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    Effects of RDI on apple tree (cv. Royal Gala) growth, yield and fruit quality in a humid environment : a thesis presented in partial fulfilment of the requirements for the degree of Doctor in Philosophy in Horticulture at Massey University
    (Massey University, 1990) Durand, Gladys
    The feasibility of using Regulated Deficit Irrigation in the humid environment of New Zealand was evaluated on trees of apple cv. Royal Gala (Malus domestica Borkh.). The study was carried out in a glasshouse experiment and a field experiment. In the glasshouse experiment, it was evaluated the pattern of soil water extraction by the winter mutant of lucerne (Medicago sativa sensu lato) ASR13R from a 'synthetic' soil layered in the same way that it occurs in the research orchard, under trickle and sprinkler irrigation. Results indicated that lucerne extracted soil water at a high rate and explored deep areas of soil. The field experiment was conducted during two consecutive seasons (1987-1989). Lucerne as under tree cover and black polyethylene mulch were compared with conventional herbicide strip to control excess of water in the root zone of the crop that would otherwise promote vegetative growth. These treatments were applied in combination with an irrigation schedule divided into three Phases. In Phase I, water was withheld, in Phase II RDI was compared with full irrigation, and during Phase III which coincided with the rapid fruit growth, all treatments received the full irrigation rate. During the first season, RDI and full irrigation treatments were based on 25% and 100% replacement EPS (evaporation in the planting square) respectively. In the second season, after a 50% of the soil water content in the top 600 mm of soil, between Drainage Upper Limit and me Lower Limit was reached, full irrigation treatments were replenished to the DUL, while RDI treatments received 25% of that amount. Results showed that under the conditions of this study evaluation of crop water requirements based on soil moisture measurements was more reliable than those based on pan evaporation. The degree of reduction of summer pruning obtained under lucerne X RDI treatment, reflected levels of soil and plant water deficit similar to those obtained in arid environments. Results confirmed my hypothesis that by using lucerne as under tree cover, a RDI strategy can be used in this environment. In contrast, black plastic mulch appeared to maintain soil moisture rather than prevent its accumulation. Nevertheless, effects were obtained which reflected positively in fruit growth and yield. Similar results were obtained under the control treatment, although it was less effective for in reducing tree vigour. The latter treatment, however, can be implemented in most orchards at no cost and generate important savings. Apple fruit growth proved to be relatively insensitive to water deficit imposed during early stages of growth, whereas vegetative growth was checked. Restoring full irrigation to coincide with rapid fruit growth stimulated growth of RDI fruits resulting in higher yield under control and plastic X RDI. Lucerne showed higher rates of water use that were not compensated by the irrigation which affected fruit growth and size. Results showed that fruits from RDI treatments were firmer, accumulated higher T.S.S. and had lower bruise susceptibility than fruits from fully irrigated treatments. Fruit quality remained higher after 10 weeks of cool storage.
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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.
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    The physiological basis of vigour control by apple rootstocks - an unresolved paradigm : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Physiology at Massey University, Palmerston North, New Zealand
    (Massey University, 2009) van Hooijdonk, Benedict Michael
    For millennia, scions have been grafted onto dwarfing apple rootstocks to reduce final tree size. However, it is unclear how scion architecture is first modified by the dwarfing apple rootstock, the time from grafting when this occurs and the endogenous hormonal signalling mechanisms that may cause the initial modifications in growth that then define the future architecture of the scion. In this study, the dwarfing (M.9) rootstock significantly decreased the mean total shoot length and node number of ‘Royal Gala’ apple scions by the end of the first year of growth from grafting when compared with rootstock(s) of greater vigour (MM.106, M.793 and a ‘Royal Gala’ rootstock control). Similarly, the auxin transport inhibitor 1-N-naphthylphthalamic acid (NPA) applied to the stem of vigorous rootstocks significantly decreased mean total shoot length and node number of the scion, and the architectural changes imposed were generally similar to those imposed by M.9. For example, both treatments decreased the mean length and node number of the primary shoot, reduced the formation of secondary axes on the primary shoot and caused a greater proportion of primary and secondary shoots (if present) to terminate growth early. Decreased formation of secondary axes imposed by both treatments was reversed by applying the cytokinin benzylaminopurine (BAP) repeatedly to the scion, whilst applications of gibberellins (GA4+7) reduced the proportion of primary and secondary shoots that terminated growth early, therefore increasing the final mean length and node number of these shoot types. Both M.9 and NPA also significantly decreased the final mean dry mass and length of the root system. Given these general similarities, it is proposed that the basipetal IAA signal is of central importance in rootstock-induced scion dwarfing, and that a shoot/root/shoot signalling mechanism may exist whereby the stem tissue of the M.9 rootstock decreases the basipetal transport of IAA to the root during summer, thereby decreasing root growth and the amount of rootproduced cytokinin and gibberellin transported to scion. Reduced amounts of cytokinin transported to the scion may decrease branching, whilst reduced amounts of gibberellins may decrease the duration for which a large proportion of primary and secondary shoots grow. Analysis of endogenous hormones for newly grafted composite ‘Royal Gala’ apple trees on rootstocks of different vigour provided some additional support for these ideas. It is recommended that future studies elucidate what unique properties of the M.9 bark act to restrict IAA transport, whilst it is concluded that gene(s) regulating rootstock-induced scion dwarfing are likely to control processes within the rootstock that modify the metabolism of IAA, its basipetal transport and the subsequent synthesis of root-produced vigour-inducing hormones including cytokinins and gibberellins.