2008 Annual Report
1a.Objectives (from AD-416)
To develop new or improved methods for hydroponic and greenhouse crop
production and greenhouse disease and pest management; to clone geranium
(Pelargonium spp.) genes involved in post-transcriptional gene silencing
(PTGS) to boron and silicon; and to develop a consistent mechanical inoculation
method for infecting geranium (Pelargonium spp.) with Tobacco ringspot
viruses (TRSV) and Tomato ringspot viruses (ToRSV) present in several
accessions derived from the Ornamental Plant Germplasm Center, Columbus,
1b.Approach (from AD-416)
A joint research project on Hydroponic and Soilless Culture will be
initiated between the USDA, ARS and the University of Toledo. Proper
management of insect and disease will enhance profitability and
competitiveness of American growers. USDA, ARS will hire a Research
Horticulturist and a Research Plant Pathologist to be located at the
University of Toledo as an ARS Worksite of the USDA, ARS, Application
Technology Research Unit in Wooster. Virus diseases of Pelargonium spp.
are relatively common but different to assess because the host is usually
not killed by infection. Develop a consistent mechanical inoculation
method. Infect plants with TRSV and ToRSV and expose to varying
concentrations of boron and silicon to determine their effects on viral
disease and virus titers will be examined by serology and RT-PCR. The
effects of photoperiod and temperature on virus infection will be examined
in a similar manner.
Since it may take some time to develop a consistent method of mechanical
inoculation with TRSV and ToRSV in Pelargonium species, it would be
advantageous to use plant material that is already infected. However, it
would be important to first find out what viruses are present within these
infected plants. At least two of the accessions obtained from the
Ornamental Plant Germplasm Center are apparently infected with a ringspot
virus. Therefore, we will need to characterize these viruses. This will
be done by electron microscopy, serological techniques, and RT-PCR.
Cuttings would be propagated from this previusly infected material and
exposed to different nutrient and environmental conditions and their
effects on virus infection would be analyzed as described above.
Two of the most common viruses of Pelargonium were detected in a survey of plants from the Ornamental Plant Germplasm Center are Pelargonium flower break virus (PFBV) and Pelargonium line pattern virus (PLPV). Copper is the active ingredient of several commonly-used pesticides. It is also used by one of the local growers on pepper to control bacterial leaf-spot. The major nutrient modified in these experiments was silicon, a beneficial element. Control tobacco inoculated with Tobacco Ring Spot Virus typically showed chlorotic lesions that eventually turned necrotic. Plants supplemented with silicon showed a delay in viral systemic spread and a delay in necrotic symptom formation. These data show that silicon helps plants to defend themselves against viral infection and we are assembling these data for a manuscript. Copper toxicity is a problem in plug production and at other stages with other crops. One of the local growers uses a copper-based spray on pepper to control bacterial leaf spot. Therefore, a study was performed to examine copper stress. Silicon was reported to alleviate heavy metal (Mn in this case) toxicity, so the role of silicon in copper toxicity was investigated. Soluble silicon was shown to alleviate copper toxicity by reducing symptoms on hydroponically-grown Arabidopsis. Copper toxicity usually caused increased chlorosis on the older leaves of Arabidopsis plants, co-treatment with silicon alleviated the symptoms. Roots of plants treated with elevated copper were stunted and dark brown, while those treated with elevated copper and silicon were more normal in length and lighter brown. The leaves of Arabidopsis plants treated with high levels of copper showed elevated phenylalanine ammonia lyase (PAL) activity, a commonly-assayed ‘stress enzyme'. However, the PAL activity of leaves from plants treated with elevated copper and silicon was reduced to nearly control levels. Copper treatment also induced the expression of copper transporter genes, such as COPT1 and HMA5, while the silicon treatment caused a reduction in expression of these genes. Data show that silicon acts at a variety of levels to alleviate copper stress in Arabidopsis. This project was monitored through regular phone calls and site visits.