Emerging plant pathogenic bacteria are a significant threat to global agriculture, forestry and ecosystems. These pathogens, often newly identified or exhibiting increased virulence and host range, are driven by changing environmental conditions, global trade and agricultural intensification. Notable examples include Xylella fastidiosa, Pseudomonas syringae (emerging pathovars), and Ralstonia pseudosolanacearum. These bacteria are characterized by their rapid adaptability, ability to exploit plant weaknesses, and sophisticated mechanisms for invasion and colonisation. Through horizontal gene transfer, they acquire virulence factors and antibiotic resistance, complicating efforts to manage their spread and mitigate their impact.
Emerging pathogens often originate from previously benign or poorly understood bacterial populations. Opportunistic bacteria, which are typically non-pathogenic or weakly pathogenic, are becoming significant contributors to plant disease emergence. These bacteria exploit stressed plants, wounds, or favourable environmental conditions to cause disease. For instance, species within the Dickeya and Pectobacterium genera, historically associated with soft rot in localized outbreaks, have expanded their geographic and host range in recent years. Similarly, Burkholderia gladioli, once considered a minor pathogen, has emerged as a notable threat to crops such as rice and onions, thriving in humid and warm conditions created by climate change.
A defining characteristic of many emerging plant pathogens is their ability to thrive in diverse environments, including water systems, soils, and the plant microbiome. This adaptability enables them to persist in asymptomatic hosts or reservoirs, often escaping detection. Opportunistic pathogens such as Acidovorax avenae, which causes bacterial stripe in cereals, and Serratia marcescens, linked to cucurbit yellows, exemplify this dual lifestyle. They may transition from commensal to pathogenic behavior under conducive conditions, complicating management strategies. The increasing frequency of extreme weather events, coupled with globalised trade, accelerates the emergence of these bacterial threats. Warmer temperatures, higher humidity, and waterlogging create environments that not only stress plants but also favour the growth and dispersal of opportunistic and emerging pathogens. Xylella fastidiosa, for example, has rapidly expanded its host range and geographical reach, devastating olive groves in Europe. The pathogen’s persistence in insect vectors and asymptomatic hosts highlights the challenges of early detection and containment.
Emerging plant pathogens have significant economic and ecological consequences, including reduced crop yields, increased production costs and threats to food security. Addressing this crisis requires a multifaceted approach. Advances in genomics and metagenomics are enabling the identification and monitoring of these pathogens, revealing their evolutionary trajectories and interactions with hosts. Integrated disease management strategies that include resistant plant varieties, improved cultural practices and biocontrol agents are critical. Additionally, fostering healthy plant microbiomes may suppress opportunistic pathogens and enhance plant resilience.