Pathogen and chemical induction of systemic protection in broad bean and barley, and effects on plant growth and development

Boyle, Celia (2002) Pathogen and chemical induction of systemic protection in broad bean and barley, and effects on plant growth and development. PhD thesis, University of Glasgow.

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The efficacy of different fungal and chemical elicitors of systemic protection and their effects on plant growth and development were examined in barley (Hordeum vulgare) and broad bean (Vicia faba). Powdery mildew (Blumeria graminis syn. Erysiphe graminis f sp. hordei) of barley and rust (Uromyces viciae fabae) of broad bean, two biotrophic pathogens, were used as fungal elicitors to induce systemic protection in barley and bean respectively, and the upper leaves of plants were subsequently challenged with the same pathogens. Powdery mildew applied to the lower leaves of barley was found to induce systemic protection against powdery mildew in upper leaves. However, whole plant fresh and dry weight, and total leaf area was approximately 50% lower in barley 14 d after inoculation of the first leaves with mildew. The total number of leaves and tillers were also reduced by approximately 30%. Consequently, although there was a reduction in total infection in the mildew treated plants this was probably due to the reduction in growth. Rust infection was reduced in upper leaves of broad bean plants following inoculation of the lowest leaf with rust. However, it was only in plants challenged 6 d following the inducer inoculation that the reduction in infection was significant. This was consistent with reports that maximal gene expression associated with SAR in tobacco was attained for most of the genes 6 d after inoculation. The strength of the protection response was lower than in previous reports of systemic protection in bean induced by rust. The degree of protection produced in upper leaves may be related to the number of lower leaves inoculated with the inducing pathogen. Induction of resistance with rust had no significant effect on bean growth, except an increase in total leaf area in plants challenged 14 d after rust treatment. Due to the limited effect of rust induced protection on growth of bean plants, it was decided to investigate further the effect of rust on plant growth. Whole plant fresh weight, dry weight and total leaf area increased 1 wk and decreased 3 wk after inoculating three leaves of the plants with rust. This may be consistent with a transient increase followed by a decrease in photosynthesis that is thought to occur in rust infected leaves. Changes in water uptake were in accordance with inhibition of stomatal opening in the early stages of infection and later, increased transpiration due to rupture of the leaf cuticle caused by sporulation. Chlorophyll fluorescence analysis identified that rust infection resulted in Fo quenching and photoinhibition. In addition, rust infection was found to affect the photochemical efficiency of PSII reaction centres from 1 wk after rust inoculation. Non photochemical quenching was higher in controls compared with leaves on rust infected plants, except in healthy leaves on rust infected plants 4 wk after inoculation. This is indicative of increased metabolic activity and increased demand for ATP in the infected tissue. Phosphate, Salicylic acid (SA), and saccharin applied as a drench did have some detrimental effect on barley growth. In contrast, phosphate, SA and foliar applications of saccharin had no significant effect on growth of bean plants. Saccharin applied as a drench was more effective as an inducer of systemic protection compared with foliar application of saccharin. However, associated with the increased efficacy of saccharin when applied as a drench, was a detrimental effect on plant growth. In barley, chemical induced protection was found to be stronger in lower leaves, whereas in mildew induced protection, a significant response was only observed in leaves 3 and 4 and not in leaf 2. In broad bean, regardless of whether resistance was pathogen or chemically induced, the resistance response was stronger in the lower leaves, except with saccharin when the reverse was true. The differences observed may be related to signal strength. Saccharin was found to be a very effective inducer of systemic protection, but the mode of action is unknown. Consequently, the effects of saccharin on phenylpropanoid metabolism were examined. Saccharin was found to have no significant effect on lignin or free phenolic compounds. Despite the lack of increased PAL activity, enhanced CAD and peroxidase activity were observed. It is possible that the increase in PAL activity is transient and had occurred before the period examined. The increase in CAD activity in saccharin treated plants occurred both prior to and after inoculation with powdery mildew, which suggests that saccharin is priming CAD activity prior to pathogen challenge.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Plant sciences.
Subjects: S Agriculture > SB Plant culture
Colleges/Schools: College of Science and Engineering
Supervisor's Name: Walters, Prof. Dale
Date of Award: 2002
Depositing User: Enlighten Team
Unique ID: glathesis:2002-71068
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 10 May 2019 10:49
Last Modified: 18 May 2021 11:28

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