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Jianyu Chen, Keith A. Funnell and Ed R. Morgan

Observations of leaf number accumulation rate (LNAR) and light integrals (DLI) were used to develop a predictive model for time to flower for a novel hybrid of Limonium sinuatum (L.) Mill. × Limonium perezii (Stapf) Hubb. Plants were established in a temperature-controlled greenhouse at seven planting times from fall to late spring. Long days were maintained using daylength extension lighting. Two light regimes, full sun or 50% shade, were also used. DLI was highly correlated with the time to appearance of the first visible flower bud, explaining in excess of 80% of the variation. When combined with plant growth variables describing either LNAR or rates of increase in groundcover index, a second model was able to predict the date of first visible flowers and accounted for more variation than DLI alone. Daily average temperature (DAT) did not significantly contribute to variation in time to first visible flower because temperatures were uniform between successive plantings at 18 to 21.7 °C. However, DAT was significant for the period from visible flower through to flower harvest maturity. Growers of these hybrids for cut flowers can therefore use historical records of DLI to determine planting dates to schedule flowering. Once planting has occurred, by measuring actual DLI, DAT, and leaf number per plant, growers can use the second model to more accurately predict the dates for visible flowers and flower harvest.

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John F. Seelye, Garry K. Burge and Ed R. Morgan

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Ed R. Morgan, Garry K. Burge, John F. Seelye, Andrew G.F. Warren and David J. Brundell

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Uttara C. Samarakoon, Keith A. Funnell, David J. Woolley, Barbara A. Ambrose and Ed R. Morgan

Shoot productivity and overwintering survival of gentians (Gentiana sp.) are determined by the initiation and subsequent development of crown bud clusters. Understanding of the anatomical features and origins of crown buds and bud clusters, and plant ontogeny, the morphological features of crown buds, and their associated development is required to achieve manipulation of bud initiation, emergence, and development. Anatomical features of the crown bud clusters were examined using both light and confocal microscopy using hybrids of Gentiana triflora × G. scabra. The initiation of bud clusters presented characteristics typical of adventitious buds in terms of their origin and presence of external vascular connection to the parental tissue. In contrast, crown buds forming subsequently within the cluster developed as axillary buds within that initial bud, collectively forming on a compact stem with minimal internode elongation. Stem elongation within the cluster after application of gibberellic acid enabled identification of a hierarchical arrangement of buds within the cluster with one bud at each node and arranged spirally at 90°. Arrangements of buds within the cluster were different from the opposite decussate phyllotaxis in floral shoots with two axillary buds at each node. Based on the current study, a crown bud cluster originated from a first bud initial, which was adventitious followed by development of subsequent crown buds within the cluster as axillary buds from this first bud initially with a single bud developing at each node.

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Uttara C. Samarakoon, David J. Woolley, Ed R. Morgan and Keith A. Funnell

Cut flower productivity and quality of gentian is associated with growth and development of crown buds. Experiments were carried out with the gentian cultivar Showtime Diva to identify the response to treatments that break dormancy [cold temperature (chilling), gibberellic acid (GA3)] applied at different stages of development of crown buds (plants with nonemerged crown buds, shoots recently emerged, or shoots emerged and elongated). The comparative growth potential of crown buds within the cluster was also investigated. At the stages of development examined, the application of GA3 (100 ppm) increased emergence of crown buds as shoots, leading to development of more flowering shoots. A similar response was observed with exposure to cold, but only on plants with nonemerged crown buds. Shoot emergence increased in response to increased duration of cold from 0 to 42 days (5 °C). Both chilling and GA3 could potentially be used to reduce the duration to, and spread of, harvest maturity if applied before shoot emergence. The hierarchical relationship of buds in crown bud clusters led to differential responses to application of GA3. Buds ontogenetically positioned at the proximal end of the bud cluster took a similar duration to reach shoot emergence or harvest maturity. For buds located at the distal end there was a positive correlation between ontogenetic bud position and the duration to reach shoot maturity. Shoot length and number of nodes at harvest maturity showed slight negative correlations with the position of the bud in the bud cluster. The results provide an explanation for possible sources of the variation in quality and quantity of floral shoots, and spread in time to harvest maturity within a single plant, and with development stage.