Molecular analysis of whitefly-transmitted tomato geminiviruses from Southeast and East Asia

Abstract

Tomato cultures are under the constant threat of geminiviruses transmitted by the whitefly Bemisia tabaci. In the affected regions, yield losses often reach 100%. In Southeast and East Asia, as well as in many countries of the Old World, these viruses have been termed tomato yellow leaf curl virus (TYLCV) or tomato leaf curl virus (ToLCV). These viral diseases are becoming more widespread, usually following appearance or increases in whitefly populations. Although leaf curl-related diseases of tomato have been reported throughout Southeast and East Asia, the molecular data available on these viruses is still scarce. The genome of TYLCV and ToLCV isolates has been cloned from infected tomato plants from Bangladesh, China, India, Malaysia, Sri Lanka, Taiwan, The Philippines and Thailand, and sequenced partially or entirely. DNA and protein sequence comparisons indicate that many TYLCV and ToLCV isolates analyzed so far constitute distinct virus species and are not strains of the same species. Analysis of their coat proteins indicate that these viruses group into two branches that include the viruses from China, Malaysia, Taiwan and Thailand (together with the virus from Australia) and those from Bangladesh, India and Sri Lanka. The whitefly-transmitted tomato geminiviruses from Southeast and East Asia constitute a cluster of geminiviruses distinct from those of the Middle East, Southeast Europe and of the Americas.