The effects of temperature, irradiance, supplementary UV-B and RlFR ratios on volatile oil compounds and plant growth parameters in basil plants have been determined. The base temperature for plant growth, the variation in chemical composition between leaves, the variation in chemical composition during the day and the effect of storage at 4°C for 24 h were also determined. Basil is a warm climate plant and its base temperature for growth is 10.9°C. The optimum temperature for plant growth is 25°C and this temperature also enhances the volatile oil content in leaves. Plants grown at 25°C for two weeks were taller and possessed more dry matter and larger leaves than plants grown at other temperatures. The total volatile oil content in fresh leaves was three times the level compared with plants at lSoC. Temperature also affected the composition of volatile oils. Warm conditions resulted in the accumulation of eugenol and cis-ocimene. whereas cool temperatures resulted in more camphor and trans-p-farnesene. There was no effect, however, on the relative contents of 1,8-cineole and linalool. Treatments with alternating temperature that supplied the same accumulated day degrees (ADD), but with a different sequence of temperatures, did not affect most of the plant growth parameters, however, volatile oil content and composition were strongly affected by the temperature regime of the final two weeks. The higher the temperature before harvesting, the higher the volatile oil content and the relative content of eugenol produced. Basil plants grow well in full sun, however they can tolerate light shade. Heavy shade (75% and 50% shade) resulted in small plants with reduced dry matter, and the volatile oil content in fresh leaves was five times lower than in control plants. Heavy shade significantly increased the content of methyl eugenol, but strongly decreased the contents of eugenol and Iinalool. Two weeks treatment with supplementary UV-B (ultraviolet - B) light resulted in short plants with higher dry matter and thicker leaves. It also stimulated the synthesis of volatile oil compounds, i.e. phenyl-propanoids (eugenol) and terpenoids (notably 1,8-cineole and linalool). There was no effect, however, on volatile oil composition. Use of supplementary light to produce a high RlFR (red / far-red light) ratio resulted in shorter plants with less dry matter and smaller leaves. But the volatile oil content of the leaves was greatly increased. The content of eugenol was decreased whereas the content of ~-myrcene was increased. There were no effects on the relative contents of 1,8-cineole, linalool and other compounds. There were no differences in the volatile oil content and composition of fresh basil leaves harvested during the daytime, i.e. between morning (9.00am) and late afternoon (5.00pm). After storage for 24 h at 4°C in dark conditions, there were no differences in volatile oil content and composition in fresh leaves. There was a great difference, however, in the content and composition of volatile oils between young and mature leaves. The sensory analysis showed that trained panellists could perceive different intensities of volatile oils and consumers preferred the stronger intensity of volatile oils in fresh basil leaves.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:415628 |
| Date | January 2005 |
| Creators | Chang, Xianmin |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://eprints.nottingham.ac.uk/28500/ |
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