Comparison of two artificial whitefly-mediated inoculation techniques in breeding for resistance to TYLCV Pico, B., Diez, M.J., and Nuez, F. Department of Biotechnology, Genetics and Breeding, Polytechnic University of Valencia, E-46022, Valencia, Spain. Breeding for resistance to Tomato yellow leaf curl virus (TYLCV) has been often limited by the lack of reliable and efficient selection procedures (Kheyr-Pour et a1., 1994). Mechanical transmission is not possible in TYLCV (Mansour and AI-Musa, 1992). Although grafting and agro-inoculation have been sometimes used, the whitefly-mediated inoculation is the technique most commonly used in breeding programs (Pico et al., 1996). Variations in field TYLCV incidence make difficult to ensure 100% success in transmission, as well as to control inoculum pressure in each assay. This situation lead to contradictory results, attributing different resistance levels to the same genetic source. Two artificial whitefly-mediated inoculation techniques (mass and cage inoculation) were compared. Four commercial hybrids and one variety with different levels of resistance to TYLCV were tested using both inoculation techniques. The tomato cultivar NE-1 was used as susceptible control. Cage-inoculation was conducted in insect- proof cages. Ten plants of each cultivar were separately exposed to an average of 15/20 viruliferous white flies per plant during 48 h. After this feeding period white flies were killed with pesticide. Mass-inoculation was carried out in a screen-protected greenhouse. NE-1 TYLCV-infected tomato plants, maintaining a high Bemisia tabaci population, were used as source of inoculum. All cultivars were assayed at the same time. No treatments were realized to control vector population. TYLCV infection was confirmed by TAS-ELISA and PCR. The severity of symptoms and the effect of the infection on flowering and fruit-set were visually evaluated per plant (Table 1). All cultivars reached 100% infection with both techniques. At the end of the assay, symptoms were more severe after mass-inoculation (2.2-3.7) than after cage-inoculation (1.8-3.3). Severity of symptoms increased from 30 to 60 days post inoculation in the longer and more severe mass-inoculation process. However, the most resistant cultivars, Tyking, F3522, and TY-20, maintained a moderate symptom severity after cage-inoculation. The high inoculum pressure of mass-inoculation led to an important effect on flowering and fruit-set, similar in all the cultivars. In this sense, cage-inoculation better discriminate cultivars with different levels of resistance. Tyking seems to be the most resistant cultivar. Its response is less influenced by inoculum level. F3522 and TY-20 have a medium level of resistance that depends on the disease pressure, developing moderate or severe symptoms after cage or mass inoculation respectively. The results show the efficiency of these techniques to ensure a 100% of infection in cultivated material. In addition, this work emphasizes the need of controlling inoculum pressure to evaluate TYLCV response in partially resistant materials. ACKNOWLEDGMENTS This research was supported by the project N° PB-94-0530-C03-02 of the DGICYT program. Literature cited: Kheyr-Pour, A., Gronenborn, B. and Czosnek, H.1994. Agroinoculation of Tomato yellow leaf curl virus (TYLCV) overcomes the virus resistance of wild Lycopersicon species. Plant Breeding 112. 228-233. Mansour, A. And Al-Musa, A. 1992. Tomato yellow leaf curl virus: host range and virus relationships. Plant Pathol., 41: 122-125. Pico, B., Diez, M.J. and Nuez, F. 1996.Viral diseases causing the greatest economic losses to the tomato crop Il. The Tomato yellow leaf curl virus-a review. Scientia Hortic. 67: 151-196.

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