THE INFLUENCE OF THE GROWTH RETARDANTS PACLOBUTRAZOL, ANCYMIDOL AND S-3307 ON GROWTH AND DEVELOPMENT OF ACHIMENES LONGIFLORA, DC. 'VIOLA MICHELSSEN' GROWN UNDER TWO LIGHT REGIMES.

Growth retardants are used commercially in Achimenes to reduce height of main stem and to promote development of axillary shoots in order to get a more compact plant. The growth retardants used in this experiment have not been previously applied on Achimenes. The effect of these three growth retardants on height, branching and flowering are studied. Furthermore, the hypothesis that by reducing growth of the aerial parts of the plant might induce the formation of more and/or bigger rhizomes is investigated.

Plants of Achimenes longiflora DC., cv Viola Michelssen, propagated by stem cuttings and uniform in height (2 cm) with 3 to leaf whorls, were sprayed once or twice with one of the following three growth retardants in three different concentrations each:

Paclobutrazol at 25, 50, and 100 ppm

Ancymidol at 12.5, 25 and 50 ppm

S-3307 at 0.05, 0.5 and 5 ppm

Each plant, depending on application treatment, was sprayed with 5 ml on the first application, and with 10 ml of solution on the second. Plants were kept in a greenhouse at 21°C either under natural daylight (unshaded) or under a shading cloth (shaded) that provided a 40% light reduction for 12 weeks. The experimental layout was a split-plot design with 4 replications, two light regimes (main plots) and 2 application frequencies(sub-plots). There were 10 growth retardant treatments randomized within each sub-plot. 4 plants per replication were the experimental unit. Halfway and at the end of the 12 week period height of the main stem and numbers of leaf whorls and axillary shoots were recorded. The number of days to first flower was also observed. At the end of the experimental period the following data were collected: total number of flowers, number of rhizomes and dry weight of aerial parts and rhizómes. Data were analysed according to analysis of variance and means were compared by the Wilcoxon test (p=0.05).