For several years, bean pod mottle virus and alfalfa mosaic virus were considered the two most common viruses infecting soybean in Illinois. Then in 2008, Dr. Ioannis Tzanetakis at the University of Arkansas and Dr. Reza Hajimorad at the University of Tennessee identified a new virus in soybean, which they named soybean vein necrosis virus, that induces characteristic patches of brown necrotic tissue along major veins of sensitive infected cultivars . Dr. Tzanetakis developed a detection assay for the virus and confirmed its presence in Arkansas, southern Illinois, Kansas, Kentucky, Missouri, and Tennessee in 2009. Little is known about the virus, but the two researchers showed that it is related to a group of thrips-transmitted viruses called tospoviruses. The most infamous tospovirus, tomato spotted wilt virus, causes significant damage throughout the southeastern United States in lettuce, peanut, pepper, potato, tobacco, and tomato. The USDA Cooperative State Research, Education, and Extension Service recently issued a national pest alert for tospoviruses because of their increasing prevalence in the US and their potential to cause serious crop damage. Tospoviruses are somewhat unusual in that they infect and replicate within plants and their thrips vectors. Consequently, tospovirus- infected thrips retain the ability to transmit the viruses for long periods.
The source or sources of soybean vein necrosis virus infections are not known. Unlike alfalfa mosaic virus, soybean mosaic virus, and tobacco ringspot virus, tospoviruses usually are not transmitted through seed. The two most common species of thrips in Illinois soybean fields are the soybean thrips (Sericothrips variabilis) and the flower thrips (Frankliniella tritici). Tobacco thrips (Frankliniella fusca) can also be found in soybean fields in southern Illinois, but at much lower levels than the other two species. Dr. Tzanetakis and coworkers reported that symptoms of Soybean vein necrosis virus infection were first seen in soybean fields in mid- to late June, which is consistent with the arrival of thrips in that region a couple of weeks earlier . The three species of thrips do not overwinter in Illinois but migrate into the state each spring from south-central states and even from Mexico. Early in the growing season soybean thrips colonize alfalfa and other broadleaf plant species before they immigrate to soybean fields, where they reproduce throughout the growing season. In contrast, flower thrips colonize a wider variety of plants, including corn and some grasses, before colonizing soybean fields. Hence, thrips could acquire soybean vein necrosis virus in southern states and bring it north into Illinois each spring or could acquire it from local weeds and move it into neighboring soybean fields.
In 2010, we conducted a survey of Illinois soybean fields for virus infections and detected soybean vein necrosis virus infection in southern as well as northern Illinois counties. The levels of infections were similar to that of bean pod mottle virus, but they appeared to be more uniform across the sampled counties. This distribution of soybean vein necrosis virus infections is consistent with the life cycles of the flower and soybean thrips, which tend to spread relatively uniformly within soybean fields during the growing season. As observed by Dr. Tzanetakis, soybean vein necrosis virus in Illinois showed very little genetic variability, suggesting that the virus is either a recent introduction into soybean or is genetically very stable. The effects of its infection on soybean yields have not been investigated, although differences in sensitivities of soybean cultivars have been noted in the field. Dr. Tzanetakis and Dr. Stella Kantartzi at Southern Illinois University are currently evaluating cultivars for their susceptibility to soybean vein necrosis virus infection.
Leslie L. Domier
Professor of Crop Sciences