Interrelationships among a virus-resistance transgene, herbivory, and a bacterial disease in a wild cucurbita

Virus-resistant transgenic squash are grown throughout the United States, where they are interfertile with co-occurring wild taxa of Cucurbita. The transgene is likely to escape into wild populations. The environmental impacts of the transgene will depend on its fitness during introgression into wild populations. In a large field study, we examined the effects of the transgene on plant fitness, herbivory by the primary herbivores (cucumber beetles), and the incidence of a nontarget pathogen in the presence and absence of viral pathogens during introgression into wild Cucurbita pepo. In the absence of the virus, reproductive output of transgenic introgressive plants did not differ from that of nontransgenic introgressive plants, and these plants did not experience a greater rate of herbivory or a higher incidence of wilt disease. In the presence of viral pathogens, both the transgenic and nontransgenic introgressives had lower reproductive output despite the resistance of the transgenic introgressives to viral infection. This incongruous result is partially explained by increased cucumber beetle herbivory on the transgenic plants and an increased incidence of the nontarget bacterial disease that the beetles transmit. These findings suggest that the fitness of pathogen-resistance transgenes in crop-wild plant hybrids can only be determined within the context of the full pathosystem.