A dissertation submitted in partial fulfilment of the requirements of the degree of
Master of Science
in
Environmental science
School of Animal, Plant and Environmental Sciences
University of Witwatersrand, Johannesburg. March 2017. / Plant growth promoting rhizobacteria (PGPR) promotes plant growth in a variety of modes of action and also suppresses several phytopathogens causing plant diseases. There is evidence that Pseudomonas strains are able to induce systemic resistance, thereby enhancing the defensive capacity of many plant species, and they do so without any negative impact on the environment. Currently, many agricultural systems rely more on the use of chemical pesticides to combat plants diseases. The chemicals have several negative impacts on both human health and the environment. Therefore, there is need to investigate the ability to fight plant pathogens of alternatives like the Pseudomonas spp that do not harm the environment. Several strains of this genus are yet to be tested to see if they induce systemic resistance. Previous studies showed that bio surfactants produced by Pseudomonas koreensis exhibited strong effect against oomycetes P. ultimum in tomato plants. Induced systemic resistance (ISR) potential of P. koreensis following exposure to viruses has not been fully demonstrated to date. This study sought to investigate whether this strain has an effect on viruses and if it is able to induce systemic resistance against viral pathogens. The study started by growing the model plant N. benthamiana. The second stage involved carrying out assays of tobacco mosaic virus (TMV) after inoculating this virus in three bio treatments: (i) seed treatment of N. benthamiana with P. koreensis (referred to as the early treatment), (ii) root treatment at the transplanting stage (late treatment) and (iii) the control. In bio treatments (i) seeds were first sterilized by dipping them into 70% alcohol for 3 minutes and 0.1 % HgCl2 for 1 minute and washing them with distilled water. Each seed was then soaked into 20ml of bacteria suspension for 30 minutes and in (ii) a litre of P. koreensis culture was then poured onto the roots of 36 N. benthamiana plants. The bacteria suspension was added at 107 colony forming units per gram of soil to each tray. It was observed that disease severity was lower in the P. koreensis plant treatments than for the control. Results of this investigation have shown that
P. koreensis can induce systemic resistance in foliar parts when plant seeds or roots are inoculated with this strain. This was demonstrated by separation of plant growth promoting rhizobacteria (PGPR) bacteria and TMV. Seeds and roots were inoculated with bacteria while the leaves were inoculated with TMV. The early bio treatment had the lowest mean number of necrotic lesions, and exhibited the mildest effects from TMV compared to the late bio treatment and control. Plants in the late bio treatment were moderately affected while the control was severely affected (P˂0.0001) ˂0.05. The early and the late bio treatment both had higher leaf surface area than the control; (P˂0.0001) ˂0.05. The early bio treatment lost the fewest leaves, and the late bio treatment lost a moderate number while the control lost the highest number (P˂0.0001)˂0.05.The reduced symptoms exhibited by plants inoculated with P. koreensis is an indication that P. koreensis has anti-viral activity against TMV. It was concluded that P. koreensis can reduce plant‟s viral susceptibility and result in ISR. It is hence proposed that P. koreensis can be used as a biological control (bio control) agent against viruses.
Key words: Tobacco Mosaic Virus (TMV), Pseudomonas koreensis (P. koreensis), induced systemic resistance (ISR) / LG2018
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/24992 |
| Date | January 2017 |
| Creators | Nyamuvurudza, Spiwe |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (ix, 77 leaves), application/pdf |
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