Effect of soilpH and temperature on the biological control of Rhizoctonia solani by Bacillus megaterium and Trichoderma harzianum
Dal Soglio, Fabio Kessler
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https://hdl.handle.net/2142/21766
Description
Title
Effect of soilpH and temperature on the biological control of Rhizoctonia solani by Bacillus megaterium and Trichoderma harzianum
Author(s)
Dal Soglio, Fabio Kessler
Issue Date
1995
Doctoral Committee Chair(s)
Eastburn, Darin M.
Department of Study
Crop Sciences
Discipline
Crop Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Microbiology
Agriculture, Plant Pathology
Language
eng
Abstract
The root rot and seedling blight of soybean, caused by Rhizoctonia solani isolate 2B-12 and controlled by Bacillus megaterium and Trichoderma harzianum, was the disease/biocontrol model used for a systematic study of the effect of soil pH and temperature on the biological control of soilborne plant pathogens. In vitro experiments showed that T. harzianum isolate Th008 was antagonistic to R. solani and compatible to B. megaterium strain B153-2-2. Under greenhouse conditions, disease was more severe at soil pH 7.0 than 5.5 and at soil temperature of 25 C than at 15 or 35 C. Trichoderma harzianum and Bacillus megaterium achieved disease control, but it was dependent on soil conditions. When antagonists were used in combination, a synergistic effect was observed at soil pH 5.5, but not at pH 7.0. Bacillus megaterium was responsible for the improvement of root colonization by Trichoderma harzianum, especially at soil pH 5.5. Rhizosphere colonization by T. harzianum, when it was alone, was more effective at soil pH 7.0 and high temperatures than at pH 5.5 and low temperatures. Soil populations of B megaterium increased with increase of soil temperature. The study shown that the system of host/pathogen/antagonist/environment exists in a very delicate balance, which knowledge may permit the improvement of biological control of soilborne pathogens by introduced or indigenous antagonists.
A method using the combination of HPLC and colorimetric assays was developed for determination of the origin of chitinolytic enzymes and ($\beta$ 1$\rightarrow$3) glucanase in soybean rhizosphere during resistance/pathogenicity/antagonism process. This method could be used for study the effect of soil factors in the mechanism of antagonism of T harzianum. Trichoderma harzianum and soybean produced in culture $\beta$-N-acetylhexosaminidase, chitobiosidase, endochitinase and ($\beta$ 1$\rightarrow$3) glucanase, and R. solani 2B-12 produced all these enzymes but endochitinase. Under greenhouse conditions, cv. Williams 82 seeds, noninoculated or inoculated with Th008, were planted in soil noninfested or infested with 2B-12. At day 15 after emergence, the rhizosphere was assayed for enzyme activity. Trichoderma harzianum did not controlled the disease but was responsible for production of endochitinase. $\beta$-N-acetylhexosaminidase production was related to root infection by 2B-12, probably associated with plant resistance mechanism.
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