Host Specificity and Fitness Cost of Pasteuria penetrans Spore Attachment to Second-Stage Juveniles of Meloidogyne javanica, Meloidogyne luci and Meloidogyne arenaria

Pasteuria penetrans (Pp) is a mycelial and endospore-forming bacterium that parasitizes Meloidogyne spp. A single Pp population may contain multiple genotypes that differ in their spore-attachment specificity. Consequently, a subpopulation within a Pp isolate, which can attach to one Meloidogyne species, may fail to attach to another. Repeated culturing of that Pp isolate, on different Meloidogyne species, may therefore lead to shifts in host specificity. We tested this hypothesis using M. luci and M. arenaria, both of which are quite poor hosts of the Pp3 isolate maintained on M. javanica. Using relatively high spore concentrations (106 spores/mL), low levels of attachment and infection were obtained, and after three successive selection cycles, Pp3 sub-isolates adapted to M. luci and M. arenaria were generated. This selection process was associated with a fitness cost, expressed as reduced spore attachment on M. javanica. The shift in host specificity proved reversible. When the adapted Pp3 M. arenaria and Pp3 M. luci sub- isolates were subsequently selected on M. javanica, for two generations, they regained the ability to attach on M. javanica but with a corresponding fitness cost, of spore attachment on M. arenaria and M. luci. These results demonstrate that Pp host specificity is plastic and capable of rapid selection-driven changes in attachment patterns, although such shifts are accompanied by fitness trade-offs.