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Hosta Virus X

 

<em>H</em>. 'Gypsy Rose'

Transmission of Hosta Virus X (HVX) Under Normal Conditions of Hosta Cultivation and Commercial Production

Principal Investigator: Benham E. Lockhart, Professor
 Department of Plant Pathology,
University of Minnesota
 St. Paul, MN.

Introduction and background

This research proposal has been prepared at the request of the American Hosta Society and will be carried out as a research agreement funded by AHS. Hosta virus X (HVX) was first identified and described at the University of Minnesota in 1996 (Currier and Lockhart, 1996). Since then HVX has been found to occur widely in the US and in a number of other countries including Canada, Korea, the U.K. and New Zealand.  The danger posed by HVX to both hobby and commercial hosta cultivation has led to a need for an empirical determination of the dynamics of HVX spread in order to provide hosta growers and producers with the information needed to manage the disease.
    Hosta virus X is a member of the plant virus genus Potexvirus. Potexviruses characteristically occur in high concentration in infected plants are very stable, outside the plant cell, and are not spread by insects, mites, fungi, nematodes seed or pollen. Viruses like HVX are known to be spread only by vegetative propagation of infected mother plants or by infected plant sap that enters a healthy plant via non-lethal tissue damage (wounding). This mode of virus spread may possibly occur during normal gardening and commercial production, but there is not empirical evidence for its occurrence or probability. This research project is designed to provide research-based information.

Organization of this research proposal:

    • Goal and Objectives
    • Experimental approach
    • Project duration and schedule of activities
    • Expected outcome
    • Budget and budget justification
    • Proprietary issues, fund disbursement, reporting
  • Goal and Objectives

The goal of this proposed research project is to provide empirically derived information that answers the questions of major concern. The objectives leading to this goal are divided into primary and secondary objectives.
        Primary Objectives

  • Can HVX spread from infected to healthy hostas in any of the following ways:
    • On tools (e.g. pruning or cutting tools)
    • On sap-contaminated hands
    • From residual infected plant material in soil
    • By root contact
  • If HVX can be spread by any of these means, how long does the virus remain infective on contaminated tools, in soil, on hands etc.
  • If HVX can be spread by any of these means, and if the virus retains infectivity, then what are the most practical cost-effective and safest methods of decontamination?

        Secondary Objectives

  • Are all HVX isolates transmissible?
  • How variable is HVX?
  • Is transmission of HVX related to the amount of virus present in the source plant?
  • What is the most sensitive and reliable method for the detection of HVX?
  • Experimental Approaches

The experimental approach chosen for this project is designed to provide simple, straightforward answers to each research questions described above, the details of these proposed experiments are as follows:

  • Propagation of HVX to be used as a virus source. The virus isolate will be obtained from the Hosta clausa ‘Normalis’ and will be maintained in H. ‘Honeybells’ by mechanical transmission.
  • Question:  Can HVX be transmitted during normal cultivation?

To determine this experiment will be done to determine if HVX can be transmitted by mechanical contact on tools, fingers, plant debris in soil, or root contact.  In each experiment twenty healthy plants of H. ‘Honeybells’ will be used. After exposure, plants will be grown in the greenhouse for  up to one year and will be observed for disease symptoms and tested for presence of HVX by ELISA and RT-PCR.

  • Question: If HVX can be spread during normal cultivation practices, how long does the virus remain infective on tools and in soil?

To determine this healthy test plants of H. ‘Honeybells’ will be exposed to contaminated tools and soil at different periods.

  • Question: If HVX remains infective on contaminated tools or in soil, what practical measures can be used to eliminate it?

To determine this treatment with commonly available viricidal agents such as detergent, trisodium phosphate, detergent plus sodium hydroxide (caustic soda) etc. will be tested for efficacy in eliminating viral infectivity.

  • Question: Is HVX transmission dose dependent?

Because the concentration of HVX can vary widely between hosta varieties experiments will be done to determine whether the rate of virus transmission by mechanical contact differs significantly according to virus concentration in the source plant.

  • Question: Are all HVX isolates transmissible?

This question arises from the observation that two viruses present in hostas, Arabis mosaic virus (ArMV) and Cucumber mosaic virus (CMV) cannot be transmitted by mechanical inoculation from the plants in which they occur. Experiments will be done to determine if a similar phenomenon might occur in the case of some HVX isolates.

  • Question: Is HVX variable?

Experiments will be done to determine whether serological or genomic (nucleotide sequence) differences exist among isolates of HVX. Such differences will have a significant impact on virus detection.

  • Question: What is the most sensitive and reliable method for detection of HVX.

This question is especially relevant to future attempts to eliminate HVX from hosta cultivars using in vitro propagation (tissue culture) techniques. It will be important to have assay methods capable of detecting subliminal
levels of virus infection at early stages of growth following tissue culture.

  • Project duration and schedule of activities:

This project is designed to be completed in two calendar years. Primary objective number one will be dealt with first since its outcomes will determine the subsequent course of researcH. It is expected that most of the primary
objectives will be completed by the middle of year two, and that the secondary objectives will be completed by the end of year two.

  • Expected outcomes:

The expected outcomes of this research project are;

    • A body of experimentally based information that will be of practical use to amateur and professional hosta growers.
    • One or more publications based on this information and made widely available.

     

     

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