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dc.contributor.authorHerewini, Echo
dc.date.accessioned2018-01-25T02:22:24Z
dc.date.available2018-01-25T02:22:24Z
dc.date.issued2017
dc.identifier.urihttp://hdl.handle.net/10179/12738
dc.description.abstractThe iconic Agathis australis (kauri) of New Zealand, is under serious threat from kauri dieback disease caused by the soil-borne pathogen Phytophthora agathidicida. Infected kauri express symptoms of root and collar rot, bleeding resins at the base of the trunk, yellowing of foliage, canopy thinning, and tree mortality. Phytophthora agathidicida was first associated with kauri decline in 1972, where it was initially identified as P. heveae however, there was some uncertainty about its significance and taxonomy. The pathogen was officially identified as a new organism in 2008 and was called Phytophthora taxon Agathis until its formal description as Phytophthora agathidicida in 2015. This pathogen is easily vectored through root to root contact and mobile zoospores. Management and research has focused on mapping pathogen distribution, reducing spread, improving detection, ex situ conservation and clonal production using tissue culture techniques. In order to gain better understanding of the disease epidemiology and to develop better breeding programmes, a reliable in vitro resistance screening assay is required. This research focused on the development of a screening assay using detached leaves from tissue culture material as a means of accelerating screening assays compared to the more labour-intensive root inoculation assays. Foliar inoculations and assessment techniques were initially optimised on kauri leaves from tissue culture lines. The most successful inoculation method involved placing P. agathidicida-colonised agar plugs on wounded detached leaves. The assay was further tested on 2 year old kauri seedlings. Variation in susceptibility across kauri genotypes and leaf age, and variation in virulence among P. agathidicida isolates was observed. To further investigate the impact of leaf age on lesion extension, an assay was conducted on detached leaves from six rooted kauri saplings over 5 years of age, across three leaf age groups with P. agathidicida, P. multivora, and P. cinnamomi. Variation in virulence among these Phytophthora species was observed. Leaf necrosis was most severe with young tissue and susceptibility tended to decrease with increasing leaf age. Preliminary studies with 50 kauri clones identified different levels of susceptibility and tolerance across the different genotypes to P. agathidicida. The methods developed within this study have increased our understanding of the overall response of kauri to P. agathidicida foliar inoculations. This study demonstrated variation in the susceptability of kauri foliage to Phytophthora inoculation, although no complete resistance was observed. Further work is required to determine if there is a relationship between root and leaf responses which will help establish if in vitro genotypic variation can accurately predict natural genotypic variation seen within kauri forests.en_US
dc.language.isoenen_US
dc.publisherMassey Universityen_US
dc.rightsThe Authoren_US
dc.subjectKaurien_US
dc.subjectDisease and pest resistanceen_US
dc.subjectDiseases and pestsen_US
dc.subjectPhytophthoraen_US
dc.subjectBiological assayen_US
dc.subjectNew Zealanden_US
dc.subjectAgathis australisen_US
dc.subjectPhytophthora agathidicidaen_US
dc.subjectKauri diebacken_US
dc.subjectResistanceen_US
dc.subjectSusceptibilityen_US
dc.subjectScreening assayen_US
dc.subjectPathogenicityen_US
dc.subjectVirulenceen_US
dc.subjectNew Zealand taonga speciesen_US
dc.titleDevelopment of an in vitro assay to screen Agathis australis (kauri) for resistance to Phytophthora agathidicida : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science at Massey University, Manawatū, New Zealanden_US
dc.typeThesisen_US
thesis.degree.disciplineAgricultureen_US
thesis.degree.grantorMassey Universityen_US
thesis.degree.levelMastersen_US
thesis.degree.nameMaster of AgriScience (MAgriScience)en_US


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