2010 Annual Report
1a.Objectives (from AD-416)
Objective 1: Determine the effects of the plant growth regulator TDZ on the quality and display life of cut flowers and potted flowering plants. Objective 2: Develop effective and environmentally-sound treatments to protect cut rose flowers from postharvest loss due to infection by Botrytis cinerea. Sub-objectives: 2a) Determine optimal time for applying treatments to control Botrytis on cut roses; 2b) Evaluate efficacy of anti-fungal GRAS compounds for the control of Botrytis cinerea on cut roses. Objective 3: Determine molecular processes in flower senescence for the purposes of developing 'freshness' indicators for cut flowers and future genetic manipulation of flower senescence. Sub-objectives: 3a) Utilize virus-induced gene silencing (VIGS) technology to down-regulate the expression of NAC and MADS-box transcription factor genes and to test the effect of silencing these genes on flower longevity; 3b) Test a range of genes that are associated with floral aging and senescence for use as molecular indicators of freshness.
1b.Approach (from AD-416)
In Objective 1, we will test TDZ, a non-metabolized cytokinin, for its potential to extend the display life of cut flowers and potted flowering plants. In Objective 2, we will characterize the basic biology of Botrytis-rose flower interactions with a view to developing effective disease control measures. We will evaluate GRAS chemicals as they offer a cost effective and environmentally friendly alternative to current conventional fungicides. In Objective 3, we will identify regulatory genes that mediate retardation or acceleration of petal senescence. This will provide a foundation for the development of diagnostic molecular indicators of 'freshness' for cut flowers and for downstream analysis of the effects of loss of function of these genes on the genetic regulation of the senescence network. The integrated nature of this project will enhance the quality and longevity of flowers, leading to greater industry-wide profitability. Formerly 5306-13210-002-00D (11/08).
Postharvest losses and poor quality for floricultural crops usually results from the combination of infection by Botrytis cinerea, earlier leaf and flower senescence and abscission, and germplasm that lacks desirable postharvest qualities. This past year we continued to investigate, develop and implement strategies for improving postharvest performance for floriculture crops. Specific areas advanced included the following:.
1)We characterized the efficacy of thidiazuron (TDZ), a compound with plant hormone cytokinin-like activity, to improve longevity and to prevent leaf yellowing in bulb flower tulips. A postharvest spray with TDZ significantly extended the vase life of tulip flowers. Leaves of tulip plants treated with TDZ delayed yellowing for considerable time..
2)We continued our investigation into the potential of Chlorox (sodium hypochlorite) to reduce Botrytis infection on cut rose flowers. We showed Clorox reduced Botrytis infection on rose flowers when applied as a postharvest dip treatment. We determined the efficacy of different bleach solutions to reduce Botrytis on rose flowers and compared the effectiveness of the optimal bleach solution to conventional fungicides. The capacity of household bleach to reduce Botrytis on flowers exposed to commercial shipment also was determined..
3)We developed Virus-Induced Gene Silencing (VIGS) technology in four o’clock plants, a model crop for investigating flower senescence and abscission. We are continuing to investigate a large number of ‘transcription factors’ to identify a ‘master switch’ protein that may be the key to regulate senescence and abscission. VIGS-silencing of genes such as a proline-rich protein and a transcriptional regulator delayed leaf and flower abscission in tomato..
4)We hypothesize that inhibition of protein synthesis or preventing targeted protein degradation at the onset of senescence could extend flower life. Silencing protein synthesis (by silencing a ribosome component) or protein degradation (by silencing a proteasome subunit) significantly extended flower life in transgenic petunia plants. Identification of effective targets for the inhibition of protein synthesis and targeted protein degradation paves the way for further research into the mechanisms and control of floral senescence..
5)Flower senescence is under tight genetic control and involves changes in the transcriptome. To identify a common set of genes up-regulated during floral senescence, in a broad range of cut flower species, we developed a microarray that represents almost all the unique EST's from petunia, tomato and potato. Preliminary results indicate more than a hundred genes with modified expression patterns during floral senescence, including some transcriptional regulators.
Application of thidiazuron (TDZ), a non-metabolized cytokinin, extends the life of bulb flower plants. Early wilting and leaf yellowing are significant quality problems in a wide range of ornamental potted and bedding plants. Application of low concentrations of thidiazuron (TDZ) has been shown to be a very effective means of delaying leaf yellowing and flower senescence in alstroemeria, stock, lilies and cyclamen. ARS Researchers in Davis, CA examined the possible use of this compound for delaying leaf yellowing and flower senescence in a range of bulb flower plants, including tulips. Spray treatments with TDZ at the end of the production cycle dramatically delayed leaf yellowing and extended flower longevity. Our results indicate significant potential for TDZ as a tool to improve the postharvest life of bulb flower plants.
Silencing of a Proteasome Component Delays Floral Senescence. Targeted protein degradation via the ubiquitin/26S proteasome pathway is known to play an important function in many phases of plant growth and development. In previous research we demonstrated that silencing a putative E3 ubiquitin ligase (a component of the pathway) delayed floral senescence. To further test the function of targeted protein degradation in flower senescence, ARS Researchers in Davis, CA chose to silence an endopeptidase component in the 20S core of the 26S proteasome. Petunia hybrida was transformed with a construct allowing for chemically-inducible silencing of this protein. Flowers from transgenic plants treated with the chemical inducer showed doubled vase life than controls (transgenic flowers held in water). These results indicate that targeted protein degradation plays an important regulatory role in floral senescence.
Treatments with Clorox reduces Botrytis disease in cut rose flowers. Infection with the fungal pathogen Botrytis cinerea reduces the market value of many cut flower species. ARS Scientists in Davis, CA continued investigations into the potential of Clorox (sodium hypochlorite) to reduce Botrytis infection on cut rose flowers and showed that Clorox could reduce Botrytis infection on rose flowers when applied as a postharvest dip treatment. Given that given that sodium hypochlorite is the active ingredient in household bleach, we determined the efficacy of different bleach solutions to reduce Botrytis on rose flowers. Our results highlight the potential for Clorox use as a simple alternative postharvest treatment for the control of Botrytis on cut rose flowers. Our findings also point to an exciting opportunity to include testing the effectiveness of this benign compound on additional rose varieties and flower species.
Jiang, C., Wu, L., Macnish, A., King, A., Yi, M., Reid, M.S. 2009. Thidiazuron, a non-metablized cytokinin, shows promise in extending the life of potted plants. Acta Horticulturae. 847: 59-65.
Macnish, A., De Theije, A., Reid, M.S., Jiang, C. 2009. An Alternative postharvest handling strategy for cut flowers-dry handling after harvest. Acta Horticulturae. 847: 215-221.
Macnish, A.J., Negre-Zakharov, F., Jiang, C., Reid, M.S. 2010. PHYSIOLOGICAL AND MOLECULAR CHANGES DURING OPENING AND SENESCENCE OF NICOTIANA MUTABILIS FLOWERS. Plant Science. 179:267-272.