Submitted to: Biocontrol Science and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/20/2005
Publication Date: 5/20/2005
Citation: Ahn, B., Paulitz, T.C., Jabaji-Hare, S., Watson, A. 2005. Enhancement of colletotrichum coccodes virulence by inhibitors of plant defense mechanisms.. Biocontrol Science and Technology. 15:299-308. Interpretive Summary: Colletotrichum coccodes is a mycoherbicide being developed to control velvetleaf, an important weed in Eastern Canada. This is part of a program to reduce the use of herbicides by using natural pathogens of weeds. However, the plant can often overcome the effects of inoculating with this fungus. Various chemicals were tested to see if they could enhance the virulence of this fungus by inhibiting the plant defenses in the target weed. These chemicals did not reduce disease, possibly because of their direct anti-fungal effect on the pathogen or because of the lack of defense targets in the plan.
Technical Abstract: alpha;-Amino-oxyacetic acid (AOA), 2-deoxy-D-glucose (DDG), mannose, and oxalic acid were tested as possible synergizers to enhance the efficacy of Colletotrichum coccodes, as a biological control agent of Abutilon theophrasti. All the chemicals reduced C. coccodes conidia germination and appressoria formation, but the virulence of C. coccodes was significantly enhanced when C. coccodes was applied to A. theophrasti after mannose and oxalic acid were vacuum-infiltrated through the leaf cuticle. Lipophilic analogues, 1-amino-ethyl-phosphonic acid diisopropyl ester of oxalic acid, oxalic acid diammonium salt, and 4,6-di-O-methyl-D-mannose, did not result in more severe disease on velvetleaf and there was no impact on A. theophrasti growth. These results may be due to strong antifungal effects, possible functional changes due to chemical structural changes, size of the chemical molecule, or lack of inhibitory effect of these chemicals on plant defense mechanisms. It is also possible that the defense mechanisms that these chemicals can influence are not active in A. theophrasti. Comprehensive understanding of the defense mechanisms of A. theophrasti that limit C. coccodes infection and ways to breach these defense strategies should result in improved weed suppression.