Physiological and metabolic responses of two rose varieties to plant growth regulators

Rose (Rosa hybrida) is one of the most popular cut flowers with a worldwide production of more than 300 million stems per year. The perfume industry, which relies on a range of scented rose varieties, is also an important industrial application for roses. Among the numerous types of roses are some recent varieties including Hybrid Tea and Floribunda roses. The major problem in Australia is accelerated pre- and post-harvest flower drop and senescence, caused by deficiencies in endogenous plant growth regulators (PGRs). PGRs play important roles in the growth and development of flowers, especially in aromatic plants, stimulating the emission of volatile organic compounds (VOCs). The PGRs benzyladenine (BA) and naphthalene acetic acid (NAA) which belong to cytokinin and auxin group of PGRs respectively, are used by the floriculture industry as important growth regulators for promoting rose growth and development. However, it is still unknown that how these regulators and their application dosages influence rose plants. Therefore, this thesis aimed to evaluate and determine the efficacy of various concentrations of BA and NAA on arrange of morphological and physiological characteristics of roses to increase flowers longevity in two rose varieties (Floribunda and Hybrid Tea). In addition, this study was conducted to understand how different concentrations of BA and NAA effect the metabolic changes in different rose tissues together with a comparison of VOCs changes. This work in this thesis developed and optimized the headspace solid-phase microextraction (HS-SPME) with three-phase fibre 50/30μm divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) coupled with gas chromatography-flame ionization detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS) method for exploring and analysing VOCs emitted from the intact and excised flowers, leaves, and stems as well as from the rhizosphere and whole plants of the two rose varieties. This study has optimized different environmental factors involved in the performance of the two rose varieties was conducted, and three physiological characteristics photosynthesis rate, respiration rate, and chlorophyll content were assessed. Three different concentrations (0, 100 and 200 mg/L) of BA and NAA were applied to the two rose varieties, and different morphological and physiological characteristics were evaluated. For physiological effects (photosynthesis rate and chlorophyll index) studies, application of 200 mg/L of both BA and NAA were shown to increase plant height, numbers of branches and flowers, stem and flower diameters, length of flower stems and flower longevity, compared to the control. However, for the respiration rate, the control plants had significantly superior performance to the plants treated with 100 and 200 mg/L BA and NAA, for both rose varieties. The VOC profiles of the two rose varieties were characterized by the optimized HS-SPME-GC method. The effects of different concentrations (0, 100 and 200 mg/L) of BA and NAA on the VOCs emitted from different rose tissues for the two rose varieties were determined. The highest amounts extracted, and evaluated from the sum of peak areas were achieved after the application of 200 mg/L BA and NAA in both varieties. Of the emitted VOCs, 20 were significantly different in treated compare to non-treated Floribunda and Hybrid Tea roses from different rose tissues. Moreover, five compounds 4-heptyn-2-ol, cis-muurola-4(14)5-diene, γ -candinene, y-muurolene and prenyl acetate increased significantly after applications of 200 mg/L of BA and NAA. These five compounds have great potential to develop commercially important new rose growth regulators. The actual dosages of BA applied to the leaves was determined using filter paper as 11.16 mg/cm2 and 7.17 mg/cm2 for Hybrid Tea and Floribunda respectively. In conclusion, the application to rose plants of different concentrations of BA and NAA can promote a number of changes to both morphological and physiological parameters, and in turn have a significant effect on metabolite changes in different rose tissues. Application BA and NAA method could be applied to other floriculture plants to increase the flowers production in rose or other ornamental plants