Plant Pathology (1997) 46, 897-909

H.R. Kataria, B. Wilmsmeier and H. Buchenauer (1997)
Efficacy of resistance inducers, free-radical scavengers and an antagonistic strain of Pseudomonas fluorescens for control of Rhizoctonia solani AG-4 in bean and cucumber
Plant Pathology 46 (6), 897-909
Abstract: Sixteen chemicals from different groups of known resistance inducers were tested as a soil drench in a humosoil : sand mix infested with an isolate of Rhizoctonia solani AG-4. Among these, 5-nitrosalicylic acid (2 mM aqueous solution), o-acetylsalicylic acid (2 mM), 2,6-dichloroisonicotinic acid (0.25 mM), 2-aminoisobutyric acid (2 mM) and lichenin (2 mM) controlled pre-emergence damping-off and post-emergence seedling mortality of bean cv. Dufrix, but gave little or weak and variable disease control in cucumber cv. Delikatess. Two-component mixtures of these five chemicals controlled the disease effectively in bean, mixtures containing 2-aminoisobutyric acid being the most effective, with seedling stands of up to 94% in infested soil. As none of these five chemicals (< 2 mM) reduced mycelial growth of R. solani on PDA plates, induced resistance in seedling tissues is implied in their disease control. Control was augmented in both hosts when any one of the five inducers was applied in a mixture with a cell suspension (1 x 10⁹ cells mL^-1) of an antagonistic fluorescent strain of Pseudomonas fluorescens; these mixtures showed additive effects and provided much better disease control in bean than in cucumber. The free-radical scavengers (antioxidants) ascorbic acid, benzoic acid, gluconic acid lactone and thiourea inhibited R. solani growth in vitro and efficiently controlled both pre-emergence damping-off and post-emergence seedling mortality of bean; ascorbic acid and benzoic acid also offered significant protection in cucumber. However, disease control values were reduced substantially when inducers were applied with antioxidants, because of strong antagonistic interactions in most of these mixtures. Probable mechanisms of disease control by 5-nitrosalicylic acid, o-acetylsalicylic acid, 2,6-dichloroisonicotinic acid, 2-aminoisobutyric acid and lichenin and their interactions with P. fluorescens and antioxidants are discussed.
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Research topic(s) for pests/diseases/weeds:
resistance/tolerance/defence of host
biocontrol - natural enemies
Research topic(s) for beneficials or antagonists:
general biology - morphology - evolution

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Rhizoctonia solani	Beans (Phaseolus)
	Rhizoctonia solani	Cucumber (Cucumis sativus)
Pseudomonas fluorescens (antagonist)	Rhizoctonia solani	Beans (Phaseolus)
Pseudomonas fluorescens (antagonist)	Rhizoctonia solani	Cucumber (Cucumis sativus)