Invasive Potential of Xylella fastidiosa

Abstract

Evaluating the risks of invasion by the bacterium Xylella fastidiosa to geographic regions where this plant pathogen currently does not occur is an important challenge. Various strains of X. fastidiosa, differentiated by their plant host range, comprise a formidable variety of serious plant diseases throughout the tropical through subtropical Americas. These diseases do not seem present as significant threats outside the Western Hemisphere, except for Taiwan, which has recorded diseases in pear and grape caused by X. fastidiosa. Identifying the factors limiting or even prohibiting the spread of X. fastidiosa and their modes of action would be useful in attempts to estimate risks of new invasions by this bacterium and-more importantly-to identify the most effective phytosanitary strategies to prevent the bacterium from establishing in new regions. Although it is clear that cold severity of sub-freezing winter climates limit the geographic spread of X. fastidiosa, we lack an understanding of the underlying mechanisms of how freezing eliminates it from plants. Other aspects of climatic temperature regimes, such as limiting high temperatures or sustained cool but above freezing temperatures need to be addressed. For some regions, the lack of suitable insect vectors or suitable alternative hosts of X. fastidiosa may prevent introductions of X. fastidiosa in infected plant hosts from establishing a permanent presence. It is likely the permanent establishment of X. fastidiosa requires a suitable combination of vectors’ distribution, abundance, plant preferences, phenology, transmission efficiency, and dispersal behavior in conjunction with the abundance and distribution of plant hosts of X. fastidiosa and the characteristics of the plant communities in which they are embedded. The intriguing possibilities of interactions with other bacteria and viruses have only begun to be explored as limiting factors.