Analysis of genetic bottlenecks during horizontal transmission of Cucumber mosaic virus

Abstract

Genetic bottlenecks may occur in virus populations when only a few individuals are transferred horizontally from one host to another, or when a viral population moves systemically from the infection site. Genetic bottlenecks during the systemic movement of an RNA plant virus population were reported previously (H. Li and M. J. Roossinck, J. Virol. 78:10582-10587, 2004). In this study we mechanically inoculated an artificial population consisting of 12 restriction enzyme marker mutants of Cucumber mosaic virus (CMV) onto young leaves of squash plants and used two aphid species, Aphis gossypii and Myzus persicae, to transmit the virus populations from infected source plants to healthy squash plants. Horizontal transmission by aphids constituted a significant bottleneck, as the population in the aphid-inoculated plants contained far fewer mutants than the original inoculum source. Additional experiments demonstrated that genetic variation in the artificial population of CMV is not reduced during the acquisition of the virus but is significantly reduced during the inoculation period.

FIG. 1.

Reduction in CMV populations during aphid transmission from mechanically inoculated leaves to healthy plants. Experiments 1 to 5 are independent experiments. All values are means plus standard errors. Bars with different letters (a and b) are significantly different from each other (P < 0.05), as determined by the significant difference test.

FIG. 2.

Frequency of recovery of mutants from tissues of test plants infected by A. gossypii and M. persicae. The recovery percentage of each mutant in test tissue was calculated for each experiment as for Fig. 1. Values are means plus 1 standard error.

FIG. 3.

Acquisition efficiency of CMV populations by single A. gossypii or M. persicae aphids. Source represents the squash cotyledon tissue mechanically inoculated with single mutants, double mutants, or all 12 mutants (12-mix). Values are means plus 1 standard error.