Effects Of Transgenic Virus Resistance On Populations Of Cucurbita Texana

Open Access
Author:
Deveney, Troy Wilson
Area of Honors:
Biology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Andrew George Stephenson, Thesis Supervisor
  • Stephen Wade Schaeffer, Honors Advisor
Keywords:
  • Cucurbita pepo
  • Erwinia tracheiphyla
  • plant-herbivore-pathogen interaction
  • virus resistant transgene
  • zucchini yellow mosaic
Abstract:
Virus resistant transgenic squash are grown throughout the USA and much of Mexico and it is likely that the virus resistant transgene (VRT) has been introduced to wild populations repeatedly. The evolutionary fate of a resistance gene in wild populations and its environmental impacts depend upon trade-offs between the costs and benefits of the resistance gene. In a 2010 field study using a wild gourd and transgenic and non-transgenic introgressives, the effects of the transgene on fitness, the transgenes increase in frequency in the next generation, and the relationship between the introduction of the mosaic virus and an increase in the percentage of transgenic male flowers was examined. During the 2010 field season four identical plots of 90 Cucurbita pepo ssp texana and 90 BC6 plants(C. peop ssp. Texana x Lib III C. pepo cultivar hybrid. Liberator III was backcrossed to texana for 6 generation and half of the backcross six plants were transgenic, half were not) were established. An outbreak of zucchini yellow mosaic virus occurred in early July and spread rapidly through the susceptible plants of two fields while no outbreak occurred in two fields. It was found that the transgenic plants had greater reproduction through both male and female function than the susceptible plants, indicating that the VRT has a direct fitness benefit for wild gourds under the conditions of our study. Moreover, the presence of the VRT in the subsequent generation greatly exceeded expected values exhibiting strong selection for the transgene in all fields. Moreover when the percentage of male flowers on transgenic plants was examined a relationship between the introduction of virus within the fields and an increase in the percentage of transgenic flowers was observed while fields that lacked a virus outbreak had failed to increase their percentage of transgenic flowers. This study clearly exhibits the beneficial effect of the VRT on the fitness of the squash in the presence of disease and postulates on the pathways that allow for strong selection for the VRT.