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Next generation, environmental friendly plant protection against bacterial pathogens

 

 

An important strategic aim for Norway is the support of rice cultivation especially in underdeveloped regions (e.g. see the Noragric Report No. 71., made by Norwegian University of Life Sciences, Faculty of Social Sciences, Dept. of International Environment and Development Studies). This development offers an environmentally friendly solution to get higher yields and greater productivity, therefore we can ensure secure livelihood for people living in underdeveloped regions. With this technology we can replace some currently used illegal or non-environmentally friendly products such as human antibiotics used for agricultural production. The causative agent of bacterial blight of rice (Xanthomonas oryzae pv. oryzae) is a quarantine pathogenic organism, against which there are currently no effective plant protection products. Xanthomonas oryzae pv. oryzae is a gram-negative bacterium which enters the rice through natural openings and wounds. The bacterium invades the vascular system and spreads through the xylem vessels, causing wilting of the plant (Agrios et al., 2005, Plant Pathology, Elsevier Press). Xoo causes serious economic losses mainly in Asia, therefore the export of the pesticide developed by Enviroinvest Corp. is expected. Bacterial leaf blight mostly occurs in the monsoon season (Nino-Liu et al., 2006, Mol. Plant. Pathol.: 303-324). Rice breeders try to develop resistant species against the disease. In 2009, the Vietnamese ambassador visited our predecessor’s laboratory in Szekszárd and interested in bacteriophage based pesticide against bacterial blight. Due to the lack of resources, the project was not implemented. The disease can destroy 80% of the crop. Copper and other antibiotics are ineffective in the treatment of the disease (http://www.thehindu.com/news/national/kerala/article2509635.ece). The application of bacteriophages as biocontrol agents can be an alternative option. Phages are specific viruses that infect only bacteria. The discovery of bacteriophages was reported by Frederick Twort in 1915 and Felix d'Hérelle in 1917. Immediately after their discovery, the thought of using phages for fighting bacterial infections was already apparent (Sincler Lewis, Arrowsmith). After the development of penicillin in 1928 therapeutic use of phages decreased. This was mainly due to the fact that there were no molecular biological methods with which the genetic characterization of phages could have been performed. In the absence of this, the use of phages would have been risky (we did not know, which DNA fragments can be integrated from the host bacterium into the phage’s genome) and the isolation of different strains were impossible. However, less than 5 years after the application of penicillin 50% of the Staphylococcus aureus isolates developed resistance against it. Methicillin was developed in 1959, but methicillin resistant S. aureus strains have been found in 1961. The fight against pathogens never ends; new antibiotics are discovered and introduced but sooner or later the bacteria become resistant. If we use phages instead of antibiotics, the resistance of bacteria become limited. As bacteria evolve resistance, the relevant phages naturally evolve alongside. It is faster and cheaper to develop new phages than new antibiotics. Nowadays, the phage-based biocontrol is again in the focus of attention (Waldor et al, 2005). Advantages of phage therapy over the use of antibiotics and pesticides: • Bacteriophages are self-replicating as well as self-limiting. Bacteriophages replicate exponentially as long as the specific bacteria are available in abundance. With a decreasing amount of bacteria, the number of phages declines too. • Bacteriophages are natural component of the biosphere. • Bacteriophages are non-toxic to the eukaryotic cells (Greer, 2005). • They are host species- or strain specific, therefore they are harmless to the soil bacteria. It means that environmental impact of their application is minimal because they will infect only the pathogen bacterium species which is intended to be attacked, living e.g. the soil microflora intact. • Phage based products can be developed and produced easily. They can be stored at +4°C for long time (Greer, 2005). Furthermore, most of the agrochemicals has no effect on phages (Zaccardelli, 1992). • They can be used as biocontrol agents. • They totally decompose in the environment because they contain only proteins and DNA. • They could be applied also for bio-production. It is important to note, that the phage based products cannot be regarded as static as traditional pesticides or antibiotics. They need constant development, which means new phages are needed to isolate and characterize. This procedure is cost effective and the costs can be included in the prize. Thanks to the developments, we constantly get new scientific information about bacteriophages and phage-host interactions.

 

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