Overview of TSWV transmission by Thrips tabaci in Bulgarian tobacco fields
Karadjova O, Krumov V
Plant Protection Institute, Kostinbrod 2230, Bulgaria.
Correspondence: oliakaradjova@abv.bg
Tobacco is a traditional field crop of great economic importance to Bulgaria. Tomato Spotted Wilt Virus (TSWV) was first reported in 1952 in Bulgaria and Thrips tabaci Lind was proved to be the only vector of the virus (Kovatchevsky I.1952. Bulletin Rastitelna Zashtita 3, 18每20; Ivancheva-Gabrovska. 1984. Studies on TSWV (Tomato Spotted Wilt Virus) in Bulgarian tobacco field. Doctoral dissertation, Plovdiv, Bulgaria; Dimitrov A. 1991. Biocenological studies on tobacco in Bulgaria and possibility for control of Thrips tabaci Lind. 每 the most important pest. Doctoral dissertation, Plovdiv, Bulgaria; Hristova D. et. al. 2001. Journal of Phytopathology 149, 1每5). Two different Th. tabaci populations 每 arrhenotokous (Th.t.1) and thelotokous (Th.t 2) were tested for their ability to transmit two TSWV isolates (BR-01 and GD from tobacco). DAS-ELISA was used to confirm the infection in individual thrips. The transmission efficiency of adult Th. tabaci was tested on petunia leaf discs (Wijkamp, I. 1995. Virus-vector relationships in the transmission of tospoviruses. Ph. D thesis, Wageningen, the Netherlands). Thrips and TSWV incidences were investigated in Bulgarian tobacco fields for a period of 50 years and the climatic conditions for every year were taken into account. The data analysis shows that TSWV epidemic has a 5每6 year interval of occurrence. The main outbreaks of TSWV were observed country wide in 1969 (57 %) and 1983 (53 %). Although the climatic conditions through these two years were favorable for both development of Th. tabaci and viral infection, during the remaining years no relation between TSWV epidemics and thrips infestation has been established. For example in 1972 there was 35% thrips infestation of tobacco plants, but TSWV infection was only 5%. The opposite phenomenon occurred in 1960 每 9% of thrips infestation corresponded to 23% of TSWV infection. Positive ELISA values were found only in the arrhenotokous population (Th.t.1). The average ELISA values were higher for TSWV 每GD isolate, male individuals (OD = 0.377). Comparative laboratory studies for measuring of TSWV transmission efficiency of arrhenotokous and thelytokous populations have been conducted. Our investigation showed that the arrhenotokous population of Th. tabaci from tobacco is an efficient vector of TSWV (range from 2.08 to 39.58 %). The transmission rates of male specimens were higher than those of female ones. TSWV isolate GD from tobacco was transmitted more efficiently than BR-01. The telotokous population was not able to transmit both tested isolates.
