De bloemproduktie van Gerbera

The morphology of gerbera seedlings was studied in order to establish which factors determine flower yield and to see whether there are differences between the plants concerning their characteristics.The gerbera has a sympodial rhizome which forms 7 - 24 leaves before initiating a flower bud. This flower is formed by the apical meristem. Almost simultaneously a second flower bud develops in the axil of the uppermost leaf primordium while a vegetative axis develops in the axil of the second leaf primordium from the top. After a number of leaves (2 - 8; see Chapter 2) this axis forms a terminal flower bud, a lateral flower and again a vegetative continuation. The sympodium thus formed, has been regarded as the main stem.Shoots initiated in the lower leaf axils are called lateral shoots; these also show sympodial growth.Results of a one-year experiment with seedlings show a positive correlation (at flower initiation as well as after 1 year) between the number of lateral shoots and the number of leaves and flowers. No correlation was found, however, between leaf production and flower yield, although as the number of leaves increases the production of flower buds is promoted. This can be explained by flower bud abor tion: the more leaves, the higher the percentage of aborting flower buds.In order to investigate the influence of external factors on the plant characte ristics important for flower production, four different phaenotypes have been propagated vegetatively and subjected to treatments with different daylengths, light intensities and temperatures.I. DaylengthAll clones performed best at a daylength of 8 to 10 hours. Short day (8 hours) promotes flower yield as compared to long day (16 hours) because under short day conditions- the main axis shows earliest flowering and also the highest number of continua tions,- the highest number of lateral shoots are initiated and also form the highest amount of continuations,- these combined reactions of main axis and lateral shoots result in optimum flower bud formation.Daylength does not seem to influence flower bud abortion.II. Light intensityHigh light intensity increases flower yield. This has been demonstrated in an experiment with high and low light intensities, as well as in all experiments carried out in autumn when the amount of natural light is diminishing. The reason is that under high light intensity conditions:- the highest number of lateral shoots are formed, with a high number of conti nuations,- consequently flower bud production is larger,- the highest flower bud abortion is found during the months with the lowest light intensity.In the experiment with different light intensities no difference in abortion ra te could be found, however.III. TemperatureLow temperature enhances all the effects caused by short day: more lateral shoots are initiated and more shoots flower. Low temperature also causes less flower bud abortion than high temperature in this case. Under high light intensity conditions low temperature enhances the above mentioned effects by accelerated continuation of the lateral shoots as compared with high temperature. The reason for this pheno menon is the formation of less leaves per continuation at low temperature.All clones showed the same tendency in their reaction to daylength and light in tensity, although there were quantitative differences. With respect to the tem perature the clones behave differently: three of them prefer a low temperature, while the fourth prefers a high temperature.Main shoot and lateral shoots influence eachother. When the main shoot is taken away, more lateral shoots are formed; when the lateral shoots are taken away, the main axis continues faster. However, neither treatment increases total flower yield.Again the four clones show the same tendency. but the rate of reaction varies. The stronger the apical dominance of the main axis, the stronger also the influence of the lateral shoots on the main axis.Defoliation to various degrees serves no purpose, as this does not affect leaf, shoot or flower bud production, nor flower bud abortion, which means that there is no difference in flower yield. This held true for all clones