REPLICATION OF TOMATO YELLOW LEAF CURL VIRUS (TYLCV) DNA IN AGROINOCULATED LEAF-DISKS FROM SELECTED TOMATO GENOTYPES

The leaf disc agroinoculation system was applied to study tomato yello w leaf curl virus (TYLCV) replication in explants from susceptible and resistant tomato genotypes. This system was also evaluated as a poten tial selection tool in breeding programmes for TYLCV resistance. Leaf discs were incubated with a head-to-tail dimer of the TYLCV genome clo ned into the Ti plasmid of Agrobacterium tumefaciens. In leaf discs fr om susceptible cultivars (Lycopersicon esculentum) TYLCV single-strand ed genomic DNA and its double-stranded DNA forms appeared within 2-5 d ays after inoculation. Whiteflies (Bemisia tabaci) efficiently transmi tted the TYLCV disease to tomato test plants following acquisition fee ding on agroinoculated tomato leaf discs. This indicates that infectiv e viral particles have been produced and have reached the phloem cells of the explant where they can be acquired by the insects. Plants rege nerated from agroinfected leaf discs of sensitive tomato cultivars exh ibited disease symptoms and contained TYLCV DNA concentrations similar to those present in field-infected tomato plants, indicating that TYL CV can move out from the leaf disc into the regenerating plant. Leaf d iscs from accessions of the wild tomato species immune to whitefly-med iated inoculation, L. chilense LA1969 and L. hirsutum LA1777, did not support TYLCV DNA replication. Leaf discs from plants tolerant to TYLC V issued from breeding programmes behaved like leaf discs from suscept ible cultivars.