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Item Genetic diversity analysis of cacao (Theobroma cacao L.) germplasm in Samoa using microsatellite markers : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in Plant Breeding at Massey University, Palmerston North, New Zealand(Massey University, 2025) Liu, TianmiaoCacao (Theobroma cacao L.) is an important tropical crop with significant economic and ecological value. However, its genetic diversity is still insufficiently studied in Samoa. In this study, microsatellite markers were used to assess the genetic diversity of 183 cacao varieties collected from four plantations in Samoa. Six polymorphic SSR loci were used to identify 108 alleles revealing genetic variation in cacao among plantations (expected heterozygosity = 0.49). Both Structure and Neighbor-Net analyses showed that the SIU plantations were mainly Criollo and the SAT plantations were mainly Nanay, while the ALE and SAL plantations were mixtures of several varieties. Four different genetic groups were delineated by cluster analysis (UPGMA) and principal coordinate analysis (PCoA). It was finally determined that the cacao in the Samoa region consists of Amelonado, Trinitario, Nanay, Criollo and LAFI-7. The results of this study revealed the key role of microsatellite markers in analyzing cacao diversity, identified the major Samoa cacao types and provided feasible insights for Samoa molecular marker-assisted cacao breeding. It provides a direction for future improvement of cacao germplasm for biotic and abiotic resistance and the construction of modernized cacao plantations.Item Constraints to carrot seed production in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Horticulture, School of Agriculture and Environment, College of Sciences, Massey University, Palmerston North, New Zealand(Massey University, 2025) Godwin, Asharp SharmecNew Zealand is one of the largest producers of carrot seeds globally. However, carrot seed production is increasingly vulnerable to the effects of climate change, which may force the geographical shifts in cultivation locations. These shifts increase the possibility of genetic contamination from wild carrots, which could have a consequential impact on the cultivar purity of carrot seeds. There are limited studies that have explored the impact of climatic factors and wild carrots on carrot seed production within the context of New Zealand. This literature mainly focused on the effect of climate change on floral characteristics of cultivated carrots and management of wild carrots rather than risk of seed contamination or climate interactions specific to wild and cultivated carrots. The overall aim of this thesis is to investigate two key constraints on carrot seed production in New Zealand, especially those caused by climate change and the existence of wild carrots. A panel data modelling study was conducted to investigate the effects of maximum and minimum temperature, and precipitation during critical phenological stages on carrot seed yield. This modelling study was carried out by using cross-sections from 28 locations within the Canterbury and Hawke's Bay regions of New Zealand that cultivate carrot seed crops and time series from 2005 to 2022. Findings show that there were significant (p < 0.01) variabilities in temperature and precipitation across different growing phases, except for precipitation at the vernalization phase. According to the analysis of marginal effects, the highest significant effect of minimum (187.724 kg/ha of seed yield reduction for each 1 ˚ C increment) and maximum temperature (1 ˚C rise increases seed yield by 132.728 kg/ha), and precipitation (1 mm increment of precipitation declines the seed yield by 1.745 kg/ha) on carrot seed yield were reported at vernalization, and flowering and seed development, respectively. Results from the modelling study conclusively show that carrot seed production will be negatively affected by climatic change. Meanwhile, the germination phase, including seed germination and seedling emergence, is extremely sensitive to adverse temperature, particularly temperatures above the optimum, conditions and represents a critical stage for the successful establishment of seed crops. However, further studies were needed to accurately determine the impact of temperature on the germination of carrot seeds, including wild and cultivated carrots. Therefore, germination experiments were carried out to investigate how extreme temperature can affect the seed germination of carrot male line and female line, and wild carrots by using a temperature gradient plate. The findings indicated that the germination percentage, mean germination time, and time required for 50 % germination of wild and cultivated carrots can be significantly (p < 0.05) affected by the interaction effects of temperature and genotypes. The highest (87 %) and rapid germination (6.8 days) of wild carrots was observed at 21 ˚C and 25 ˚C, respectively. The highest percentage of germination was recorded at temperatures of 20 ˚C for cultivated carrots, including male (98 %) and female (97 %) lines; however, these differences were not statistically (p > 0.05) significant. The exponential model was chosen based on statistical criteria to determine the base, optimal, and ceiling temperatures for the seed germination of wild and cultivated carrots. The values of base, optimum, and ceiling temperatures of wild, and cultivated carrots ranged from -0.22 to 2.98 ˚C, 22.11 to 25.55 ˚C, and 37.88 to 38.64 ˚C, respectively. According to the climate change projections, the germination rate (GR50) of wild and cultivated carrots is predicted to increase along with the increasing temperature. Given the comparatively increasing germination rate of wild carrots under projected temperature increments, it is important to manage their vegetative growth and development efficiently. However, further investigations are required to precisely determine the most effective timing and growth stage for managing wild carrots. Consequently, a glasshouse experiment was conducted to compare and model the vegetative growth pattern of different morphological traits, such as plant height, leaf number, root diameter and length, and shoot and root fresh and dry weight, in both wild and cultivated carrots, to understand appropriate weed management strategies with respect to their growth stages. Studying the vegetative growth pattern of wild carrots helps determine the most appropriate growth stages for implementing effective weed control methods, such as timing of herbicide application or mechanical control. This study comprised two main factors; 1. Genotype (T1: cultivated and T2: wild carrots) and 2. Length of juvenile phase, defined as the time duration between sowing and initiation of vernalization (J1: 12-week, J2: 8-week, and J3: 4-week). The morphological traits studied included plant height, leaf number, shoot fresh and dry weight, root fresh and dry weight, root diameter and root length. The recorded data were analyzed using analysis of variance (ANOVA), correlation, and regression analysis, and principal component analysis (PCA). The interaction effect between ‘genotype × juvenile stage’ has shown a significant (p < 0.05) effect on all the traits except plant height. Shoot and root growth of wild carrots exhibited rapid growth after reaching 8-week juvenile stage (9-11 leaves stage). Results from correlation and regression analysis, especially power regression, indicated that the above-ground morphological traits can be used to determine the characteristics of below-ground parts of both wild and cultivated carrots. PCA presented that morphological characteristics, except plant height, can be used to differentiate wild and cultivated carrots. According to the findings of this study, it is clear that wild carrots grow more rapidly than cultivated carrots. Therefore, it is important to manage the wild carrots at their early growth stages, especially prior to the flowering. Meanwhile, further studies are required to compare and understand the reproductive phase of wild and cultivated carrot genotypes found in New Zealand. Therefore, an experiment was executed to evaluate the effect of different juvenile phases (J1-12 weeks, J2- 8 weeks, and J3- 4 weeks), and vernalization phases (V1- 12 weeks, V2- 4 weeks, and V3- no vernalization) on floral characteristics and flowering behaviour of cultivated (G1) and wild (G2) carrots, to understand the life history strategies of both wild and cultivated carrots. The findings indicated that the interaction effect between G × J × V on the percentage of flowering and time required for flowering was significant (p < 0.05). Cultivated carrots flowered only under treatments with 12-week vernalization, whereas wild carrots exhibited 100 % flowering across all treatments. Overwintering survival was comparatively higher for wild carrots (94.9 % - 100 %) than cultivated carrots (66.1 % - 98.3 %), likely due to their higher cold stress tolerance and deeper root systems. This study also shows that wild carrots can establish themselves as either summer annual or winter annual in New Zealand, whereas commercial carrots may only be cultivated as biennials for seed production. The overall findings of this doctoral research demonstrate that climate change can have a significant impact on carrot seed production in New Zealand. As a result, shifting the production regions to wild carrot-prone locations can detrimentally affect the genetic purity of the cultivated carrots since wild carrots can establish as a winter annual and summer annual, and have a strong capability of surviving over the winter. Therefore, it is important to control the wild carrot prior to the flowering, especially at their early growth stages. Further research is recommended to investigate the contribution of pollinators on pollen flow from wild to cultivated carrots and to determine the optimum isolation distance by incorporating the factors like range of pollinators, climatic factors, and density of the wild carrot population.Item Plant germplasm diversification strategies : a case study using Limonium : 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, 2024) Cordoba-Sanchez, JuanaLimonium Mill. was chosen for this research as it has an established market for ornamental use and faces significant challenges in breeding including access to germplasm with traits of interest, self-incompatibility in most species, and pollen/stigma dimorphism which limits the types of cross combinations that can be performed. In interspecific crosses, challenges can be the low hybridisation rate (<1%), and the sterility/low fertility of interspecific hybrids. To address these challenges, increase the germplasm diversity available, and speed the development of cultivars, two breeding strategies were evaluated in this research: ploidy manipulation and physically induced mutations. The main outcomes were: 1. Efficacy of those strategies in: • Increasing the ploidy levels of the selected genotypes and therefore the germplasm diversity for The New Zealand Institute for Plant & Food Research Ltd (PFR)’s germplasm bank. • Increasing the hybridisation rate in interspecific crosses. • Fertility restoration in interspecific hybrids 2. Development of plants with new characteristics or different ploidy levels (i.e., triploids, tetraploids, or even higher ploidy levels). 3. Breeding protocols for Limonium using N2O which could be further used in other plant breeding programmes. The use of Limonium for the development of a new breeding strategies for increasing genetic diversity has a direct impact on other breeding programmes i.e., food crops. In addition, the Limonium industry could have access to continued novelty, ensuring industry access to new cultivars would benefit New Zealand’s economy mainly through royalties.Item UV photomorphogenesis : gene expression in cannabis in response to UV exposure : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Horticultural Science at Massey University, Manawatū, New Zealand(Massey University, 2022) Dods, ReubenGlobally, changes in legislation have led to a significant increase in large scale commercial cultivation of Cannabis sativa (cannabis). For commercial growers, both yield and the concentration of cannabinoids in the harvested flower are key metrics for determining the value of a crop. In cannabis, the concentration of cannabinoids is determined both by underlying cultivar genetics and environmental factors. Ultraviolet (UV) radiation is already known to impact the growth and development of crop plants and has shown potential for use in beneficially controlling agronomically desirable outcomes, including improved disease resistance, increased yields, and greater accumulation of flavonoids in a range of crops. There are few historical studies on the impact of UV light on cannabis, however, preliminary research from BioLumic Limited – a New Zealand biotechnology company, has shown that short duration UV light treatments of young plants could be used to increase the yield and the content of commercially valuable cannabinoids THC and CBD. Little is known about the underlying molecular-level responses of cannabis to UV and extending this knowledge may reveal gene expression diagnostic targets that could be used in increasing the speed and impact of commercial UV light treatment development. In this study, a series of trials were carried out, where young cannabis clonal plants from a range of cannabis genetics were exposed to a number of proprietary UV light treatments. Plants were removed on a timeseries throughout the UV treatment regimens and were assayed via RT-qPCR to provide a timeseries of the expression of genes known to be involved in either UV signalling response, or cannabinoid biosynthesis. UV treatment induced several significant timepoint-based changes in relative expression of UV-response genes CHS and HY5, but induced limited expression-based change in the cannabinoid biosynthesis genes CBDAS and THCAS. Study results also indicated that plants displaying (pre-UV treatment) stress symptoms may be primed to respond more strongly to UV treatments, as indicated by higher levels of initial CHS gene expression. This study also showed that clone plants originating from different mother plants from the same variety (or 'strain') of cannabis, exhibited differences in gene expression when exposed to the same UV treatment. Future work will further explore the response of cannabis to UV treatments, including the expression of genes that may be used as markers for increasing the speed of commercially valuable UV treatment development.Item Functional and structural characterisation of the Eop1 effector from Erwinia amylovora and related species : a thesis submitted to Massey University for the degree of Master of Science in Plant Breeding, School of Agriculture and Environment(Massey University, 2022) Tomar, VishantErwinia amylovora is the etiologic agent of the fire blight disease of apples (Malus species), pears (Pyrus species), and many other members of the Rosaceae family. Fire blight affects virtually all pome species and encompasses major pome fruit-producing countries worldwide. Moreover, it is gradually progressing into the far east Asian countries, which hold a prime position in the pome fruits production. Management of the fire blight disease is challenging due to the lack of effective control measures capable of suppressing its necrogenic effects in the diseased plants or restricting the pathogen's spread. Using resistant cultivars for pome fruit production is one of the most environmentally friendly and sustainable methods. However, it is not a permanent solution due to the pathogen's ability to evolve and overcome host resistance by employing proteinaceous virulence factors termed 'effectors' and restoring host susceptibility. This dynamism of host-pathogen molecular interactions and their role in disease development in the host plant and eliciting an immune response in the non-host plant necessitates a thorough understanding of pathogen-delivered effectors, their mechanisms, and host targets. In this study, non-host resistance was used to decipher the activity, molecular mechanism, and potential host targets of Eop1, one of the effectors secreted by E. amylovora and many other related species during pathogenesis. Firstly, it is demonstrated that Eop1 and its sequence homologs function as a 'putative' avirulence factor in the non-host plant Nicotiana tabacum. Following that, evidence was produced to show that the effector utilises an enzymatic mechanism for its activity; additionally, Eop1s' tertiary structure and catalytic motif were also examined using in-silico protein modelling. Moreover, it was discovered that RIN4, a plant immune regulator, and an R-protein, RPA1, are crucial for the Eop1s' recognition in the tobacco plant. Finally, by connecting all the aforementioned pieces of evidence, a model for Eop1s' activity and its recognition in the host and non-host plants is proposed, which follows the 'guard' paradigm of effector recognition. A thorough understanding of the Eop1 effectors, including their structure, activity mechanism and host targets, would contribute to a better understanding of host-pathogen interaction in the Erwinia-Rosaceae pathosystem, ultimately assisting in the delivery of elite cultivars with durable resistance.Item Ex situ conservation of orchid seeds of the Lycaste genus : a thesis presented in partial fulfilment of the requirements for the degree of Master of Sciences in Plant Breeding at Massey University, (Manawatū campus) Palmerston North, New Zealand(Massey University, 2022) Alfaro Pinto, Maria AlejandraThe orchid family (Orchidaceae) is the second largest family in the plant kingdom with about 28000 species. Most orchid species are endangered. Both in situ and ex situ approaches are necessary for the conservation of endangered and threatened species, including orchids. In situ conservation should be the priority, however, ex situ conservation can complement initiatives to ensure species survival in situ. More information on orchid seed dispersal mechanisms, pollination, and germination biology is needed to support conservation efforts. This study included three endangered species from Mesoamerica, Lycaste virginlis, L. cochleata, and L. lasioglossa that should be considered a high conservation priority. The primary intention of the different experiments was to contribute information that favours seed conservation of endangered orchid species from the Mesoamerica biodiversity hotspot. For this, characterization of the seed capsule morphology and seed micro-morphological traits were investigated followed by the assessment of the effect of three media on in vitro asymbiotic seed germination and the viability and germination of the seeds under different storage conditions. The qualitative traits of the seed capsules and the seeds were similar in appearance and colour for the three Lycaste species evaluated. However, high variability was found in the quantitative traits of both seed capsules and seeds. Based on the micro-morphological traits’ findings, it is possible to speculate that these three epiphytic Lycaste species which all grow under dense tropical canopies are dispersed by water drops falling onto the orchid plant from the canopy and by gravity. This suggestion is consistent with their having small-sized seeds, relatively large embryos, and low air volume (in comparison with other epiphytic and terrestrial orchid species). Specifically, those traits may allow the seeds to be dispersed in vegetation-dense and humid natural environments. Further research needs to be done to validate these findings, including more species of the Lycaste genus. For the successful implementation of conservation plans, it is important to understand the specific nutritional requirements for seed germination of the target species. This study assessed three different germination media (Murashige and Skoog (MS), Knudson C, and terrestrial orchid medium BM-1) to identify the most suitable one for asymbiotic in vitro germination. The germination percentages and seedling development significantly varied across the three Lycaste species. MS media sustained the highest germination percentages with high-quality plantlets (in stage 4). Still, germination did not reach the potential suggested by the tetrazolium test for viability, meaning that further media optimization is required. Knudson C media was also a good option for the seed germination and seedling development for two of the three species (L. cochleata and L. lasioglossa). The effect of different storage conditions (temperature, RH, and time) on seed viability and germinability was tested. The differential scanning calorimetry (DSC) method was used to identify each species' lipid melting and crystallization points. Based on the DSC findings, storage temperatures below -75°C is recommended for the storage of three Lycaste species. Still, further research needs to be done by testing more and different storage temperatures to validate these findings.Item Aspects of fruit growth and rootstock/scion influence on field performance in kiwifruit (Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson var. deliciosa) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Horticultural Science at Massey University(Massey University, 1994) Cruz, Castillo Juan GuillermoThe influence of nine Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson var. de!iciosa rootstocks and four 'Hayward' strains on the growth and cropping performance of kiwifruit vines four, five, and six years after grafting was determined. Multivariate analysis of variance on phenotypic data was an effective technique to distinguish main effects of rootstock and scion and the interactions between the two. Canonical Variate Analysis was particularly useful for distinguishing between root systems, 'Hayward' selections and their interaction on the basis of field performance. This statistical technique was highly effective in summarizing the complex relationships of the data and provided a useful method of reducing the dimensionality of the problem. A rootstock effect on plants topworked on root system 4 (male) was characterised by high field performance, as expressed by high floral bud burst and high yield of large size fruit in each of three seasons. Own rooted vines had the highest field performance in one season. Own rooted 'Hayward' B strain had a large trunk diameter and high yield in comparison to the other three own rooted 'Haywards', in two seasons. In contrast, when strain 'B' was topworked across eight root systems the vines produced a low yield of small fruit in two seasons. 'Hayward' A as a scion achieved the best field performance in yield and fruit sizing across eight root systems in two seasons. Root system and scion interactions were characterised by differences in 'Hayward' selection effects on individual root systems, and root system effects on individual 'Hayward' selections. In particular scion performance on root system 9 differed significantly, as did the effect of rootstock on the scion selection 'Hayward' D. Fruit from some vines had a significant increase in percentage of soluble solids and fruit firmness at harvest, and during storage. Scion effects on percentage of soluble solids present at harvest were lost after fifteen weeks of cold storage. Conversely, in some cases, significant interaction between rootstock and scions on that variate were found only after a period of fruit storage. Rapid fruit softening during storage occurred in some rootstock scion combinations, particularly 'Hayward' Con its own roots and three of the eight rootstocks. The effects of early summer partial defoliation on fruit size, return bloom, and carbohydrate content of 'Hayward' kiwifruit vines were studied. An arbitrary distinction was made between shoots arising from the 'replacement cane zone' (RCZ), the wide horizontal area between the T-bar support wires, and the fruiting zone (FZ), comprising all growth arising outside the T-bar support wires. A 75 % defoliation of new shoots in the RCZ significantly reduced mean fruit size 13 and 7 g, in the RCZ and FZ, respectively, and starch content of the shoots as determined in March. The treatments did not significantly alter the root starch content over several dates sampled. The return bloom of the vines was significantly reduced by 50 and 75 % defoliation. Pre-anthesis factors and early fruit growth were important in determining final fruit size. Ovaries from early opening flowers had significantly greater fresh weight than late ovaries. Cell number and cell size in the inner and outer pericarp of the ovary at anthesis were similar for early and late opening flowers but core cell number was significantly higher for ovaries from early flowers. At commercial harvest, the cell number in the outer pericarp of fruit from early flowers was greater than fruit from late flowers. When treated with the synthetic cytokinin CPPU (N-(2-chloro-4-pyridil)-N-phenylurea), fruit from early flowers achieved a larger fruit size than fruit from late flowers. Fruit weight response to the synthetic cytokinin CPPU was enhanced when applied in combination with GA₃ (gibberellic acid) + 2,4-D (2,4-dichlorophenoxyacetic acid) in three seasons. In treated 'Hayward' fruit, the relative thickness of the outer pericarp was increased, and the inner pericarp decreased. Low and high seeded fruit treated with the hormone mixture had mean fresh weights of 102 and 136 g, respectively, compared with 47 and 90 g in untreated fruit. In kiwifruit inner pericarp cultured in vitro there was no callus growth in the absence of hormones, even when seed were present. A mix of 2,4-D + GA₃ + BAP (6-benzylaminopurine) stimulated callus growth. In the presence of 2,4-D + GA₃ , seeds or BAP increased fruit callus growth and reduced the phytotoxicity effect of abscisic acid (ABA). The uptake of ¹⁴C-CPPU and ¹⁴C-CPPU + 2,4-D + GA₃ by 'Hayward' kiwifruit, and the distribution of radioactive label in fruit tissues was examined. After 21 days the recovery of radioactivity was significantly greater from fruit treated with mixture compounds to CPPU alone. At commercial harvest radio-active metabolites of CPPU were on average 6.2 and 4.8 ppb (fresh weight basis) for soluble and insoluble acetone fractions, respectively. Of this activity, 90 % was present on the skin, and 10 % in the flesh.Item The effect of intercropping on the yield and quality of forage oats and peas : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Agricultural Science at Massey University, Palmerston North, New Zealand(Massey University, 2021) Mabedi, FranciscaCereal-legume intercrops have the potential to improve dry matter yield and quality of forage. A study was conducted at Massey University in Palmerston North, New Zealand in 2020, to determine the effect of intercropping on the yield and quality of forage oats (Avena sativa L.) and peas (Pisum sativum L.). Oats and peas were sown in the oat: pea ratios; 100:0, 75:25, 50:50, 25:75 and 0:100. The sowing rates of 100% oats and peas were 150kg and 250kg ha⁻¹ respectively, from which seed rates for mixtures were calculated. Two harvests were taken, the boot (harvest 1) and milky dough stage (harvest 2) of oats and the dry matter yield and forage quality traits including crude protein (CP), Acid Detergent Fiber (ADF), Neutral Detergent Fiber (NDF) and metabolisable energy (ME) were determined. The sowing ratios significantly (P=0.05) affected the dry matter yield of forage at both harvests. At harvest 1, the sole cropped peas produced a significantly lower yield (5930 ha⁻¹) compared to the other treatments which were similar, producing yields that ranged from 14083kg ha⁻¹ to 15823kg ha⁻¹. At harvest 2, the 25% oat:75% pea treatment mixture had a significantly higher yield (21110kg ha⁻¹) than the sole cropped unfertilisedl oats (14353kg ha⁻¹), while the rest of the treatments were not significantly different from each other and produced yields ranging from 14885kg ha⁻¹ to 16690kg ha⁻¹. All forage quality parameters were significantly affected by sowing ratios at harvest 1 while at harvest 2 only the CP and NDF were significantly influenced by sowing ratios. At harvest 1, the CP content was significantly (P=0.05) higher in the sole cropped peas and mixtures compared to sole cropped oats and ranged from 13.24-17.45% while the ME was only significantly higher in the sole cropped peas. Sole cropped peas and mixtures also had significantly lower ADF and NDF levels compared to sole cropped oats. At harvest 2, only the 25% oat:75% pea mixture had significantly higher CP content (8.81%) content compared to sole cropped unfertilised oats (5.02%). Intercropping evaluation indices showed that all three mixtures had a yield advantage as mixtures produced land equivalent ratios of 1.06, 1.12, and 1.26 for the 50:50, 75:25, and 25:75 oat: pea ratios respectively. The plant height and leaf area index in this study were not significantly affected by sowing ratios at both harvests. Intercropping significantly improved the quality of forage harvested at the boot stage of oats, by increasing the CP and lowering the ADF and NDF content, improving palatability and digestibility of the forage. Land equivalent ratios of greater than 1 showed that intercropping produced greater yield per unit area compared to monoculture. Intercropping with peas can be used by farmers in the Manawatū area to improve the quality of oats grown for silage, the optimum seed ratio being 25% oat:75% peas.Item Enhancement of calcium concentration in Zantedeschia plants : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Horticultural Science in Plant Science at Massey University(Massey University, 1995) Rodil, Carlos NAs part of a research programme developing the use of enhanced calcium (Ca) concentrator of plant tissue as a means of control of bacterial soft rot in hybrid Zantedeschia, changes in Ca concentration were monitored using two methods of application. Gypsum application at 9 kg/m³ and a pre-plant vacuum application of 75% calcium chloride (CaCl₂) solution were used to follow changes in calcium (Ca) in concentration and its forms in tuber peel and matured leaves of hybrid Zantedescia plants. Throughout the period of growth, gypsum application increased approximately 2.0 mg/g Ca concentration of tuber peel tissue and matured leaves. The concentration in tuber peel tissue was increased to a maximum of 17.42 mg/g at 84 days after planting, then, declined to the concentration recorded at planting by 140 days. In contrast, the calcium concentration of the matured leaves increased continuously throughout the growing period. Plant available Ca in the gypsum amended medium was approximately three fold greater compared to that of the control (13.08 and 4.33mg/g at 14 days after planting or 15.53 and 4.96 mg/g at 98 days after palnting), and neither treatment showed any consistent trend of change over time. The decline in Ca concentration in tuber peel tissue coincided with the period of rapid tuber growth. Hence, it was suggested that this increase in tuber growth may have diluted the Ca concentration throughout the period of tuber enlargement. As evident by the continued accumulation of Ca within leaves, a further factor contributing to the decline in Ca concentration of the tuber peel may have been the limited ability of plants to regulate Ca distribution between the high (leaves) and low (tubers) transpiring tissues. lt was concluded that the application of gypsum is able to enhance the Ca concentration of the plant tissue. It was also concluded that there were no relationship between the trend of plant tissue calcium concentration and the plant available Ca in the growing medium. Pre-plant vacuum infiltration of 7.5% CaCl₂ increased the total Ca concentration of the tuber peel in addition to the different forms of Ca (i.e., soluble Ca, calcium oxalate and the Ca bound in the cell wall). However the increase was not maintained for the whole duration of growth. The concentration of all forms of Ca was increased to a maximum at post vacuum (PV) sampling and then subsequently declined before planting (BP). Once planted, and throughout the duration of growth, tubers vacuum infiltrated with 7.5% CaCl₂ did differences in the total Ca concentration or in the different forms of Ca were evident compared with those vacuum infiltrated with 0% CaCl₂ or the non vacuum treated tubers. Similarly with the matured leaves, the concentration of the total Ca and the different forms of Ca, did not result in any differences between treatments.Item Initial exploration of unreduced gamete (2n gamete) pollen development through nitrous oxide (N₂O) application in Limonium sinuatum : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Horticultural Science at Massey University, Palmerston North, New Zealand(Massey University, 2021) Siregar, Ahmad SyahrianHybridisation and polyploidisation are techniques that can rapidly generate proprietary diversity in plant breeding programs. Limonium sinuatum (2n = 16) is diploid, with polyploid plants being of potential value for breeding and commercial applications. Although somatic polyploidisation has been reported in Limonium, sexual polyploidisation potentially offers scope to speed up hybridisation and breeding. Sexual polyploidisation results in increased ploidy level via formation of unreduced (2n) gametes. Unreduced gametes are produced naturally but usually at levels too low to be of practical use, and production can be dependent on genotype and environmental conditions. Practically useful levels of unreduced gametes can be artificially induced by judicious timing of treatment with nitrous oxide (N₂O). Flower buds at the onset of meiosis are suggested as the best stage to treat with N₂O. However, there is no information available on when meiosis occurs in relation to flower development, nor what the optimum conditions of treatment might be in L. sinuatum. The aims of this study were to identify the stage of flower development when meiosis occurs and then to test the effect of N₂O treatment on 2n gamete formation before investigating the potential of 2n gametes in direct hybridisation. The results showed that meiosis across the raceme is asynchronous and occurs in very small flowers (0.8 mm in diameter) on each array of a spike in raceme. Additionally, meiotic division occurred from just after 6 AM., reaching its peak between 7 and 8 AM. (sunrise at ca 6.15 AM). N₂O treatments (600 Kpa) of 24 hours and 48 hours durations gave significant increases in formation of 2n gametes as indicated by a wider size range or bimodal pollen grain size distribution of pollen. Though legitimate combinations were used in crosses using 2n pollen to a diploid female plant did not result in polyploid progeny. The most likely reason for this is that a triploid block mechanism operates preventing normal embryo development.