Rapid evolution of the population of begomoviruses associated with the tomato yellow leaf curl disease after invasion of a new ecological niche

Epidemics of tomato yellow leaf curl disease (TYLCD) caused by monopartite begomoviruses (family Geminiviridae) result in devastating damage to tomato (Solanum lycopersicum L.) crops in Spain since early 1990's. Initially, the ES strain of the species Tomato yellow leaf curl Sardinia virus (TYLCSV) was reported as the causal agent. The population of this virus exhibited a high genetic stability. However, introduction of new virus types also associated with TYLCD occurred which rapidly altered the virus population structure and diversity. Thus, isolates of the Mld and the IL strains of Tomato yellow leaf curl virus (TYLCV) were introduced, which resulted in a progressive displacement of TYLCSV Single, undifferentiated subpopulations were observed for each virus type, compatible with founder effects. Mixed infections were detected in single plants, rationalizing the occurrence of recombinants. In fact, natural recombinants between TYLCSV and TYLCV with selective advantage over the parental genotypes rapidly emerged and spread in the virus population. These data evidenced the great dynamism of the begomovirus population associated with the TYLCD after the invasion of a non-native area and the contribution of genetic migration and recombination to the genetic diversification.