It is believed that certain endophyte bacteria trigger
a phenomenon known as induced systemic resistance (ISR),
which is phenotypically similar to systemic-acquired resistance
(SAR). SAR develops when plants successfully activate
their defence mechanism in response to primary infection by
a pathogen, notably when the latter induces a hypersensitive
reaction through which it becomes limited in a local necrotic
lesion of brown desiccated tissue (van Loon et al., 1998). ISR
is effective against different types of pathogens but differs
from SAR in that the inducing bacterium does not cause
visible symptoms on the host plant (van Loon et al., 1998).
Bacterial endophytes and their role in ISR have been
reviewed recently by Kloepper & Ryu (2006).