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Oral: Virus-Host Interactions


Understanding superinfection exclusion by complex populations of Citrus tristeza virus
S. KANG (1), M. Bergua (1), S. Folimonova (1) (1) University of Florida, U.S.A.

Superinfection exclusion (SIE) is a phenomenon in which a primary viral infection restricts a secondary infection with the same or closely related virus. For plant viruses, SIE, referred to as cross-protection, was implemented as an agricultural practice to protect crops against aggressive viruses by pre-immunizing plants with mild virus isolates. Recently we showed that SIE by Citrus tristeza virus (CTV), an economically important virus of citrus, occurs only between isolates of the same strain, but not between isolates of different strains. This work, however, was done using “pure” isolates of CTV, each containing a single virus strain, while most citrus trees in the field harbor complex populations made up of different CTV strains. The objective of this study was to assess how SIE works in plants simultaneously pre-infected with several CTV strains. Co-inoculation of citrus trees with variants of T36, T68 and/or T30 strains demonstrated that multi-strain populations equilibrate soon after establishment of infection, show uniform intra-host distribution and maintain the established equilibrium over time. SIE experiments showed that exclusion of a secondary infection by a CTV variant was triggered by the presence of another variant of the same strain in the primary population, which was in the agreement with our previous observations. The same rule appeared to be in effect when SIE by mixed virus populations was tested in a series of different citrus varieties.