Tomato Spotted Wilt Virus
Tomato spotted wilt virus (TSWV) has a long history as an object of research in plant pathology. J.G. Bald’s studies of the spatial pattern of disease plants in experimental plots at the Waite Institute in Australia in the 1930’s were among the first publications on the spatial analysis of plant disease and stimulated the elucidation of the underlying statistical model for cluster sampling for incidence data by W.G. Cochran. Despite the length of time over which TSWV has been studied it remains a practical problem in California agriculture, and in many respects an intriguing biological puzzle.
TSWV is spread by thrips. In California the major vector is the Western Flower Thrips, Frankliniella occidentalis. The virus has a persistent-propagative relationship with its vector meaning that it multiplies in the vector: once infected, individual thrips remain infective throughout their lifespan. Thrips can only become infected with the virus if they feed on an infected plant as juveniles; adult thrips do not acquire the virus from feeding on infected plants. Only infected adults which acquired the virus while in the juvenile stage can spread it to healthy plants; juveniles do not move from plant to plant.
In a similar way to our work on grape leafroll, QBE lab is collaborating in a team effort to improve the management of TSWV in practice and to increase basic understanding of the biology and epidemiology of the disease. Current information for growers on integrated pest management (IPM) approaches to TSWV control can be found by following this link.
In the QBE lab we are developing a two-step risk categorization system for processing tomato crops and also collaborating on basic research on the dynamics of this type of vector-virus system. Our two-stage risk categorization system consists of a field-based risk index which is calculated from information available at or before planting, and a thrips population projection model, based on degree-days, which indicates the timing of thrips adult generations to help guide insecticide use. The risk index form can be found at this link, and the thrips population population projections can be found here.