Cut flower vase life is extended when plants are produced with microbial biostimulants

This report is funded by the ASCFG Research Foundation.
Laura Chapin and Michelle Jones, The Ohio State University DC Kiplinger Floriculture Crop Improvement Program

Biostimulants can improve the quality of flowering plants

Biostimulants are a diverse group of products or active ingredients marketed to promote plant growth and stress tolerance. The use of biostimulants during production may result in higher quality plants with increased flower numbers and size, increased shoot or root biomass, and greener leaves. The active ingredients in biostimulants may include humic substances, protein hydrolysates, biopolymers, botanical extracts, and/or beneficial microorganisms. These biostimulants promote growth and crop quality by increasing nutrient update and nutrient use efficiency, or stimulate plant defense responses to environmental stresses.   

The most common active ingredients in commercial biostimulants are microorganisms, including beneficial bacteria and /or fungi.  While many biostimulants claim efficacy in a wide range of greenhouse crops, many produce inconsistent and unreliable results in greenhouse environments.  While the application of beneficial bacteria or fungi to greenhouse production systems can improve flowering and increase the size of finished plants in containers, almost nothing is known about how these improvements to plant health may affect the vase life of cut flowers. We hypothesized that the improved nutrient uptake efficiency afforded by various biostimulant treatments would improve the postharvest quality and vase life of cut flowers. The goal of the research summarized in this article was to determine if producing plants with microbial biostimulants could extend the vase life of the cut flowers.  
Evaluating the effect of microbial biostimulants on cut flower vase life

Zinnia elegans Benary’s ‘Giant Purple’ plants were propagated by seed and grown to flowering under standard greenhouse production conditions. Plants were fertilized weekly with 75ppm N 15-5-15-CalMg. In addition to the fertilizer, plants were treated with biostimulants weekly. The biostimulant treatments included seven bacterial isolates from a unique collection of bacteria identified by researchers at The Ohio State University (OSU1-OSU7) and two commercial products (MycoApply Endo and Cease). There were also plants that did not receive any treatment (negative control). Plants were arranged in a random complete block design with one plant per treatment in each of the 12 blocks (Figure 1). Bacteria treatments (1-7) were applied as a weekly drench to the growing media. MycoApply Endo (Mycorrhizal Applications) was incorporated into the potting media prior to transplant at a 1-Tbsp per pot rate following label instructions, with no additional application. Cease (BioWorks) was applied as a weekly media drench at 2-fl oz. per 100-gal rate. Negative control plants were drenched with diluted liquid bacteria media (no bacteria added). Cease and MycoApply Endo are commercial biostimulants chosen for this experiment because we have shown that their application to bedding plants increases plant size, flower number, and chlorophyll content.

 

Flowers were harvested between 9:00 a.m. and 10:00 a.m. from each plant on the day the bloom was fully open (outermost whorl of petals was fully unfolded), stems were immediately placed in buckets of reverse osmosis (RO) water, and taken to an interior evaluation room.  The interior evaluation room temperature was set to 21°C and fluorescent lighting was provided for 12 h (7:00 a.m. – 7:00 p.m.).  The average day temperature was 22.2°C, relative humidity was 50.7%, and light intensity was 16.4 µM·m-2·s-1 as collected by WatchDog 2475 Plant Growth Station (Spectrum Technologies).  Stems were recut to a 30 cm length under water. The initial size was determined by measuring the diameter of the bloom and the fresh weight of the cut flower. Stems were placed in clear crystal bud vases with RO water, one stem per vase. Vases were arranged in a random complete block design to mimic the design of the greenhouse portion of this experiment (Figure 2). The vase life of each cut flower was recorded.  Vase life was terminated when 50% of the petals were wilted, necrotic, discolored, or showed symptoms of disease (i.e. gray mold/ botrytis blight) or when the stem exhibited bent neck.    
Microbial biostimulant treatments extend vase life
 
There was no difference in the cut flowering stem weight or bloom diameter and no visible differences in plants during production (data not shown). Cut flowers from plants treated with OSU2, OSU3, OSU4, or the commercial products had a much longer average vase life than the untreated (negative control) flowers. These treatments extended vase life approximately 5.6-10.1 days longer than the untreated flowers (Table 1). 

The addition of beneficial microorganisms during the production of zinnia plants did not alter plant growth or scheduling as we had originally predicted, however there was a very large positive influence on the postharvest performance of the cut flowers. Treatment with beneficial microorganisms increased the vase life of zinnia cut flowers. One treatment, OSU2, resulted in cut flowers that lasted 10 days longer than the flowers from the untreated plants.  Further studies are needed to determine how these differences are influenced by the addition of cut flower preservatives and to evaluate different cut flower species.