influence on growth and aflatoxin production by A. flavus strains.