The impact of three pre-plant herbicides, pendimethalin, prometryn and trifluralin on the incidence and the development of Rhizoctonia solani-induced cotton seedling damping-off, on biocontrol activity of Burkholderia cepacia against R. solani, and on the efficacy of commonly used fungicides (metalaxyl, triadimenol, thiram) against R. solani-induced cotton seedling damping-off was investigated in the microcosm and in the field. In the microcosm experiments, pendimethalin, prometryn and trifluralin were applied to the soil at 2.4, 3.6 and 1.8 μg a.i. g⁻¹ soil, respectively (equivalent to the respective recommended field concentrations of 0.9, 1.3 and 0.7 kg a.i. ha⁻¹ In the microcosm experiments application of prometryn, to the soil caused a significant (P < 0.05) increase in pre-emergence damping-off incidence. Post emergence damping-off increased significantly (P < 0.05) in the presence of pendimethalin and prometryn. Biocontrol activity of B. cepacia (isolate D1) in controlling cotton seedling damping-off was significantly (P < 0.05) reduced by pendimethalin and prometryn in the microcosm experiments. In a field experiment conducted in Safford, Arizona, pre-plant application of pendimethalin or prometryn caused significant (P < 0.05) increases in disease incidence. In another field experiment in Tucson, Arizona, significant (P < 0.05) increase in disease incidence was observed in plots treated with prometryn. In both microcosm and field experiments, application of herbicides affected disease development as judged by the slope of disease progress curves. Biocontrol activity of an indigenous isolate (D1) of B. cepacia also was reduced significantly by pendimethalin and prometryn in both field experiments. Commercially available isolate (Deny®) of B. cepacia as a soil drench and as a seed treatment failed to protect cotton seedlings against R. solani-induced damping-off in both field experiments. The efficacy of commonly used fungicides (metalaxyl, triadimenol, thiram) against R. solani in the field was not significantly affected by herbicides in two field experiments at final assessment time. Pendimethalin and prometryn mediated changes in cotton seedling damping-off incidence and biocontrol activity of B. cepacia seem to be due to the changes in cotton seedlings susceptibility and changes in populations and structure of antagonistic bacteria in the plant rhizosphere.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/282570 |
| Date | January 1997 |
| Creators | Heydari, Asghar, 1955- |
| Contributors | Misaghi, Iraj J. |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | en_US |
| Detected Language | English |
| Type | text, Dissertation-Reproduction (electronic) |
| Rights | Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. |
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