The Response of Tulips to Gibberellins Following Different Durations of Cold Storage

SummaryTo attempt to reduce or eliminate the cold requirement necessary for high quality tulip blooms, gibberellins (GA) were applied to non-cooled, partly cooled and fully cooled direct-forced bulbs of cvs Apeldoorn and Paul Richter. These cultivars have long-and medium-length cold requirements, respectively. GA3 was applied by bulb injection, by bulb immersion and by root feeding. Greatest effects were obtained by injecting 1 mg GA, per bulb: this treatment increased Apeldoorn flower survival in non-cooled bulbs, and in partly and fully cooled bulbs gave earlier flowers with longer first internodes but shorter overall stem length. Other GA treatments were less effective or ineffective. With cv Paul Richter all these treatments were ineffective. In other trials, however, both cultivars responded to injections of GA4/7. GA appeared to substitute for the cold period in respect of speed of flower development and, to a lesser extent, for first internode extension: but GA-treated partly cooled bulbs lacked the rapid pre-flowering upper internode extension associated with fully cooled bulbs. The reasons for the apparent failure of GA more than partly to substitute for cold in tulip bulbs are discussed.