CAA Fungicides
Membership

The Working Group is comprised of the following members:

Michael Merk (chairman) BASF SE, Cesano Maderno, Italy
Randall Gold BASF, Limburgerhof, Germany
Gerd Stammler BASF, Limburgerhof, Germany
Christoph Andreas Braun Bayer CropScience, Monheim, Germany
Dominique Steiger Bayer CropScience, Monheim, Germany
Marie-Pascale Latorse Bayer CropScience, Lyon, France
Martin Huttenlocher Feinchemie Schwebda, Köln, Germany
Luigi Burri Isagro Ricerca S.r.l., Novara Italy
Alessandro Bermano Isagro SpA, Milano, Italy
Satoshi Usami KI-Chemical, Brussels, Belgium
Isao Kaneko KI-Chemical, Brussels, Belgium
Helge Sierotzki Syngenta, Basel, Switzerland
Duncan McKenzie Syngenta, Basel, Switzerland
Introduction

The FRAC CAA Working Group was set up in 2005 to generate common resistance management recommendations for the Oomycete fungicides dimethomorph, flumorph, iprovalicarb, benthiavalicarb, mandipropamid and valifenalate.

All of the above-mentioned fungicides exhibit cross resistance and are grouped under the FRAC Code No. 40 in the FRAC Code List.

CODE TARGET SITE OF ACTION GROUP NAME CHEMICAL GROUP COMMON NAME COMMENTS
40 Cellulose synthesis CAA -fungicides
(Carboxylic acid
a
mides)
cinnamic acid amides

dimethomorph
flumorph

Low to medium risk. Resistance management required.
valinamide carbamates

benthiavalicarb iprovalicarb
valifenalate

mandelic acid amides mandipropamid

As shown in the table, the group name Carboxylic Acid Amides (CAA) has been chosen. This name best represents compounds from three different chemical groups.

The mode of action of CAA compounds is directly linked to the inhibition of cellulose synthesis in the Oomycete plant pathogen (Blum et al., 2010).

Uptake studies with 14C labelled Mandipropamid (MPD) showed that this Oomycete control agent acts on the cell wall and does not enter the cell. Furthermore, 14C glucose incorporation into cellulose was perturbed in the presence of MPD. Gene sequence analysis of cellulose synthase genes in laboratory mutants, insensitive to MPD, revealed two point mutations in the PiCesA3 gene, known to be involved in cellulose synthesis. Both mutations in the PiCesA3 gene result in a change to the same amino acid (Glycine-1105) in the protein.

Sensitivity monitoring studies over several years revealed that in populations of the late blight pathogen, Phytophthora infestans, all isolates were fully sensitive to CAA fungicides. However, in populations of the grape downy mildew pathogen, Plasmopara viticola, isolates can be found in certain regions, which are resistant to all CAA fungicides.

Inheritance studies (Gisi et al., 2007) showed that sexual crosses between sensitive and CAA resistant isolates of Plasmopara viticola lead to a co-segregation of resistance to dimethomorph, iprovalicarb, benthiavalicarb and mandipropamid, but not to the phenylamide, mefenoxam, which was tested in parallel as an independent marker.

Further, the inheritance studies showed that the gene(s) for resistance to CAA fungicides are inherited in a recessive manner. Therefore, the entire F1 generation of crosses between sensitive and CAA resistant isolates was sensitive, and only in the F2 progeny did CAA resistance reappear in some isolates. These results suggest that the resistance risk can be classified as moderate (as compared to high for phenylamide and QoI fungicides) and that it can be managed by appropriate product use strategies (see below).



Monitoring Methods

 
Contact



Dr. Michael Merk

Chairman

BASF Italia Srl
Cesano Maderno (Milan)
Italy
Tel. +39 0362 512-415 FAX: +39 0362 512-640 Email: michael.merk@basf.com

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