Influence of photoperiod regime and exogenous plant growth regulators on crown bud formation in gentian

• Influence of photoperiod and exogenous applications of plant growth regulators on the formation of crown buds were investigated.
• Short photoperiod regime increased the number of crown buds compared to long photoperiod.
• Under the long photoperiod regime, ethephon increased the number of crown buds and the promotional effects doubled when applied with paclobutrazol or thidiazuron.
• When these exogenous growth regulators were applied under the short photoperiod regime, buds formed on storage roots instead of the transition zone.

Following vegetative propagation of interspecific hybrids of Gentiana such as ‘Showtime Diva’ there can be a delay or failure in formation of crown buds, sometimes resulting in the death of the plant. The influence of photoperiod and exogenous applications of plant growth regulators were investigated in order to identify factors that could induce the formation of crown buds earlier in the season. The transfer of plant material to a naturally occurring short photoperiod increased the number of crown buds 5-fold compared to a long photoperiod. Application of gibberellic acid inhibited bud formation under all photoperiod regimes investigated. When applied under the normally inhibiting long photoperiod regime, ethephon tripled the number of crown buds and shoots compared to the control, with the promotional effects doubled when paclobutrazol or thidiazuron was also applied. When exogenous growth regulators, that promoted crown bud formation under a long photoperiod regime were applied under the naturally occurring short photoperiod regime, buds formed on storage roots instead of the normal position on the transition zone between the shoot and roots. The change in location of crown buds with growth regulator application and photoperiod regime is discussed in terms of changes in sink strength and carbohydrate accumulation.

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