Molecular epidemiology of Zucchini yellow mosaic virus in France: an historical overview.

Cucurbit viruses are involved in complex and changing pathosystems in France, with new virus strains or species regularly reported. Zucchini yellow mosaic virus (ZYMV) is an archetypal emerging virus that was reported in France in 1979. It has since caused sporadic but occasionally very severe economic losses and its epidemiology still remains poorly understood. Partial sequencing of the viral genome has been used to characterize ZYMV isolates that occurred over a 29-year period in experimental plots at Montfavet, France (n=227), or that were received through a national survey for cucurbit viruses conducted in France from 2004 to 2007 (n=198). A total of 34 haplotypes were differentiated belonging to five molecular groups, three including isolates already described in France and two corresponding to isolates that emerged in France within the last 5 years. Comparison of haplotypes found at one location during successive years revealed contrasting situations. When they were either the same or closely related haplotypes, this suggested the availability of overwintering hosts, whereas when they belonged to different molecular groups this indicated shifts in viral populations with possible new introductions. The contribution of molecular epidemiology in tracing the origin of ZYMV in the French West Indies is also reviewed.