Identification of sources of resistance in Lycopersicon species to Tomato leaf curl geminivirus (ToLCV) by agroinoculation

A total of 90 genotypes of Lycopersicon species were tested for resistance to the Tomato leaf curl geminivirus (ToLCV) by agroinoculation and the vector whitefly ( Bemisia tabaci Genn.) inoculation techniques under insect-proof glasshouse conditions. The rate of infection in the inoculated plants was determined by detection of the viral DNA in individual plants by the nucleic acid spot hybridization (NASH). Of the 38 cultivars and 11 breeding lines of L. esculentum Mill. tested, none was highly resistant or resistant while three and seven were moderately resistant when exposed to the cloned virus DNAs by agroinoculation and whitefly inoculation respectively. On the other hand, among the 38 commercial cultivars screened, 16 (42.1%) were highly susceptible in vector inoculations and 31 (81.6%) in agroinoculation. Among the exotic collection (EC) accessions six were highly resistant, eleven resistant to whitefly inoculation and none was highly susceptible in either of the two tests, indicating the presence of resistance among the EC accessions. A higher degree of resistance was observed in other species of Lycopersicon. While only one accession of L. cheesmanii Riley was tested, it could not be infected by either of the two methods. L. pimpinellifolium (Jusl.) Mill. genotype EC 251580 was similarly resistant. In L. peruvianum (L.) Mill., five EC accessions could not be infected by whitefly inoculation, with three of these being resistant and two moderately resistant in agroinoculation. This study demonstrates the importance of the agroinoculation technique in the virus resistance screening programs and identifies several good sources of resistance to the Tomato leaf curl virus in Lycopersicon species.