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A Recessive Allele (tgr-1) Conditioning Tomato Resistance to Geminivirus Infection Is Associated with Impaired Viral Movement

First, second, third, fourth, and seventh authors: CSIRO Plant Industry, PO Box 350, Glen Osmond, SA 5064, Australia; fifth author: Asian Vegetable Research and Development Centre, P.O. Box 42, Shanhua, Tainan 741, Taiwan; and sixth author: CSIRO Entomology, Long Pocket Laboratories, Indooroopilly, QLD 4068, Australia.

Begomoviruses (the family Geminiviridae) are transmitted by the whitefly Bemisia tabaci and contain monopartite or bipartite circular single-stranded (ss)DNA genomes. They have emerged as severe problems in the production of agricultural and horticultural crops worldwide. Here, we report the identification of a tomato breeding line, FLA653, that confers a high level of resistance to Tomato leaf curl virus (TLCV, monopartite). Genetic analysis indicated that the resistance is controlled by a single recessive allele named tgr-1, which is in contrast to previous reports that multiple genetic factors are involved in tomato resistance to begomoviruses. Particle bombardment of an infectious TLCV DNA construct into the detached leaves of FLA653 resulted in the viral replication, but the viral ssDNA accumulated at a much lower level than that in susceptible controls. In situ localization of TLCV in the bombarded leaves suggests that tgr-1 impaired TLCV movement, raising the possibility that it may specify a host factor essential for viral systematic infection. This makes tgr-1 a strong candidate for developing resistance in major crops carrying the gene homologue.