POSTHARVEST TREATMENT WITH GLYPHOSATE TO DEVITALIZE ROSE AND CARNATION CUT FLOWERS

Glyphosate is being used presently to devitalize buds and cuttings of roses and carnations, respectively, for export to Australia. This is aimed at preventing the use of buds or cuttings as planting materials, thus reducing possible spread of diseases in the importing countries. The objectives of this study were to examine the uptake and accumulation of glyphosate and to determine the propagation ability of glyphosate-treated flower buds of roses and stem cuttings of carnations. The basal stem-ends of cut rose and carnation flowers were treated with ¹⁴C-glyphosate at activities of 1.42 and 0.58 Mbq respectively for 20, 120 and 180 min. Uptake and accumulation of ¹⁴C-glyphosate were determined by standard radioassay and autoradiography methods. Phytotoxicity of glyphosate was determined by histological technique and macropropagation.

Autoradiography of rose buds and carnation nodes revealed the presence of ¹⁴C, indicating uptake and translocation of ¹⁴C-glyphosate by the excised flower stalks. The buds and nodes were above the 10 cm soaking level of the flower stalks. Radioassay of the buds and nodes indicated that the radioactivity of ¹⁴C-glyphosate in rose buds ranged between 152 to 692 dpm·g^-1 sample while radioactivity of ¹⁴C-glyphosate in carnation nodes ranged between 150 to 241 dpm'g^-1 sample. The buds had higher radioactivity than the nodes presumably because they represent younger organs with higher metabolic activity. ¹⁴C uptake was higher in the first and third buds of the rose flower compared to the second and fourth buds. However in the carnation nodes, ¹⁴C uptake varied with different soaking times. In nodes soaked with ¹⁴C-glyphosate for 120 and 180 min, uptake of ¹⁴C was quite similar, whereby uptake was high in the first and fourth nodes from the flower. However in nodes soaked for 20 min, ¹⁴C uptake was high in the first and second nodes. Although ¹⁴C uptake and radioactivity varied in the different buds and nodes, as also reported for other plant parts (Bowmer et al., 1993; Tucker et al., 1994), the amount of labeled glyphosate in the treated flower stalks was sufficient to inhibit propagation. The use of matured buds from glyphosate-treated rose flower stalks for budding failed to develop a union between the bud and the rootstock. Stem cuttings from glyphosate-treated carnation did not survive through to 15 days compared to the control. Failure of budding was due to death and rupture of the outer cells. Glyphosate disrupts the shikimic acid pathway that produces aromatic amino acids required for protein synthesis and cell division in the meristematic regions of plants (Armhein et al., 1980).