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Subject: search.filters.subject.310804 Plant developmental and reproductive biology

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    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, Juana
    Limonium 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.
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    Aspects of the biology and control of old man's beard (Clematis vitalba) : 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, 2023) Jarvis-Lowry, Brenda
    Old man’s beard (Clematis vitalba) is an increasingly problematic liana in New Zealand, but the factors that contribute to its invasiveness are not fully understood. The work in this thesis investigated elements of old man’s beard seed biology and ecology, seedling establishment, and vegetative reproduction that were unclear or unknown. The findings point to a reproductive diversification strategy that contributes to old man’s beard’s success as an invasive plant, due in part to dual dispersal mechanisms (by wind and water), dual seed banks (aerial and soil), dual seed dormancies (physiological and morphological), and dual reproductive modes (seeds and vegetative spread). Summary of findings regarding the biology • The aerial seed bank is transient: half of all achenes tagged and monitored were dispersed via anemochory during complete dormancy in autumn, and all but 5% of the remainder were gone by early spring. • The likelihood of secondary water dispersal is high, as seeds tolerated up to 6 weeks of immersion, germinated readily in water, and produced seedlings that remained robust, if removed from water within the 6-week period. • Pre-chilling was found to be unnecessary for germination, even for seeds that had not undergone a full winter of after-ripening: although it increased the speed at which seeds incubated at constant temperatures germinated, it did not promote total germination as successfully as a fluctuating temperature regime without pre-chilling. • Seeds collected off the vine and tested for germination over a 2-year period were fully physiologically dormant until completely senesced. Thereafter, dormancy declined during winter, and seeds were largely non-dormant by early spring. However, morphological dormancy did not change until seeds were exposed for several days to suitable germination conditions. Fewer than 72% of seeds were ultimately viable. • The soil seed bank was confirmed to be relatively small but persists at least for two years. Seeds in the soil experience the same cyclic physiological dormancy changes as those in the aerial seed bank, though can also enter a secondary dormancy when appropriate germination conditions are not met. • Seedlings were not able to survive competition exerted by established perennial grass cover unless the cover was very sparse. However, seedlings that survived began producing multiple, elongating stems within six months of emergence. • Vegetative growth produces an extensive network of creeping stems on the ground. Also, two-node woody stem fragments from both creeping and climbing stems are capable of rooting and growing vigorously as individual, clonal plants. Current management of old man’s beard infestations necessarily involves chemical control. The efficacy of two types of herbicide control was also assessed. As a precision technique for climbing vines that avoids non-target damage, the basal bark method with triclopyr in oil provides highly effective chemical control of individual stems, with >95% mortality. The cut stem method, using a 45% glyphosate gel formulation was less effective (55% mortality). For creeping stems, triclopyr alone and a triclopyr/picloram/aminopyralid mixture were effective herbicide sprays that preserved grass cover. Favouring a dense grass cover can help suppress subsequent establishment of old man’s beard by seed. Management should also consider that waterways are potential conduits of propagule spread, and that mechanical fragmentation of stems serves to produce more individuals, due to regeneration.
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    Application of microsatellite markers for population genetics of three New Zealand Corybas taxa (Orchidaceae) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Plant Biology at Massey University, Manawatū, New Zealand
    (Massey University, 2022) Qin, Tingyu
    Many New Zealand Corybas orchid species are endangered due to habitat destruction caused by changes in land use. Conservation efforts are needed to secure survival of those endangered species. Unfortunately, there are very few studies on these orchids and several aspects of their ecology, biology, and reproductive biology remain unknown. It is difficult to develop efficient conservation plans for those species without this information. This study describes the first genetic investigation in Corybas species and provides insight to their reproductive methods. Genetic diversity assessment was conducted in population(s) of three Corybas taxa, and the results were used to infer their genetic structure and reproductive methods. Pollination experiments and pollinator observations were carried out in one species, Corybas carsei, to understand the pollination strategies in this endangered species. Twelve previously developed microsatellite markers were used to genotype 37 Corybas “Remutaka” individuals collected from one population; these detected a medium level of genetic variation within population. No correlation between genetic and geographic distances were found. The genetic assessment results indicated that self-pollination, cross-pollination, and asexual reproduction likely occur in this population. As the readily available Corybas microsatellite markers were not transferable to C. carsei, novel microsatellite markers were developed using next-generation sequencing. Eleven markers were used to genotype 29 C. carsei individuals sampled from the single remaining C. carsei population. With the finding of only monomorphic loci, no, or possibly extremely low, genetic variation was detected within the population and, hence, reproductive methods employed by the C. carsei population could not be inferred. Conversely, 11 microsatellite markers used to genotype 67 Corybas macranthus individuals from three populations detected low to medium genetic variation within populations, and a low degree of genetic differentiation between populations. The results of within-population genetic assessment indicated that cross-pollination, self-pollination, and clonal propagation occurred. Pollination experiments in C. carsei showed that this orchid is self-compatible and autonomous self-pollination may occur. Its putative pollinator, flies, approaching the flower was captured on camera. No pollination events were observed and the species of IV those flies were not identifiable. Overall, the findings contribute to our understanding of New Zealand Corybas orchids and offer future directions for their conservation.