Screening for TYLCV-Resistance Plants using Whitefly-Mediated Inoculation

Today, tomato yellow leaf curl disease has become the limiting factor for tomato production in many tropical and subtropical regions of the world. This disease is induced by a number of begomoviruses, the type member being Tomato yellow leaf curl virus (TYLCV), transmitted by the whitefly Bemisia tabaci (Gennadius), whose severe population outbreaks are usually associated with high incidence of the disease. Control measures in infected areas usually rely on seclusion of the whitefly vector, mainly through multiple applications of insecticides or physical barriers (Antignus & Cohen, 1994; Hilje et al., 2001; Palumbo et al., 2001; Polston & Anderson, 1997). Due to the large populations of whiteflies, and their ability to develop pesticide resistance, vector seclusion is not an ideal way of fighting the spread and damage induced by TYLCV. Hence, development of genetic resistance in the tomato host is the best solution for any virus problem, and especially for whitefly-transmitted viruses such as TYLCV, since it requires no chemical input and/or plant seclusion and may be stable and longlasting. Thus, the best way to reduce TYLCV spread is by breeding tomatoes resistant or tolerant to the virus (Lapidot & Friedmann, 2002; Morales, 2001; Pico et al., 1996). Wild tomato species have been screened for their response to the virus and a number of TYLCV-resistant accessions identified, because no resistance has been found in the domesticated tomato (Solanum lycopersicum) (Lapidot & Friedmann, 2002; Nakhla & Maxwell, 1998; Pico et al., 1996). Thus, breeding programs have been based on the transfer of resistance genes from accessions of wild origin into the cultivated tomato. Progress in the breeding for TYLCV resistance has been slow, due in part to the complex genetics of the resistance and the presence of interspecific barriers between the wild and domesticated