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Occurrence of CAA fungicide resistance and detection of G1105S mutation in Plasmopara viticola isolates from vineyards in Sangli, Maharashtra, India

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Title Occurrence of CAA fungicide resistance and detection of G1105S mutation in Plasmopara viticola isolates from vineyards in Sangli, Maharashtra, India
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Creator S.D. Sawant, M.R. Ghule and I.S. Sawant
 
Subject Fungicide resistance, CAA fungicide, Downy mildew, Grapes
 
Description Not Available
Downy mildew, caused by Plasmopara viticola (Berk. & Curt.) Berl. & de Toni, is a destructive disease of grape (Vitis spp.), and it is controlled by fungicides including those from quinone outside inhibitors (QoI) and carboxylic acid amide (CAA) groups. Resistance to QoI fungicides in P. viticola was recently reported in India (Sawant et al. 2016). Downy mildew control failures were also observed from vineyards in Sangli, Maharashtra, India, where CAA fungicides were used for disease management. This study was conducted to detect the possible development of CAA resistance in P. viticola isolates in commercial vineyards in Sangli using biological and molecular methods. Four field isolates of P. viticolawere collected in October 2014 from three vineyards of Sangli district that were reported with failure of downy mildew control. These vineyards had a history of six to 13 applications of CAA fungicides in previous growing (fruiting) seasons but no CAA applications during the subsequent growing (vegetative) season. Infected leaf samples were brought to the lab in individual polypropylene bags (pp) and kept overnight in pp bags inserted with a wet paper at 22°C for sporulation. A sensitive isolate of P. viticola, collected from ICAR-National Research Centre for Grapes, was included for the study. Sensitivity to mandipropamid (Revus 23.4% SC, Syngenta, India) and dimethomorph (97%, BASF, India) was determined by leaf disc bio-assay in 24 well plates (FRAC 2013). Working solutions of 100, 50, 10, 1, 0.1, and 0 μg/ml concentrations were prepared by appropriate dilutions of the 1,000 μg/ml stock solutions using sterile distilled water. The experiment was conducted in completely randomized design (CRD) with four replicates. Fungicides were applied by camel hair brush to the abaxial surface of 15 mm leaf discs 24 h before inoculation. Discs were centrally inoculated with a 10 μl suspension of P. viticola containing 50,000 sporangia/ml and incubated at 22°C with alternating periods of 12 h light and dark. After 6 to 8 days, the lesion diameter was measured and converted to area. Then the percent area of infection was calculated, considering the area in control as 100%, and plotted against the log10fungicide concentration to obtain the EC50 value. The glycine to serine amino acid point mutation at position 1105 (G1105S) in the cellulose synthase gene (PvCesA3) (Blum et al. 2010) was detected by the PCR-RFLP method (Aoki et al. 2011). The P. viticola isolate from this center (ICAR-NRC for grapes) recorded less than 0.1 μg/ml EC50 values for both dimethomorph and mandipropamid, showing its sensitivity to CAA fungicides. The EC50values of the four isolates from the commercial vineyards were 54.28 to >100 for dimethomorph and 42.54 to >100 for mandipropamid, showing their insensitivity to the CAA fungicides. Furthermore, the 144-bp PCR product of PvCesA3 gene was not cleaved by AluIrestriction enzyme in the sensitive isolate from this center, while it was cleaved into a 107-bp and a 37-bp product in the insensitive isolates, confirming development of resistance. The frequent reports of failure of disease control and detection of resistance to CAA fungicides in P. viticola from three vineyards in Sangli, Maharashtra, India, requires concerted efforts for monitoring and mitigating the problem for successful management of downy mildew in commercial vineyards.
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Date 2017-05-31T06:06:05Z
2017-05-31T06:06:05Z
2017-01-01
 
Type Research Paper
 
Identifier S.D. Sawant, M.R. Ghule and I.S. Sawant
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http://krishi.icar.gov.in/jspui/handle/123456789/4222
 
Language English
 
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Publisher Not Available