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| Author(s): |
Deise Renata Gonzalez Agnani
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC) |
| Defense date: | 2002-04-23 |
| Advisor: | Adriana Parada Dias da Silveira |
| Abstract | |
Studies on interactions of arbuscular mycorrhizal fungus (AMF) and other rhizospheric microorganisms have shown the effect of AMF on these microorganisms and vice versa. Species of the genus Trichoderma have been used to control root pathogens. This fungus produces some extracellular enzymes that degrade fungal cell wall, what is considered an important factor of biocontrol. Plant growth-promoting rhizobacteria, such as some Pseudomonas of the fluorescent group, can act in root pathogens biocontrol, producing antagonist substances or siderophoros. Besides, it is known the importance of organic matter as a factor of soil improvement, decreasing soil and rhizosphere pathogens. One of the major citrus diseases is the root rot caused by Phytophthora parasitica. Our purposes were to study the interactions that may occur in rhizosphere and host plant in the presence of P. parasitica, AMFs and biological control agents; to evaluate the effect of different substrates in this microbe interaction and to select rhizospheric bacteria to control P. parasitica in vitro (B King media, carrot media and wheat seeds) and in vivo, using Citrus limonia. The first experiment had the purpose of evaluating the microbe interactions in plants, using an inert substrate, testing the effect of AMF (Glomus intraradices inoculated at seed nursery- GI before transplanting, or, G. intraradices inoculated at transplanting- GI), biological control agent (Trichoderma harzianum and Bacillus subtilis) and the pathogen (P. parasitica). A second experiment had a factorial 3x3x2 completely randomized design, where the factors were: biological control agents (T. harzianum, B. subtilis and no agent), AMFs (G. intraradices, G. etunicatum and no AMF), P. parasitica (with and without), with previous, afterwards and concurrent inoculation of AMF and biological control agent. A last experiment had a factorial 2x2x2x3 completely randomized design, where the factors were: T. harzianum (with or without), G. intraradices (with or without), P. parasitica (with or without), substrates (soil with addition of 2 kinds of organic matter- dairy manure and plantmax- and no addition). The plant growth was enhanced by AMF and biological control agents inoculated previously or concurrently with AMF, observing that these antagonists did not affect the radicular colonization. There was disease control in treatments 1° Tri/GE, 1° GI/Tri, exclusively with Trichoderma and Bacillus inoculation. In vitro assays showed that Pseudomonas sp isolates 80S, A5 and I6 were antagonists to the pathogen. Most of the bacteria isolates, 78%, showed pathogen control in vivo and root weight was not affected by the presence of P. parasitica. When using inert substrate (sand) all treatments controlled P. parasitica. The radicular colonization with no pathogen inoculation was significantly higher with previous AMF inoculation. Trichoderma decreased significantly the AMF colonization when it was inoculated previously. Colonized plants by G. intraradices and GI+ Tri, inoculated or not with P. parasitica, showed a significantly higher growth in the 3 substrates tested. The mycorrhizal plants, in the presence or absence of Trichoderma, controlled P. parasitica. (AU) | |