Novel plant bio-protectants based on Trichoderma spp. strains with superior characteristics
Abadi, Khalid M. (2008) Novel plant bio-protectants based on Trichoderma spp. strains with superior characteristics. [Tesi di dottorato] (Inedito)
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Global warming caused by the greenhouse effect will alter the geographical distribution of host and pathogen populations, thus affecting the natural physiology of their interaction and reducing the efficacy of chemical and biological control strategies presently used in agriculture. In perspective to this scenario, new management practices will be required. The main task of this thesis was to isolate and characterize new biocontrol agents of the genus Trichoderma originating from Libya, where these fungi are the most applied antagonists in the country’s agriculture. The intention was to obtain microbes having a natural adaptability to function in adverse climate conditions (low rainfall, drought, extreme temperatures, poor soil quality, etc.) and actively control plant pathogens. Three pure cultures of Libyan isolates, Lib1, Lib2 and Lib3, were isolated and characterized from different agricultural areas in the northwestern part of Libya. An integrated approach to species characterization using morphological, physiological and molecular techniques was used. The Libyan isolates showed an improved mycelia growth on enriched medium (PDA) at 30°C compared to controls. In plate confrontation assays with fungal pathogens, temperature did not affect the antagonistic abilities of Libyan isolates; in fact, both at 25°C and 30°C the the Libyan isolates reduced growth of Rhizoctonia as well as the biocontrol strain T22, but a lower antagonistic effect was registered against Alternaria and Fusarium spp. The biotechnological use of the isolated strains in bioremediation projects was also be assessed and preliminary results have shown that the isolated microbes can withstand, not only high temperatures, but also toxic compounds like MTBE. The analysis of the ribosomal DNA ITS sequences, through homology searches in GenBank database, identified the Lib1 and Lib3 isolates as T. longibrachiatum strains, while Lib2 is T. harzianum. Further, the metabolic profile of Libyan isolate Lib1 was similar to that observed in a T. longibrachiatum strain able to produce Trichogin A IV as major compound. New possible applications of the selected Trichoderma strains as plant growth promoters and inducers of systemic resistance were evaluated. The results varied according to the combination of plant cultivar and the Trichoderma strain tested, but they were comparable to those of the biocontrol strain T. harzianum T22 whose growth promoting activity is well known. This finding may represent the starting point for novel applications of biocontrol in Libya. A novel bio-pesticide based on the Libyan Lib1 Trichoderma isolate that has demonstrated superior characteristics was developed and analyzed. The bio-formulate contains the living fungus, mycelia and conidia, and a mixture of Trichoderma originating compounds capable of stimulating plant defense response and growth, as well as directly controlling pathogenic microbes. Conditions optimizing both the growth and development of the living organism and the natural substances that the fungus produces were tested, including different substrates, inducing agents, agitation, aeration, preservatives and conservation compounds. The final product was prepared by liquid fermentation in selected inexpensive media, showed sufficient shelf-life, and retained the multiple beneficial effects of the living fungus useful for application in numerous agricultural situations.
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