Articles
THE INVOLVEMENT OF GA4/7 IN GROWTH AND FLOWERING OF TULIP CV. APELDOORN
If the cold-requirement is not fullfilled, slow growth and incomplete flowering with discoloured tepal tips will follow.
Gibberellins (GA’s) can greatly influence this process.
Application, in general, will increase the flowering percentage and diminish the number of days from planting to flowering (Van Bragt and Zijlstra, 1971; Rudnicki et al., 1976; Bylov and Smirnova, 1979; Hanks,1982.; Hanks, 1985; Jones and Hanks, 1985).
Growth is also under the influence of GA’s, depending on the internode studied.
Much understanding has come from determining the changes in endogenous GA’s (Van Bragt, 1971; Aung and De Hertogh, 1968; Aung et al., 1969; Alpi and De Hertogh, 1975; Okubo and Uemoto,1985; Okubo and Uemoto, 1986; Okubo et al., 1986) as well as from studying growth after the application of GA’s, sometimes in combination with anti-GA’s (Op den Kelder et al., 1971; Shoub and De Hertogh, 1974; Hanks and Rees, 1977; Cocozza Talia and Stellaci, 1979; Moe, 1980; Hanks and Rees, 1983; Saniewski, 1989; Kawa and Saniewski, 1990; Saniewski et al., 1990; Deneke and Keever, 1992; Suh et al., 1992; Rebers et al., 1994).
Much research in applying GA’s has been done for practical purposes, to eliminate the lengthy cold-period or to obtain pot tulips.
For cut tulips, stem length should be at least equal to that of control plants as the length of the tulip stem is still a quality factor.
Stem length of the tulip flower after applying GA’s has been reported to be longer, shorter or equal to untreated control plants at the moment of flowering.
However, the reported data are difficult to compare, as there are differences in the cultivar used, the time after stage G before the cold period started, the duration of the cold-treatment and the way the cold-treatment was applied, the different GA’s used, and the method and time of GA application.
We looked at this problem from a different angle, considering growth as a kinetic process of several weeks, and flowering as a moment within this process.
Experiments were performed with cultivar Apeldoorn, twice a year during two years.
The bulbs received a cold-treatment of either 6, 9, 12 or 15 weeks at 5°C, and were thereafter injected with GA4/7 at a rate of 0, 1, 10 or 100 μg/bulb respectively.
As a control, uninjected bulbs were used.
The tulips were grown under low light conditions, or in total