Drought Stress Tolerance Induced in Ornamental Plants Through Foliar Application of Synthetic Abscisic Acid (s-ABA)

Drought stress is a major contributing factor to inventory loss in shipping and retailing phases of bedding plant production.  Plug transplants (seedlings grown at high densities in small, individual cells) are particularly susceptible to drought stress during post-production due to their small root to shoot ratios and low media volume from which to absorb water.  An exogenous application of the synthetically derived form of abscisic acid (s-ABA) should reduce transpirational water loss, allowing plants to remain marketable longer when periods of drought stress are experienced.  To test the effectiveness of s-ABA in extending marketability of bedding plants in 288 cell plug trays (one plant per 2 cm²), foliar applications of 0, 300, 600, or 900 mg·L^-1 s-ABA were applied to half trays of Impatiens walleriana (impatiens) or Petunia x hybrida (petunia), and treatments of 0, 250, 500, or 750 mg·L^-1 s-ABA were applied to half trays of Tagetes patula (marigold). For each species, a randomized complete-block design with 4–5 blocks was utilized and each experiment was conducted twice.  Plug trays were shipped overnight from the producer and maintained in a greenhouse (38.0 °C day/18.0 °C night).  Water was withheld until plants were no longer marketable (more than 50% of evaluated plants per experimental unit visibly wilting).  Tray mass was measured and wilting and chlorosis of 100 plants in the center of each tray were evaluated daily.  For impatiens and petunias, evapotranspiration (as measured by tray weight) was significantly lower for s-ABA treated plants as compared to controls on the first two days following s-ABA application and treated marigolds had significantly lower evapotranspiration than controls for the first day following s-ABA application.  Additionally, s-ABA treatments resulted in significant extensions in marketability (1 to 4 days) as compared to controls.  For impatiens and petunias, 600 mg·L^-1 and 900 mg·L^-1 s-ABA treatments provided significantly greater extensions in marketability than 300 mg·L^-1.  For marigolds, days of marketability were not significantly different between the s-ABA treatments.  Chlorosis was not observed in impatiens, but was noted in the cotyledons of petunias and marigolds; however, chlorosis was not severe enough to cause unmarketability of plant material.  Taken together, these results demonstrate that s-ABA applications can significantly extend the marketability of impatiens, petunia, and marigold plug trays, suggesting that s-ABA can be utilized to extend plug tray shelf life during incidents of drought stress common in shipping and retail environments.