Impatiens Necrotic Spot Virus
Impatiens necrotic spot virus (INSV) is a common plant virus found throughout the world, which is named after the characteristic necrotic spots and rings formed by some plant species infected with this virus. It causes a wide variety of symptoms. This virus can be difficult to manage because it is spread by thrips. The key to control this virus in plant production facilities is the conbination of monitoring and managing thrip levels, investing in virus free propagating material, and testing and destroying infected plants.Introduction
Impatiens necrotic spot virus (INSV) is a prevalent plant virus found in horticultural production facilities. INSV was originally described as a strain of Tomato spotted wilt virus (TSWV) and was called the Tomato spotted wilt virus-Impatiens strain (TSWV-I) (Law & Moyer 1990). This name is rarely used today but can be observed in literature prior to the early 1990's.
Differences in TSWV strains were first reported in 1955 (Best & Gallus 1955). INSV responded weakly or not at all with antiserum to TSWV (Law & Moyer 1990; Wang & Gonsalves 1990). In addition, distinct structures could be seen in thin sections of plants infected with INSV but not TSWV (Law & Moyer 1990, Urban et al. 1991). This data drove the research that characterized INSV and today allows it to be detected separately from TSWV.
INSV is classified in the genus Tospovirus and has a single stranded RNA genome consisting of three segments. These segments are packaged into quasi-spherical particles (Law & Moyer 1991).
The best defense against INSV is to invest in virus free propagating material. Any new plants brought into the production facility should be inspected closely for symptoms of viral pathogens or thrip vectors. New plants should be isolated until they are verified to be INSV and thrip free. Thrip populations can be monitored with blue sticky traps placed at plant height. High thrip populations can be managed through use of insecticides but care must be taken to properly apply them due to the fact that thrips prefer to hide inside flowers and leaf buds. Insecticides should also be rotated to decrease the risk of allowing insects to become resistant to them as some thrip populations are already resistant to various chemicals (Daughtrey et al. 1997).
It is important to remember that even if thrips are present, if the plants are free from virus no losses will be attributed to INSV.
Transgenic crops were developed in the 1990's to resist INSV (and other Tospoviruses) but they have not been utilized (Gonsalves et al. 1995).
INSV can be detected through the use of immuno-strips in the field. These can be purchased directly by growers or plants can be submitted to a local plant disease clinic for testing. Symptomatic tissue should be used for testing.
INSV can also be detected through the use of indicator plants such as Nicotiana benthamiana, Petunia hybrida, and dwarf fava bean (Daughtrey et al. 1997).
Law, M. D., & Moyer, J. W. (1990). A tomato spotted wilt-like virus with a serologically distinct N protein. Journal of General Virology, 71(4), 933-938.
Best, R.J. & Gallus, H.P. (1955). Strains of tomato spotted wilt virus. Australian Journal of Science. 15, 212-214.
Wang, M., & Gonsalves, D. (1990). ELISA detection of various tomato spotted wilt virus isolates using specific antisera to structural proteins of the virus. Plant Disease, 74(2), 154-158.
Urban, L. A., Huang, P. Y., & Moyer, J. W. (1991). Cytoplasmic inclusions in cells infected with isolates of L and I serogroups of tomato spotted wilt virus. Phytopathology, 81(5), 525-529.
Gonsalves, D., Pang, S. Z., Gonsalves, C., Xue, B., Yepes, M., & Jan, F. J. (1995). Developing transgenic crops that are resistant to tospoviruses. Tospoviruses and Thrips of Floral and Vegetable Crops 431, 427-431.
Law, M. D., Speck, J., & Moyer, J. W. (1991). Nucleotide sequence of the 3? non-coding region and N gene of the S RNA of a serologically distinct tospovirus. Journal of General Virology, 72(10), 2597-2601.