School of Engineering and Science - Jacobs University

More documents

Recommendations

Info

Introduction 2.1 Biological control of plant disease A promising alternative approach to minimize infectious plant disease is the application of antagonizing organisms with the ability to suppress pathogen development. This concept is referred to as “biological control” and the operative organism is called biocontrol agent (Wilson, 1997a). 2.1.1 Advantages and limitations The targeted use of microbial antagonists offers several benefits. Mass production of the active substance (i.e. fermentation of the control organism) is low-priced compared to chemical synthesis of pesticides (Shoda, 2000). Since biocontrol products can by applied by conventional techniques like spraying or drenching, their ability to proliferate and establish stable populations reduces application cost to a minimum (Montesinos, 2003). The impact of a biocontrol agent on the on indigenous microbial communities or other organisms in the ecosystem is less severe as compared to broad-spectrum pesticides (Emmert & Handelsman, 1999). Another significant advantage of biological control results from the flexibility of the control agent as living organism. The control organism can interact with a pathogen in many different ways and it is able to co-evolve with target and environment. This minimizes the risk of resistance formation and contributes to the potency of disease control (Emmert & Handelsman, 1999; Handelsman & Stabb, 1996). Biological control systems can be classified into three major groups: Rhizospherical biocontrol, biological control in the phyllosphere, and post harvest disease control. Post-harvest disease control offers the unique possibility to keep environmental conditions constant and adjust them in favor of the control organism (Janisiewicz & Korsten, 2002). Disease control in the rhizosphere underlies more variable conditions, yet root exudates provided by the plant stabilize nutrient supply and increase microbial density by orders of magnitude. Biocontrol agents have to cope with high microbial competition, but they can be assisted through direct support by the host plant (Weller et al., 2002). 3
Introduction In contrast to the rhizosphere, the phyllosphere represents a rather hostile environment with low nutrient content, sudden changes in temperature and humidity, and exposure to UV-radiation. These obstacles resulted in rather pessimistic predictions for biological control in the phyllosphere, but several control agents able to sustain these harsh conditions have been identified (Braun-Kiewnick et al., 2000; Ji & Wilson, 2003; Stromberg et al., 2004; Völksch & May, 2001b; Wilson, 1997b). The versatility of plant-associated microorganisms provides a large pool of potential biocontrol agents. Many screenings for disease suppressive strains have been conducted, yet the number of registered patents is rather low (Fig.1) and even less products have become commerciallized (Tab. 1; Agrios, 2005; Montesinos, 2003). Despite the advantages listed above, the practical significance of biological control in agriculture is negligible at present time. What is the reason for this? The biggest advantages of biological control, the flexibility of the control agent and its complex interactions with the environment, represent the biggest drawbacks of the system as well. First of all, in many cases there is no correlation between in vitro inhibition and in planta efficiency against the pathogen. This complicates screening for a suitable control agent. Even thriving 100 93 Number of patents 80 60 40 20 0 64 11 9 5 Bacteria Fungi Yeast Nematode Virus Biocontrol organism Fig. 1. Patents on biocontrol agents. Number of patents on biocontrol agents according to the type of active organism. Source: Montesinos, 2003 4
Page 1 and 2: Siderophore production of Pseudomon
Page 3 and 4: Acknowledgements This project was s
Page 5 and 6: Abbreviations Ach achromobactin-lik
Page 7 and 8: Contents 4.1.2 Pseudomonas syringae
Page 9 and 10: Contents 5.3 Influence of sideropho
Page 11: Introduction 2 Introduction Like hu
Page 15 and 16: Introduction 2.1.2 Host, pathogen a
Page 17 and 18: Introduction The relationship betwe
Page 19 and 20: Introduction developement of resist
Page 21 and 22: Introduction Fe 2+ + H 2 O 2 → Fe
Page 23 and 24: Introduction 1997a; May et al., 199
Page 25 and 26: Introduction Pss22d demonstrated a
Page 27 and 28: Introduction 2.4 Aim of this study
Page 29 and 30: Material and Methods Tab. 4. Antibi
Page 31 and 32: Material and Methods Iron-free 5b m
Page 33 and 34: Material and Methods Solution3, car
Page 35 and 36: Material and Methods 3.6 Plasmids T
Page 37 and 38: Material and Methods PCR-Screening
Page 39 and 40: Material and Methods on ice for 10
Page 41 and 42: Material and Methods stained in eth
Page 43 and 44: Material and Methods 4.2.5.3 Conver
Page 45 and 46: Material and Methods 4.2.5.9 Ligati
Page 47 and 48: Material and Methods strains were s
Page 49 and 50: Material and Methods 9.5). For sign
Page 51 and 52: Material and Methods gentle shaking
Page 53 and 54: Material and Methods columns were w
Page 55 and 56: Results 5 Results 5.1 Analysis of s
Page 57 and 58: Results The 13-kb open reading fram
Page 59 and 60: Results If integration is due to a
Page 61 and 62: Results Yersiniabactin is a siderop
Page 63 and 64:
Results Next, a large number of tra
Page 65 and 66:
Results Nevertheless the site of tr
Page 67 and 68:
Results Achr2_KpnI_rev binding site
Page 69 and 70:
Results Interestingly the mutant Ps
Page 71 and 72:
Results XAD4-purification yielded i
Page 73 and 74:
Results After changing the mobile p
Page 75 and 76:
Results P P A Fig. 21. Isoelectic f
Page 77 and 78:
Results reduced in comparison to th
Page 79 and 80:
Results A-E represents single inocu
Page 81 and 82:
Results Tab. 10. Development of pop
Page 83 and 84:
Results Tab. 11. Distribution of th
Page 85 and 86:
Discussion bacteria with redundande
Page 87 and 88:
Discussion 6.2 Possible regulation
Page 89 and 90:
Discussion stationary phase transit
Page 91 and 92:
Discussion and bacterium (Loper et
Page 93 and 94:
Literature Bultreys, A., Gheysen, I
Page 95 and 96:
Literature Galperin, M. Y. (2006).
Page 97 and 98:
Literature Mazzola, M. (2002). Mech
Page 99 and 100:
Literature Schubert, S., Rakin, A.,
Page 101:
Literature Zou, J., Rodriguez-Zas,
show all

School of Engineering and Science - Jacobs University

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?