Flaming Phlox and the Ubiquitous Powdery Mildew Disease

Abstract

Phlox is a diverse genus of ornamental plants that is native to the North American continent. These popular plants, which are known for flowers with “the color of glowing flame”, are particularly appreciated in naturalistic arrangements and increasingly emphasized in native gardens for their ability to attract pollinators. Despite the plant’s popularity, the main limitation to its cultivation is the fungal disease powdery mildew (PM). Hence, cultivars deployed through the years have been selected not just for desirable horticultural traits but also for resistance to PM. Although some studies on the Phlox-PM pathosystem have begun to unravel the mechanisms underpinning host-pathogen interactions, numerous questions remain unanswered, including what are the genes involved in the retarded senescence of the infected host tissue, what are the molecular mechanisms associated with the host ontogenic resistance, and what is the role of phytohormones in the resistance of Phlox to PM? PM pathogens, already predominant on Phlox, are now likely to be ubiquitous due to the exchange of plants throughout the world. Research into the genetic diversity of Phlox-PM populations will help identify the routes of disease spread and evolutionary potential of the pathogens. Here, we review what is known about Phlox and the PM disease, and we identify knowledge gaps that have yet to be addressed.