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ARS Home » Plains Area » Fargo, North Dakota » Edward T. Schafer Agricultural Research Center » Sunflower and Plant Biology Research » Research » Publications at this Location » Publication #147653
Title: FIRST REPORT OF RESISTANCE TO METALAXYL IN DOWNY MILDEW (PLASMOPARA HALSTEDII) OF SUNFLOWER IN SPAIN

Author
item MOLINERO-RUIZ, M - I.A.S.-C.S.I.C., SPAIN
item MELERO-VARA, J - I.A.S.-C.S.I.C, SPAIN
item Gulya Jr, Thomas
item DOMINGUEZ, J - C.I.F.A., CORDOBA, SPAIN

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2003
Publication Date: 6/1/2003
Citation: Molinero-Ruiz, M.L., Melero-Vara, J.M., Gulya Jr, T.J., Dominguez, J. 2003. First report of resistance to metalaxyl in downy mildew (Plasmopara halstedii) of sunflower in Spain. Plant Disease. 87(6):749.

Interpretive Summary: The fungus causing downy mildew of sunflower has been controlled for the past two decades using a single, seed-applied fungicide, metalaxyl, sold as APRON. The downy mildew fungus, as with other fungi, eventually developes resistance to fungicides to the point where the chemical no longer controls the disease. This "metalaxyl resistance" was first observed in downy mildew isolates from France in 1996 and in the United States in 1998. The note records the first observation of metalaxyl resistance in Spain. With the continuing occurrence of this fungicide resistance, it is imperative that other control options be explored, namely the use of genetic resistance and/or the use of a different, unrelated fungicide.

Technical Abstract: Fifty-two isolates of Plasmopara halstedii Farl. Berl. & de Toni (causal agent of sunflower downy mildew collected from sunflower (Helianthus annuus L.) in Spain during 1994-2000 were evaluated for metalaxyl resistance. Apron 20% LS was applied to seed of susceptible sunflower `Peredovik' at 2.0 g a.i./ kg seed. Two replications of 40 plants were established and inoculations were repeated three times. Two-day-old untreated and treated seedlings were dipped in a suspension of 60 x 103 sporangia/ ml for 4 h, planted in sand and perlite (2:3 vol/vol) and grown at 16-21 C with a 12-h photoperiod. After 12 days, sporulation and systemic chlorosis were evaluated in plants. Metalaxyl provided total control of 51 isolates. The remaining isolate caused symptoms in 67% of treated plants. This isolate was tested in another experiment where `Peredovik' seed was treated with metalaxyl at doses of 0, 0.5, 2.0, 3.5 and 5 g a.i./kg seed, with four replications of 12 seedlings/ treatment. The incidence of downy mildew was similar on all treated plants, except at the highest rate, which is twice the labeled European rate. This is the first report of resistance of sunflower downy mildew to metalaxyl in Spain.