Master of Science (MS)


Plant, Environmental Management and Soil Sciences

Document Type



Heat stress is one of the greatest challenges affecting growth and development of bedding plants during greenhouse production and in the landscape. Inducing an acquired stress tolerance during production may greatly improve postproduction marketability and survival in the landscape when exposed to heat stress. Few researches have investigated the morphological effects of bedding plants during heat shock or enduring heat stress preconditioning in the greenhouse and subsequent landscape performance. The present objectives were to quantify morphological and physiological responses to heat stress and use this information to develop a greenhouse protocol for inducing acquired thermotolerance for improved landscape survivability using Petunia x hybrida. Preliminary studies revealed petunia Dreams ‘Midnight’ grown at 35/25 or 40/30ºC caused desirable traits such as compact growth for improved landscape performance but also decreased flowering during production resulting in poor marketable quality. Heat shock at 35 or 40ºC for 2 h every 7 d did not significantly effect petunia growth and development. Determination of optimum heat shock temperature and duration for development of acquired thermotolerance revealed that heat shock every 3 d or enduring heat stress was most effective at 45ºC. However, the critical duration or frequency of exposure necessary for promotion of a heat tolerant marketable plant at 45ºC was not fully elucidated within the treatments investigated. Chlorophyll fluorescence (maximum quantum efficiency of PSII - Fv/Fm) was measured in young and mature leaves to investigate stress response and photosynthetic performance of petunia pre and post acquired thermotolerance test. Fv/Fm ratios indicated the heat shock or enduring heat stress treatments did not cause permanent damage to photosynthetic apparatus. Nineteen previously evaluated petunia cultivars from three plant classes were heat shocked at 45ºC for 4 h every 3 d during greenhouse production followed by landscape evaluation. Greenhouse and field results indicated the heat shock treatment did not significantly promote heat tolerance compared to control. The critical temperatures used in this study were effective for promoting heat tolerance in petunia, but specific durations or frequency of exposure at 45ºC should be further investigated in order to define an effective acquired thermotolerance protocol to improve landscape survivability.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Kuehny, Jeff S.