The 2009 ASHS Annual Conference

Standard greenhouse bedding plant production protocol may provide for alleviating heat stress if the environment is closely monitored.  However, plants entering postproduction in the market and eventually the landscape often face an inconsistent environment and can be subject to long periods of stress. Preconditioned plants (acquired stress tolerance) may greatly improve postproduction marketability and survival in the landscape when exposed to a challenging environment. The objective of this study was to determine the efficacy of acquired temperature tolerance by imposing heat shock during greenhouse production for improving landscape survivability of Petunia x hybrida. Nineteen petunia cultivars from three plant classes (floribunda, grandiflora, or spreading) were previously evaluated, where cultivars within the same plant class and series were grouped as either best or worst overall landscape performance and then subjected to heat shock. Petunias were grown in a greenhouse at 30° C and exposed to heat shock of 45° C for 4 hours, every 3 days, for 3 weeks. Weekly harvests showed a significant increase in flower count, flower size, internode length, leaf area, leaf area ratio and relative growth rate regardless of heat shock exposure.  However, the heat shock treatment significantly decreased shoot dry weight and absolute growth after three weeks of treatment.  Field performance evaluations of these greenhouse grown plants indicated that some cultivars appeared to develop acquired stress tolerance based on the heat shock treatment.