Tomato leaf curl disease in Taiwan and breeding for resistance against it.

Abstract

In the past few decades, whiteflies have become more important as agricultural pests in many areas. The whitefly-transmitted geminiviruses (begomoviruses) have also become major constraints to tomato production worldwide. A tomato-infecting begomovirus, Tomato leaf curl Taiwan virus (ToLCTV), was first detected in Taiwan in 1981, and was endemic throughout the island by the early 1990's. Since then, three other tomato-infecting begomoviruses have been detected in Taiwan; Ageratum yellow vein Hualien virus (AYVHuV) and Tomato leaf curl Hsinchu virus (ToLCHsV) have been detected only occasionally from tomato, whereas Tomato yellow leaf curl Thailand virus (TYLCTHV), which was probably imported to Taiwan in about 2005, is now widespread throughout Taiwan. TYLCTHV is a bipartite and mechanically transmissible begomovirus, whereas ToLCTV is monopartite and not mechanically transmissible. Through monitoring the begomoviruses in the tomato production areas over time, it is apparent that the introduced TYLCTHV is now displacing ToLCTV in most areas. The tomato leaf curl resistance gene Ty-2 was identified in Taiwan using ToLCTV, and was incorporated into tomato cultivars to help manage the leaf curl disease. However, tomato cultivars carrying the Ty-2 gene are not resistant to TYLCTHV which causes severe disease symptoms on them. The combining (pyramiding) of different Ty resistance genes in new tomato cultivars shows potential for resistance to leaf curl disease in Taiwan. The combined use of resistant cultivars and cultural methods to exclude vector whiteflies and prevent virus infection is the most effective and sustainable strategy to manage the tomato begomovirus complex in Taiwan and elsewhere.