Virus infections in wild plant populations are both frequent and often unapparent.
OBJECTIVE
Pathogens are thought to regulate host populations. In agricultural crops, virus infection reduces yield. However, in wild plants little is known about the spatial and temporal patterns of virus prevalence. Thus, pathogen effects on plant population dynamics are unclear. Prevalence data provide necessary background for (1) evaluating the effects of virus infection on plant population size and dynamics and (2) improving risk assessment of virus-resistant transgenic crops.


METHODS
We used ELISA and RT-PCR to survey wild Cucurbita pepo populations over 4 years for five viruses, aphid-transmitted viruses of the genus Potyvirus as a group and PCR to survey for virus-resistance transgenes. In addition, we surveyed the literature for reports of virus prevalence in wild populations.


RESULTS
In 21 C. pepo populations, virus prevalence (0-74%) varied greatly among populations, years, and virus species. In samples analyzed by both ELISA and RT-PCR, RT-PCR detected 6-44% more viruses than did ELISA. Eighty percent of these infections did not cause any visually apparent symptoms. In our samples, the virus-resistance transgene was not present. In 30 published studies, 92 of 146 tested species were infected with virus, and infection rates ranged from 0.01-100%. Most published studies used ELISA, suggesting virus prevalence is higher than reported.


CONCLUSIONS
In wild C. pepo, the demographic effects of virus are likely highly variable in space and time. Further, our literature survey suggests that such variation is probably common across plant species. Our results indicate that risk assessments for virus-resistant transgenic crops should not rely on visual symptoms or ELISA and should include data from multiple populations over multiple years.
School of Biological Sciences, 348 Manter Hall, University of Nebraska, Lincoln, Nebraska 68588-0118, USA. hp8j@virginia.edu
Holly R
HR
Prendeville
Xiaohong
X
Ye
T Jack
TJ
Morris
Diana
D
Pilson
D000818:Animals; D001042:Aphids / Q000821:virology; D018556:Crops, Agricultural / Q000235:genetics* / Q000821:virology; D028464:Cucurbita / Q000235:genetics* / Q000821:virology; D060467:Disease Resistance / Q000235:genetics; D004797:Enzyme-Linked Immunosorbent Assay; D054884:Host-Pathogen Interactions / Q000235:genetics; D010935:Plant Diseases / Q000235:genetics* / Q000821:virology; D018515:Plant Leaves / Q000235:genetics / Q000821:virology; D010942:Plant Viruses / Q000145:classification / Q000235:genetics* / Q000502:physiology; D030821:Plants, Genetically Modified / Q000235:genetics* / Q000821:virology; D017800:Potyvirus / Q000145:classification / Q000235:genetics / Q000502:physiology; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D012367:RNA, Viral / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012196:Review Literature as Topic; D013997:Time Factors
D018749:RNA, Plant; D012367:RNA, Viral