Abstract

TONIN, R.B; REIS, E.M  and  GOMEZ, D.E. Sensibilidad a fungicidas in vitro de micelios de Drechslera siccans aislada a partir de trigo. RIA. Rev. investig. agropecu. [online]. 2015, vol.41, n.2, pp.192-200. ISSN 1669-2314.

The main leaf blight of wheat is yellow leaf spot caused by Drechslera tritici-repentis (Dtr). During the last growing seasons, producers noted the low rate of chemical control achieved its control. A new species of fungus, D. siccans (Ds), was identified when seeking to clarify the causes of failure in the control of Dtr isolates. It was found that Ds is associated to the yellow leaf spot symptoms in wheat. The events can be attributed to alterations in the sensitivity of Dtr or to the lowest sensitivity of Ds to fungicides. The objective of this study was to determine the in vitro mycelial sensitivity of Ds, isolated from wheat, to the fungicides. We tested demethylation inhibitor fungicides (DMIs) (cyproconazole, epoxiconazole, propiconazole, tebuconazole and prothiocona and quinone outside inhibitors (QoIs) (azoxystrobin, picoxystrobin, pyraclostrobin and trifloxystrobin) at seven concentrations: 0.00, 0.01, 0.10, 1.00, 10.00; 20.00 and 40.00 mg/L a.i. (active ingredient) and five fungus isolates. We evaluated mycelial growth by measuring the diameter of the colonies in agar cultures. The percentage of inhibition of mycelial growth was subject to logarithmic regression analysis and we calculated the IC50. The data shows a variation in the fungitoxicity in D. siccans isolates, ranging from nontoxic to highly fungitoxic. IDM fungicides presented the lowest IC50 (< 0.1 to 0.66 mg/L.) when compared to QoIs. The IC50 values for QoI ranged from 0.84 to 72.90 mg/L. A low sensitivity of the fungus is reported for the active ingredients azoxystrobin, trifloxystrobin and picoxystrobin in the studied isolates.

Keywords : Triticum aestivum; Yellow leaf spot; Fungitoxicity; IC₅₀.

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