Sensitivity of Phytophthora infestans population in Peru to Mefenoxam and Cymoxanil W. Pérez 1, J. Lara 2 and G.A. Forbes 1 1 International Potato Center, Lima, Peru 2 Universidad Nacional Agraria La Molina, Lima, Peru
42% of Peruvian potato growing area is endemic for Late blight Losses between US$ 7 to 25 millions/year
Climate conducive to LB Subsistence and semi commercial farmers Huánuco (351,239 t/year) First Growing potato area Susceptible potato varieties
Farmers spraying fungicides (94.7% ) Number of sprays: 6.6 ( 0-14 ) 1-5 sprays (63%) 6-10 sprays (32%) 11-14 sprays (5%) Fungicides more used: Metalaxyl Cymoxanil Mefenoxam
Lineage: EC-1 PE-3 US-1 PE-7 Lineage EC-1 PERU Mating type: Isoenzyme: GPI PEP Mt DNA: Metalxyl resistance: A1 90/100 96/100 II a Resistant
Objectives: To establish a baseline sensitivity for Mefenoxam and cymoxanil To provide a preliminary evaluation of the risk resistance fungicide
Materials and methods: Fifty eight isolates collected in 1999-2005 All EC -1, mating type A1, all resistant to metalaxyl (Previous results) Metalaxyl resistance test R CONTROL 5 ppm 50 ppm 100 ppm S R MR if growth > 40% of the 0 ppm control at 100 ppm if growth <40% of the control at 100 ppm, but not at 5 ppm S if growth < 40% of the 0 ppm control even at 5 ppm (Therrien et. al. 1993)
In Vitro assays: Method emended Agar (V-8 juice) Mefenoxam 95.9% (a.i.) Cymoxanil 98.3 % (a.i.) 10 Concentrations 0.01 to 1000 ppm Stock in DMSO 6 Concentrations 0.01 to 4 ppm Stock in DMSO Incubation at 18 C for 10 days 58 isolates
Mean colony diameter (minus diameter of the inoculation plug) Four replications/ isolate/concentration Relative mycelia growth (RMG) Dx = Mean growth diameter on the emended medium RMG = 100 ( Dx 1mm ) ( Dy 1mm ) Dy = Mean growth diameter on non emended agar Daayf and Platt, 2002 EC 50 analyzed by Probit analysis (Statistical Program R)
In Vivo assays: Detached leaf Mefenoxam 95.9% (a.i.) 0.01 ppm to 1000 ppm Stock in DMSO Cymoxanil 98.3 % (a.i.) 0.001 ppm to 4 ppm Stock in DMSO Five isolates with low In vitro EC 50 Concentration 3000 sp/ml Incubation at 18 C for 6 days, photoperiods of 12 hr
Detached leaf Area foliar disease Foliar area calculated by Sigma Scan Pro EC 50 analyzed by Probit analysis (Statistical Program R)
In Vivo assays: Mefenoxam 95.9% (a.i.) 0.01 to 5000 ppm Sotck in DMSO Whole plants Cymoxanil 98.3 % (a.i.) 0.001 to 1024 ppm Stock in DMSO Isolate with the lowest EC 50 in Detached leaf assays Concentration 3000 sp/ml, spray run off Incubation at 18 C for 6 days, photoperiods of 12 hr
( arcsenx 1) ) Whole plants Percentage of disease foliar area (7 d.a.i.) Percentages transformed by (arcsen x -1) EC 50 analyzed by Probit analysis (Statistical Program R)
Results Sensitivity to Mefenoxam EC50 values (ppm) Mefenoxam Assays Range Mean SD In vitro 1 374.17-778.52 583.73 83.32 In vivo Detached leaf 2 261.79 809.97 559.06 225.3 Whole plants 3 781.19 1 Data from 58 isolates 2 Data from 5 isolates selected 3 Data from 1 isolate selected
Reports worldwide of EC 50 values of Phytopthora infestans isolates to Metalaxyl. Fungicide EC50 Values Range mean Method 0.00002-1 mg/l 0.2 mg/l Petri dish 10-277 mg/l 47 mg/l Petri dish Reference Power et. al. (1995) Metalaxyl > 100 ppm a Petri dish Sujkowski et. al (1995) >200 ppm a Whole plants >200 ppm a Detached leaf Sozzi an Staub (1987) 100 ppm a Petri dish 07-90 ppm Petri dish 01-70 ppm Whole plant Klinkennberg et. al. (1998) 1000 2000 µg/ml b Detached leaf Holmes and Channon (1984) 182 c Petri dish Porter et al (2007) a Values not considered as range. Values reported as sensibility up to or more than this value. b Authors reported treatment with metalaxyl at 1000 or 2000 µg/ml was associated with phytotoxic symptoms. c Value reported for P. erythroseptica Equivalence : 1ppm = 1mg/l, 1µg/g, 1mg/kg
Sensitivity to Cymoxanil EC50 values (ppm) Cymoxanil Assays Range Mean SD In vitro 1 0.22 1.05 0.49 0.16 In vivo Detached leaf 2 1.67 3.06 2.24 0.51 Whole plants 3 60.69 1 Data from 58 isolates 2 Data from 5 isolates selected 3 Data from 1 isolate selected
Reports worldwide of EC 50 values of Phytopthora infestans isolates to Cymoxanil. Fungicide EC50 Values Range mean Method Reference 0.06-1.48 mg/l 0.42 mg/l Petri dish 0.22 mg/l b 0.46 mg/l c Petri dish Hamlen and Power (1998) 0.22 mg/l b 0.50 mg/l c Petri dish Cymoxanil < 10 ppm a 0.8 ppm Petri dish 3 mg/l Detached leaf Sujkowski et. al (1995) Gisi et. al (1997) Ziogas and Davidse (1987) 1 µg/ml Petri dish 0.04-0.52 mg/l 0.17 mg/l Petri dish 0.10-1.48 mg/l 0.3 mg/l Petri dish Power et. al. (1995) a Values not considered as range. Values reported as sensibility up to or more than this value. b Values reported pre-commercialization of the fungicide. c Values reported after 10 or more years after commercialization. Equivalence : 1ppm = 1mg/l, 1µg/g, 1mg/kg
Commercial fungicide formulations based on metalaxyl (Mefenoxam) and Cymoxanil commercialized in Peru. Common name a Commercial dose ppm b Metalaxyl 35% 150-250 g/ 200 L 262.5-437.5 Mancozeb 64% + Metalaxyl 8% 2-3 kg/ Ha or 50 g/ 20 L 200 Cupper hydroxide 46 % + Cymoxanil 6 % 0.5 kg / 200 L 150 Mancozeb 64 % + Cymoxanil 8 % 500 g / 200 L 200 Propineb 70 %+ Cymoxanil 6% 0.5-0.6 Kg / Cylinder 150-180 a Current active ingredients commercialized in Peru b 1 ppm = 1 mlg / L Mean EC 50 values (ppm( ppm) ) reported in this study Assays Mean EC 50 values (ppm) Mefenoxam Cymoxanil In vitro 583.73 0.49 Detached leaf 559.06 2.24 Whole plants 781.19 60.69
Conclusions: Baseline sensitivity established for Mefenoxam and cymoxanil in Peru High risk for resistance to Mefenoxam Low risk for resistance to cymoxanil
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