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    Studies in the promotion of precocity in 'Doyenne du Comice' pear : a thesis presented in partial fulfilment of the requirements for the degree of Master of Horticultural Science at Massey University, New Zealand
    (Massey University, 1993) Pegler, Deane A
    Flower evocation is the process, generally hormonally controlled, that occurs before the vegetative bud apex changes from the differentiation of leaves to the differentiation of floral structures, and at that stage the bud has begun the reproductive cycle. Four treatments were chosen that had been shown in the literature to stimulate flower evocation and differentiation in pipfruit, and were applied in an experiment on 'Doyenne du Cornice' pear trees. These treatments were applied to experimental potted trees during the 1990 - 1991 growing season, and consisted of the application of one of the following: nitrogen fertiliser in the form of ammonium sulphate, subtoxic levels of simazine herbicide, plant growth regulator paclobutrazol or a period of regulated deficit irrigation (R.D.I.). A Control treatment was also monitored The flower clusters were monitored in the spring of 1991 and all treatments had increased flower clusters per centimetre of wood compared to the Control, however only the Paclobutrazol and the R.D.I. treatments increased flower clusters significantly (P < 0.01). Trunk diameter and shoot extension growth were both reduced although only the former was significantly reduced by the Paclobutrazol treatment (P < 0.01). The total free nitrogen levels were monitored in the leaves and the buds of the experimental 'Doyenne du Cornice' at various harvest dates during the season, which included assessment of ammonium, nitrate, arginine and total amino acids. There were no clear seasonal trends among the treatments in the levels of any individual nitrogenous components or the total free nitrogen levels. The R.D.I. treatment reduced the photosynthetic rate during its application period to a maximum significance of P < 0.01 just prior to the reinstatement of full irrigation. The water deficit imposed significantly reduced the xylem water potential for a period of 50 days although no statistically significant differences in water content of the growing medium was demonstrated. Examination of the bud apex with a Scanning Electron Microscope (SEM) during the development of floral structures was made during the season. This linked with a defoliation study done on spur buds on mature trees in an orchard near Wanganui which showed that defoliation before 4.12.90 significantly reduced bloom and defoliation after 11.2.91 had no effect. Evocation occurred between 14.12.90 and 8.1.91 as shown by the SEM. Fruitlet retention was also significantly affected by defoliation and the presence or absence of the bourse shoot. The ability of the spur bud to produce flowers depends on its position in the canopy of a mature 'Doyenne du Cornice' tree and a separate study showed that positions in the tree that had low PPFD had reduced flower numbers. A further study showed tying branch angle down from the vertical during winter is beneficial in terms of increased flower formation and reduced vegetative growth.
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    Maturation and ripening of Doyenne du Comice pears : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Science in Horticultural Science at Massey University, Palmerston North, New Zealand
    (Massey University, 1998) Cabrera Bologna, Carlos Danilo
    Characterisation of fruit quality attributes before and at harvest, during coolstorage and during ripening was made using standard and new, non-destructive devices during both the 1996 and 1997 seasons. Fruit firmness was linearly related to time when measured either by 'Kiwifirm' or penetrometer before harvest. Destructive techniques, the penetrometer and the texture analyser, were used to measure firmness and compared with non-destructive devices, the Kiwifirm and the softness meter. It is suggested that expressing rates of softening will be much more straightforward using a device such as the Kiwifirm. This device and the softness meter provided firmness data for pears that were too soft to measure by penetrometer. The effects of harvest date (1,11 and 21 March, 1996) and three crop loads on fruit maturity after a period of 6 weeks in coolstorage were investigated. Fruit size increased considerably during the 20 days before harvest, suggesting that periodical harvests need to be made in order to pick optimum size fruit each time. Maturity at harvest influenced the quality of 'Comice' stored at 0°C in air. Fruit from different harvests behaved differently in terms of softening behaviour and colour changes after 6 weeks in coolstorage. Crop load did not affect fruit quality attributes assessed after coolstorage. The characterisation of the nature and degree of within-tree and between tree fruit variability in harvest maturity and final ripening behaviour of 'Doyenne du Comice' pear was assessed by measuring firmness and colour. These attributes were measured non-destructively on fruit from different positions on the trees, and subsequently measured at harvest and during ripening at 20°C after 7 weeks in coolstorage at 0°C in air. Fruit behaved differently in terms of softening behaviour and colour changes depending on their position on the tree. Fruit maturity was delayed when fruit came from shaded areas, fruit from inner locations were greener than fruit from the outside and top positions. Selective picking and the association of harvest and ripening data may be important in making predictions that could reduce variability in fruit quality in the market place.
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    Genetic metabolite and phenotypic determination of friction discolouration in pear : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, New Zealand
    (Massey University, 2015) Saeed, Munazza
    Friction discolouration (FD) of pears is a postharvest disorder responsible for significant consumer discontent in markets because of the unattractive appearance of the fruit surface. New Zealand pear breeders are aiming to develop novel pear varieties with consumer desired fruit characters (skin colour, flavour and storability), with reduced susceptibility to FD. Therefore understanding the genetic control of FD is essential to enable development of new pear cultivars using genomics-informed breeding. FD is influenced by agronomic and genetic factors. Previous research on this disorder has been limited to a small number of commercial cultivars and no study has been done to understand its genetic basis. Biochemical constituents (polyphenol oxidase activity, phenolic compounds and ascorbic acid concentration) and skin anatomy have been proposed to play important roles on FD susceptibility in a limited number of cultivars. The Plant and Food Research (PFR) breeding population with hundreds of closely related seedlings is an ideal resource to test whether these previously identified associations hold true across multiple genotypes. In this study, 241 genotypes from two segregating populations (POP369 and POP356) derived from interspecific crosses between Asian (Pyrus pyrifolia Nakai and P. bretschneideri Rehd.) and European (P. communis) pears were used to identify biochemical and genetic factors associated with susceptibility to FD. In 2013, a small replicated trial involving eight genotypes was conducted. Large variability for FD and other variables was recorded. Four different trends were observed for genotypes for which multiple harvests were obtained in a single season. Most of the genotypes were consistently low or consistently high throughout the season, but a proportion (26.1 %) showed an increase in FD susceptibility during the season and a further 15.7 % showed a decreasing trend in susceptibility. Twenty genotypes had multiple harvests in each of 2011 and 2012, and 13 of these showed consistent trends from year to year. These results indicate a significant genetic component to FD but with additional influence from the stage of fruit maturity at harvest and external environmental conditions. Single nucleotide polymorphism (SNP)-based linkage maps suitable for QTL analysis were developed for the parents of both populations. The maps for population POP369 comprised 174 and 265 SNP markers for the male and female parent, respectively, while POP356 maps comprised 353 and 398 SNP markers for the male and female parent, respectively. Phenotypic data for 22 variables measured over two successive years (2011 and 2012) were used for quantitative trait locus (QTL) analysis. QTLs linked to phenotyped variables were identified, including QTLs for FD on linkage groups 2, 3, 7, 10 and 14. A number of stable QTLs across the years were detected for some aspects of fruit quality as well as potential risk factors for FD incidence. Overall, no single underlying phenotypic variable (enzyme or substrate) appeared to act as a rate limiting factor to susceptibility of FD in both populations and in 2013 trial. However certain phenolics consistently appeared to have weak negative association with FD. This suggests a separate role from their typical concept of being a substrate. Identification of stable QTLs controlling firmness, PPO activity, and phenolic compound concentration have also provided future opportunities for identification of candidate genes by utilizing the reference genome sequences of ‘Bartlett’ and ‘Dangshansuli’ pears and syntenic apple ‘Golden Delicious’. This study also demonstrated that FD is controlled by multiple small effect QTLs and genomic selection could be employed to select elite genotypes with reduced susceptibility to FD, early in the breeding cycle.
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    The effect of mild water stress on vegetative growth in tomato (Lycopersicon esculentum Mill.) and Pyrus betulaefolia Bunge : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Horticultural Science at Massey University
    (Massey University, 1991) Saunders, Andrew Barrington
    The effects of mild water stress and physical root restriction on leaf parameters and assimilate partitioning have been studied in order to understand and refine orchard management techniques which utilise both of the above stress elements (e.g. regulated deficit irrigation (RDI)). Initially, a system for applying a controlled level of water stress was developed and plant responses within this system defined. The system involved using aeroponic tanks with water stress generated by cycling the misting pumps on and off (intermittent misting). Similar systems have been used by other workers to stimulate hormonal changes but no work has been reported detailing vegetative growth responses. The intermittent misting technique was compared to polyethylene glycol (PEG) generated water stress, using tomato (Lycopersicon esculentum Mill. cv. Virosa Fl) as a model plant. Water stress studies were then carried out on Pyrus betulaefolia (an important root-stock for the asian pear (nashi) fruit crop (Pyrus serotina)) using intermittent misting. These results were compared to those from a root restriction trial involving P. betulaefolia in a circulating hydroponic system. The performance of polyethylene glycol in the aeroponic system appeared to be better than in the various hydroponic systems which have been reported. Polyethylene glycol 4000 gave the best results (from PEG 1000, 4000 and 6000), in terms of in minimum level of phytotoxicity, up to a total nutrient solution water potential ('Pw) of around -6 bar. Under an intermittent misting regime, tomato plants were subjected to a range of misting pump off-times up to 1.55 hours, with a constant on-time of 1 minute (to saturate the root system). It was found that important plant parameters could be related in a negative logarithmic fashion to misting pump off-time (e.g. leaf Ww, p lant part dry weights, allometric k value, net photosynthetic · rate and stomatal conductance). For P. betulaefolia trees, exposed to misting pump off-times of up to two hours, plant parameters were also related to the negative logarithm of the misting pump off-time. This was despite the fact that the tomato seedlings grew approximately exponentially while P. betulaefolia plants grew in a more linear fashion. Hence it was concluded that intermittent misting was an ideal method for generating a controlled water stress (under which plant responses could be predicted) in both pure and applied experimental work. Under physical root restriction (with water stress minimized), no significant differences were found in several important parameters, including net photosynthetic rate. Also, in contrast to the water stress response, assimilate partitioning to the shoot system increased (increase in the allometric k value) . The relative increase in partitioning was greatest in the stem component, this being the plant part most severely affected by water stress.- Under both water stress and physical root restriction the allometric k value appeared to change rapidly, following application of the treatment, and then remain constant. This constancy was tested by using a previously unutilized plot involving the shoot/root ratio versus time linearized plant dry weight. The results of pl ant responses to both water stress and physical root restriction are discussed in relation to vegetative growth control measures in frui t crops such as RDI. Consideration is also given to the overall mechanisms behind observed growth responses under the two stress regimes.