2012 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.
Postharvest losses and poor quality for potted plants and cut flowers usually results from a combination of factors which includes, infection by Botrytis cinerea, earlier leaf and flower senescence and abscission, and germplasm which lacks desirable postharvest qualities. This past year we continued to investigate, develop and implement strategies for improving postharvest performance for potted plants and cut flowers. Specific areas advanced include;.
1)Confirmed potential utility of thidiazuron (TDZ), a compound with plant hormone cytokinin-like activity, to control plant growth in potted plants. Spraying with TDZ up to 400 ppm significantly reduced plant growth of potted minirose plants. Plants treated with TDZ showed shorter internodes and thicker stems compared with plants treated with water as control..
2)Investigated the potential of an environmentally-friendly household disinfectant bleach (sodium hypochlorite) to reduce Botrytis infection on minirose plants. Our results demonstrated bleach solutions (200 ppm) reduced Botrytis infection on rose flowers when sprayed or applied as a dip treatment. 3). Flower senescence and abscission are under tight genetic control. Using Virus-Induced Gene Silencing (VIGS) technology, ARS scientists in Davis, CA, have identified a large number of genes that may play key roles in controlling leaf and flower senescence and abscission. VIGS-silencing of regulatory genes delayed leaf and flower senescence and abscission. 4). Plant hormone abscisic acid (ABA) plays important roles in the plant drought tolerance pathway. ARS scientists in Davis, CA, have generated petunia plants in which a key limited factor gene in the ABA biosynthesis pathway (NCED) is over-expressed under the control of a specific stress-inducible promoter. The plants develop normally under non-stress conditions. The transgenic plants survived and recovered much better after re-watering when the plants are held under extremely drought conditions (i.e. two weeks without water). Characterization of the genes controlling drought tolerance and an understanding of their regulation will facilitate development of drought tolerant genotypes for all crop species.
Application of thidiazuron (TDZ) reduced plant height. A common problem in the production of ornamental potted plants is undesirably tall growth, so inhibitors of gibberellic acid (GA) biosynthesis including A-rest (ancymidol), B-nine (daminozide), Bonzi (paclobutrazol), Cycocel (chlormequat chloride), and Sumagic (uniconazole), are commonly used to control plant height. We studied the effects of TDZ applications on the growth and development of potted miniature roses. Plants treated with foliar sprays of TDZ (up to 200µM) exhibited a considerable reduction in plant height compared to the controls (0 µM). TDZ-treated plants tended to have shorter internodes and thicker stems. Our results indicate significant potential for TDZ as an alternative way to control plant height.
Improving drought tolerance in potted plants. Plant hormone abscisic acid (ABA) plays important roles in the plant stress tolerance pathway against drought. Plants constitutively expressing a key gene in the ABA biosynthesis pathway (NCED) exhibit dramatically enhanced drought tolerance, but show a variety of defects including poor germination, growth and development. We have generated transgenic petunia plants in which NCED is over-expressed under the control of a specific stress-inducible promoter. The plants develop normally under non-stress conditions. The transgenic plants survived and recovered after re-watering when the plants are exposed to low water availability under extreme drought conditions (two weeks without water). This approach overcomes most of the defects associated with constitutive ABA production and provides excellent means for improving drought tolerance.
De Freitas, S.T., Jiang, C., Mitcham, E.J. 2011. Mechanisms involved in calcium deficiency development in tomato fruit in response to gibberellins. Journal of Plant Growth Regulation. DOI 10.1007/s00344-011-9233-9.
Reid, M.S., Jiang, C. 2011. Florigen unmasked - exciting prospects for horticulture. Chronica Horticulturae. 51:7-9.
Singh, A., Liang, Y., Kumar, P., Reid, M., Jiang, C. 2012. Co-silencing the mirabilis antiviral protein permits virus-induced gene silencing in Mirabilis jalapa. Journal of Horticultural Science and Biotechnology. 87:334-340.
Reid, M.S., Jiang, C. 2012. Postharvest: Cut flowers and potted plants. Review Article. In "Ornamental Geophytes: From Basic Science to Sustainable Production" by CRC Press, Eds. Rina Kamenetsky, Hiroshi Okubo.