Efficacy of Uniconazole as a Phytoprotectant Against $SO_2$ Injury in Snap Bean

This study was conducted to determine the efficacy of using uniconazole,[(E)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazole-1-yl)-1-penten-3-ol)] as a phytoprotectant against $SO_2$ injury in snap been (Phaseolus vulgaris L. 'Strike'). Thirteen days prior to $SO_2$ fumigation, plants were given a 100 ml soil drench of uniconazole solution at concentrations of 0.02, 0.10, 0.25 and 0.50 mg/pot. All four uniconazole concentrations were significantly effective in providing protection against $SO_2$ exposure(3 h at 1.5 ppm), but uniconazole treatment above 0.02 mg/pot severely reduced stem elongation, leaf enlargement, flowering date and pod number and weight. Uniconazole treatment had little or no effect on stomatal conductance but reduced transpiration rate on a whole plant basis by nearly 40%. This may reflect an alteration in canopy structure by reducing stem elongation and leaf enlargement. Although uniconazole did not increase the activities of superoxide dismutase(SOD) and peroxidase(POD) in non-$SO_2$-fumigated plants, it significantly increased those enzyme activities in $SO_2$-fumigated plants. Chlorophyll concentration on the basis of unit area was increased 50-60% by uniconazole. However, the difference was not detected on the basis of dry weight. $SO_2$ increased variable chlorophyll fluorescence (Fv) 48% after 1.5 h of exposure in non-uniconazole treated plants but decreased Fv in the plants after 3 h of exposure. By appliing uniconazole, it was possible to maintain high Fv values in the latter group of plants. These results suggest that the phytoprotective effects of uniconazole are related to its growth-retarding properties as an anti-gibberellin as well as the increase of activites of free radical scavengers such as SOD and POD.