The 2012 ASHS Annual Conference

Strobilurin fungicides are widely used on turf and ornamentals for disease control.  Additionally, they have been reported to increase stress tolerance in agronomic crops through increased production of antioxidant enzymes.  Pageant (pyraclostrobin + boscalid), a strobilurin fungicide labeled for disease control and plant health, was applied to Impatiens walleriana ‘Super Elfin XP White’ 72, 48, 24, or 1 hour before exposing plants to a heat event.  There were two control treatments, one with plants exposed to the heat event and one with plants maintained at 18.3 °C /21.1 °C (day/night).  The heat event was expressed in a programmable growth chamber over three 24-hr periods with 12-hr days at 35.5 °C (90 °F) and 12-hr nights at 32.2 °C (83 °F).  Pageant was applied as a foliar spray: 0× (non-treated) or 1× (0.228 g·L^-1).  Photosynthesis (Pn), stomatal conductance (Gs), and leaf area index [LAI (leaf dry weight per leaf area as g·cm³)] were measured before, during, and the day after the heat event. In addition, leaf samples were collected at the end of the heat event, immediately frozen in liquid nitrogen, and stored in a -80 °C freezer until determination of glutathione reductase concentration.  Prior to the heat event, Pn, Gs, and LAI showed no significant differences among treatments.  After the third day of the heat event, heat-treated plants had significantly higher Pn readings compared with nontreated plants maintained at ideal conditions (P = 0.0088).  However, after the heat event, Pn and Gs were similar among all treatments, whereas LAI was greater in impatiens sprayed with Pageant 48 or 24 hr before the heat event compared to the nontreated plants receiving no heat event (P = 0.0039).  Preliminary enzyme analysis indicates impatiens treated with Pageant did not have increased concentration of glutathione reductase (P = 0.3282).  Based on these results, Pageant applied to impatiens does not appear to increase heat tolerance.