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    An evaluation of fungal bioassay procedures for assessment of soil phosphate status : thesis presented at Massey University College of Manawatu in part fulfilment of the requirements for the degree of Master of Agricultural Science
    (Massey University, 1963) Mantjika, N. M. D.
    Microbiological assays, especially with A. niger, have been used rather widely to assess phosphate status of soils. The merits as well as shortcomings of these procedures have been discussed in the literature by various investigators. The speed, cheapness, and simplicity with which microbiological assays may be carried out have been used as arguments in favour of their use. It was this type of argument, considered in relation to the fact that good correlations have been reported by a number of workers between results obtained by A. niger and by field tests, which suggested to the writer that micro­ biological assay might have special merit in those developing countries where a rapid assessment of soil potential is required in the interests of food production but where limited finance is available for full-scale soil investigations. The work reported here was undertaken to investigate further the value of the A. niger procedure as a means of evaluating soil phos­phate status and to examine the possibility that other fungi including some not previously employed for this purpose might be even more suitable. The present investigation was confined to a range of New Zealand soils. As field response data were not available for these soils a pot experiment incorporating a number of crops was conducted to provide plant growth data with which the results of microbiological assay could be correlated. [From Introduction]
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    Development 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 Zealand
    (Massey University, 2017) Herewini, Echo
    The 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.
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    Development of assays for biomarkers of oxidative damage to assess the efficacy of fruit-derived antioxidants : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Biochemistry at Massey University
    (Massey University, 2003) Barnett, Laura Evelyn
    The diet is a very important part of maintaining a healthy lifestyle. Increased consumption of fruits and vegetables is one practice postulated to decrease the incidence of diseases such as cancer, cardiovascular disease and other disorders. Although there are a number of possible beneficial compounds in fruit, it is believed that the antioxidant components found in these foods may decrease the oxidative damage that could lead to such diseases. Oxidative damage to cellular proteins, lipids and DNA is considered to result from an increase in the production of free radicals, which overwhelm the body's defence system. This research investigated fruit-derived antioxidants, and developed biomarker assays to measure the potential health benefits they may offer. To determine the in vivo antioxidant efficacy of berry fruit anthocyanins, oxidative damage to proteins, lipids and DNA was measured in rats fed several combinations of natural and synthetic diets. Mild oxidative damage was induced by the inclusion of fish oil in these diets. DNA oxidation was determined by measuring urinary 8-hydroxy-2'-deoxyguanosine using reversed-phase high performance liquid chromatography with electrochemical detection. ELISA and colorimetric techniques were used to measure protein carbonyl content of plasma as a reflection of protein oxidation. Oxidation to lipids was assessed by measuring malondialdehyde, which results from lipid peroxidation. Supplementation with fish oil induced a mild form of dietary oxidative damage, as shown by an increase in lipid and protein oxidation. In most cases the berry fruit extracts had little effect on the level of fish oil-induced oxidative damage, however, boysenberry anthocyanin extract significantly reduced protein oxidation when used in combination with the natural diet. Taken together the results suggest that oxidative damage to biomacromolecules may occur by different pathways of oxidative stress, which selectively target either DNA, protein or lipids at varying levels, and the antioxidant is effective only with selected mechanisms of oxidative damage.