Ferguson worked on a variety of systems including Fungi, Pine and Petunia.
His and Carolyn Napoli's observations of pigment gene 'cosuppression' in Petunia flowers are examples of post transcriptional gene silencing that predated the discovery of RNA interference (RNAi) and contributed to the current understanding of the commonality of RNA-mediated gene silencing in eukaryotes.
These include pepper, petunia, snapdragon, delphinium and marigold and a great many other plants to a lesser extent.