Treatment of tulips with gibberellic acid by vacuum infiltration

Summary

Initial attempts to reduce the glasshouse period of tulips by vacuum infiltration with GA₃ in 200 ppm (v/v) aqueous Tween 80 resulted in over 90% flower losses because of bulb, shoot or flower rot and floral bud blasting. In subsequent experiments fungicides (benomyl, etridiazole, formaldeyhyde and thiram) were added to the solution, GA₃ solutions were tested with and without added surfactants (Tween 80 and Agral 90) and two infiltration techniques were tested using a range of vacuums and durations of treatments. The fungicides and surfactants used increased flower losses; vacuum infiltration itself caused some flower losses compared with untreated bulbs. In most cases these flower losses were reduced when GA₃ (150-200 ppm) was added to the solution used for infiltration. For cv Apeldoorn previously cooled at 5°C for 12 weeks, vacuum infiltration with GA₃ (150-250 ppm) at 10 torr for 5-15 min reduced the duration of the glasshouse period by 5-7 d, compared to untreated bulbs. GA₃ treatments also reduced stem (and particularly last internode) length at flowering, and increased flower length. Vacuum infiltration can cause unacceptably high flower losses, although these can be reduced by omitting surfactants and by controlling the vacuum at between 10 and 260 torr.