UV-B priming for disease resistance : the use of UV-B light to reduce susceptibility of lettuce plants to downy mildew disease : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Pathology at Massey University, Manawatū, New Zealand

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dc.confidentialEmbargo : Noen_US
dc.contributor.advisorWargent, Jason
dc.contributor.authorMcLay, Emily
dc.date.accessioned2020-03-03T22:36:06Z
dc.date.accessioned2020-11-13T03:10:06Z
dc.date.available2020-03-03T22:36:06Z
dc.date.available2020-11-13T03:10:06Z
dc.date.issued2019
dc.descriptionThese Figures were removed for copyright reasons: 1.1 (=Bent & Mackey, 2007 Fig 1a ), 1.4 (=Camagna & Takemoto, 2018 Fig 3) & 1.7 (=Redovnikovic et al., 2008 Fig 4).en
dc.description.abstractBiotrophic disease is one of the largest causes of decreased yield in horticulture. Integrated Pest Management (IPM) systems are required to control disease in a manner which is effective and sustainable, yet there are still a limited number of new approaches available. Pretreatments of UV-B light (280-320 nm) have been previously observed to reduce plant susceptibility to disease, and may be a potential disease control tool to use as part of an IPM approach. Here, I characterised the capability of UV-B LED technology to reduce susceptibility of a range of lettuce (Lactuca sativa) cultivars to downy mildew disease caused by the obligate biotroph Bremia lactucae. Reductions in disease susceptibility of UV-B-pretreated plants was observed as: delayed disease incidence, reduced visual disease rating and lower B. lactucae conidia count. UV-B-induced reductions to conidia counts were sufficient to reduce the infectivity of the diseased plant. Secondary infections caused by UV-B-pretreated plants exhibited yet further reduced disease severity. UV-B light has been observed to induce a similar gene expression profile to that of disease defence in plants. To determine the mechanism of a UV-B-induced disease defence, similarities between UV-B and disease defence pathways were identified. Analysis of previously published gene expression data revealed similarities in flavonoid-related gene expression between exposure to UV-B light in Arabidopsis thaliana, and resistance to downy mildew (Hyaloperonospora arabidopsidis). The specific role of flavonoids in UV-induced defence was further investigated, with B. lactucae conidia counts of lettuce plants negatively correlated with flavonoid level in a UV-B-dependent manner. LC-MS was used to identify metabolic features which contribute to this correlation, and of these, quercetin 3-O-(6″-O-malonyl)-β-D-glucoside had the strongest negative correlation with B. lactucae conidia count. The direct effect of quercetin 3-O-(6″-O-malonyl)-β-D-glucoside was tested through infiltration into lettuce leaves followed by subsequent downy mildew infection. Decreased B. lactucae conidia count was observed in two lettuce cultivars infiltrated with quercetin 3-O-(6″-O-malonyl)-β-D-glucoside concentrations similar to those induced by a UV-B-treatment. It was concluded that UV-B-pretreatments can decrease disease susceptibility to downy mildew in lettuce, and that this defence is underpinned in part by UV-B-induced phenolics. These findings highlight the opportunity for UV-B morphogenesis to be exploited in the development of next-generation, sustainable disease control tools.en_US
dc.identifier.urihttp://hdl.handle.net/10179/15813
dc.publisherMassey Universityen_US
dc.rightsThe Authoren_US
dc.subjectLettuceen
dc.subjectDisease and pest resistanceen
dc.subjectDowny mildew of lettuceen
dc.subjectBremia lactucaeen
dc.subjectPlants, Effect of ultraviolet radiation onen
dc.subject.anzsrc300804 Horticultural crop protection (incl. pests, diseases and weeds)en
dc.titleUV-B priming for disease resistance : the use of UV-B light to reduce susceptibility of lettuce plants to downy mildew disease : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Pathology at Massey University, Manawatū, New Zealanden_US
dc.typeThesisen_US
massey.contributor.authorMcLay, Emilyen_US
thesis.degree.disciplineAgriculture and Horticultureen_US
thesis.degree.grantorMassey Universityen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophy (PhD)en_US
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