Productivity and Timing of Harvest Maturity of Gentian 'Showtime Diva'; Influence of Dormancy-breaking Treatments, Development Stage, and Crown Bud Ontogeny

In the recent years new gentian cultivars have been released for production of cut flowers or potted plants. Cut flower productivity and spread in duration of harvest maturity of these cultivars has been identified as a concern by commercial growers. Flowering shoots of gentian develop from overwintering crown buds produced with a requirement of chilling for shoot emergence. Inadequate accumulation of chill units, was hypothesized as a possible reason for variation in timing in shoot emergence and flowering. Since crown buds originate from bud clusters, the hierarchical arrangement of buds within clusters was also hypothesized to contribute to this variation. Experiments were carried out with the gentian cultivar ‘Showtime Diva’, to determine the response to treatments that break dormancy (chilling (5º C), gibberellic acid (GA₃)) applied at different stages of development of crown buds. The application of GA₃ (100 mg.L^-1) increased emergence of crown buds as shoots, leading to development of more flowering shoots. A similar response was observed with exposure to chilling, but only on plants with non-emerged crown buds or with shoot emergence commencing. Both chilling and GA₃could reduce the time to, and spread of, harvest maturity, if applied prior to shoot emergence. The hierarchical relationship of buds in crown bud clusters led to differential responses to application of GA₃. Buds 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 the duration to reach shoot maturity took an extra 14 days to reach harvest maturity with each increment in hierarchical position. The response to chilling and/or GA₃ therefore varied based on, the development stage of the plant at the time of application and, the hierarchical position of the crown buds within the cluster. The current study enabled identification of factors associated with the variation in number of floral shoots and spread in time to harvest maturity in gentian.