Adaptation without Dominance in Pseudomonas syringae Pathovars.

Area of Science:

• Microbiology
• Plant Pathology
• Evolutionary Biology

Background:

• Phytopathogens like Pseudomonas syringae cause significant agricultural losses.
• Intraspecific lineages (pathovars) are often defined by host-of-isolation.
• The distinction between local adaptation and local dominance in pathovars is often unclear.

Purpose of the Study:

• To investigate whether five Pseudomonas syringae pathovars are locally adapted and/or dominant in their hosts.
• To determine if pathovar classification accurately reflects pathogen phenotypes.
• To assess the predictability of in planta performance from in vitro growth and gene content.

Main Methods:

• In vitro growth assays were conducted.
• Factorial controlled infections were performed across multiple hosts.
• Pathogen gene content, including virulence factors, was analyzed.

Main Results:

• Local adaptation was found in 3 of 5 tested pathovars; only 1 was also locally dominant.
• Some strains showed cost-free generalism, performing well in non-native hosts.
• In vitro growth did not correlate with in planta growth; pathovar designations were unreliable for predicting phenotypes.

Conclusions:

• Local adaptation is prevalent but not universal in P. syringae.
• Pathovar classification and in vitro assays are poor predictors of pathogen behavior.
• P. syringae exhibits significant intraspecific variation and diverse adaptive strategies, including generalism.