Evolutionary consequences of gene flow from crop to wild sunflower: Studies of fitness, herbicide resistance, and germination

Crop-wild gene flow can influence the evolution of wild populations. The ultimate degree of introgression of crop genes will depend on their fitness effects, which may vary based on a number of factors: the genetic background of the specific wild populations and the specific crop variety involved; the crop's specific transgenes or traits of interest; the abiotic and biotic environmental factors, including interspecific interactions; and the resulting changes to life history characteristics. This dissertation elucidates how these factors affect fitness in order to better estimate their effects on crop gene introgression in annual sunflower.; Chapter 1 investigated the effects of nine wild populations and three crop lines on the fecundity and survival to reproduction with and without competition. My results showed that wild populations varied in the relative fitness of their hybrids and wilds and that relative fitness increased with competition. These differences in relative fitness will influence the introgression of crop genes. In Chapter 2, I measured the effects of nine wild populations and a sulfonylurea herbicide resistant crop line on fitness with and without herbicide application. Sulfonylurea resistant hybrids possessed a growth advantage immediately following herbicide application. However, by the end of the season, the wild and conventional hybrids reestablished their fitness advantage due to compensatory growth. The stress of the herbicide application increased the relative fitness of hybrids, though the relative fitness of herbicide resistant hybrids was lower than that of conventional hybrids. In Chapter 3, I assessed how wild populations and crop lines influenced seed germination and dormancy under laboratory and field conditions. Germination increased, due to hybridization, in most of the nine populations, although relative germination of wilds and hybrids varied by population and environment. Higher germination could hasten crop gene introgression by promoting hybrids over wilds within the standing plant population. As a group, these chapters indicate that crop gene introgression will vary across the landscape because the fitness effects of crop genes will vary by both wild population and crop variety. Gene flow into more stressful environments may result in higher crop gene introgression. And increased hybrid germination could encourage crop gene introgression.