Transmission of tomato leaf curl geminiviruses by Bemisia tabaci
Studies have been carried out in order to determine the frequency of transmission from tomato to tomato by 3 biotypes of Bemisia tabaci (EPPO A2 quarantine pest) of 3 serologically distinguishable geminivirus isolates that cause leaf curl diseases in different countries. The three biotypes of B. tabaci were from: Côte d'Ivoire, Pakistan and USA (B biotype, also called B. argentifolii). The three tomato geminivirus isolates were: Indian tomato leaf curl geminivirus from India, tomato yellow leaf curl geminivirus (TYLCV - EPPO A2 quarantine pest) from Nigeria and from Senegal. The results showed a wide range of transmission frequencies depending on whitefly biotype, virus isolate and also other factors not yet defined (e.g. feeding behaviour, virus content, etc.). It was found that B. tabaci biotype B (USA) and B. tabaci (Côte d'Ivoire) transmitted TYLCV (Senegal) more frequently than Indian tomato leaf curl. B. tabaci (Pakistan) transmitted Indian tomato leaf curl more frequently than TYLCV (Senegal). In general, B. tabaci biotype B (USA) was the most efficient vector, as it transmitted Indian tomato leaf curl and TYLCV (Senegal) 4 to 9 times more frequently than B. tabaci (Côte d'Ivoire). TYLCV (Nigeria) was rarely transmitted by B. tabaci biotype B (USA) and not at all by B. tabaci (Côte d'Ivoire).
The authors noted that in previous studies there had been some indirect evidence that the coat protein of geminiviruses determined their vector specificity. It had also been noted that whitefly-transmitted geminiviruses from different hosts in the same major geographical area tend to be more antigenically similar to one another than they are to geminiviruses causing the same diseases in the same hosts in other geographical regions. In fact, results of this study supports the idea that the coat protein of each virus could be specifically adapted for transmissibility by the B. tabaci biotypes present in its area of occurrence.
The authors pointed out that the high frequency with which B. tabaci biotype B (USA) transmit geminiviruses is indeed a worrying fact, as this biotype has recently become established in European glasshouses and in fields in Italy and Spain, and its spread in southern USA and Central America has led to an increase of the incidence of geminiviruses. However, other studies carried out in California (US) have shown that lettuce infectious yellows closterovirus (EU Annex I/A1) is more often transmitted by the A biotype than the B biotype.
Sources
McGrath, P.F.; Harrison, B.D. (1995) Transmission of tomato leaf curl geminiviruses by Bemisia tabaci: effects of virus isolate and vector biotype.
Annals of Applied Biology, 126(2), 307-316.