Abstract Detail

Host/Plant Pathogen Interactions and Plant Health Management

Stephenson, Andrew G. [1], Harth, Jacquelyn [2], Weakland, Danelle [2], Nowak, Kayla [2], Ferrari, Matthew [2].

Viral infection negatively impacts the establishment and spread of a powdery mildew in populations of Cucurbita pepo ssp. texana, mitigating the fitness benefits of a virus-resistant transgene.

Gene exchange between crops and their wild relatives is common and difficult to contain. Unlike most traits of cultivated species, there are concerns that transgenes conferring resistance to herbivores or pathogens could enhance the fitness and weediness of wild species during introgression and/or have indirect impacts on non-target species such as pollinators, herbivores, predators, soil fauna, and other plants in the community. Gene flow between cultivated squash and its wild counterpart (Cucurbita pepo ssp. texana) may result in the introduction of a virus resistant transgene (VRT) that confers resistance to three common viruses in wild populations. We have extensively studied the interactions among wild C. pepo, its primary herbivores (cucumber beetles and aphids), and the pathogens they transmit (Erwinia tracheiphila, the causative agent of bacterial wilt disease, and three mosaic viruses) and found that the fitness of the transgene during escape is influenced by the full ecological community. Our previous studies have shown that indirect costs associated with increased exposure to herbivory by cucumber beetles and the bacterial wilt disease they transmit can mitigate the fitness benefits of the VRT. Here, we report the results of two years of large scale field studies using wild C. pepo and wild C. pepo X cultivated C. pepo introgressives (backcross generations 8 and 9) containing the VRT. These studies reveal that because the transgenic plants remain virus free during the growing season, transgenic plans reproduce more male flowers and a greater number of fruits than non-transgenic plants. These results would suggest that transgenic plants have a strong selective advantage. However, we find that the flower and fruit production of transgenic plants is only marginally greater than that of wild C. pepo. In part, this can be explained by increased exposure of transgenic plants to Erwinia. Our data also show that virus free plants get proportionally more powdery mildew than virus infected plants. As a consequence, during widespread viral epidemics, transgenic plants get proportionally more powdery mildew than non-transgenic plants further reducing the fitness benefits of the VRT. Additionally, powdery mildew symptoms are significantly more severe on virus free plants. Because transgenic plants remain healthy during viral outbreaks, they are disproportionately affected by powdery mildew.

1 - Pennsylvania State University, Department Of Biology, 208 Mueller Lab, University Park, PA, 16802, USA
2 - Penn State University, Biology, 208 Mueller Lab, University Park, PA, 16802, USA

Keywords:
Plant-Pathogen Interaction
transgenic plants
Cucurbita pepo
Vector transmitted disease
cucumber beetle
powdery mildew
Erwinia tracheiphila.

Presentation Type: Oral Paper:Papers for Topics
Session: 65
Location: Salon 9/The Shaw Conference Centre
Date: Wednesday, July 29th, 2015
Time: 11:30 AM
Number: 65006
Abstract ID:80
Candidate for Awards:None