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Poster: Biology & Disease Mgmt: Chemical Control


Progress towards a novel chemical control for common scab disease of potato
R. TEGG (1), H. Thompson (2), C. Wilson (1) (1) Tasmanian Institute of Agriculture, University of Tasmania, Australia; (2) Department of Agriculture, Australia

Common scab is a globally important potato disease caused by pathogenic Streptomyces spp. with no one effective control strategy. Essential for disease induction is the production by the pathogen of the toxin, thaxtomin A. This study sought to develop disease control options targeting the interaction of thaxtomin A with the host, using novel chemical applications. Trials identified two compounds, 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,5-dibromobenzoic acid (2,5-DBB) that when applied to the foliage of newly emerged plants prior to tuber initiation, could significantly reduce common scab tuber disease incidence and severity by over 85%, compared to the untreated control. Seed tuber treatments with 2,4-D prior to planting were also effective at reducing disease although the level of control was not as great as from foliar treatments. Disease resistance was correlated with decreased sensitivity of the tuber material from treated plants to thaxtomin A. High application rates (>200mg/L) of 2,4-D were associated with negative traits including twisted foliage, tuber deformation and yield loss. Further trials demonstrated that greatly reduced 2,4-D application rates down to 1.7-25mg/L retained effective disease control but avoided detrimental phytotoxicity effects. Field trials within Australia, China and USA testing foliar and seed treatments are on-going, with initial results indicating useful field efficacy of these chemical treatments for disease control.