EVALUATION OF WHITEFLY-MEDIATED INOCULATION TECHNIQUES TO SCREEN LYCOPERSICON-ESCULENTUM AND WILD RELATIVES FOR RESISTANCE TO TOMATO YELLOWLEAF CURL VIRUS

For two consecutive years nine hybrids and three varieties of tomato, four Lycopersicon peruvianum and four Lycopersicon chilense accessions were screened for Tomato yellow leaf curl virus (TYLCV) resistance. T hree inoculation techniques using Bemisia tabaci, the vector of TYLCV, were compared: (1) artificial mass inoculation-simultaneous infection of cultivated and wild material in greenhouses; (2) artificial cage i noculation-individual infection in insect-proof cages; (3) natural fie ld infection. Artificial inoculations led to higher levels of infectio n, but different patterns of response to each inoculation technique we re found depending on the resistance level. Tomato varieties showed an important fruit set reduction after both artificial and natural inocu lations. In contrast, field infection was milder in tomato hybrids, in which yield was barely affected. These hybrids showed a wide range of reactions with the two artificial inoculation techniques, but infecti on was always more severe after mass inoculation. Extreme severity of mass infection made it difficult to differentiate among variable degre es of resistance that were more reliably detected with cage inoculatio n. The hybrids F3524, F3522, Fiona, and Tyking showed the highest leve l of resistance. F3524 and F3522 had an acceptable yield in field and cage assays, but their resistance collapsed under massive conditions o f infection. Tyking and Fiona exhibited the best response in all condi tions, although their yield was moderately reduced in mass assays. Mas s inoculation was not adequate for the screening of wild Lycopersicon. Some susceptible plants escaped infection, probably as a consequence of non-preference mechanisms and loss of vector infectivity. Individua l inoculation in cages prevented the risk of non-infection, ensuring 1 00% disease incidence. This technique allowed the selection of highly resistant wild sources. L. chilense LA 1969 and LA 1963 had the highes t level of resistance with the three inoculation techniques. L. peruvi anum PI-126944 and L. chilense LA 1932, which were only tested in mass and field conditions, also exhibited a promising response. The result s proved that the inoculation technique influences the response of tom ato and wild Lycopersicon spp to TYLCV. It is concluded that artificia l cage inoculation, although more time-consuming, is the most efficien t, adequate, and reliable technique to screen both cultivated and wild Lycopersicon species for resistance to TYLCV.