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    Postharvest apple softening : effects of at-harvest and post-harvest factors : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2001) Johnston, Jason William
    'Cox's Orange Pippin' (COP) and 'Royal Gala' (RG) are rapid softening apple cultivars. This makes it difficult for growers to meet minimum firmness standards in the marketplace. Research was undertaken to characterise softening curves of COP and RG in relation to different at- and post-harvest factors, and to compare these cultivars with the slower softening cultivars 'Granny Smith' (GS) and 'Pacific RoseTM' (PR). Regular measurement of firmness during low-temperature storage showed that the postharvest softening curve for all cultivars was triphasic with an initial slow softening phase (I), followed by a phase of more rapid softening (II), and then a final slow softening phase (III). Phase I largely determined the fruit market life for firmness, as fruit with a short phase I had less market life than fruit with a longer first phase. Phase I of RG and COP was lengthened by harvesting fruit at an earlier rather than later maturity, by rapidly cooling fruit after harvest to 0.5-3°C, and by placing fruit in controlled atmospheres (CA). Rate of phase II softening was not affected by harvest maturity, but decreased as storage temperature was reduced from 22 to 0°C, and was reduced in CA relative to air. A modified Arrenhius equation described softening rates of COP and RG at different temperatures, where softening rate increased from 0°C to a maximum at 22°C, and then decreased through 35°C. In contrast, this equation could not describe softening rates of PR and GS at different temperatures, as both cultivars softened slowly at similar rates from 0-12°C, and phase II did not occur at 20-35°C. Prior cold or ethylene treatment induced phase II softening at 20°C for GS, but not PR. Internal ethylene concentration (IEC) may have a role in regulating onset of phase II softening in RG and COP at 0-35°C, while for GS and PR fruit sensitivity to ethylene may have a more important regulatory role than IEC. A prototype model was developed for estimating loss of RG and COP firmness through the postharvest handling chain. This model has potential to improve commercial management of the "soft fruit" problem in the marketplace.
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    Partial rootzone drying in apple and in processing tomato : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Physiology at Institute of Natural Resources, Massey University, Palmerston North, New Zealand
    (Massey University, 2003) Zegbe-Domínguez, Jorge Artemio
    New water saving irrigation strategies need to be explored and partial rootzone drying (PRD) is such a strategy as it involves irrigating only part of the rootzone with the complement left to dry to a pre-determined level. In other deficit irrigation (DI) methods the entire rootzone is irrigated with less water than evapotranspiration. I focussed on PRD for its effects on apple and on processing tomato. For apple three field experiments were done, two on 'Pacific RoseTM' in Manawatu and one on 'Royal Gala' in Hawke's Bay. In all three, leaf water potential (ψleaf) was similar between PRD and commercially irrigated (CI) treatments and so were yield and fruit quality. However, 'Pacific RoseTM' PRD fruit in one experiment had lower water loss in storage than did CI fruit. For 'Royal Gala', PRD fruit quality was improved in terms of flesh firmness and total soluble solids concentration. In all apple experiments PRD trees received only 50% of water given to CI trees. I recommend PRD as a feasible irrigation strategy for apples in New Zealand, but suggest further research for drier areas. 'Petopride' tomato was studied in six glasshouse experiments. Depending on the experiment, PRD irrigation was shifted to the previously-unwatered rootzone on the basis of volumetric soil water content, on a daily basis, and on intervals of 2, 4, and 6 days. Maintenance of ψleaf, photosynthetic rate, stomatal conductance, yield, and fruit quality in PRD depended on the extent of soil drying. Irrigation use efficiency was almost twice higher in PRD plants than in CI plants. Blossom-end rot was higher in some of the PRD treatments, but in an especially-designed experiment I found out that PRD per se could not be the cause. From an experiment involving the measurement of root water potential, I concluded that water does not move from the wet roots to dry roots during PRD. I found that the tomato fruit, which is normally a stronger sink than vegetative parts, becomes a weaker sink during water stress. I recommend PRD for processing tomato, but with a suitable irrigation frequency to avoid lowering the midday ψleaf to a value of less than -1.2 MPa. This necessitates field trials in various environmental conditions.