Host Range of Impatiens Necrotic Spot Virus (INSV) and Tomato Spotted Wilt Virus (TSWV) an Herbaceous Perennials
William B. Miller, Simon W. Scott, James H. Blake and Ted Whitwell Departments of Horticulture and Plant Pathology and Physiology

Download the Adobe Acrobat version of this document (with complete list of hosts of TSWV and INSV).

Introduction

Starting in July 1995, a project was funded through the Clemson University Ornamentals Enhancement Program dealing with the issue of herbaceous perennials and the host range of Tomato Spotted Wilt Virus and Impatiens Necrotic Spot Virus. The objectives of this project are to assess the state of knowledge about the host range of this virus complex within ornamental plants, especially herbaceous perennials, to begin to expand the known host list by documenting outbreaks of the virus in new species, and to communicate this information to the industry.

One of the major reasons for initiating the project was the discovery of TSWV/ INSV-infected Lobelia liners ("plugs") in a shipment to one of the state's container nurseries. Plants from this shipment were observed in early spring, 1995, and were hypothesized to be infected with virus. Subsequent testing was positive for virus, and in fact the virus killed most of the plants. The virus complex is vectored by thrips, especially the western flower thrips, an insect pest widespread in the southeast and difficult to kill.

Materials and Methods

To begin this project, two collecting trips were made to commercial nurseries in early October, 1995, and April, 1996, and numerous (70+) samples were returned to Clemson. Numerous photographs were taken to document symptoms. Dr. Simon Scott performed ELISA tests on "healthy" plants collected from various sources (mainly home gardens), and in some cases, plants from the collection site that showed no visible symptoms.

Results

The results to date are presented below:

INSV was detected in the following plants from the fall of 1995:

1. An Aucuba plant tested positive. This showed that thrips can transmit the virus to plants with very waxy cuticles.
2. The Myosotis that were located next to the Monarda . The Monarda gave mixed results which differed only slightly from our negative control.
3. Veronica .
4. Lobelia cardinalis .
5. Stokesia plant with marked symptoms.
6. Virus was possibly found in one of 2 hostas collected, and also in one of the 2 red tip (Photinia ) samples.

INSV was detected in the following plants from the fall of 1996:

Veronica sp. 'Red Fox'	Both the plant with symptoms and the healthy plant
Phlox maculata 'Rosalinde'	Only the plant with symptoms
Tradescantia 'J.C. Wiguelin'	Both the plant with symptoms and the healthy plant
Penstemon 'Rondo'	Only the plant with symptoms
Veronica 'Sunny Border Blue'	Both the plant with symptoms and the healthy plant. Note: these were newly arrived plugs from a commercial propagator
Penstemon 'Husker Red'	Only the plant with symptoms
Aucuba	Both the plant with symptoms and the healthy plant
Veronica latifolia	Both the plant with symptoms and the healthy plant
Gaura lindheimeri	A heavily-brown-spotted plant was infected with INSV

All other plants (listed below) did not give positive results irrespective of whether they had symptoms or not.

Salvia leucantha	Boltonia 'Snowbank'	Melampodium
Phlox 'Catahoochee'	Tiarella wherryi	Milkweed
Euryops viride	Chelone glabora
Helenium spp.	Lobelia

In addittion, James Blake has searched the Plant Problem Clinic database and has found the following instances of positive INSV/TSWV in herbaceous perennial samples submitted since 1988:

Adenophora	Gaura	Lisianthus
Amaryllis	Hart's-Tongue Fern	Lobelia
Belamcanda Lily	Monarda	Dahlia
Verbena

Finally, appended to this report are results of an extensive computer literature survey on the virus complex conducted by Dr. Scott and his team. Several woody species (Ilex, Photinia i.e.:holly, red tip) are on the list, and numerous weed species including relatives of bittercress and oxalis. As well, numerous herbaceous perennials are on the list including Myosotis, Sedum, Veronica, Verbena, Lantana, Digitalis, Phlox, and Hibiscus .

Implications

Clearly, the virus can be assumed to be resident in a large number of overwintered ornamental crops in nurseries throughout South Carolina, the southeast, and possibly nationwide. This statement is based on the existence of efficient transportation schemes in the industry, where vegetatively propagated plugs are distributed nationwide from a relatively small number of suppliers. As well, virus may be located in nearby woody plants and certain weeds present in and around container production facilities. Additionally, the virus is known to be brought in with new plugs from reputable national propagators. Thus, within southeastern nurseries, there may be a resident pool of virus, with possible new sources arriving frequently throughout the fall, winter, and spring.

Possible management techniques for southeastern nurseries include rigorous scouting of incoming plant materials to catch severe problems before the plants are moved into the nursery. Vegetatively propagated materials are especially suspect, but even seeded material can obviously become infected in the plug production stage if viruliferous thrips are present. We are fairly sure the virus is not seed transmitted, but it appears as if the literature has not fully sorted this issue out. There may be possibilities for biological control with thrips natural enemies, although the current insecticide schedules used in many nurseries may kill off most of these beneficials. The role of weeds in this virus complex is probably critical, as well, given that relatives of some of our major southeastern weeds (oxalis, bittercress) are known to host the virus.

See the list of Hosts Of Tomato Spotted Wilt Virus And Impatiens Necrotic Spot Virus.

Last Updated 7/16/98