Use of Linear Correlation between in Vitro And in Vivo Tests for Evaluating Efficiency of Some Fungicides in Controlling Net Blotch of Barley (Hordeum Vulgare)

Drechslera teres, the causal agent of net blotch of barley (H.  vulgare L.), is a seed-borne and foliar pathogen. In the present study, six fungicides (Epoxiconazole, Azoxystrobin, Iprodion, Propiconazole, Thiophanate methyl and Mancozeb) were tested in vitro for their inhibitory effects against D. teres. Fungicidal toxicity was expressed as a percentage inhibition of mycelial growth. Inhibition concentration, which reduced 50% of mycelial growth (Ic₅₀) was calculated for each tested active ingredient. Among tested fungicides triazoles (Epoxiconazole and Propiconazole) were the most effective with Ic₅₀ values of 0.254 and 0.263 mg/L respectively. In contrast, Thiophanate methyl showed the greatest Ic₅₀ values was 334.584 mg/L compare with the other fungicides. These fungicides were evaluated in the field at two locations; Kafre El-Hamam and Sakha Agricultural Research stations in Sharkia and Kafre El.Sheikh governorates during 2014/2015 growing season. The first three fungicides were used as seed dressing alone (single application) or with one foliar spray (double application), and the second three fungicides were used as one or two sprays. Experiments carried out in planta under field conditions showed variation between fungicides in disease control, 1000 kernel weight (TKW), and grain yield/plot. The variable performance of the tested fungicides could be attributed the different active ingredient, application method, and the changing environmental conditions from one location to another. Triazoles fungicides also, showed greater efficacy than other fungicides. The correlation between both assays in vitro and in vivo showed that I_C50 could be used as a complementary and not as an alternative to field trials to evaluate the performance of the tested fungicides.