Epidemiological studies on tomato mottle geminivirus and Bemisia tabaci
Studies were carried out in Florida (US) on the spatial distribution and incidence of both tomato mottle geminivirus (EPPO A1 quarantine pest) and Bemisia tabaci biotype B (EPPO A2 quarantine pest), in order to determine whether a correlation could be established between the abundance of B. tabaci and the incidence of tomato mottle geminivirus. The authors recalled that, so far, tomato mottle geminivirus is only known on tomato. The incidence of the virus in tomato fields is variable (from 0 to 100 %). It is transmitted in a persistent manner by adults of B. tabaci biotype B. The minimum time required for acquisition is approximately 1 h, followed by a latent period of several hours and a transmission feeding period of approximately 1 h. Tomato mottle geminivirus virus is a major concern in tomato production in Florida. The estimated cost to the industry was estimated to 125 million dollars in 1991, due to reduced yields and increase of insecticide treatments.
In 1992 and 1993, 91 experimental plots located on 10 commercial tomato farms were monitored. Chemical insecticide treatments were applied on these farms. The final incidence of tomato mottle geminivirus ranged from 0 to 23.6 % in 1992 and 0 to 34 % in 1993. Over the two years, 21 plots had final disease incidences greater than 5 % and 8 plots had values greater than 15 %. On two plots which had incidences greater than 5 %, the observed pattern of the disease was characterized as having numerous small clusters of symptomatic plants scattered throughout plots prior to harvest. Dispersion pattern of adults B. tabaci fluctuated throughout the season, the index used in these studies indicated a uniform dispersion pattern at some time (especially at the end of the season) and an aggregated pattern at other times. No relationship was observed between disease incidence and the degree of aggregation of the vector. The authors concluded that abundant sources of immigrating viruliferous whitefly vectors from other infested fields, rather than secondary spread within fields, appear to be the essential means of spread of the virus. However, it must be recalled that the tomato system production in Florida is characterized by frequent applications of insecticides which alter the dispersion patterns of the vector. As it appears that harvested tomato fields are the main virus reservoirs, the authors recommend to the growers that harvested plants should be eliminated as soon as possible. In particular, harvested tomato plants which were planted in the autumn should be removed several weeks prior to new tomato plantation in spring.
Sources
Polston, J.E.; Chellemi, D.O.; Schuster, D.J.; McGovern, R.J.; Stansly, P.A. (1996) Spatial and temporal dynamics of tomato mottle geminivirus and Bemisia tabaci (Genn.) in Florida tomato fields.
Plant Disease, 80(9), 1022-1028.