The challenge of searching for Xylella fastidiosa genetic diversity in its natural habitats

From a mycologist and plant pathologist perspective with little background on prokaryotes, the lifestyle of Xylella fastidiosa (Xf) is still fascinating and enigmatic. In recent years, several studies have largely improved our understanding on the genetic diversity and phylogeny while unraveling the center of origin of the three main Xf subspecies. Yet, surprisingly, these works rely exclusively on isolates collected from human-related environments, i.e., crops, ornamental and landscape plants, out of their native geographic range and mostly from non-native hosts. Such scientific gaps hamper our interpretation on the new advances in the biology of Xf and its vectors. We must therefore recognize the paucity of our knowledge on the ecological niche in its native range and the need to survey in candidate ecosystems such as tropical rain forests of Central and South America. The purpose of this work is to generate debate on how to approach the problem of searching for Xf isolates in natural ecosystems. Although at first glance it might seem an easy task, the challenge requires some previous thoughts. To increase our chances of finding the needle in the haystack, we must ask ourselves what role Xf might have in its natural habitat. This needs a reverse path of ecological inference from the collection of scattered information from the lab and observations in the realized niche. In other words, we need to speculate on the evolutionary ecology of Xf in its natural habitat on the base of what we have. There are many questions and few solid answers about the interspecific interactions, host range, geographic size and population genetics, among other issues. These answers must be integral, cohesive and open-minded because our preconceptions can be wrong. Understanding Xf’s ecological niche in its natural habitat would aid to evaluate future risks and improve our control strategies.