Location: Crops Pathology and Genetics Research2009 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).
3. Progress Report
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 following: 1). Developed a postharvest control method for Botrytis cinerea infection of rose varieties using environmentally-friendly chemicals. We have demonstrated that a common household disinfectant Clorox (sodium hypochlorite) could be used as a potential biocide for effectively controlling Botrytis in cut rose flowers. We also found that the efficacy of the fungicide to prevent Botrytis infection on rose flowers was greatest when fungistatic compounds were applied at about 6 hours after harvest. 2). We tested the efficacy of thidiazuron (TDZ), a phenyl urea compound with cytokinin-like activity, to improve opening and longevity for some cut flowers. A postharvest pulse with TDZ significantly extended the vase life of iris flowers. TDZ treatment also stimulated an extension in the length of flower shoots that, in turn, led to more complete opening of flowers. Provision of 20% sucrose in the TDZ plus GA3 treatment had an additive effect, and increased vase life and shoot growth. Flowers pulsed with this combined treatment prior to storing flowers dry for two-week at 0°C were also associated with maximum flower opening and display life upon their placement in vases. The postharvest life of Bird-of-Paradise was also improved up to 30% by pulsing cut stems with TDZ. Pulsing with TDZ plus 20% sucrose doubled the number of florets that opened on each inflorescence. 3). we have developed a universal primer for isolation of fragments of a gene encoding phytoene desaturase (PDS) for use in Virus-Induced Gene Silencing (VIGS) studies. We are continuing to investigate a large numbers of so-called ‘transcription factors’ to identify a ‘master switch’ protein that may be the key to regulate floral longevity. VIGS-silencing one of NAC transcription factors dramatically reduced flower longevity in petunia, suggesting that this gene may play an important role in regulating flower senescence. Abscission, the separation of organs from the parent plant, results in postharvest quality loss in many ornamentals and other fresh produce. Silencing KD1, a transcriptional regulator, delayed flower abscission in tomato, suggesting that KD1 may be involved in the formation of abscission zone. 4). We have conducted tests on the efficacy of postproduction treatment with abscisic acid (ABA) to increase the drought tolerance of potted nursery plant species during retail display with one of the largest growers in California. ABA shows promise as a postproduction treatment for improving the drought tolerance of potted miniature rose and Spanish lavender plants. We have also determined if potted flowering Phalaenopsis plants could be hardened to tolerate chilling temperatures by acclimatization at moderately low temperatures.
1. Screen chemical compounds for controlling Botrytis infection. Infection by the fungus Botrytis cinerea is one of the most common and elusive pathogen problems in postharvest ornamentals. A range of compounds including environmentally-friendly oxidizers (i.e. benzoic acid, chlorine dioxide, hydrogen peroxide, peroxyacetic acid, potassium permanganate, and sodium hypochlorite) were evaluated by ARS scientists in Davis, CA as postharvest dip treatments for the control of Botrytis cinerea infection on cut rose flowers. Several highly promising fungistatic compounds such as a chlorine-based oxidizer were identified with potential to control Botrytis disease on cut rose flowers. Dipping rose flowers in the oxidizer significantly reduced Botrytis development. These results highlight the potential of this simple and safe biocide for reducing postharvest Botrytis infection on rose flowers.
2. Optimal Treatment Time for controlling of Botrytis infections. Botrytis spores cause disease in cut flowers that reduce post harvest quality. Airborne Botrytis spores are known to adhere to rose petal tissues during growth and development of flowers. Exposure of these flowers to free moisture or high relative humidity for as little as 3 hours is generally sufficient to trigger spore germination and initiation of subsequent tissue infection. ARS scientists in Davis, CA found that the efficacy of fungicides to prevent Botrytis infection on rose flowers was greatest when fungistatic compounds were applied at about 6 hours after harvest. These data indicate the opportunity to optimize the effectiveness of our relatively benign biocides, by treating the fungus when is at its most vulnerable development stage.
3. Thidiazuron (TDZ), a non-metabolized cytokinin, shows promise in extending the life of cut flowers. The failure of some cut flowers to open fully after dry transport and storage is a major postharvest problem. The marketability of these flowers is also limited by their short display life. TDZ is a non-metabolized phenyl urea compound with cytokinin-like activity, and is a potent inhibitor of leaf senescence in cut flowers. ARS scientists in Davis, CA found that a postharvest pulse with TDZ or TDZ containing formulation extended life of Iris and Bird-of-Paradise flowers. Our findings highlight the potential use for TDZ as a postharvest pulse treatment to improve the opening and longevity of cut flowers.
4. A universal primer for isolation of fragments of a gene encoding phytoene desaturase (PDS) for use in Virus-Induced Gene Silencing (VIGS) studies. Although VIGS is a powerful tool for assaying the effects of gene silencing in plants, most taxa that have been studied using this approach, are in the Solanaceae family. ARS scientists in Davis, CA typically use silencing of PDS in preliminary tests of the feasibility of using VIGS. Silencing this gene results in a characteristic photobleaching phenotype in the leaves. Efficient silencing requires the use of fragments that are more than 90% homologous to the target gene. We designed a set of universal primers to a region of the PDS gene that is highly conserved among species. These allow investigators to isolate a fragment of the homologous PDS gene from any species of interest.
5. Functional analysis of regulatory genes associated with flower senescence and abscission by VIGS. We used virus-induced gene silencing (VIGS) as a tool for evaluating the possible regulatory role of a number of transcription factors in leaf and flower senescence and abscission. The genes encoding transcription factors were identified from a public database and cloned from cDNA libraries of petunia and tomato. The time to pollination-induced petal wilting was increased by silencing a petunia homolog of a MADS-box gene while silencing of NAC type of transcription factors accelerated flower senescence. These results suggest the possibility that, as in leaf senescence, floral senescence is the result of a regulatory network. Our research will benefit the industry in the longer term, providing more effective means of increasing the vase life and reducing leaf and flower abscission.
Reid, M.S., Chen, J., Jiang, C. (2009) VIRUS-INDUCED GENE SILENCING FOR FUNCTIONAL CHARACTERIZATION OF GENES IN PETUNIA. In Petunia: Evolutionary, Developmental and Physiological Genetics. T. Gerats ed. Springer, New York, pp381-394.