Thesis Abstract and Dissertation Abstracts
Analysis of the effects of environmental factors on Trichoderma and breeding for antagonistic strains
Abstract Category: Science
Course / Degree: Molecular and cell biology
Institution / University: University of Szeged, Hungary
Published in: 2001
The Trichoderma genus, due to the antagonistic features of some of its members against phytopathogenic fungi, and their outstanding extracellular enzyme production abilities, is the subject of extensive investigations. Since antagonism is a feature associated not with the species, but with certain strains, the isolation from the environment of Trichoderma strains best suited to the varied agricultural environment and industrial expectations, the selection of promising strains, the investigation of antagonistic abilities and the production of extracellular enzymes, and the breeding of the strains are in progress to this day. The work of our research group is also connected to these topics.
At first we examined the in vitro antagonistic abilities of six Trichoderma strains against plant pathogenic fungi. All of the strains were able to significantly inhibit the colony growth of the plant pathogens, in some cases the Trihoderma strains overgrew them.
Between the strains involved in our experiments the T. viride T124 has the most favourable properties for the purposes of biological control, so the preliminary examination of extracellular enzyme systems was carried out with this strain. We examined the aspecific chitinase, protease and ƒÒ-1,3-glucanase activities of this strain on different carbon- and nitrogen sources. The activity levels of the selected enzymes was higher in the case of NaNO3 as nitrogen source than in the presence of NH4Cl, while glycerol as carbon source had more favourable effects on secretion than mannitol. All of the examined enzymes were repressable by certain carbon- and nitrogen sources.
While numerous different enzyme systems together reveal the background of the antagonistic ability of Trichoderma strains with biocontrol potential, the detailed examination of the extracellular enzyme profiles of Trichoderma strains is of serious practical importance. We examined the enzyme profiles of extracellular ƒÒ-glucosidase, cellobiohydrolase, endocellulase, ƒÒ-xylosidase, endoxylanase, trypsin- and chymotrypsin-like protease, ƒÒ-1,4-N-acetyl-glucosaminidase and laminarinase in the case of six Trichoderma strains belonging to three different species groups, the profiles of the enzymes showed significant similarities between the examined strains.
The competitive abilities of Trichoderma species are significantly influenced by different environmental parameters, like temperature, water conditions, the presence of pesticides, heavy metals and antagonistic bacteria in the soil. When planning the application of biocontrol strains it is suggested to collect information about the effects of such parameters on the activities of Trichoderma species, because biocontrol agents should have better stress tolerance levels than the pathogens against which they are going to be used during biological control.
We examined the effects of water potential and temperature on the growth of a Trichoderma harzianum strain, and on the secretion and in vitro activities of enzymes ƒÒ-glucosidase, cellobiohydrolase, ƒÒ-xylosidase, ƒÒ-1,4-N-acetyl-glucosaminidase and chymotrypsin-like protease produced by this strain. Higher water potential values resulted in higher linear growth rate. Enzyme secretion was influenced by water potential in liquid cultures, different water potential values proved to be optimal for the secretion of the different enzymes. Temperature and water potential had significant effect on the in vitro activities of the examined enzymes, however, based on our results, the enzymes of T. harzianum could remain active even at water potential values completely inhibiting mycelial growth. So breeding Trichoderma strains for xerotolerance could result in biocontrol strains effective against plant pathogenic fungi even in soils with lower water potentials.
We also examined the effects of three fungicides and four herbicides on the growth and in vitro activities of extracellular enzymes of our strains. In the case of the examined herbicides the IC50 concentrations were found to be so high, which values can not be present in the soil during their application. However, the fungicide susceptibility of our strains may cause problems during their combined application with antifungal compounds, for such purposes fungicide resistant mutants should be applied.
Because of their different point of attack, the pesticides did not influence the activity of the extracellular enzymes produced by the Trichoderma strains.
Several pesticides applied in the paractice of plant protection contain different heavy metals, thus they may have unfavourable effects on biocontrol Trichoderma strains, when combined with them. We examined the effects of ten heavy metals (aluminium, copper, nickel, cobalt, cadmium, zinc, manganese, lead, mercury and iron) on the linear mycelial growth of our strains and on the in vitro activities of their enzymes involved in antagonism against plant pathogenic fungi (ƒÒ-glucosidase, cellobiohydrolase, ƒÒ-xylosidase, endoxylanase, ƒÒ-1,4-N-acetyl-glucosaminidase, trypsin-like protease, chymotrypsin-like protease and ƒÒ-1,3-glucanase). Based on our results the extracellular enzymes could remain active under heavy metal concentrations which strongly inhibit mycelial growth.
The susceptibility of biofungicide Trichoderma strains to bacteria has detrimental effects on their biocontrol activity, the application of strains with good antagonistic properties against bacteria for the purposes of biological control is therefore reasonable. We examined the bacterium-degrading ability of three strains, which proved to be variable in the degree and specifity of degradation. Based on or results, the strains produced both ƒÒ-1,4-N-acetyl-glucosaminidase and proteases in low, constitutive level, and the presence of bacterial cells induced the enzyme secretion of the strains. Two of our strains produced bacterium-tolerant sectors by spontaneous mutation in the presence of Bacillus subtilis.
More attention should be paid to the mutagenic methods of breeding of biocontrol Trichoderma strains, because strains bred by mutagenesis can get registration for on field use from environmental protection agencies more easily than strains produced by protoplast fusion, or transformation. We isolated 177 heavy metal resistant mutants by UV-mutagenesis from the six investigated Trichoderma strains. Cross-resistance was found in several cases when the mutants were tested on the heavy metals, this makes possible the one-step development for mutants resistant to more heavy metals. Some of our mutants were effective antagonists of the plant pathogenic test organisms even on media containing the respective heavy metals. Such mutants might be the preferred choice for combined application with heavy metal-containing pesticides in the frame of a complex integrated plant protection.
For the further breeding of our strains we developed transformation systems based on hygromycin B resistance. In several cases we could reach optimal transformation frequencies. The compact morphological mutants isolated from strain T. viride T124 could also be transformed to hygromycin B resistance. The development of methods resulting in high transformation frequencies is of great importance: such methods are valuable not only for the insertion of extracellular enzyme genes, they might also be used for breeding for heavy metal resistance eg. via the expression of heterologous methallothionein genes.
Thesis Keywords/Search Tags:
Trichoderma, ecophysiology, water activity, metal tolerance, strain improvement
This Thesis Abstract may be cited as follows:
No user preference. Please use the standard reference methodology.
Submission Details: Thesis Abstract submitted by Laszlo Kredics from Hungary on 22-Nov-2004 15:25.
Abstract has been viewed 3698 times (since 7 Mar 2010).
Laszlo Kredics Contact Details: Email: kredics@bio.u-szeged.hu
Disclaimer
Great care has been taken to ensure that this information is correct, however ThesisAbstracts.com cannot accept responsibility for the contents of this Thesis abstract titled "Analysis of the effects of environmental factors on Trichoderma and breeding for antagonistic strains". This abstract has been submitted by Laszlo Kredics on 22-Nov-2004 15:25. You may report a problem using the contact form.
© Copyright 2003 - 2024 of ThesisAbstracts.com and respective owners.