Sensitivity of western Canadian Pyrenophora teres f. teres and P. teres f. maculata isolates to propiconazole and pyraclostrobin

Figures & data

Table 1. The effective concentration of propiconazole (mg L⁻¹) required to inhibit fungal growth by 50% (EC₅₀) in eight isolates each of Pyrenophora teres f. teres (Ptt) and P. teres f. maculata (Ptm).

Ptt	Experiment 1	Experiment 2	Average	Ptm	Experiment 1	Experiment 2	Average
MB15	0.842	0.780	0.811	MB22	1.182	0.993	1.088
SK26	1.011	0.763	0.887	SK88	1.956	2.289	2.123
ABV01	1.236	0.786	1.011	SK69	1.367	3.052	2.210
SK24	1.340	0.876	1.108	AB82	2.064	2.453	2.259
ABV28	1.383	1.622	1.503	MB23	2.705	1.821	2.263
MB10	1.862	1.717	1.790	AB61	1.726	2.375	2.051
AB01	2.334	2.194	2.264	MBV37	2.116	2.809	2.463
AB38	3.043	2.935	2.989	SKV12	4.322	3.052	3.687
Average	1.632	1.459	1.545	Average	2.180	2.356	2.268

These isolates were randomly selected from across western Canada to establish a baseline sensitivity to propiconazole. A paired t-test indicated that there was no significant difference between EC₅₀ values calculated in each of the two independent experiments conducted for Ptt (P = 0.07) and Ptm (P = 0.61). Therefore, the two EC₅₀ values for each isolate were averaged. A log10-transformed fungicide concentration was used to linearize fungal growth inhibition (as a proportion of the control) to fit a regression line to estimate the EC₅₀ using probit analysis.

Fig. 1 Dose response curve of the mean fungal growth inhibition of representative Pyrenophora teres f. teres and P. teres f. maculata isolates from western Canada in response to propiconazole (a) and pyraclostrobin (b). Eight and 12 isolates each of Ptt and Ptm, respectively, were employed in the experiments with propiconazole (16 isolates in total) and pyraclostrobin (24 isolates in total). Three replicate wells were included for each combination of isolate and concentration. Experiments were conducted twice, and the mean fungal growth inhibitions were averaged. Growth inhibition is relative to non-amended control treatments.

Table 2. Propiconazole sensitivity of Pyrenophora teres f. teres (Ptt) and P. teres f. maculata (Ptm) isolates collected in 2009–2012 from Alberta, Saskatchewan and Manitoba, Canada.

Ptt	Per cent growth inhibition	Sensitivity	Ptm	Per cent growth inhibition	Sensitivity
AB28	95.2	Sensitive	ABV14	92.1	Sensitive
MB10	93.3	Sensitive	MB22	91.7	Sensitive
MB14	93.3	Sensitive	AB61	91.6	Sensitive
ABV01	91.4	Sensitive	SK100	90.5	Sensitive
SK16	90.7	Sensitive	SK87	89.8	Sensitive
SK41	90.2	Sensitive	AB57	89.2	Sensitive
MB02	90.0	Sensitive	AB68	86.1	Sensitive
SK53	89.3	Sensitive	AB82	82.6	Sensitive
ABV28	89.1	Sensitive	MB16	81.8	Sensitive
AB53	88.3	Sensitive	AB58	80.9	Sensitive
SK03	88.1	Sensitive	MB32	80.6	Sensitive
AB01	87.9	Sensitive	MB24	79.3	Sensitive
MB05	87.6	Sensitive	SK73	77.2	Sensitive
ABV18	87.1	Sensitive	SK88	75.5	Sensitive
AB04	86.1	Sensitive	SKV08	74.2	Sensitive
AB35	86.0	Sensitive	SKV10	72.4	Sensitive
SK05	85.9	Sensitive	SKV12	72.3	Sensitive
SK26	85.8	Sensitive	AB74	72.0	Sensitive
AB06	85.6	Sensitive	MB23	71.4	Sensitive
MB04	85.6	Sensitive	SK69	70.4	Sensitive
SK24	84.9	Sensitive	MB21	67.3	Intermediate
SK52	81.3	Sensitive	AB79	66.1	Intermediate
MB11	79.4	Sensitive	MBV25	64.7	Intermediate
SK08	78.9	Sensitive	MBV37	58.7	Intermediate
MB01	78.5	Sensitive	MB26	49.2	Intermediate
AB51	78.0	Sensitive	SK64	48.4	Intermediate
MB06	77.7	Sensitive	SK60	48.2	Intermediate
MB03	76.4	Sensitive
SK33	76.3	Sensitive
AB38	74.7	Sensitive
AB34	72.7	Sensitive
SK01	71.4	Sensitive
SK07	70.2	Sensitive
AB12	68.6	Intermediate
MB15	64.2	Intermediate
AB16	63.2	Intermediate
AB32	62.6	Intermediate
AB11	22.1	Insensitive
AB48	12.4	Insensitive

Sensitivity to propiconazole was assessed based on the reduction in fungal growth in a microtitre plate bioassay at a discriminatory dose of 5 mg L⁻¹. The endpoint optical density (OD) of samples in the 96-well microtitre plates was measured at 405 nm immediately after filling the plates. Plates were then incubated in darkness at 20°C for 7 days. Following incubation, the OD was measured and final values for absorbance were obtained by subtracting the values of the initial reading from those of the final reading. Subsequently, for each of the three isolate replicates, growth inhibition was calculated using the equation: 1 – [(absorption for the treatment /absorption of non-amended control)], and then averaged. The experiments were then repeated and the mean of the two growth inhibition values for each isolate was presented as a percentage.

Fig. 2 Frequency distribution of inhibition of fungal growth in 39 Pyrenophora teres f. teres and 27 P. teres f. maculata isolates from western Canada in response to 5 mg L⁻¹ propiconazole in potato dextrose broth. Inhibition of fungal growth is expressed as a percentage relative to a control treatment in which no propiconazole was included.

Table 3. The effective concentration of pyraclostrobin (mg L⁻¹) required to inhibit fungal growth by 50% (EC₅₀) in 12 isolates each of Pyrenophora teres f. teres and P. teres f. maculata.

Ptt	Experiment 1	Experiment 2	Average	Ptm	Experiment 1	Experiment 2	Average
MB03	0.002	0.003	0.002	SK69	0.004	0.012	0.008
MB10	0.003	0.001	0.002	AB74	0.009	0.01	0.009
MB01	0.007	0.001	0.004	AB58	0.005	0.014	0.01
AB38	0.002	0.006	0.004	MBV25	0.011	0.013	0.012
SK01	0.006	0.009	0.008	AB82	0.007	0.024	0.016
ABV28	0.01	0.007	0.009	MB23	0.013	0.019	0.016
SK53	0.009	0.01	0.01	MB22	0.023	0.026	0.024
MB15	0.002	0.018	0.01	SKV12	0.036	0.015	0.026
AB01	0.014	0.012	0.013	AB61	0.04	0.026	0.033
ABV01	0.021	0.026	0.024	SK88	0.026	0.042	0.034
SK26	0.026	0.043	0.034	SK60	0.025	0.062	0.043
SK24	0.056	0.062	0.059	MBV37	0.059	0.063	0.061
Average	0.013	0.017	0.015	Average	0.021	0.027	0.024

Four isolates from each of the three provinces of Alberta, Saskatchewan and Manitoba, Canada, were selected randomly to establish the baseline sensitivity to pyraclostrobin. A paired t-test indicated that there was no significant difference between EC₅₀ values calculated in each of two independent experiments conducted for Ptt (P = 0.13) and Ptm (P = 0.20). Therefore, the two EC₅₀ values for each isolate were averaged. A log10-transformed fungicide concentration was used to linearize fungal growth inhibition (as a proportion of the control) to fit a regression line to estimate the EC₅₀ using probit analysis.

Table 4. Pyraclostrobin sensitivity of Pyrenophora teres f. teres (Ptt) and P. teres f. maculata (Ptm) collected in 2009–2012 from Alberta, Saskatchewan and Manitoba, Canada.

Ptt	Per cent growth inhibition	Sensitivity	Ptm	Per cent growth inhibition	Sensitivity
ABV28	100	Sensitive	AB79	100	Sensitive
SK01	100	Sensitive	SKV10	99.9	Sensitive
MB05	100	Sensitive	SKV12	99.6	Sensitive
MB04	99.8	Sensitive	MB32	99.2	Sensitive
AB53	99.5	Sensitive	AB58	99.2	Sensitive
MB06	99.4	Sensitive	MB24	98.6	Sensitive
MB15	99.2	Sensitive	AB68	98.1	Sensitive
AB51	99.1	Sensitive	ABV14	97.9	Sensitive
MB10	98.4	Sensitive	AB74	97.0	Sensitive
SK08	98.3	Sensitive	SK69	96.0	Sensitive
MB02	98.3	Sensitive	SK88	95.8	Sensitive
AB34	97.9	Sensitive	MBV25	95.8	Sensitive
AB38	97.6	Sensitive	AB61	95.7	Sensitive
AB04	97.4	Sensitive	SK60	95.0	Sensitive
SK41	97.2	Sensitive	MB26	94.5	Sensitive
SK03	96.8	Sensitive	MB23	94.2	Sensitive
SK05	96.6	Sensitive	MB21	93.7	Sensitive
MB11	96.1	Sensitive	MBV37	92.6	Sensitive
AB16	96.0	Sensitive	SK73	89.2	Sensitive
SK33	94.9	Sensitive	AB57	85.5	Sensitive
MB01	94.7	Sensitive	AB82	83.5	Sensitive
MB14	94.5	Sensitive	SK87	64.3	Intermediate
MB03	93.2	Sensitive	SKV08	58.8	Intermediate
AB01	91.9	Sensitive	MB16	49.6	Intermediate
AB48	90.3	Sensitive	MB22	48.8	Intermediate
SK53	90.3	Sensitive	SK100	38.3	Intermediate
AB12	89.9	Sensitive	SK64	23.8		Insensitive
AB35	86.1	Sensitive
SK52	85.4	Sensitive
SK26	85.4	Sensitive
AB06	85.3	Sensitive
ABV18	84.4	Sensitive
AB11	81.1	Sensitive
SK07	75.3	Sensitive
AB32	72.3	Sensitive
AB28	63.2	Intermediate
SK16	61.7	Intermediate
SK24	44.9	Intermediate
ABV01	40.5	Intermediate

Sensitivity to pyraclostrobin fungicide was assessed based on the reduction in fungal growth in a microtitre plate bioassay at a discriminatory dose of 0.15 mg L⁻¹. The endpoint optical density (OD) of samples in the 96-well microtitre plates was measured at 405 nm immediately after filling the plates. Plates were then incubated in darkness at 20°C for 7 days. Following incubation, the OD was measured and final values for absorbance were obtained by subtracting the values of the initial reading from those of the final reading. Subsequently, for each of the three isolate replicates, growth inhibition was calculated using the equation: 1 – [(absorption for the treatment /absorption of non-amended control)], and then averaged. The experiments were then repeated and the mean of the two growth inhibition values for each isolate was presented as a percentage.

Fig. 3 Frequency distribution of inhibition of fungal growth in 39 Pyrenophora teres f. teres and 27 P. teres f. maculata isolates from western Canada in response to 0.15 mg L⁻¹ pyraclostrobin in potato dextrose broth. Inhibition of fungal growth is expressed as a percentage relative to a control treatment in which no pyraclostrobin was included. Experiments were performed in the presence of 100 mg L⁻¹ salicylhydroxamic acid (SHAM).