S. Pearson

Substantial UV-B-mediated induction of essential oils in sweet basil (Ocimum basilicum L.)

The effect of supplementary UV-B treatment on the essential oils of glasshouse-grown sweet basil (Ocimum basilicum L.) was examined. Two weeks treatment with supplementary UV-B given in the early morning was found to enhance the levels of most of the major volatiles, both phenyl-propanoids (eugenol, methyl eugenol) and terpenoids, notably linalool, 1,8-cineole and trans-β-ocimene. The phenyl-propanoids were sensitive to UV-B at an earlier developmental stage than the terpenoids. Overall, the effect of UV-B was a nearly fourfold stimulation in the oldest plants examined.

A model of the effects of temperature on the growth and development of cauliflower (Brassica oleracea L. botrytis)

Abstract A model is described which predicts the time to curd initiation, and the duration or rate of curd growth of cauliflowers. The model was calibrated with data collected from commercial crops grown during the 1989, 1990 and 1991 seasons. The reciprocal of the time from planting to curd initiation, for cultivar ‘Revito’, was linearly related to effective temperature determined with an optimum of 14°C. Curd initiation occurred after the accumulation of 296 degree-days above a base temperature of 2.8°C. Curd growth of three cultivars, ‘Jubro’, ‘Revito’ and ‘White Fox’ was described by a simple model which incorporated two terms; one describing a linear ontogenetic decline in potential relative curd growth rate (RGR) with thermal time and the second which described the instantaneous effects of temperature on RGR. The optimum temperatures for curd growth of cultivars ‘Jubro’, ‘Revito’ and ‘White Fox’ were 16°C, 25°C and 21°C, respectively. The model accounted for 37.4%, 40.4% and 95.8% of the variance in curd growth of the varieties ‘Jubro’, ‘Revito’ and ‘White Fox’, respectively. The curd initiation and curd growth components of the model accurately described several independent data sets. The model can be used for both crop scheduling and for predictions of crop maturity.

The effect of temperature on inflorescence initiation and subsequent development in chrysanthemum cv. Snowdon (Chrysanthemum×morifolium Ramat.)

Abstract The relationships between temperature and time to inflorescence initiation and subsequent development in chrysanthemum cv. Snowdon (Chrysanthemum×morifolium Ramat.) were investigated. From pinching, flowering occurred most rapidly in plants grown at a mean temperature of 20.4°C, whilst those grown at 10.9°C had the lowest leaf number at flowering. The final leaf number, from the pinch to the inflorescence, increased with increasing temperature above 10.9°C. This could be attributed to a marked sigmoidal increase in the rate of leaf initiation with temperature, not delayed initiation. Above 20°C temperature had little effect on the time of floral initiation (plants initiating after 8–9 days), although temperatures below this led to a considerable delay in floral initiation (20.5 days at 9.6°C). Once initiated the inflorescences developed most rapidly at 20.2°C, however, unlike the process of flower initiation, subsequent flower development was delayed by both warmer and cooler temperature regimes.

The effect of photoperiod and temperature on reproductive development of Cape Daisy (Osteospermum jucundum cv. ‘Pink Whirls’)

Abstract The flowering responses to photoperiod and vernalising temperatures were examined in Cape Daisy ( Osteospermum jucundum cv. ‘Pink Whirls’). At a day/night temperature of 18/12 °C, flowering occurred 10 days earlier (60 days) when plants were grown under glasshouse conditions at a photoperiod of 16 h day −1 compared with 8 h day −1 . Photoperiod had no significant effect on the number of side-shoots produced. Plants grown at 8 h day −1 attained half the height of those grown at 16 h day −1 . A reciprocal transfer experiment between plants maintained in growth cabinets at 12 and 22 °C was used to investigate the time when (and if) the plants were sensitive to cold. Plants transferred to and from each cabinet on seven weekly occasions indicated that Osteospermum had a requirement for cold prior to flowering. Plants maintained at warm temperatures (22 °C) were still vegetative 120 days after planting, whilst plants grown at 12 °C flowered after 81 days. Plants required at least 2 weeks of cold temperatures to induce flowering. Following this, flower development rate was increased by warmer temperature. Flowers took 38 days longer to develop at 12 °C than those maintained at 22 °C. Leaf number initiated before the flower was constant in plants exposed to 12 °C for at least the first 2 weeks after planting; however, all plants maintained initially at 22 °C had higher leaf numbers. Owing to delayed flower initiation, progressively longer durations of warm temperatures led to progressively higher final leaf numbers. Vernalising treatments (12 °C) had no effect on branch number. Final flower size declined when the plants matured at 22 °C.

The effect of spectral filters and nitrogen dose on the growth of chrysanthemum (Chrysanthemum morifolium Ramat., cv. Snowdon)

SummaryThis study has searched for interactions between the effects of nitrogen dose, applied at one of four levels, 0.316, 1.0, 3.16 and 10 mM, and four different spectral filters on the growth and development of chrysanthemums. The filters used included two controls with different overall transmissions to photosynthetically active radiation (PAR) and two further materials, which selectively filtered either red or far-red light, but with PAR transmission similar to one of the controls. Increasing the nitrogen dose to a maximum of 10 mM from the lowest level led to a four-fold increase in plant dry mass, and a near two-fold increase in plant height. The FR absorbing spectral filters produced significantly shorter plants than both controls (by ca. 10% at final flowering) and for this variable there were no interactions with nitrogen dose. At 10 mM N, the FR-absorbing material also led to an increase in leaf area compared with the R-absorbing material (by 55% after 40.d). However, a significant interaction ...

The effects of radiation frost on freezing damage and apical abortion in calabrese (Brassica oleracea var. italica) transplants

SummaryFreezing damage has been reported to be associated with apical abortion (blindness) in calabrese, preventing the formation of a marketable head. In the past, laboratory based experiments studying the freezing of whole plants using convective freezing have resulted in death of the plants while failing to induce blindness. Using a unique radiation freezing facility, capable of reproducibly simulating glasshouse frost conditions, we investigated the effect of hardening and freezing duration on calabrese transplants. Four cultivars were raised and subjected at four different growth stages (3, 5, 7 and 9 leaves) to a factorial combination of frost (0-4 d of frost between 22 to 248C) and hardening regimes (0-6 d at 48C prior to freezing). Following each frost/hardening treatment, half the sample was dissected and the remainder potted up and grown on. Light and transmission electron microscopy of the dissected plants revealed that the apical region of all the varieties at each of the growth stages remaine...

Environmental regulation of flowering time in heliotrope (Heliotropium arborescens L. cv. Marine)

The aim of this study was to examine the environmental regulation of flower initiation and subsequent development in heliotrope (Heliotropium aborescens L. cv. Marine). Five experiments were conducted, two examined whether flowering could be advanced by cool temperatures. The duration of cool temperature required to induce rapid flowering was also investigated. The final three experiments examined the effects of light integral, photoperiod and temperature on flower initiation and development. It was found that plants grown for 9 days at 108C and than transferred to 208C flowered significantly earlier (first flowering recorded after 55 days) than plants held constantly at 208C (65.9 days to flowering). Plants grown at a constant temperature of 208C had significantly more leaves than all other treatments. This suggested that ‘cool’ temperatures, prior to initiation, advanced flowering. In a transfer experiment, plants were moved from 10 to 208C at 3 days intervals postpinching. Earliest flowering (by 20 days compared to the 208C constant treatment) occurred when plants were exposed to 108C for 9 days and then transferred to 208C. Photoperiod was shown to have no effect on either flower bud initiation or development (postinitiation). Both temperature and light integral strongly influenced flower development post-flower bud initiation. However, the response to temperature plotted in terms of the reciprocal of days to flowering was non-linear. # 2000 Elsevier Science B.V. All rights reserved.