UC Davis

Lima beans (Phaseolus lunatus) are a globally important crop with great potential to contribute to future food security through their high nutritional value, vigor, drought tolerance, and ability to fix nitrogen. A major limiting factor for the contribution of Lima beans to the global food supply is their susceptibility to herbivory by insects like Lygus hesperus. The goal of the research presented in this dissertation is to understand the domestication history, current variability, and breeding potential of the anti-herbivore defense traits in Lima bean with a special emphasis on cultivars adapted to the Central Valley of California, and on cyanogenesis as a mechanism of defense against L. hesperus. Chapter 1 is a comprehensive review of the existing research on the effect of domestication on anti-herbivore defense traits. In chapter 2, a genome-wide association study is used to explore the inheritance of cyanogenesis in Lima beans within the Mesoamerican gene pool. This study identified highly significant SNPs for the release of cyanide immediately following tissue disruption that could contribute to a deterrence defense strategy. Significant SNPs were also identified for a more sustained release of cyanide that could contribute to a defense strategy of herbivore intoxication. In chapter 3, the trait of cyanogenesis is characterized and studied for its plasticity in the presence of L. hesperus and its effect on the survival and growth of L. hesperus populations. This study found that cyanogenesis was not induced by the presence of L. hesperus and the survival and reproduction of L. hesperus was negatively correlated with the cyanogenic capacity of their Lima bean host. These results advance the study of anti-herbivore defense mechanisms and the complex relationships between crop plants and their insect pests. They will contribute to efforts of crop improvement for reduced pesticide use and increased food security.