THE PLANT-GROWTH REGULATOR ACTIVITY OF THE FUNGICIDE, EPOXICONAZOLE, ON GALIUM-APARINE L (CLEAVERS)

The plant growth regulator activity of epoxiconazole, a new triazole fungicide, was investigated by time-course, dose-response and histology experiments with Galium aparine L. (cleavers). Seven days after treatment with 125 g ai ha(-1) epoxiconazole (field rate), plant height was reduced by 43%. After seventeen days, leaflet area was reduced by 27% but leaflet fresh weight was not significantly influenced. This was partly because leaflet thickness had increased by 20% following epoxiconazole application. Chlorophyll concentrations were also increased on a unit area basis. Examination of leaflet anatomy showed that epoxiconazole elongated palisade, spongy mesophyll and upper epidermal cells. For example, 125 g ai ha(-1) caused a 35% increase in the length of spongy mesophyll cells. Epoxiconazole also prevented cell separation as there were significantly more palisade and spongy mesophyll cells per unit area than in leaflets sprayed with water. Stem development was reduced and 125 g ai ha(-1) inhibited the elongation of pith cells in stem tissue by 53%. However, the simultaneous application of gibberellin A(3) (GA(3)) with epoxiconazole resulted in stem elongation similar to that of control plants. These observations are consistent with the expected effects following the inhibition of cytochrome P-450 dependent enzyme activity.